diff --git a/.clang-format b/.clang-format
index 6aa77c4..c773cb2 100644
--- a/.clang-format
+++ b/.clang-format
@@ -34,14 +34,14 @@ EmptyLineBeforeAccessModifier: Always
 FixNamespaceComments: false
 IncludeBlocks: Regroup
 IncludeCategories:
-    - Regex: '<[[:alnum:].]+>'
-      Priority: -10
-    - Regex: '^<fontconfig/'
+    - Regex: '^<fontconfig'
       Priority: -5
-    - Regex: '^<SDL2/'
+    - Regex: '^<SDL'
       Priority: -5
     - Regex: '^<basic_widgets/'
       Priority: 0
+    - Regex: '<[[:alnum:]._]+>'
+      Priority: -10
     - Regex: '^".*"$'
       Priority: 5
 IndentCaseLabels: true
diff --git a/.clang-tidy b/.clang-tidy
index f46dd98..0e50ac5 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -1,2 +1,2 @@
-Checks: 'bugprone-*,cert-*,misc-*,modernize-*,performance-*,portability-*,readability-*,-misc-non-private-member-variables-in-classes,-bugprone-easily-swappable-parameters,-readability-braces-around-statements,-cppcoreguidelines-non-private-member-variables-in-classes,-readability-named-parameter,-modernize-use-trailing-return-type'
+Checks: 'bugprone-*,cert-*,cppcoreguidelines-*,misc-*,modernize-*,performance-*,portability-*,readability-*,-misc-non-private-member-variables-in-classes,-bugprone-easily-swappable-parameters,-readability-braces-around-statements,-cppcoreguidelines-non-private-member-variables-in-classes,-readability-named-parameter,-modernize-use-trailing-return-type,-cppcoreguidelines-avoid-magic-numbers'
 FormatStyle: file
diff --git a/README.md b/README.md
index 8a6cd24..44821b8 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,125 @@
 # sdl2_basic_widgets
 
-A (very) basic widget library for SDL applications.
+A (very) basic and incomplete widget library for SDL applications.
 
+## Build
+The build dependencies are SDL2, SDL_ttf and fontconfig dev libs
+and headers. Meson is used as build system, so you'll need it too.
+
+As the code use some C++20 features, you'll need a recent compiler
+which support that version of the standard.
+
+Then, inside the project root directory, run the following commands:
+
+```ShellSession
+$ meson build
+$ meson compile -C build -j0
+```
+
+After that you'll have in the build directory the static library and the
+example programs.
+
+## API overview
+
+The library API is divided in two main parts:
+- the core, which provides some basic wrapping of
+  SDL, SDL_ttf and fontconfig functionalities.
+- the widget API built on top of the core.
+
+### Core
+
+The main classes of the core are:
+
+- [Font](inc/basic_widgets/core/font.hpp):
+  wraps TTF_Font object with the most common operations
+  of SDL_ttf. Also provide a helper function to
+  search system fonts by using fontconfig.
+- [Renderer](inc/basic_widgets/core/renderer.hpp):
+  wraps SDL_Renderer object with common operation from
+  the SDL 2D accelerated rendering API.
+- [Texture](inc/basic_widgets/core/texture.hpp):
+  wraps SDL_Texture object with common operations
+  to manipulate it.
+
+Apart from the SDL API wrappers, some generic utility functions and
+data types are defined:
+
+- [Color](inc/basic_widgets/core/type/color.hpp):
+  wraps SDL_Color object and adds convenience operators
+  overloads to operate on all color channels and/or
+  alpha channel.
+- [draw.hpp](inc/basic_widgets/core/draw.hpp):
+  2D drawing utilities. Currently, provides a couple of basic utility
+  functions for software rendered textures: circle rendering
+  and an antialising algorithm.
+- [math.hpp](inc/basic_widgets/core/math.hpp): mostly provides
+  frequently used formulas to work with rectangles and points
+  on a 2D coordinate system.
+- [concepts.hpp](inc/basic_widgets/core/type/concepts.hpp):
+  a few concept definitions for used for generic programming.
+- [Size](inc/basic_widgets/core/type/size.hpp): representation
+  of a 2D size. There are also a few operator overloads to
+  operate on Size objects.
+
+## Widgets
+
+Widgets are classes that implements the common widget interface and
+optionally one or more "handler" interfaces. Handlers are interfaces
+for event or external resources handling.
+
+These interfaces are:
+
+- [Widget](inc/basic_widgets/w/base/widget.hpp): the common base
+  interface of every widget.
+- [EventHandler](inc/basic_widgets/w/feat/event_handler.hpp): base
+  interface for event handlers.
+- [FocusHandler](inc/basic_widgets/w/feat/focus_handler.hpp): base
+  interface for handler having a focus notion.
+- [KeyboardHandler](inc/basic_widgets/w/feat/keyboard_handler.hpp):
+  interface for key and text input events handling.
+- [MouseHandler](inc/basic_widgets/w/feat/mouse_handler.hpp):
+  interface for mouse events handling. Handle click and focus state
+  changes and also introduce a notion of "pushed" state.
+- [FontHandler](inc/basic_widgets/w/feat/font_handler.hpp): interface
+  for widgets using a font. Declares methods to set the widget font and
+  set background and text color used for text rendering.
+- [TextureHandler](inc/basic_widgets/w/feat/texture_handler.hpp): it exists
+  but I'm thinking now that it shouldn't.
+
+Based on these interfaces, there's implementation for a few basic widgets.
+Currently, the following ones are defined:
+
+- [Button](inc/basic_widgets/w/button.hpp): a push button.
+- [Caption](inc/basic_widgets/w/caption.hpp): a caption
+  that displays a rendered string. No multiline support.
+- [Input<T>](inc/basic_widgets/w/base/input.hpp): base
+  class for widgets using an input field.
+- [NumericInput<Numeric>](inc/basic_widgets/w/numeric_input.hpp) an
+  input widget for numeric values with two buttons to increase/decrease
+  the hold value.
+
+There are also "containers" widgets which are widget that hold a collection of
+widgets and manage their geometry:
+
+- [Layout](inc/basic_widgets/w/base/layout.hpp): abstract class for container widgets.
+- [AlignedLayout](inc/basic_widgets/w/aligned_layout.hpp): layout that is done by distributing
+  widgets on a horizontal or vertical row.
+
+To create widget objects, the corresponding function from [widget_factory.hpp](inc/basic_widgets/w/widget_factory.hpp)
+should be used. It's done this way for interface-implementation sake.
+
+## Source code organization overview
+
+The header and source directory hierarchies is organized in the following way:
+
+- core: C→C++ wrappers and commonly used generic functions.
+- core/type: basic data types and concepts.
+- w: the widget library
+- w/base: the abstract widget classes.
+- w/feat: handlers (optional widget features)
+
+Widget code intent to separate public API from implementation details. For that
+a Widget has two classes, a pure virtual one (Widget) which is the public API and another
+class (WidgetImpl) that implements the interface of the first one. Unless an access
+to implementation details is required, the interface (pure virtual) type should
+be used.
diff --git a/examples/button_example.cpp b/examples/button_example.cpp
index 12b334b..56f70e9 100644
--- a/examples/button_example.cpp
+++ b/examples/button_example.cpp
@@ -1,19 +1,19 @@
 #include <iostream>
 
-#include <basic_widgets/w/button.hpp>
+#include <basic_widgets/w/widget_factory.hpp>
 
 #include "run.hpp"
 
-using bwidgets::Button;
-
 auto main() -> int
 {
-    run_example<Button>([](auto* w, auto* f, auto x, auto y) {
-        w->click_handler = [x, y](const SDL_MouseButtonEvent&) {
-            std::cout << "button(" << x << ',' << y << "):click!" << std::endl;
-        };
-        w->font(f);
-        w->text("+");
-    });
+    run_example<bwidgets::Button>(
+      []() { return bwidgets::create_button(); },
+      [](auto w, auto f, auto x, auto y) {
+          w->click_handler([x, y](const SDL_MouseButtonEvent&) {
+              std::cout << "button(" << x << ',' << y << "):click!" << std::endl;
+          });
+          w->font(f);
+          w->text("click me");
+      });
     return 0;
 }
diff --git a/examples/caption_example.cpp b/examples/caption_example.cpp
index d539d12..4f9ef6a 100644
--- a/examples/caption_example.cpp
+++ b/examples/caption_example.cpp
@@ -1,17 +1,16 @@
-#include <basic_widgets/w/caption.hpp>
+#include <basic_widgets/w/widget_factory.hpp>
 
 #include "run.hpp"
 
-using bwidgets::Caption;
-
 auto main() -> int
 {
-    run_example<Caption>(
-      [](auto* w, auto* f, auto, auto) {
-          w->alignment = Caption::Alignment::CENTER;
-          w->text("¡jello!");
-          w->font(f);
-      },
-      4, 8); // NOLINT(readability-magic-numbers)
+    run_example<bwidgets::Caption>([]() { return bwidgets::create_caption(); },
+                                   [](auto w, auto f, auto, auto) {
+                                       w->alignment =
+                                         bwidgets::Caption::Alignment::CENTER;
+                                       w->text("¡jello!");
+                                       w->font(f);
+                                   },
+                                   4, 8); // NOLINT(readability-magic-numbers)
     return 0;
 }
diff --git a/examples/example_example.cpp b/examples/example_example.cpp
index 736f196..28f54e0 100644
--- a/examples/example_example.cpp
+++ b/examples/example_example.cpp
@@ -3,9 +3,11 @@
 
 auto main() -> int
 {
-    run_example<Example>([](auto* w, auto*, auto x, auto y) {
-        w->cycle_r = (x + 1) * 3000;              // NOLINT(readability-magic-numbers)
-        w->cycle_b = (y + 1) * 3000;              // NOLINT(readability-magic-numbers)
-        w->cycle_b = (1 + x + y) * (y + 1) * 400; // NOLINT(readability-magic-numbers)
-    });
+    run_example<Example>(
+      []() { return std::make_unique<Example>(); },
+      [](auto w, auto, auto x, auto y) {
+          w->cycle_r = (x + 1) * 3000;              // NOLINT(readability-magic-numbers)
+          w->cycle_b = (y + 1) * 3000;              // NOLINT(readability-magic-numbers)
+          w->cycle_b = (1 + x + y) * (y + 1) * 400; // NOLINT(readability-magic-numbers)
+      });
 }
diff --git a/examples/example_widget.hpp b/examples/example_widget.hpp
index 69c6edc..6777a58 100644
--- a/examples/example_widget.hpp
+++ b/examples/example_widget.hpp
@@ -1,20 +1,19 @@
 #ifndef BWIDGETS_EXAMPLES_EXAMPLE_WIDGET
 #define BWIDGETS_EXAMPLES_EXAMPLE_WIDGET
 
-#include <SDL2/SDL_timer.h>
+#include <chrono>
 
 #include <basic_widgets/core/math.hpp>
 #include <basic_widgets/core/renderer.hpp>
-#include <basic_widgets/w/base/widget.hpp>
+#include <basic_widgets/w/base/widget_impl.hpp>
 
 using bwidgets::Color;
 using bwidgets::rect_margin;
 using bwidgets::Size;
-using bwidgets::Widget;
+using bwidgets::WidgetImpl;
 
-class Example final : public Widget
+class Example final : public WidgetImpl
 {
-private:
     void _handle_geometry_change(const SDL_Rect& vp) noexcept override
     {
         _widget_area = {2, 2, vp.w - 4, vp.h - 4};
@@ -22,12 +21,13 @@ private:
 
     void _handle_rendering() override
     {
-        const auto    now = SDL_GetTicks();
-        const uint8_t r   = 255 * (now % cycle_r / (float)cycle_r); // NOLINT
-        const uint8_t g   = 255 * (now % cycle_g / (float)cycle_g); // NOLINT
-        const uint8_t b   = 255 * (now % cycle_b / (float)cycle_b); // NOLINT
-        // NOLINTNEXTLINE(readability-magic-numbers)
-        const Color   base_color {r, g, b, 255};
+        const auto now = std::chrono::duration_cast<std::chrono::milliseconds>(
+                           std::chrono::steady_clock::now().time_since_epoch())
+                           .count();
+        const uint8_t r = 255 * (now % cycle_r / (float)cycle_r); // NOLINT
+        const uint8_t g = 255 * (now % cycle_g / (float)cycle_g); // NOLINT
+        const uint8_t b = 255 * (now % cycle_b / (float)cycle_b); // NOLINT
+        const Color   base_color {r, g, b, SDL_ALPHA_OPAQUE};
 
         const int border = 10;
         for (auto i = 0; i < border; i += 3) {
@@ -49,6 +49,8 @@ public:
     unsigned int cycle_g {3500}; // NOLINT(readability-magic-numbers)
     unsigned int cycle_b {3500}; // NOLINT(readability-magic-numbers)
 
+    using WidgetImpl::WidgetImpl;
+
     [[nodiscard]] auto size() const noexcept -> Size override
     {
         return {128, 64}; // NOLINT(readability-magic-numbers)
diff --git a/examples/input_example.cpp b/examples/input_example.cpp
index f16bcad..594bd54 100644
--- a/examples/input_example.cpp
+++ b/examples/input_example.cpp
@@ -1,15 +1,15 @@
-#include <basic_widgets/w/numeric_input.hpp>
+#include <basic_widgets/w/widget_factory.hpp>
 
 #include "run.hpp"
 
-using bwidgets::NumericInput;
-
 auto main() -> int
 {
-    run_example<NumericInput<float>>([](auto* w, auto* f, auto, auto) {
-        w->font(f);
-        w->button_step = 0.5;       // NOLINT(readability-magic-numbers)
-        w->value_range(-3.14, 8.5); // NOLINT(readability-magic-numbers)
-    });
+    run_example<bwidgets::NumericInput<float>>(
+      []() { return bwidgets::create_input_float(); },
+      [](auto w, auto f, auto, auto) {
+          w->font(f);
+          w->button_step = 0.5;       // NOLINT(readability-magic-numbers)
+          w->value_range(-3.14, 8.5); // NOLINT(readability-magic-numbers)
+      });
     return 0;
 }
diff --git a/examples/run.hpp b/examples/run.hpp
index df569ce..796f283 100644
--- a/examples/run.hpp
+++ b/examples/run.hpp
@@ -3,58 +3,50 @@
 
 #include <functional>
 #include <iostream>
-#include <stack>
 
-#include <SDL2/SDL.h>
-#include <SDL2/SDL_ttf.h>
-
-#include <basic_widgets/core/font.hpp>
-#include <basic_widgets/core/renderer.hpp>
-#include <basic_widgets/w/aligned_layout.hpp>
-#include <basic_widgets/w/base/widget.hpp>
+#include <basic_widgets/core/type/deleter.hpp>
+#include <basic_widgets/w/widget_factory.hpp>
 
 template<typename T>
 concept WidgetType = std::derived_from<T, bwidgets::Widget>;
 
 template<WidgetType W>
-void run_example(const std::function<void(W*, bwidgets::Font*, int, int)>& setup,
-                 int w = 3, int h = 3)
+void run_example(
+  std::function<std::unique_ptr<W>()>                                      factory,
+  std::function<void(W*, const std::shared_ptr<bwidgets::Font>, int, int)> setup,
+  int w = 3, int h = 3)
 {
-    std::stack<std::function<void()>> cleaners;
+    std::atexit([]() {
+        TTF_Quit();
+        SDL_Quit();
+    });
     try {
-        bwidgets::SDLError::success_or_throw(SDL_Init(SDL_INIT_VIDEO), __FILE__,
-                                             __FUNCTION__, __LINE__);
-        cleaners.emplace([]() { SDL_Quit(); });
-        bwidgets::SDLError::success_or_throw(TTF_Init(), __FILE__, __FUNCTION__,
-                                             __LINE__);
-        cleaners.emplace([]() { TTF_Quit(); });
-
+        bwidgets::success_or_throw<bwidgets::SDLError>(SDL_Init(SDL_INIT_VIDEO));
+        bwidgets::success_or_throw<bwidgets::SDLError>(TTF_Init());
         const bwidgets::Size size_init {854, 480};
-        auto*                font {new bwidgets::Font(bwidgets::Font::find("Monospace"),
-                                                      16)}; // NOLINT(readability-magic-numbers)
-        cleaners.emplace([font]() { delete font; });
-        auto* win {SDL_CreateWindow("basic_widgets example", SDL_WINDOWPOS_CENTERED,
-                                    SDL_WINDOWPOS_CENTERED, size_init.w, size_init.h,
-                                    SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE
-                                      | SDL_WINDOW_UTILITY)};
-        cleaners.emplace([win]() { SDL_DestroyWindow(win); });
-        auto* renderer {new bwidgets::Renderer(win, -1, SDL_RENDERER_ACCELERATED)};
-        cleaners.emplace([renderer]() { delete renderer; });
+        auto                 font =
+          std::make_shared<bwidgets::Font>(bwidgets::Font::find("Monospace"),
+                                           16); // NOLINT(readability-magic-numbers)
+
+        auto win = std::unique_ptr<SDL_Window, bwidgets::Deleter>(
+          bwidgets::ptr_or_throw<bwidgets::SDLError>(SDL_CreateWindow(
+            "basic_widgets example", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
+            size_init.w, size_init.h,
+            SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE | SDL_WINDOW_UTILITY)));
+
+        auto renderer =
+          std::make_shared<bwidgets::Renderer>(win.get(), -1, SDL_RENDERER_ACCELERATED);
         renderer->blend_mode(SDL_BLENDMODE_BLEND);
 
-        auto* layout {
-          new bwidgets::AlignedLayout(bwidgets::AlignedLayout::Alignment::HORIZONTAL)};
-        cleaners.emplace([layout]() { delete layout; });
-
+        auto layout = bwidgets::create_horizontal_layout();
         for (auto x = 0; x < w; x++) {
-            auto* col =
-              new bwidgets::AlignedLayout(bwidgets::AlignedLayout::Alignment::VERTICAL);
+            auto col = bwidgets::create_vertical_layout();
             for (auto y = 0; y < h; y++) {
-                auto* widget = new W();
-                setup(widget, font, x, y);
-                col->add_widget(widget);
+                auto widget = factory();
+                setup(widget.get(), font, x, y);
+                col->add_widget(std::move(widget));
             }
-            layout->add_widget(col);
+            layout->add_widget(std::move(col));
         }
 
         layout->renderer(renderer);
@@ -85,11 +77,8 @@ void run_example(const std::function<void(W*, bwidgets::Font*, int, int)>& setup
             layout->render();
             renderer->present();
         }
-        while (!cleaners.empty()) cleaners.top()(), cleaners.pop();
-    } catch (const bwidgets::SDLError& e) {
-        std::cerr << "Error: " << e.file << ":" << e.func << ":" << e.line << ": "
-                  << e.what << std::endl;
-        while (!cleaners.empty()) cleaners.top()(), cleaners.pop();
+    } catch (const std::exception& e) {
+        std::cerr << "Error: " << e.what() << std::endl;
     }
 }
 
diff --git a/inc/basic_widgets/core/draw.hpp b/inc/basic_widgets/core/draw.hpp
index 2747ff4..ef2be54 100644
--- a/inc/basic_widgets/core/draw.hpp
+++ b/inc/basic_widgets/core/draw.hpp
@@ -1,8 +1,8 @@
 #ifndef BWIDGETS_DRAW_HPP
 #define BWIDGETS_DRAW_HPP
 
-#include <cstdint>
 #include <functional>
+#include <memory>
 
 struct SDL_PixelFormat;
 struct SDL_Point;
@@ -13,12 +13,21 @@ namespace bwidgets
     class Renderer;
     class Texture;
 
-    [[nodiscard]] auto aa(const Color&, int, float) noexcept -> Color;
-    [[nodiscard]] auto filled_circle(const Color&, int resolution, Renderer*,
-                                     int aa_pixels = 3) -> Texture*;
-    void               set_pixels_color(
-                    Texture*,
-                    const std::function<uint32_t(const SDL_Point&, const SDL_PixelFormat*)>&);
+    // Add transparency to color base_color relative to the distance d from
+    // a limit to produce an AntiAliasing effect.
+    // d >= 0                → full transparency;
+    // −(aa_pixels) <= d < 0 → smoothsteped transparency gradient;
+    // d < −(aa_pixels)      → fully opaque.
+    [[nodiscard]] auto aa(Color base_color, int aa_pixels, float d) noexcept -> Color;
+    // Render a filled circle texture of color c and diameter resolution with
+    // aa_pixels used for antialiasing.
+    [[nodiscard]] auto filled_circle(Color c, int resolution, const Renderer&,
+                                     int aa_pixels = 3) -> std::shared_ptr<Texture>;
+    // Set the color of every pixels of a Texture using the passed function to compute
+    // pixel color.
+    void
+    set_pixels_color(Texture*,
+                     const std::function<uint32_t(SDL_Point, const SDL_PixelFormat&)>&);
 }
 
 #endif
diff --git a/inc/basic_widgets/core/error_helper.hpp b/inc/basic_widgets/core/error_helper.hpp
new file mode 100644
index 0000000..cca3001
--- /dev/null
+++ b/inc/basic_widgets/core/error_helper.hpp
@@ -0,0 +1,47 @@
+#ifndef BWIDGETS_ERROR_HELPER_HPP
+#define BWIDGETS_ERROR_HELPER_HPP
+
+#include <functional>
+
+#include <basic_widgets/core/type/sdl_error.hpp>
+
+extern "C" {
+    auto SDL_GetError() -> const char*;
+}
+
+namespace bwidgets
+{
+    // Throw a E exception with message w if ptr is null. Otherwise return ptr.
+    template<Exception E, typename T>
+    inline auto ptr_or_throw(T* const ptr, const std::string_view w = "unknown") -> T*
+    {
+        std::string what;
+        if constexpr (std::is_same_v<E, SDLError>)
+            what = w == "unknown" ? SDL_GetError() : w;
+        else what = w;
+
+        if (ptr == nullptr) throw E(what);
+        return ptr;
+    }
+
+    // Check a return code with the success function passed. If success return false
+    // throw an E Exception with message w.
+    template<Exception E, typename T>
+    inline auto success_or_throw(
+      const T code, const std::string_view w = "unknown",
+      const std::function<bool(T)>& success = [](const T code) { return code == 0; })
+      -> T
+    {
+        // If exception type is SDLError and no value or unknown was passed for w, get
+        // the last error message using SDL facilities.
+        if constexpr (std::is_same_v<E, SDLError>) {
+            const std::string what {w == "unknown" ? SDL_GetError() : w};
+            if (code < 0) throw E(what);
+        }
+        else if (!success(code)) throw E(w.data());
+
+        return code;
+    }
+}
+
+#endif
diff --git a/inc/basic_widgets/core/font.hpp b/inc/basic_widgets/core/font.hpp
index 9ab53f8..7b28b96 100644
--- a/inc/basic_widgets/core/font.hpp
+++ b/inc/basic_widgets/core/font.hpp
@@ -1,18 +1,23 @@
 #ifndef BWIDGETS_FONT_HPP
 #define BWIDGETS_FONT_HPP
 
+#include <memory>
 #include <string>
 
-#include <SDL2/SDL_ttf.h>
+#include <SDL_ttf.h>
 
 #include <basic_widgets/core/type/color.hpp>
-#include <basic_widgets/core/type/opaque_struct.hpp>
+#include <basic_widgets/core/type/deleter.hpp>
 #include <basic_widgets/core/type/size.hpp>
 
 namespace bwidgets
 {
-    struct Font final : OpaqueStruct<TTF_Font>
+    // Wrap TTF_Font from SDL_ttf and provide a font finding function.
+    class Font final
     {
+        const std::unique_ptr<TTF_Font, Deleter> _data;
+
+    public:
         enum struct Hinting
         {
             LIGHT  = TTF_HINTING_LIGHT,
@@ -37,8 +42,8 @@ namespace bwidgets
             UNDERLINE     = TTF_STYLE_UNDERLINE
         };
 
-        inline static const Color default_color_bg {255, 255, 255, SDL_ALPHA_OPAQUE};
-        inline static const Color default_color_fg {0, 0, 0, SDL_ALPHA_OPAQUE};
+        static const Color default_color_bg;
+        static const Color default_color_fg;
 
         const int         ascent;
         const int         descent;
@@ -49,12 +54,15 @@ namespace bwidgets
         const int         line_skip;
         const std::string style_name;
 
-        Font(TTF_Font*);
-        Font(const std::string&, int);
+        explicit Font(TTF_Font*);
+        // Load font at given path and with given size.
+        Font(std::string_view, int);
         Font(const Font&) = delete;
-        ~Font() noexcept override;
+        Font(Font&&)      = delete;
+        ~Font() noexcept  = default;
 
-        auto operator=(const Font&) -> Font& = delete;
+        auto operator=(const Font&) = delete;
+        auto operator=(Font&&) = delete;
 
         [[nodiscard]] auto hinting() const noexcept -> Hinting;
         auto               hinting(Hinting) noexcept -> Font*;
@@ -62,13 +70,15 @@ namespace bwidgets
         auto               kerning(bool) noexcept -> Font*;
         [[nodiscard]] auto outline() const noexcept -> int;
         auto               outline(int) noexcept -> Font*;
-        auto render(RenderMode, const std::string&, const Color& fg = default_color_fg,
-                    const Color& bg = default_color_bg) -> SDL_Surface*;
+        auto render(RenderMode, std::string_view, Color fg = default_color_fg,
+                    Color bg = default_color_bg)
+          -> std::unique_ptr<SDL_Surface, Deleter>;
         [[nodiscard]] auto style() const noexcept -> uint8_t;
         auto               style(uint8_t) noexcept -> Font*;
-        [[nodiscard]] auto text_size(const std::string&) const noexcept -> Size;
+        [[nodiscard]] auto text_size(std::string_view) const noexcept -> Size;
 
-        [[nodiscard]] static auto find(const std::string&) -> std::string;
+        // Get file path of the font best matching a give fontconfig pattern.
+        [[nodiscard]] static auto find(std::string_view) -> std::string;
     };
 }
 
diff --git a/inc/basic_widgets/core/math.hpp b/inc/basic_widgets/core/math.hpp
index 8fd63f5..076894d 100644
--- a/inc/basic_widgets/core/math.hpp
+++ b/inc/basic_widgets/core/math.hpp
@@ -4,36 +4,39 @@
 #include <algorithm>
 #include <cmath>
 
-#include <SDL2/SDL_rect.h>
+#include <SDL_rect.h>
 
 #include <basic_widgets/core/type/color.hpp>
-#include <basic_widgets/core/type/concepts.hpp>
 #include <basic_widgets/core/type/size.hpp>
 
 namespace bwidgets
 {
-    // NOLINTNEXTLINE(clang-diagnostic-unused-function)
-    [[nodiscard]] static inline auto center_line(int available_len, int used_len) noexcept -> int
+    // Get the start coordinate offset required to center a ligne with a length used_len on another
+    // line with a length available_len.
+    [[nodiscard]] inline auto center_line(const int available_len, const int used_len) noexcept -> int
     {
         return (available_len - used_len) / 2;
     }
 
-    [[nodiscard]] static inline auto distance_sqrd(const SDL_Point& a, const SDL_Point& b) noexcept
+    // Get the squared distance of two points on a 2D plan. This avoid computing square root
+    // when for instance we need to compare two lenght but knowing the actual lenght is not
+    // needed.
+    [[nodiscard]] inline auto distance_sqrd(const SDL_Point a, const SDL_Point b) noexcept
       -> float
     {
-        // NOLINTNEXTLINE(bugprone-narrowing-conversions)
-        return (a.x - b.x) * (a.x - b.x)
-             + (a.y - b.y) * (a.y - b.y);
+        return float(a.x - b.x) * float(a.x - b.x)
+             + float(a.y - b.y) * float(a.y - b.y);
     }
 
-    // NOLINTNEXTLINE(clang-diagnostic-unused-function)
-    [[nodiscard]] static inline auto distance(const SDL_Point& a, const SDL_Point& b) noexcept -> float
+    // Get distance of two points on a 2D plan.
+    [[nodiscard]] inline auto distance(const SDL_Point a, const SDL_Point b) noexcept -> float
     {
         return std::sqrt(distance_sqrd(a, b));
     }
 
+    // Like std::lerp but for use with Color object. lerp function is applied only to enabled channels.
     template<FloatingPoint F>
-    [[nodiscard]] static inline auto lerp(const Color& a, const Color& b, F x, bool op_alpha=false, bool op_color=true) noexcept -> Color
+    [[nodiscard]] inline auto lerp(const Color a, const Color b, const F x, const bool op_alpha=false, const bool op_color=true) noexcept -> Color
     {
         return {{
             op_color ? (uint8_t)std::lerp(a().r, b().r, x) : a().r,
@@ -43,45 +46,48 @@ namespace bwidgets
         }};
     }
 
+    // Reverse lerp.
     template<Numeric N>
-    [[nodiscard]] static inline auto linear(N x, N a, N b) noexcept -> float
+    [[nodiscard]] inline auto linear(const N x, const N a, const N b) noexcept -> float
     {
         return (float)(x - a) / (float)(b - a);
     }
 
-    // NOLINTNEXTLINE(clang-diagnostic-unused-function)
-    [[nodiscard]] static inline auto rect_in_rect(const SDL_Rect& outer, const SDL_Rect& inner) noexcept
+    // Check if a rectangle is completly inside of another rectangle.
+    [[nodiscard]] inline auto rect_in_rect(const SDL_Rect& outer, const SDL_Rect& inner) noexcept
       -> bool
     {
-        SDL_Point top_left {inner.x, inner.y};
-        SDL_Point bottom_right {inner.x + inner.w, inner.y + inner.h};
+        const SDL_Point top_left {inner.x, inner.y};
+        const SDL_Point bottom_right {inner.x + inner.w, inner.y + inner.h};
 
         return (SDL_PointInRect(&top_left, &outer) == SDL_TRUE)
             && (SDL_PointInRect(&bottom_right, &outer) == SDL_TRUE);
     }
 
-    // NOLINTNEXTLINE(clang-diagnostic-unused-function)
-    [[nodiscard]] static inline auto rect_margin(const SDL_Rect& r, const Size& margin) noexcept
+    // Get the rectangle inside r leaving margins of given size between inner and outer rectangle.
+    [[nodiscard]] inline auto rect_margin(const SDL_Rect& r, const Size margin) noexcept
       -> SDL_Rect
     {
         return {r.x + margin.w, r.y + margin.h, r.w - 2 * margin.w, r.h - 2 * margin.h};
     }
 
-    [[nodiscard]] static inline auto rect_offset(const SDL_Rect& r, const SDL_Point& offset) noexcept
+    // Get the rectangle obtained from adding offset to its origin coordinate.
+    [[nodiscard]] inline auto rect_offset(const SDL_Rect& r, const SDL_Point offset) noexcept
       -> SDL_Rect
     {
         return {r.x + offset.x, r.y + offset.y, r.w, r.h};
     }
 
-    // NOLINTNEXTLINE(clang-diagnostic-unused-function)
-    [[nodiscard]] static inline auto rect_offset(const SDL_Rect& r, const SDL_Rect& offset) noexcept
+    // Commodity function to use another rectangle as a size for the offset to be added to r.
+    [[nodiscard]] inline auto rect_offset(const SDL_Rect& r, const SDL_Rect& offset) noexcept
       -> SDL_Rect
     {
         return rect_offset(r, SDL_Point {offset.x, offset.y});
     }
 
+    // Standard smoothstep algorithm.
     template<Numeric N>
-    [[nodiscard]] static inline auto smoothstep(N x, N a, N b) noexcept -> float
+    [[nodiscard]] inline auto smoothstep(const N x, const N a, const N b) noexcept -> float
     {
         const float x_norm = linear(std::clamp<float>(x, a, b), a, b);
         return 3 * x_norm * x_norm - 2 * x_norm * x_norm * x_norm;
diff --git a/inc/basic_widgets/core/renderer.hpp b/inc/basic_widgets/core/renderer.hpp
index 49ba120..b81d079 100644
--- a/inc/basic_widgets/core/renderer.hpp
+++ b/inc/basic_widgets/core/renderer.hpp
@@ -1,27 +1,31 @@
 #ifndef BWIDGETS_RENDERER_HPP
 #define BWIDGETS_RENDERER_HPP
 
-#include <cstdint>
-#include <vector>
+#include <memory>
+#include <span>
 
-#include <SDL2/SDL_render.h>
+#include <SDL_render.h>
 
+#include <basic_widgets/core/error_helper.hpp>
 #include <basic_widgets/core/type/color.hpp>
-#include <basic_widgets/core/type/opaque_struct.hpp>
-#include <basic_widgets/core/type/sdl_error.hpp>
+#include <basic_widgets/core/type/deleter.hpp>
 #include <basic_widgets/core/type/size.hpp>
 
 namespace bwidgets
 {
     class Texture;
 
-    class Renderer final : public OpaqueStruct<SDL_Renderer>
+    // Wrap some of SDL's 2D accelerated rendering API.
+    class Renderer final
     {
-        static inline auto _info(SDL_Renderer* r) -> SDL_RendererInfo
+        friend Texture;
+
+        const std::unique_ptr<SDL_Renderer, Deleter> _data;
+
+        static auto _info(SDL_Renderer* r) -> SDL_RendererInfo
         {
             SDL_RendererInfo info;
-            SDLError::success_or_throw(SDL_GetRendererInfo(r, &info), __FILE__,
-                                       __FUNCTION__, __LINE__);
+            success_or_throw<SDLError>(SDL_GetRendererInfo(r, &info));
 
             return info;
         }
@@ -29,59 +33,61 @@ namespace bwidgets
     public:
         const SDL_RendererInfo info;
 
-        Renderer(SDL_Renderer*);
+        explicit Renderer(SDL_Renderer*);
         Renderer(SDL_Window*, int, uint32_t);
         Renderer(const Renderer&) = delete;
-        ~Renderer() noexcept override;
+        Renderer(Renderer&&)      = delete;
+        ~Renderer() noexcept      = default;
 
         auto operator=(const Renderer&) = delete;
+        auto operator=(Renderer&&) = delete;
 
         [[nodiscard]] auto blend_mode() -> SDL_BlendMode;
         auto               blend_mode(SDL_BlendMode) -> Renderer*;
         auto               clear() -> Renderer*;
-        auto               copy(Texture*, const SDL_Rect*, const SDL_Rect*) -> Renderer*;
+        auto copy(const Texture&, const SDL_Rect*, const SDL_Rect*) -> Renderer*;
         [[nodiscard]] auto draw_color() -> Color;
-        auto               draw_color(const Color&) -> Renderer*;
-        auto               draw_line(const SDL_Point&, const SDL_Point&) -> Renderer*;
-        auto               draw_lines(const std::vector<SDL_Point>&) -> Renderer*;
-        auto               draw_point(const SDL_Point&) -> Renderer*;
-        auto               draw_points(const std::vector<SDL_Point>&) -> Renderer*;
+        auto               draw_color(Color) -> Renderer*;
+        auto               draw_line(SDL_Point, SDL_Point) -> Renderer*;
+        auto               draw_lines(std::span<SDL_Point>) -> Renderer*;
+        auto               draw_point(SDL_Point) -> Renderer*;
+        auto               draw_points(std::span<SDL_Point>) -> Renderer*;
         auto               draw_rect(const SDL_Rect*) -> Renderer*;
-        auto               draw_rects(const std::vector<SDL_Rect>&) -> Renderer*;
+        auto               draw_rects(std::span<SDL_Rect>) -> Renderer*;
         auto               fill_rect(const SDL_Rect*) -> Renderer*;
-        auto               fill_rects(const std::vector<SDL_Rect>&) -> Renderer*;
+        auto               fill_rects(std::span<SDL_Rect>) -> Renderer*;
         [[nodiscard]] auto output_size() -> Size;
         void               present() noexcept;
         [[nodiscard]] auto viewport() noexcept -> SDL_Rect;
         auto               viewport(const SDL_Rect*) -> Renderer*;
 
-        inline auto* copy(Texture* t, const SDL_Rect* src, const SDL_Rect& dst)
+        auto copy(const Texture& t, const SDL_Rect* src, const SDL_Rect& dst)
         {
             const auto d = dst;
             return copy(t, src, &d);
         }
-        inline auto* copy(Texture* t, const SDL_Rect& src, const SDL_Rect* dst)
+        auto copy(const Texture& t, const SDL_Rect& src, const SDL_Rect* dst)
         {
             const auto s = src;
             return copy(t, &s, dst);
         }
-        inline auto* copy(Texture* t, const SDL_Rect& src, const SDL_Rect& dst)
+        auto copy(const Texture& t, const SDL_Rect& src, const SDL_Rect& dst)
         {
             const auto s = src;
             const auto d = dst;
             return copy(t, &s, &d);
         }
-        inline auto* draw_rect(const SDL_Rect& r)
+        auto draw_rect(SDL_Rect&& r)
         {
             const auto rect = r;
             return draw_rect(&rect);
         }
-        inline auto* fill_rect(const SDL_Rect& r)
+        auto fill_rect(SDL_Rect&& r)
         {
             const auto rect = r;
             return fill_rect(&rect);
         }
-        inline auto* viewport(const SDL_Rect& vp)
+        auto viewport(SDL_Rect&& vp)
         {
             const auto v = vp;
             return viewport(&v);
diff --git a/inc/basic_widgets/core/texture.hpp b/inc/basic_widgets/core/texture.hpp
index 8d3c3c2..4870f02 100644
--- a/inc/basic_widgets/core/texture.hpp
+++ b/inc/basic_widgets/core/texture.hpp
@@ -1,54 +1,62 @@
 #ifndef BWIDGETS_TEXTURE_HPP
 #define BWIDGETS_TEXTURE_HPP
 
-#include <cstdint>
+#include <memory>
 
-#include <SDL2/SDL_pixels.h>
-#include <SDL2/SDL_render.h>
+#include <SDL_pixels.h>
+#include <SDL_render.h>
 
+#include <basic_widgets/core/error_helper.hpp>
 #include <basic_widgets/core/type/color.hpp>
-#include <basic_widgets/core/type/opaque_struct.hpp>
-#include <basic_widgets/core/type/sdl_error.hpp>
+#include <basic_widgets/core/type/deleter.hpp>
 
 namespace bwidgets
 {
     class Renderer;
 
-    class Texture final : public OpaqueStruct<SDL_Texture>
+    // Wrap most of the texture functions of SDL 2D rendering API.
+    class Texture final
     {
-        struct Attr
+        friend Renderer;
+
+        struct Attr final
         {
             uint32_t          format_raw;
             SDL_PixelFormat*  format;
             SDL_TextureAccess access;
             int               w, h;
-        } _attributes {};
+        };
+
+        const Attr                                  _attributes;
+        const std::unique_ptr<SDL_Texture, Deleter> _data;
 
     public:
-        Texture(SDL_Texture*);
-        Texture(Renderer* r, SDL_PixelFormatEnum f, SDL_TextureAccess a, int w, int h);
-        Texture(Renderer*, SDL_Surface*);
+        explicit Texture(SDL_Texture*);
+        Texture(const Renderer&, SDL_PixelFormatEnum, SDL_TextureAccess, int, int);
+        Texture(const Renderer&, SDL_Surface*);
         Texture(const Texture&) = delete;
-        ~Texture() noexcept override;
+        Texture(Texture&&)      = delete;
+        ~Texture() noexcept;
 
         auto operator=(const Texture&) = delete;
+        auto operator=(Texture&&) = delete;
 
         [[nodiscard]] auto alpha_mode() -> uint8_t;
         auto               alpha_mode(uint8_t) -> Texture*;
         [[nodiscard]] auto blend_mode() -> SDL_BlendMode;
         auto               blend_mode(SDL_BlendMode) -> Texture*;
         [[nodiscard]] auto color_mode() -> Color;
-        auto               color_mode(const Color&) -> Texture*;
+        auto               color_mode(Color) -> Texture*;
         [[nodiscard]] auto scale_mode() -> SDL_ScaleMode;
         auto               scale_mode(SDL_ScaleMode) -> Texture*;
-        auto               update(SDL_Rect*, const void*, int) -> Texture*;
+        auto               update(const SDL_Rect*, const void*, int) -> Texture*;
 
-        [[nodiscard]] inline const auto& attributes() const noexcept
+        [[nodiscard]] const auto& attributes() const noexcept
         {
             return _attributes;
         }
 
-        inline auto update(const SDL_Rect& r, const void* pix, int pitch)
+        auto update(SDL_Rect&& r, const void* pix, int pitch)
         {
             SDL_Rect rect = r;
             update(&rect, pix, pitch);
@@ -56,15 +64,14 @@ namespace bwidgets
             return this;
         }
 
-        [[nodiscard]] static inline auto attributes(SDL_Texture* t)
+        [[nodiscard]] static auto attributes(SDL_Texture* t)
         {
             Attr attr {};
-            SDLError::success_or_throw(SDL_QueryTexture(t, &attr.format_raw,
-                                                        (int*)&attr.access, &attr.w,
-                                                        &attr.h),
-                                       __FILE__, __FUNCTION__, __LINE__);
-            attr.format = SDLError::ptr_or_throw(SDL_AllocFormat(attr.format_raw),
-                                                 __FILE__, __FUNCTION__, __LINE__);
+            success_or_throw<SDLError>(
+              SDL_QueryTexture(t, &attr.format_raw,
+                               // NOLINTNEXTLINE(cppcoreguidelines-pro-type-cstyle-cast)
+                               (int*)&attr.access, &attr.w, &attr.h));
+            attr.format = ptr_or_throw<SDLError>(SDL_AllocFormat(attr.format_raw));
 
             return attr;
         }
diff --git a/inc/basic_widgets/core/type/color.hpp b/inc/basic_widgets/core/type/color.hpp
index 928009d..5f700ec 100644
--- a/inc/basic_widgets/core/type/color.hpp
+++ b/inc/basic_widgets/core/type/color.hpp
@@ -1,136 +1,149 @@
 #ifndef BWIDGETS_COLOR_HPP
 #define BWIDGETS_COLOR_HPP
 
-#include <cstdint>
+#include <cmath>
 #include <functional>
+#include <stdexcept>
 
-#include <SDL2/SDL_assert.h>
-#include <SDL2/SDL_pixels.h>
+#include <SDL_pixels.h>
 
 #include <basic_widgets/core/type/concepts.hpp>
 
 namespace bwidgets
 {
+    // Wrap SDL_Color to provide operator overloads.
     class Color final
     {
     public:
-        [[nodiscard]] inline auto& operator()() noexcept
+        SDL_Color sdl_type;
+
+        Color(uint8_t r, uint8_t g, uint8_t b, uint8_t a, bool op_on_alpha = false,
+              bool op_on_colors = true) noexcept
+          : sdl_type {r, g, b, a},
+            _operate_on_alpha {op_on_alpha},
+            _operate_on_colors {op_on_colors}
+        {}
+        Color(SDL_Color c = {}, bool op_on_alpha = false,
+              bool op_on_colors = true) noexcept
+          : sdl_type(c), _operate_on_alpha(op_on_alpha), _operate_on_colors(op_on_colors)
+        {}
+        Color(const Color&) noexcept = default;
+        Color(Color&&) noexcept      = default;
+        ~Color()                     = default;
+
+        // Enable/disable operations on alpha channel. Disabled by default on
+        // construction.
+        [[nodiscard]] auto alpha(const bool state = true) const noexcept -> Color
+        {
+            return {sdl_type, _operate_on_colors, state};
+        }
+
+        // Enable/disable operations on color channels.Enabled by default on
+        // construction.
+        [[nodiscard]] auto colors(const bool state = true) const noexcept -> Color
+        {
+            return {sdl_type, state, _operate_on_alpha};
+        }
+
+        // Get reference to the wrapped SDL native object.
+        [[nodiscard]] auto& operator()() noexcept
         {
             return sdl_type;
         }
 
-        [[nodiscard]] inline const auto& operator()() const noexcept
+        [[nodiscard]] const auto& operator()() const noexcept
         {
             return sdl_type;
         }
 
+        // Add operand to enabled channels.
+        template<Numeric N>
+        [[nodiscard]] auto operator+(const N operand) const noexcept
+        {
+            return _operate(operand, [](N a, N b) { return a + b; });
+        }
+
+        // Substract operand from enabled channels.
+        template<Numeric N>
+        [[nodiscard]] auto operator-(const N operand) const noexcept
+        {
+            return _operate(operand, [](N a, N b) { return a - b; });
+        }
+
+        // Multiply enabled channel values by opererand.
+        template<Numeric N>
+        [[nodiscard]] auto operator*(const N operand) const noexcept
+        {
+            return _operate(operand, [](N a, N b) { return a * b; });
+        }
+
+        // Divide enabled channel values by operand.
+        template<Numeric N>
+        [[nodiscard]] auto operator/(const N operand) const
+        {
+            if (operand == 0) throw std::domain_error("division by zero.");
+
+            return _operate<N>(operand, [](N a, N b) { return a / b; });
+        }
+
+        auto operator=(const Color& c) noexcept -> Color& = default;
+        auto operator=(Color&&) noexcept -> Color& = default;
+
+        auto& operator=(SDL_Color c) noexcept
+        {
+            sdl_type = c;
+            return *this;
+        }
+
+        // Compare for equality of the enabled channel values between two Color
+        // instances.
+        [[nodiscard]] auto operator==(const Color other) const noexcept
+        {
+            return (_operate_on_colors && sdl_type.r == other().r
+                    && sdl_type.g == other().g && sdl_type.b == other().b)
+                || (_operate_on_alpha && sdl_type.a == other().a);
+        }
+
+        // Compare for inequality of the enabled channel values between two Color
+        // instances.
+        [[nodiscard]] auto operator!=(const Color other) const noexcept
+        {
+            return (sdl_type.r != other().r || sdl_type.g != other().g
+                    || sdl_type.b != other().b)
+                && ((_operate_on_alpha && sdl_type.a != other().a)
+                    || !_operate_on_alpha);
+        }
+
     private:
         bool _operate_on_alpha;
         bool _operate_on_colors;
 
         template<Numeric N>
-        inline auto
-        _operate(const N&                                    operand,
-                 const std::function<N(const N&, const N&)>& operator_) const noexcept
+        auto _operate(const N operand, const std::function<N(N, N)>& operator_) const
         {
+            const auto overunderflow_check = [](auto x) {
+                if (x > (uint8_t)x) throw std::overflow_error("uint8_t overflow.");
+                if (x < (uint8_t)x) throw std::underflow_error("uint8_t underflow.");
+            };
+
             Color c(sdl_type, _operate_on_alpha, _operate_on_colors);
             if (_operate_on_alpha) {
-                auto a = std::round(operator_(c().a, operand));
-                SDL_assert_release(a == (uint8_t)a); // NOLINT
+                const auto a = std::round(operator_(c().a, operand));
+                overunderflow_check(a);
                 c().a = (uint8_t)a;
             }
             if (_operate_on_colors) {
-                auto r = std::round(operator_(c().r, operand));
-                auto g = std::round(operator_(c().g, operand));
-                auto b = std::round(operator_(c().b, operand));
-                // NOLINTNEXTLINE
-                SDL_assert_release(r == (uint8_t)r && g == (uint8_t)g
-                                   && b == (uint8_t)b);
+                const auto r = std::round(operator_(c().r, operand));
+                const auto g = std::round(operator_(c().g, operand));
+                const auto b = std::round(operator_(c().b, operand));
+                for (const auto x : {r, g, b}) overunderflow_check(x);
+
                 c().r = (uint8_t)r;
                 c().g = (uint8_t)g;
                 c().b = (uint8_t)b;
             }
             return c;
         }
-
-    public:
-        SDL_Color sdl_type;
-
-        inline Color(uint8_t r, uint8_t g, uint8_t b, uint8_t a,
-                     bool op_on_alpha = false, bool op_on_colors = true) noexcept
-          : _operate_on_alpha(op_on_alpha),
-            _operate_on_colors(op_on_colors),
-            sdl_type({r, g, b, a})
-        {}
-        inline Color(const SDL_Color& c = {}, bool op_on_alpha = false,
-                     bool op_on_colors = true) noexcept
-          : _operate_on_alpha(op_on_alpha), _operate_on_colors(op_on_colors), sdl_type(c)
-        {}
-        inline Color(const Color&) noexcept = default;
-
-        [[nodiscard]] inline auto alpha() const noexcept -> Color
-        {
-            return {sdl_type, _operate_on_colors, true};
-        }
-
-        [[nodiscard]] inline auto colors() const noexcept -> Color
-        {
-            return {sdl_type, true, _operate_on_alpha};
-        }
-
-        template<Numeric N>
-        [[nodiscard]] inline auto operator+(const N& operand) const noexcept
-        {
-            return _operate(operand, [](const N& a, const N& b) { return a + b; });
-        }
-
-        template<Numeric N>
-        [[nodiscard]] inline auto operator-(const N& operand) const noexcept
-        {
-            return _operate(operand, [](const N& a, const N& b) { return a - b; });
-        }
-
-        template<Numeric N>
-        [[nodiscard]] inline auto operator*(const N& operand) const noexcept
-        {
-            return _operate(operand, [](const N& a, const N& b) { return a * b; });
-        }
-
-        template<Numeric N>
-        [[nodiscard]] inline auto operator/(const N& operand) const noexcept
-        {
-            SDL_assert(operand != 0); // NOLINT
-            return _operate<N>(operand, [](const N& a, const N& b) { return a / b; });
-        }
-
-        inline auto& operator=(const Color& c) noexcept
-        {
-            if (this != &c) {
-                sdl_type = c.sdl_type;
-            }
-            return *this;
-        }
-
-        inline auto& operator=(const SDL_Color& c) noexcept
-        {
-            sdl_type = c;
-            return *this;
-        }
-
-        [[nodiscard]] inline auto operator==(const Color& other) const noexcept
-        {
-            return (_operate_on_colors && sdl_type.r == other().r
-                    && sdl_type.g == other().g && sdl_type.b == other().b)
-                || (_operate_on_alpha && sdl_type.a == other().a);
-        }
-
-        [[nodiscard]] inline auto operator!=(const Color& other) const noexcept
-        {
-            return (sdl_type.r != other().r || sdl_type.g != other().g
-                    || sdl_type.b != other().b)
-                && ((_operate_on_alpha && sdl_type.a != other().a)
-                    || !_operate_on_alpha);
-        }
     };
 }
 
diff --git a/inc/basic_widgets/core/type/concepts.hpp b/inc/basic_widgets/core/type/concepts.hpp
index f51e1b3..2e961bc 100644
--- a/inc/basic_widgets/core/type/concepts.hpp
+++ b/inc/basic_widgets/core/type/concepts.hpp
@@ -1,25 +1,27 @@
-#ifndef BWIDGETS_CONCEPTS_HPP_
-#define BWIDGETS_CONCEPTS_HPP_
+#ifndef BWIDGETS_CONCEPTS_HPP
+#define BWIDGETS_CONCEPTS_HPP
 
-#include <ostream>
 #include <string>
-
 #include <type_traits>
 
 namespace bwidgets
 {
+    // T can be converted to string with to_string.
     template<typename T>
     concept CanToString = requires(T value)
     {
         std::to_string(value);
     };
 
+    // T is a floating point type.
     template<typename T>
     concept FloatingPoint = std::is_floating_point_v<T>;
 
+    // T can be any numeric type.
     template<typename T>
     concept Numeric = std::is_arithmetic_v<T>;
 
+    // T can be converted to string by using ostream.
     template<typename T>
     concept Printable = requires(T value)
     {
diff --git a/inc/basic_widgets/core/type/deleter.hpp b/inc/basic_widgets/core/type/deleter.hpp
new file mode 100644
index 0000000..08e5c05
--- /dev/null
+++ b/inc/basic_widgets/core/type/deleter.hpp
@@ -0,0 +1,51 @@
+#ifndef BWIDGETS_OPAQUE_STRUCT_HPP
+#define BWIDGETS_OPAQUE_STRUCT_HPP
+
+#include <fontconfig/fontconfig.h>
+#include <SDL_render.h>
+#include <SDL_surface.h>
+#include <SDL_ttf.h>
+
+namespace bwidgets
+{
+    // Deleter type for fancy pointers.
+    struct Deleter
+    {
+        void operator()(FcConfig* ptr)
+        {
+            FcConfigDestroy(ptr);
+        }
+
+        void operator()(FcPattern* ptr)
+        {
+            FcPatternDestroy(ptr);
+        }
+
+        void operator()(SDL_Renderer* ptr)
+        {
+            SDL_DestroyRenderer(ptr);
+        }
+
+        void operator()(SDL_Surface* ptr)
+        {
+            SDL_FreeSurface(ptr);
+        }
+
+        void operator()(SDL_Texture* ptr)
+        {
+            SDL_DestroyTexture(ptr);
+        }
+
+        void operator()(SDL_Window* ptr)
+        {
+            SDL_DestroyWindow(ptr);
+        }
+
+        void operator()(TTF_Font* ptr)
+        {
+            TTF_CloseFont(ptr);
+        }
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/core/type/exception.hpp b/inc/basic_widgets/core/type/exception.hpp
index f119103..c8dd5ed 100644
--- a/inc/basic_widgets/core/type/exception.hpp
+++ b/inc/basic_widgets/core/type/exception.hpp
@@ -1,47 +1,22 @@
 #ifndef BWIDGETS_EXCEPTION_HPP
 #define BWIDGETS_EXCEPTION_HPP
 
-#include <any>
-#include <exception>
-#include <functional>
-#include <map>
+#include <stdexcept>
 
 #include <basic_widgets/core/type/concepts.hpp>
 
 namespace bwidgets
 {
-    struct BaseException : std::exception
+    // Base type for custom runtime errors.
+    class BaseException : std::runtime_error
     {
-        const char* file;
-        const char* func;
-        const int   line;
-        const char* what;
-
-        BaseException(const char* file, const char* func, int l, const char* w) noexcept
-          : file(file), func(func), line(l), what(w)
-        {}
+    protected:
+        using runtime_error::runtime_error;
     };
 
+    // T derives from BaseException.
     template<typename T>
     concept Exception = std::derived_from<T, BaseException>;
-
-    template<Exception E, typename T>
-    static inline auto ptr_or_throw(T* ptr, const char* file, const char* func, int l,
-                                    const char* w = nullptr) -> T*
-    {
-        if (ptr == nullptr) throw E(file, func, l, w);
-        return ptr;
-    }
-
-    template<Exception E, typename T>
-    static inline auto success_or_throw(
-      T code, const char* file, const char* func, int l, const char* w = nullptr,
-      std::function<bool(const T&)> success = [](const T& code) { return code == 0; })
-      -> T
-    {
-        if (!success(code)) throw E(file, func, l, w);
-        return code;
-    }
 }
 
 #endif
diff --git a/inc/basic_widgets/core/type/fc_error.hpp b/inc/basic_widgets/core/type/fc_error.hpp
index 62b6d6a..91b1e17 100644
--- a/inc/basic_widgets/core/type/fc_error.hpp
+++ b/inc/basic_widgets/core/type/fc_error.hpp
@@ -5,11 +5,10 @@
 
 namespace bwidgets
 {
+    // Exception type for fontconfig errors
     struct FCError final : BaseException
     {
-        FCError(const char* file, const char* func, int l, const char* w = nullptr)
-          : BaseException(file, func, l, w)
-        {}
+        using BaseException::BaseException;
     };
 }
 
diff --git a/inc/basic_widgets/core/type/opaque_struct.hpp b/inc/basic_widgets/core/type/opaque_struct.hpp
deleted file mode 100644
index ebc75f2..0000000
--- a/inc/basic_widgets/core/type/opaque_struct.hpp
+++ /dev/null
@@ -1,31 +0,0 @@
-#ifndef BWIDGETS_OPAQUE_STRUCT_HPP
-#define BWIDGETS_OPAQUE_STRUCT_HPP
-
-namespace bwidgets
-{
-    template<typename T>
-    class OpaqueStruct
-    {
-    protected:
-        T* _c_pod;
-
-    public:
-        OpaqueStruct(T* ptr = nullptr) : _c_pod(ptr) {}
-        virtual ~OpaqueStruct<T>() noexcept = default;
-
-        // NOLINTNEXTLINE(modernize-use-trailing-return-type)
-        [[nodiscard]] inline auto& operator()()
-        {
-            return _c_pod;
-        }
-    };
-
-    template<typename... Ts>
-    void discard(Ts*&... ptrs)
-    {
-        ((delete ptrs), ...);
-        ((ptrs = nullptr), ...);
-    }
-}
-
-#endif
diff --git a/inc/basic_widgets/core/type/sdl_error.hpp b/inc/basic_widgets/core/type/sdl_error.hpp
index 58f6508..9fe0f8b 100644
--- a/inc/basic_widgets/core/type/sdl_error.hpp
+++ b/inc/basic_widgets/core/type/sdl_error.hpp
@@ -3,40 +3,12 @@
 
 #include <basic_widgets/core/type/exception.hpp>
 
-extern "C" {
-    auto SDL_GetError() -> const char*;
-}
-
 namespace bwidgets
 {
+    // Custom exception type for SDL errors.
     struct SDLError final : BaseException
     {
-        SDLError(const char* file, const char* func, const int l,
-                 const char* w = nullptr) noexcept
-          : BaseException(file, func, l, w)
-        {}
-
-        template<typename T>
-        [[nodiscard]] static inline auto ptr_or_throw(T* ptr, const char* file,
-                                                      const char* func, int l,
-                                                      const char* w = nullptr) -> T*
-        {
-            if (!ptr) {
-                if (!w) w = SDL_GetError();
-                throw SDLError(file, func, l, w);
-            }
-            return ptr;
-        }
-
-        static inline auto success_or_throw(int code, const char* file, const char* func,
-                                            int l, const char* w = nullptr) -> int
-        {
-            if (code < 0) {
-                if (w == nullptr) w = SDL_GetError();
-                throw SDLError(file, func, l, w);
-            }
-            return code;
-        }
+        using BaseException::BaseException;
     };
 }
 
diff --git a/inc/basic_widgets/core/type/size.hpp b/inc/basic_widgets/core/type/size.hpp
index fed68c4..4da376f 100644
--- a/inc/basic_widgets/core/type/size.hpp
+++ b/inc/basic_widgets/core/type/size.hpp
@@ -5,30 +5,37 @@
 
 namespace bwidgets
 {
+    // Represent size of a 2D surface.
     struct Size
     {
         int w;
         int h;
-
-        [[nodiscard]] inline auto operator-() const noexcept -> Size
-        {
-            return {-w, -h};
-        }
-        [[nodiscard]] inline auto operator+(const Size& s) const noexcept -> Size
-        {
-            return {w + s.w, h + s.h};
-        }
-        [[nodiscard]] inline auto operator-(const Size& s) const noexcept -> Size
-        {
-            return {w - s.w, h - s.h};
-        }
-
-        template<Numeric N>
-        [[nodiscard]] inline auto operator*(N a) const noexcept -> Size
-        {
-            return {a * w, a * h};
-        }
     };
+
+    // Addition the dimensions of two Size objects.
+    [[nodiscard]] inline auto operator+(const Size a, const Size b) noexcept -> Size
+    {
+        return {a.w + b.w, a.h + b.h};
+    }
+
+    // Substract dimensions of a Size object from another.
+    [[nodiscard]] inline auto operator-(const Size a, const Size b) noexcept -> Size
+    {
+        return {a.w - b.w, a.h - b.h};
+    }
+
+    // Multiply dimensions of a Size instance by a number.
+    template<Numeric N>
+    [[nodiscard]] inline auto operator*(const Size a, const N b) noexcept -> Size
+    {
+        return {a.w * b, a.h * b};
+    }
+
+    template<Numeric N>
+    [[nodiscard]] inline auto operator*(const N a, const Size b) noexcept -> Size
+    {
+        return b * a;
+    }
 }
 
 #endif
diff --git a/inc/basic_widgets/w/aligned_layout.hpp b/inc/basic_widgets/w/aligned_layout.hpp
index cae76dd..5aa3bc3 100644
--- a/inc/basic_widgets/w/aligned_layout.hpp
+++ b/inc/basic_widgets/w/aligned_layout.hpp
@@ -5,21 +5,17 @@
 
 namespace bwidgets
 {
-    class AlignedLayout final : public Layout
+    enum struct LayoutAlignment
     {
-    private:
-        void _update_layout(const SDL_Rect&) override;
+        HORIZONTAL,
+        VERTICAL
+    };
 
+    // Align vertically or horizontally widgets.
+    class AlignedLayout : public virtual Layout
+    {
     public:
-        enum struct Alignment
-        {
-            HORIZONTAL,
-            VERTICAL
-        } alignment;
-
-        AlignedLayout(Alignment align) noexcept : alignment(align) {}
-
-        [[nodiscard]] auto size() const noexcept -> Size override;
+        using Layout::Layout;
     };
 }
 
diff --git a/inc/basic_widgets/w/aligned_layout_impl.hpp b/inc/basic_widgets/w/aligned_layout_impl.hpp
new file mode 100644
index 0000000..a302002
--- /dev/null
+++ b/inc/basic_widgets/w/aligned_layout_impl.hpp
@@ -0,0 +1,77 @@
+#ifndef BWIDGETS_ALIGNED_LAYOUT_IMPL_HPP
+#define BWIDGETS_ALIGNED_LAYOUT_IMPL_HPP
+
+#include <basic_widgets/core/math.hpp>
+#include <basic_widgets/w/aligned_layout.hpp>
+#include <basic_widgets/w/base/layout_impl.hpp>
+#include <basic_widgets/w/base/widget_impl.hpp>
+
+namespace bwidgets
+{
+    template<LayoutAlignment alignment>
+    class AlignedLayoutImpl final : public virtual AlignedLayout,
+                                    public virtual LayoutImpl,
+                                    public virtual WidgetImpl
+    {
+    public:
+        using LayoutImpl::LayoutImpl;
+
+        // Return smallest usable size.
+        [[nodiscard]] auto size() const noexcept -> Size override
+        {
+            Size min_size {0, 0};
+
+            if constexpr (alignment == LayoutAlignment::HORIZONTAL) {
+                for (const auto& w : _widgets) {
+                    if (w->size().w > min_size.w) min_size.w = w->size().w;
+                    if (w->size().h > min_size.h) min_size.h = w->size().h;
+                }
+
+                return {(int)_widgets.size() * min_size.w
+                          + ((int)_widgets.size() + 1) * margins.w,
+                        min_size.h + 2 * margins.h};
+            }
+
+            // Vertical
+            for (const auto& w : _widgets) {
+                if (w->size().w > min_size.w) min_size.w = w->size().w;
+
+                min_size.h += w->size().h;
+            }
+
+            return {min_size.w + 2 * margins.w,
+                    min_size.h + ((int)_widgets.size() + 1) * margins.h};
+        }
+
+    private:
+        void _update_layout(const SDL_Rect& vp) override
+        {
+            if constexpr (alignment == LayoutAlignment::HORIZONTAL) {
+                const int widget_width =
+                  (vp.w - ((int)_widgets.size() + 1) * margins.w) / (int)_widgets.size();
+
+                for (std::vector<Widget*>::size_type i = 0; i < _widgets.size(); i++) {
+                    const auto& w {_widgets[i]};
+                    w->viewport({vp.x + margins.w + (int)i * (widget_width + margins.w),
+                                 vp.y + center_line(vp.h, w->size().h), widget_width,
+                                 w->size().h});
+                }
+            }
+            else { // Vertical
+                int offset = 0;
+                for (std::vector<Widget*>::size_type i = 0; i < _widgets.size(); i++) {
+                    const auto& w {_widgets[i]};
+                    w->viewport({
+                      vp.x,
+                      vp.y + ((int)i + 1) * margins.h + offset,
+                      vp.w,
+                      w->size().h,
+                    });
+                    offset += w->size().h;
+                }
+            }
+        }
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/w/base/input.hpp b/inc/basic_widgets/w/base/input.hpp
index 48930a1..6974a90 100644
--- a/inc/basic_widgets/w/base/input.hpp
+++ b/inc/basic_widgets/w/base/input.hpp
@@ -1,18 +1,9 @@
 #ifndef BWIDGETS_INPUT_HPP
 #define BWIDGETS_INPUT_HPP
 
-#include <cmath>
-#include <exception>
-#include <iomanip>
-#include <sstream>
-
-#include <SDL2/SDL_events.h>
-#include <SDL2/SDL_keyboard.h>
-#include <SDL2/SDL_render.h>
-
-#include <basic_widgets/core/math.hpp>
 #include <basic_widgets/core/type/concepts.hpp>
-#include <basic_widgets/w/caption.hpp>
+#include <basic_widgets/w/base/widget.hpp>
+#include <basic_widgets/w/feat/font_handler.hpp>
 #include <basic_widgets/w/feat/keyboard_handler.hpp>
 #include <basic_widgets/w/feat/mouse_handler.hpp>
 
@@ -20,104 +11,13 @@ namespace bwidgets
 {
 
     template<typename T>
-    class Input : public Widget,
-                  public FontHandler,
-                  public KeyboardHandler,
-                  public MouseHandler
+    class Input : public virtual Widget,
+                  public virtual FontHandler,
+                  public virtual KeyboardHandler,
+                  public virtual MouseHandler
     {
     protected:
-        Caption _input_caption;
-
-        Input(Widget* parent = nullptr) : Widget(parent), _input_caption(this)
-        {
-            FocusHandler::_focus_area = &_widget_area;
-            MouseHandler::_click_area = &_widget_area;
-            _input_caption.text(value_to_string(value));
-        }
-
-        void _handle_focus_change(bool focus) override
-        {
-            if (focus) {
-                SDL_StartTextInput();
-            }
-            else {
-                value = value_from_string(input_text());
-                input_text(value_to_string(value));
-                SDL_StopTextInput();
-            }
-        }
-
-        void _handle_font_change(Font* f) override
-        {
-            _input_caption.font(f);
-            _handle_geometry_change(_viewport);
-        }
-
-        void _handle_font_color_change(const Color& fg,
-                                       const Color& bg) override
-        {
-            _input_caption.font_color_bg(bg)->font_color_fg(fg);
-        }
-
-        void _handle_geometry_change(const SDL_Rect& vp) override
-        {
-            const auto input_h = _input_caption.size().h + 2 * border_width;
-            _widget_area       = {0, center_line(vp.h, input_h), vp.w, input_h};
-
-            _input_caption.viewport(rect_offset(
-              {rect_margin(_widget_area, {border_width, border_width})}, vp));
-        }
-
-        void _handle_key(const SDL_KeyboardEvent& key) override
-        {
-            if (key.type == SDL_KEYDOWN) {
-                switch (key.keysym.sym) {
-                    case SDLK_BACKSPACE: {
-                        std::string txt = input_text();
-                        if (txt.length() > 0) {
-                            txt.pop_back();
-                            input_text(txt);
-                        }
-                        break;
-                    }
-                    case SDLK_RETURN:
-                    case SDLK_RETURN2: // what is return2 btw?
-                    case SDLK_KP_ENTER:
-                        value = value_from_string(input_text());
-                        focus(false);
-                        break;
-                }
-            }
-        }
-
-        void _handle_renderer_change(Renderer* r) override
-        {
-            _input_caption.renderer(r);
-        }
-
-        void _handle_rendering() override
-        {
-            for (int i = border_width - 1; i >= 0; i--) {
-                const auto  factor      = linear(i, 0, border_width);
-                const auto& color_end   = _has_focus ? color_bg_focused : color_bg;
-                const auto  color_start = color_end / 2;
-                _renderer->draw_color(lerp(color_start, color_end, factor))
-                  ->draw_rect(rect_margin(_widget_area, {i, i}));
-            }
-
-            if (MouseHandler::_is_hovered || FocusHandler::_has_focus)
-                _input_caption.font_color_bg(color_bg_focused);
-            else _input_caption.font_color_bg(color_bg);
-
-            _input_caption.render();
-        }
-
-        void _handle_text_input(const SDL_TextInputEvent& input) override
-        {
-            if (is_valid_input(input.text)) {
-                input_text(input_text() + input.text);
-            }
-        }
+        using Widget::Widget;
 
     public:
         static const int          default_border_width = 3;
@@ -128,96 +28,30 @@ namespace bwidgets
         static const int          default_min_width        = 1;
 
         int   border_width     = default_border_width;
-        Color color_bg         = default_color_bg;
+        Color color_bg_default = default_color_bg;
         Color color_bg_focused = default_color_bg_focused;
         int   float_precision  = default_float_precision;
         int   input_min_width  = default_min_width;
-        char  input_width_unit = 'W';
+        char  input_width_unit = 'W'; // char used as unit for text length computation.
         T     value {};
 
-        virtual auto color_fg(const Color& c) -> Input<T>*
-        {
-            _input_caption.font_color_fg(c);
-            return this;
-        }
+        // Get the current displayed string.
+        [[nodiscard]] virtual auto input_text() const -> std::string_view = 0;
+        // Set displayed string
+        virtual void               input_text(std::string)                = 0;
+        virtual void               input_text_color(Color)                = 0;
+        // Check if a character is allowed to be inputted. String are used because we
+        // could have multibytes characters to represent using 8bits chars.
+        [[nodiscard]] virtual auto is_valid_input(std::string_view) const noexcept
+          -> bool = 0;
 
-        [[nodiscard]] virtual auto input_text() const -> const std::string&
-        {
-            return _input_caption.text();
-        }
-
-        virtual auto input_text(const std::string& txt) -> Input<T>*
-        {
-            _input_caption.text(txt);
-            return this;
-        }
-
-        [[nodiscard]] virtual auto is_valid_input(const std::string&) const noexcept
-          -> bool
-        {
-            return true;
-        }
-
-        [[nodiscard]] virtual auto process_value(T x) const noexcept -> T
-        {
-            return x;
-        }
-
-        [[nodiscard]] inline auto size() const noexcept -> Size override
-        {
-            if (_font == nullptr) return {0, 0};
-
-            return {
-              _font->text_size(std::string(input_min_width, input_width_unit)).w
-                + 2 * border_width,
-              _font->line_skip + 4 * border_width // _why_ 4 and not 2?…
-            };
-        }
-
-        [[nodiscard]] auto value_from_string(std::string s) noexcept
-        {
-            T v;
-
-            if constexpr (std::is_arithmetic_v<T>) {
-                s = s.length() > 0 ? s : "0";
-                if constexpr (std::is_floating_point_v<T>) v = (T)std::stold(s);
-                else if constexpr (std::is_integral_v<T>) v = (T)std::stoll(s);
-            }
-            else if constexpr (std::is_same_v<
-                                 T, std::string> || std::convertible_to<std::string, T>)
-                v = s;
-            else
-                // NOLINTNEXTLINE(readability-simplify-boolean-expr)
-                static_assert((bool)sizeof(T) && false,
-                              "string cannot be converted to v type T.");
-
-            return process_value(v);
-        }
-
-        [[nodiscard]] auto value_to_string(T value) noexcept
-        {
-            std::string s;
-
-            if constexpr (std::is_same_v<std::string,
-                                         T> || std::convertible_to<T, std::string>)
-                s = std::move(value);
-            else if constexpr (CanToString<T>) {
-                std::stringstream ss;
-                ss << std::fixed << std::setprecision(float_precision) << value;
-                s = std::move(ss).str();
-            }
-            else if constexpr (Printable<T>) {
-                std::stringstream ss;
-                ss << value;
-                s = std::move(ss).str();
-            }
-            else
-                // NOLINTNEXTLINE(readability-simplify-boolean-expr)
-                static_assert((bool)sizeof(T) && false,
-                              "value cannot be converted to string.");
-
-            return s;
-        }
+        // Process a value for instance to modify it before saving it.
+        [[nodiscard]] virtual auto process_value(T) const noexcept -> T = 0;
+        // Get string representation to be shown of the stored value.
+        [[nodiscard]] virtual auto value_from_string(std::string_view) const noexcept
+          -> T                                                                      = 0;
+        // Parse a string to get its representation in T type of input value memory.
+        [[nodiscard]] virtual auto value_to_string(T) const noexcept -> std::string = 0;
     };
 }
 
diff --git a/inc/basic_widgets/w/base/input_impl.hpp b/inc/basic_widgets/w/base/input_impl.hpp
new file mode 100644
index 0000000..238d42a
--- /dev/null
+++ b/inc/basic_widgets/w/base/input_impl.hpp
@@ -0,0 +1,231 @@
+#ifndef BWIDGETS_INPUT_IMPL_HPP
+#define BWIDGETS_INPUT_IMPL_HPP
+
+#include <iomanip>
+#include <sstream>
+
+#include <basic_widgets/core/math.hpp>
+#include <basic_widgets/w/base/input.hpp>
+#include <basic_widgets/w/base/widget_impl.hpp>
+#include <basic_widgets/w/caption.hpp>
+#include <basic_widgets/w/feat/font_handler_impl.hpp>
+#include <basic_widgets/w/feat/keyboard_handler_impl.hpp>
+#include <basic_widgets/w/feat/mouse_handler_impl.hpp>
+#include <basic_widgets/w/widget_factory.hpp>
+
+namespace bwidgets
+{
+    template<typename T>
+    class InputImpl : public virtual Input<T>,
+                      public virtual FontHandlerImpl,
+                      public virtual KeyboardHandlerImpl,
+                      public virtual MouseHandlerImpl,
+                      public virtual WidgetImpl
+    {
+    public:
+        [[nodiscard]] auto input_text() const -> std::string_view override
+        {
+            return _input_caption->text();
+        }
+
+        void input_text(std::string txt) override
+        {
+            _input_caption->text(std::move(txt));
+        }
+
+        void input_text_color(const Color c) override
+        {
+            _input_caption->font_color_fg(c);
+        }
+
+        [[nodiscard]] auto is_valid_input(const std::string_view) const noexcept
+          -> bool override
+        {
+            return true;
+        }
+
+        [[nodiscard]] auto process_value(const T x) const noexcept -> T override
+        {
+            return x;
+        }
+
+        [[nodiscard]] auto size() const noexcept -> Size override
+        {
+            if (!_font) return {0, 0};
+
+            return {
+              _font
+                  ->text_size(
+                    std::string(InputImpl::input_min_width, InputImpl::input_width_unit))
+                  .w
+                + 2 * InputImpl::border_width,
+              _font->line_skip + 4 * InputImpl::border_width // _why_ 4 and not 2?…
+            };
+        }
+
+        [[nodiscard]] auto value_from_string(const std::string_view s) const noexcept
+          -> T override
+        {
+            const T v = [s]() {
+                if constexpr (std::is_arithmetic_v<T>) {
+                    const auto _s = s.length() > 0 ? s : "0";
+                    if constexpr (std::is_floating_point_v<T>)
+                        return (T)std::stold(_s.data());
+                    else if constexpr (std::is_integral_v<T>)
+                        return (T)std::stoll(_s.data());
+                }
+                else if constexpr (std::is_same_v<
+                                     T,
+                                     std::string> || std::convertible_to<std::string, T>)
+                    return std::string(s);
+                else
+                    // NOLINTNEXTLINE(readability-simplify-boolean-expr)
+                    static_assert((bool)sizeof(T) && false,
+                                  "string cannot be converted to type T.");
+            }();
+
+            return process_value(v);
+        }
+
+        [[nodiscard]] auto value_to_string(const T value) const noexcept
+          -> std::string override
+        {
+            std::string s = [value, this]() {
+                if constexpr (std::is_same_v<std::string,
+                                             T> || std::convertible_to<T, std::string>)
+                    return std::move(value);
+                else if constexpr (CanToString<T>) {
+                    std::stringstream ss;
+                    ss << std::fixed << std::setprecision(InputImpl::float_precision)
+                       << value;
+                    return std::move(ss).str();
+                }
+                else if constexpr (Printable<T>) {
+                    std::stringstream ss;
+                    ss << value;
+                    return std::move(ss).str();
+                }
+                else
+                    // NOLINTNEXTLINE(readability-simplify-boolean-expr)
+                    static_assert((bool)sizeof(T) && false,
+                                  "value cannot be converted to string.");
+            }();
+
+            return s;
+        }
+
+    protected:
+        std::unique_ptr<Caption> _input_caption;
+
+        InputImpl(Widget* parent = nullptr)
+          : WidgetImpl {parent}, _input_caption {create_caption(this)}
+        {
+            // Start text input on focus. Stop it on focus loss and save the inputted
+            // value.
+            focus_handler([this](const bool focus) {
+                if (focus) {
+                    _input_caption->font_color_bg(InputImpl::color_bg_focused);
+                    SDL_StartTextInput();
+                    return;
+                }
+                SDL_StopTextInput();
+                _input_caption->font_color_bg(InputImpl::color_bg_default);
+
+                InputImpl::value = value_from_string(input_text());
+                input_text(value_to_string(InputImpl::value));
+                _input_caption->text(value_to_string(InputImpl::value));
+            });
+
+            key_handler([this](const SDL_KeyboardEvent& key) {
+                if (key.type == SDL_KEYDOWN) {
+                    switch (key.keysym.sym) {
+                        // Discard inputted value on escape key.
+                        case SDLK_ESCAPE: {
+                            focus(false);
+                            input_text(value_to_string(InputImpl::value));
+                            break;
+                        }
+                        case SDLK_BACKSPACE: {
+                            const auto& txt = input_text();
+                            if (const auto len = txt.length(); len > 0) {
+                                input_text(std::string(txt.substr(0, len - 1)));
+                            }
+                            break;
+                        }
+                        // Save inputted value and unfocus the widget on enter key.
+                        case SDLK_RETURN:
+                        case SDLK_RETURN2: // what is return2 btw?
+                        case SDLK_KP_ENTER:
+                            focus(false);
+                            InputImpl::value = value_from_string(input_text());
+                            break;
+                    }
+                }
+            });
+            // Just keep the string representation of input in the input field caption
+            // text but don't save the parsed value until some other event
+            // (Esc/Enter/focus loss)
+            text_input_handler([this](const SDL_TextInputEvent& input) {
+                if (is_valid_input(input.text)) {
+                    input_text(std::string(input_text()) + input.text);
+                }
+            });
+            enable_keyboard_handler();
+
+            // Highlight input field on mouse hover.
+            hover_handler([this](const bool _hover) {
+                if (_hover) _input_caption->font_color_bg(InputImpl::color_bg_focused);
+                else _input_caption->font_color_bg(InputImpl::color_bg_default);
+            });
+            enable_mouse_handler(_widget_area, _viewport);
+
+            _input_caption->font_color_bg(InputImpl::color_bg_default);
+        }
+
+        void _handle_font_change(const std::shared_ptr<Font>& f) override
+        {
+            _input_caption->font(f);
+            _handle_geometry_change(_viewport);
+        }
+
+        void _handle_font_color_change(const Color fg, const Color bg) override
+        {
+            _input_caption->font_color_bg(bg);
+            _input_caption->font_color_fg(fg);
+        }
+
+        void _handle_geometry_change(const SDL_Rect& vp) override
+        {
+            const auto input_h = _input_caption->size().h + 2 * InputImpl::border_width;
+            _widget_area       = {0, center_line(vp.h, input_h), vp.w, input_h};
+
+            _input_caption->viewport(
+              rect_offset({rect_margin(_widget_area, {InputImpl::border_width,
+                                                      InputImpl::border_width})},
+                          vp));
+        }
+
+        void _handle_renderer_change(const std::shared_ptr<Renderer>& r) override
+        {
+            _input_caption->renderer(r);
+        }
+
+        void _handle_rendering() override
+        {
+            const auto& color_end =
+              focus() ? InputImpl::color_bg_focused : InputImpl::color_bg_default;
+
+            const auto color_start = color_end / 2;
+            // Render input borders.
+            for (int i = InputImpl::border_width - 1; i >= 0; i--) {
+                const auto factor = linear(i, 0, InputImpl::border_width);
+                _renderer->draw_color(lerp(color_start, color_end, factor))
+                  ->draw_rect(rect_margin(_widget_area, {i, i}));
+            }
+
+            _input_caption->render();
+        }
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/w/base/layout.hpp b/inc/basic_widgets/w/base/layout.hpp
index 196d991..0840234 100644
--- a/inc/basic_widgets/w/base/layout.hpp
+++ b/inc/basic_widgets/w/base/layout.hpp
@@ -1,42 +1,26 @@
 #ifndef BWIDGETS_LAYOUT_HPP
 #define BWIDGETS_LAYOUT_HPP
 
-#include <functional>
-#include <vector>
-
 #include <basic_widgets/core/type/size.hpp>
 #include <basic_widgets/w/base/widget.hpp>
 
 namespace bwidgets
 {
-    class Renderer;
-}
-
-namespace bwidgets
-{
-    class Layout : public Widget
+    class Layout : public virtual Widget
     {
     protected:
-        std::vector<Widget*> _widgets;
-
-        void _handle_geometry_change(const SDL_Rect&) override;
-        void _handle_renderer_change(Renderer*) override;
-        void _handle_rendering() override;
-
-        virtual void _update_layout(const SDL_Rect&) = 0;
+        using Widget::Widget;
 
     public:
-        inline static const Size default_margins {8, 8};
+        static inline const Size default_margins {8, 8};
 
+        // Margins between layout widgets.
         Size margins = default_margins;
 
-        ~Layout() override;
-
-        auto               handle_event(const SDL_Event&) -> Layout* override;
-        [[nodiscard]] auto size() const noexcept -> Size override = 0;
-
-        virtual auto add_widget(Widget*) -> Layout*;
-        virtual void for_widgets(const std::function<void(Widget*)>&);
+        // Add widget to the layout
+        virtual void add_widget(std::unique_ptr<Widget>)              = 0;
+        // Apply a function to every layout widget.
+        virtual void for_widgets(const std::function<void(Widget*)>&) = 0;
     };
 }
 
diff --git a/inc/basic_widgets/w/base/layout_impl.hpp b/inc/basic_widgets/w/base/layout_impl.hpp
new file mode 100644
index 0000000..e88a020
--- /dev/null
+++ b/inc/basic_widgets/w/base/layout_impl.hpp
@@ -0,0 +1,38 @@
+#ifndef BWIDGETS_LAYOUT_IMPL_HPP
+#define BWIDGETS_LAYOUT_IMPL_HPP
+
+#include <vector>
+
+#include <basic_widgets/w/base/layout.hpp>
+#include <basic_widgets/w/base/widget_impl.hpp>
+
+namespace bwidgets
+{
+    class Renderer;
+}
+
+namespace bwidgets
+{
+    class LayoutImpl : public virtual Layout,
+                       public virtual WidgetImpl
+    {
+    public:
+        using WidgetImpl::WidgetImpl;
+
+        void add_widget(std::unique_ptr<Widget>) override;
+        void for_widgets(const std::function<void(Widget*)>&) override;
+        void handle_event(const SDL_Event&) override;
+
+    protected:
+        std::vector<std::unique_ptr<Widget>> _widgets;
+
+        void _handle_geometry_change(const SDL_Rect&) override;
+        void _handle_renderer_change(const std::shared_ptr<Renderer>&) override;
+        void _handle_rendering() override;
+
+        // Compute and set widget geometry.
+        virtual void _update_layout(const SDL_Rect&) = 0;
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/w/base/widget.hpp b/inc/basic_widgets/w/base/widget.hpp
index c236169..efac2dc 100644
--- a/inc/basic_widgets/w/base/widget.hpp
+++ b/inc/basic_widgets/w/base/widget.hpp
@@ -1,8 +1,11 @@
 #ifndef BWIDGETS_WIDGET_HPP
 #define BWIDGETS_WIDGET_HPP
 
+#include <memory>
+
 #include <basic_widgets/core/renderer.hpp>
 #include <basic_widgets/core/type/size.hpp>
+#include <basic_widgets/w/feat/event_handler.hpp>
 
 union SDL_Event;
 
@@ -10,30 +13,26 @@ struct SDL_Renderer;
 
 namespace bwidgets
 {
-    class Widget
+    class Widget : public virtual EventHandler
     {
-    protected:
-        Renderer* _renderer {nullptr};
-        SDL_Rect  _viewport {0, 0, 0, 0};
-        SDL_Rect  _widget_area {0, 0, 0, 0};
-
-        virtual void _handle_geometry_change(const SDL_Rect&) = 0;
-        virtual void _handle_renderer_change(Renderer*) {}
-        virtual void _handle_rendering() = 0;
-
     public:
+        // Parent widget for bidirectional message passing between widgets.
+        // Currently not used by this lib.
         Widget* parent;
 
-        Widget(Widget* p = nullptr) noexcept : parent(p) {}
+        explicit Widget(Widget* p = nullptr) noexcept : parent {p} {}
 
-        virtual ~Widget() = default;
-
-        virtual auto               handle_event(const SDL_Event&) -> Widget*;
-        [[nodiscard]] virtual auto size() const noexcept -> Size = 0;
-        virtual auto               render() -> Widget* final;
-        virtual auto               renderer(Renderer*) -> Widget* final;
-        virtual auto               viewport(const SDL_Rect&) -> Widget* final;
-        [[nodiscard]] virtual auto viewport() const -> const SDL_Rect& final;
+        // Render widget on current renderer target.
+        virtual void               render()                            = 0;
+        // Set widget renderer.
+        virtual void               renderer(std::shared_ptr<Renderer>) = 0;
+        // Get prefered or minimal widget size.
+        [[nodiscard]] virtual auto size() const noexcept -> Size       = 0;
+        // Set the viewport delimiting the widget rendering area and the origin
+        // for relative coordinates.
+        virtual void               viewport(const SDL_Rect&)           = 0;
+        // Get current viewport.
+        [[nodiscard]] virtual auto viewport() const -> const SDL_Rect& = 0;
     };
 }
 
diff --git a/inc/basic_widgets/w/base/widget_impl.hpp b/inc/basic_widgets/w/base/widget_impl.hpp
new file mode 100644
index 0000000..8710bf2
--- /dev/null
+++ b/inc/basic_widgets/w/base/widget_impl.hpp
@@ -0,0 +1,35 @@
+#ifndef BWIDGETS_WIDGET_IMPL_HPP
+#define BWIDGETS_WIDGET_IMPL_HPP
+
+#include <basic_widgets/w/base/widget.hpp>
+#include <basic_widgets/w/feat/event_handler_impl.hpp>
+
+namespace bwidgets
+{
+    class WidgetImpl : public virtual Widget,
+                       public virtual EventHandlerImpl
+    {
+    public:
+        void               render() override;
+        void               renderer(std::shared_ptr<Renderer>) override;
+        void               viewport(const SDL_Rect&) override;
+        [[nodiscard]] auto viewport() const -> const SDL_Rect& override;
+
+    protected:
+        std::shared_ptr<Renderer> _renderer;
+        SDL_Rect                  _viewport {0, 0, 0, 0};
+        // Area actually used by the widget.
+        SDL_Rect                  _widget_area {0, 0, 0, 0};
+
+        using Widget::Widget;
+
+        // Called on viewport change.
+        virtual void _handle_geometry_change(const SDL_Rect&) = 0;
+        // Called on renderer change.
+        virtual void _handle_renderer_change(const std::shared_ptr<Renderer>&) {}
+        // Called on rendering.
+        virtual void _handle_rendering() = 0;
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/w/button.hpp b/inc/basic_widgets/w/button.hpp
index 9538815..77e616d 100644
--- a/inc/basic_widgets/w/button.hpp
+++ b/inc/basic_widgets/w/button.hpp
@@ -1,50 +1,36 @@
 #ifndef BWIDGETS_BUTTON_HPP
 #define BWIDGETS_BUTTON_HPP
 
-#include <functional>
 #include <string>
 
 #include <basic_widgets/core/type/color.hpp>
-#include <basic_widgets/w/caption.hpp>
+#include <basic_widgets/w/base/widget.hpp>
+#include <basic_widgets/w/feat/font_handler.hpp>
 #include <basic_widgets/w/feat/mouse_handler.hpp>
 
 namespace bwidgets
 {
-    class Button : public Widget,
-                   public FontHandler,
-                   public MouseHandler
+    class Button : public virtual Widget,
+                   public virtual FontHandler,
+                   public virtual MouseHandler
     {
-    protected:
-        Caption  _caption;
-        SDL_Rect _caption_area {};
-        Color    _color_foreground = default_color_fg;
-
-        void _handle_focus_change(bool) override {}
-        void _handle_font_change(Font*) override;
-        void _handle_font_color_change(const Color&, const Color&) override;
-        void _handle_geometry_change(const SDL_Rect&) override;
-        void _handle_renderer_change(Renderer*) override;
-        void _handle_rendering() override;
-        void _on_push(bool) override;
-
     public:
-        inline static const Color default_color_bg {150, 150, 150, SDL_ALPHA_OPAQUE};
-        inline static const Color default_color_bg_hover {175, 175, 175,
+        static inline const Color default_color_bg {150, 150, 150, SDL_ALPHA_OPAQUE};
+        static inline const Color default_color_bg_hover {175, 175, 175,
                                                           SDL_ALPHA_OPAQUE};
-        inline static const Color default_color_fg {0, 0, 0, SDL_ALPHA_OPAQUE};
+        static inline const Color default_color_fg {0, 0, 0, SDL_ALPHA_OPAQUE};
 
-        std::function<Color(int, int)> border_gradient;
-        std::function<Color(int, int)> border_gradient_pushed;
-        Size                           border_size {3, 3};
-        Color                          color_bg       = default_color_bg;
-        Color                          color_bg_hover = default_color_bg_hover;
+        std::function<Color(int, int, float)> border_gradient;
+        Size                                  border_size {3, 3};
+        Color                                 color_bg       = default_color_bg;
+        Color                                 color_bg_hover = default_color_bg_hover;
 
-        Button(Widget* parent = nullptr) noexcept;
+        using Widget::Widget;
 
-        [[nodiscard]] auto size() const noexcept -> Size override;
-
-        [[nodiscard]] virtual auto text() const noexcept -> const std::string&;
-        virtual auto               text(const std::string&) -> Button*;
+        // Get button text (label).
+        [[nodiscard]] virtual auto text() const noexcept -> std::string_view = 0;
+        // Set button text
+        virtual void               text(std::string)                         = 0;
     };
 }
 
diff --git a/inc/basic_widgets/w/button_impl.hpp b/inc/basic_widgets/w/button_impl.hpp
new file mode 100644
index 0000000..4e40707
--- /dev/null
+++ b/inc/basic_widgets/w/button_impl.hpp
@@ -0,0 +1,40 @@
+#ifndef BWIDGETS_BUTTON_IMPL_HPP
+#define BWIDGETS_BUTTON_IMPL_HPP
+
+#include <basic_widgets/w/base/widget_impl.hpp>
+#include <basic_widgets/w/button.hpp>
+#include <basic_widgets/w/caption.hpp>
+#include <basic_widgets/w/feat/font_handler_impl.hpp>
+#include <basic_widgets/w/feat/mouse_handler_impl.hpp>
+
+namespace bwidgets
+{
+    class ButtonImpl : public virtual Button,
+                       public virtual FontHandlerImpl,
+                       public virtual MouseHandlerImpl,
+                       public virtual WidgetImpl
+    {
+    public:
+        ButtonImpl(Widget* parent = nullptr) noexcept;
+
+        // Smallest valid button size.
+        [[nodiscard]] auto size() const noexcept -> Size override;
+        [[nodiscard]] auto text() const noexcept -> std::string_view override;
+        void               text(std::string) override;
+
+    protected:
+        std::unique_ptr<Caption> _caption;
+        SDL_Rect                 _caption_area {};
+        Color                    _color_foreground = default_color_fg;
+
+        void _handle_font_change(const std::shared_ptr<Font>&) override;
+        void _handle_font_color_change(Color, Color)
+        override;
+        void _handle_geometry_change(const SDL_Rect&) override;
+        void _handle_renderer_change(const std::shared_ptr<Renderer>&) override;
+        void _handle_rendering() override;
+        void _on_push(bool) override;
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/w/caption.hpp b/inc/basic_widgets/w/caption.hpp
index 19e02b9..2006dd8 100644
--- a/inc/basic_widgets/w/caption.hpp
+++ b/inc/basic_widgets/w/caption.hpp
@@ -1,8 +1,6 @@
 #ifndef BWIDGETS_CAPTION_HPP
 #define BWIDGETS_CAPTION_HPP
 
-#include <basic_widgets/core/texture.hpp>
-#include <basic_widgets/core/type/size.hpp>
 #include <basic_widgets/w/base/widget.hpp>
 #include <basic_widgets/w/feat/font_handler.hpp>
 #include <basic_widgets/w/feat/texture_handler.hpp>
@@ -11,22 +9,10 @@ struct SDL_Surface;
 
 namespace bwidgets
 {
-    class Caption : public Widget,
-                    public FontHandler,
-                    public TextureHandler
+    class Caption : public virtual Widget,
+                    public virtual FontHandler,
+                    public virtual TextureHandler
     {
-    protected:
-        Font::RenderMode _render_mode {Font::RenderMode::SHADED};
-        std::string      _text;
-        Texture*         _text_texture {nullptr};
-
-        void _handle_font_change(Font*) override;
-        void _handle_font_color_change(const Color&, const Color&) override;
-        void _handle_geometry_change(const SDL_Rect&) override;
-        void _handle_renderer_change(Renderer*) override;
-        void _handle_rendering() override;
-        void _handle_texture_update() override;
-
     public:
         enum struct Alignment
         {
@@ -34,22 +20,22 @@ namespace bwidgets
             LEFT,
             RIGHT
         };
-
         inline static const Color default_color_bg = {255, 255, 255, SDL_ALPHA_OPAQUE};
         inline static const Color default_color_fg = {0, 0, 0, SDL_ALPHA_OPAQUE};
         inline static const Size  default_margins  = {3, 3};
 
+        // Text horizontal alignment on the caption viewport.
         Alignment alignment {Alignment::LEFT};
-        Size      margins {3, 3};
+        Size      margins {default_margins};
 
-        Caption(Widget* parent = nullptr) noexcept;
-        ~Caption() noexcept override;
+        using Widget::Widget;
 
-        virtual auto               render_mode(Font::RenderMode) -> Caption*;
-        [[nodiscard]] virtual auto text() const noexcept -> const std::string&;
-        virtual auto               text(const std::string&) -> Caption*;
-
-        [[nodiscard]] auto size() const noexcept -> Size override;
+        // Set caption text rendering mode.
+        virtual void               render_mode(Font::RenderMode)             = 0;
+        // Get caption text.
+        [[nodiscard]] virtual auto text() const noexcept -> std::string_view = 0;
+        // Set caption text.
+        virtual void               text(std::string)                         = 0;
     };
 }
 
diff --git a/inc/basic_widgets/w/caption_impl.hpp b/inc/basic_widgets/w/caption_impl.hpp
new file mode 100644
index 0000000..75f1bc8
--- /dev/null
+++ b/inc/basic_widgets/w/caption_impl.hpp
@@ -0,0 +1,37 @@
+#ifndef BWIDGETS_CAPTION_IMPL_HPP
+#define BWIDGETS_CAPTION_IMPL_HPP
+
+#include <basic_widgets/w/base/widget_impl.hpp>
+#include <basic_widgets/w/caption.hpp>
+#include <basic_widgets/w/feat/font_handler_impl.hpp>
+
+namespace bwidgets
+{
+    class CaptionImpl : public virtual Caption,
+                        public virtual FontHandlerImpl,
+                        public virtual WidgetImpl
+    {
+    public:
+        CaptionImpl(Widget* p = nullptr) noexcept;
+
+        void               render_mode(Font::RenderMode) override;
+        [[nodiscard]] auto size() const noexcept -> Size override;
+        [[nodiscard]] auto text() const noexcept -> std::string_view override;
+        void               text(std::string) override;
+
+    protected:
+        Font::RenderMode         _render_mode {Font::RenderMode::SHADED};
+        std::string              _text;
+        std::shared_ptr<Texture> _text_texture {nullptr};
+
+        void _handle_font_change(const std::shared_ptr<Font>&) override;
+        void _handle_font_color_change(Color, Color)
+        override;
+        void _handle_geometry_change(const SDL_Rect&) override;
+        void _handle_renderer_change(const std::shared_ptr<Renderer>&) override;
+        void _handle_rendering() override;
+        void _handle_texture_update() override;
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/w/feat/event_handler.hpp b/inc/basic_widgets/w/feat/event_handler.hpp
new file mode 100644
index 0000000..de387be
--- /dev/null
+++ b/inc/basic_widgets/w/feat/event_handler.hpp
@@ -0,0 +1,31 @@
+#ifndef BWIDGETS_EVENT_HANDLER_HPP
+#define BWIDGETS_EVENT_HANDLER_HPP
+
+#include <functional>
+
+#include <SDL_events.h>
+
+namespace bwidgets
+{
+    class EventHandler
+    {
+    protected:
+        EventHandler() = default;
+
+    public:
+        using handler_t =
+          std::pair<SDL_EventType, std::function<void(const SDL_Event&)>>;
+
+        EventHandler(const EventHandler&) = delete;
+        EventHandler(EventHandler&&)      = delete;
+        auto operator=(const EventHandler&) -> EventHandler& = delete;
+        auto operator=(EventHandler&&) -> EventHandler& = delete;
+
+        virtual ~EventHandler() = default;
+
+        // Pass the event to be handled.
+        virtual void handle_event(const SDL_Event&) = 0;
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/w/feat/event_handler_impl.hpp b/inc/basic_widgets/w/feat/event_handler_impl.hpp
new file mode 100644
index 0000000..564d5f0
--- /dev/null
+++ b/inc/basic_widgets/w/feat/event_handler_impl.hpp
@@ -0,0 +1,30 @@
+#ifndef BWIDGETS_EVENT_HANDLER_IMPL_HPP
+#define BWIDGETS_EVENT_HANDLER_IMPL_HPP
+
+#include <unordered_map>
+
+#include <basic_widgets/w/feat/event_handler.hpp>
+
+namespace bwidgets
+{
+    class EventHandlerImpl : public virtual EventHandler
+    {
+        std::unordered_map<SDL_EventType, std::function<void(const SDL_Event&)>>
+          _event_handlers {};
+
+    public:
+        void handle_event(const SDL_Event&) override;
+
+    protected:
+        // Add an handler for a given event type. There can be only one handler by
+        // event type. Return true if handler is added successfuly. Return false
+        // if handler cannot be added because there's already an handler for that
+        // event type.
+        auto _add_event_handler(handler_t) -> bool;
+        // Remove the handler of a given event type. Return true with the removed
+        // handler on success, false otherwise.
+        auto _remove_event_handler(SDL_EventType) -> std::pair<handler_t, bool>;
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/w/feat/focus_handler.hpp b/inc/basic_widgets/w/feat/focus_handler.hpp
index bd2f755..9996725 100644
--- a/inc/basic_widgets/w/feat/focus_handler.hpp
+++ b/inc/basic_widgets/w/feat/focus_handler.hpp
@@ -1,26 +1,28 @@
 #ifndef BWIDGETS_FOCUS_HANDLER_HPP
 #define BWIDGETS_FOCUS_HANDLER_HPP
 
+#include <functional>
+
 struct SDL_Rect;
 
 namespace bwidgets
 {
     class FocusHandler
     {
-    protected:
-        const SDL_Rect* _focus_area = nullptr;
-        bool            _has_focus  = false;
-
-        virtual void _handle_focus_change(bool) = 0;
-
     public:
-        virtual ~FocusHandler() = default;
+        FocusHandler()                    = default;
+        FocusHandler(const FocusHandler&) = delete;
+        FocusHandler(FocusHandler&&)      = delete;
+        auto operator=(FocusHandler&&) = delete;
+        auto operator=(const FocusHandler&) = delete;
 
-        virtual inline void focus(bool focus) final
-        {
-            _handle_focus_change(focus);
-            _has_focus = focus;
-        }
+        virtual ~FocusHandler()                               = default;
+        // set focus state.
+        virtual void focus(bool focus)                        = 0;
+        // get focus state.
+        virtual bool focus()                                  = 0;
+        // set an handler for focus states changes.
+        virtual void focus_handler(std::function<void(bool)>) = 0;
     };
 }
 
diff --git a/inc/basic_widgets/w/feat/focus_handler_impl.hpp b/inc/basic_widgets/w/feat/focus_handler_impl.hpp
new file mode 100644
index 0000000..77d4c9d
--- /dev/null
+++ b/inc/basic_widgets/w/feat/focus_handler_impl.hpp
@@ -0,0 +1,31 @@
+#ifndef BWIDGETS_FOCUS_HANDLER_IMPL_HPP
+#define BWIDGETS_FOCUS_HANDLER_IMPL_HPP
+
+#include <basic_widgets/w/feat/focus_handler.hpp>
+
+namespace bwidgets
+{
+    class FocusHandlerImpl : public virtual FocusHandler
+    {
+        bool                      _has_focus {false};
+        std::function<void(bool)> _focus_handler {[](auto) {}};
+
+    public:
+        void focus(const bool _focus) override
+        {
+            if (_has_focus != _focus) _focus_handler(_has_focus = _focus);
+        }
+
+        bool focus() override
+        {
+            return _has_focus;
+        }
+
+        void focus_handler(decltype(_focus_handler) handler) final
+        {
+            _focus_handler = std::move(handler);
+        }
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/w/feat/font_handler.hpp b/inc/basic_widgets/w/feat/font_handler.hpp
index 4d8ebc1..c65a5b8 100644
--- a/inc/basic_widgets/w/feat/font_handler.hpp
+++ b/inc/basic_widgets/w/feat/font_handler.hpp
@@ -7,54 +7,27 @@ namespace bwidgets
 {
     class FontHandler
     {
-    protected:
-        Font*            _font {nullptr};
-        Color            _font_color_bg = default_font_color_bg;
-        Color            _font_color_fg = default_font_color_fg;
-        Font::RenderMode _font_render_mode {Font::RenderMode::SHADED};
-
-        virtual void _handle_font_change(Font*)                            = 0;
-        virtual void _handle_font_color_change(const Color&, const Color&) = 0;
-
     public:
         inline static const Color default_font_color_bg {255, 255, 255,
                                                          SDL_ALPHA_OPAQUE};
         inline static const Color default_font_color_fg {0, 0, 0, SDL_ALPHA_OPAQUE};
 
+        FontHandler(const FontHandler&) = delete;
+        FontHandler(FontHandler&&)      = delete;
+        auto operator=(const FontHandler&) = delete;
+        auto operator=(FontHandler&&)   = delete;
         virtual ~FontHandler() noexcept = default;
 
-        virtual inline auto font(Font* f) -> FontHandler* final
-        {
-            if (f != nullptr
-                && (f != _font || f->family_name != _font->family_name
-                    || f->height != _font->height || f->hinting() != _font->hinting()
-                    || f->kerning() != _font->kerning()
-                    || f->outline() != _font->outline()
-                    || f->style_name != _font->style_name))
-            {
-                _handle_font_change(f);
-                _font = f;
-            }
-            return this;
-        }
+        // Set the used font.
+        virtual void font(std::shared_ptr<Font> f) = 0;
+        // Set background color used for shaded text rendering
+        // mode.
+        virtual void font_color_bg(Color c)        = 0;
+        // Set foreground (glyphs) color.
+        virtual void font_color_fg(Color c)        = 0;
 
-        virtual inline auto font_color_bg(const Color& c) -> FontHandler* final
-        {
-            if (c != _font_color_bg) {
-                _handle_font_color_change(_font_color_bg, c);
-                _font_color_bg = c;
-            }
-            return this;
-        }
-
-        virtual inline auto font_color_fg(const Color& c) -> FontHandler* final
-        {
-            if (c != _font_color_fg) {
-                _handle_font_color_change(c, _font_color_fg);
-                _font_color_fg = c;
-            }
-            return this;
-        }
+    protected:
+        FontHandler() noexcept = default;
     };
 }
 
diff --git a/inc/basic_widgets/w/feat/font_handler_impl.hpp b/inc/basic_widgets/w/feat/font_handler_impl.hpp
new file mode 100644
index 0000000..aa8e783
--- /dev/null
+++ b/inc/basic_widgets/w/feat/font_handler_impl.hpp
@@ -0,0 +1,54 @@
+#ifndef BWIDGETS_FONT_HANDLER_IMPL_HPP
+#define BWIDGETS_FONT_HANDLER_IMPL_HPP
+
+#include <basic_widgets/w/feat/font_handler.hpp>
+
+namespace bwidgets
+{
+    class FontHandlerImpl : public virtual FontHandler
+    {
+    public:
+        void font(const std::shared_ptr<Font> f) final
+        {
+            if (f
+                && (f != _font || f->family_name != _font->family_name
+                    || f->height != _font->height || f->hinting() != _font->hinting()
+                    || f->kerning() != _font->kerning()
+                    || f->outline() != _font->outline()
+                    || f->style_name != _font->style_name))
+            {
+                _handle_font_change(f);
+                _font = f;
+            }
+        }
+
+        void font_color_bg(const Color c) final
+        {
+            if (c != _font_color_bg) {
+                _handle_font_color_change(_font_color_fg, c);
+                _font_color_bg = c;
+            }
+        }
+
+        void font_color_fg(const Color c) final
+        {
+            if (c != _font_color_fg) {
+                _handle_font_color_change(c, _font_color_fg);
+                _font_color_fg = c;
+            }
+        }
+
+    protected:
+        std::shared_ptr<Font> _font;
+        Color                 _font_color_bg = default_font_color_bg;
+        Color                 _font_color_fg = default_font_color_fg;
+        Font::RenderMode      _font_render_mode {Font::RenderMode::SHADED};
+
+        // Called on font changes.
+        virtual void _handle_font_change(const std::shared_ptr<Font>&) = 0;
+        // Called on font color changes.
+        virtual void _handle_font_color_change(Color, Color)           = 0;
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/w/feat/keyboard_handler.hpp b/inc/basic_widgets/w/feat/keyboard_handler.hpp
index 197c4bb..413a363 100644
--- a/inc/basic_widgets/w/feat/keyboard_handler.hpp
+++ b/inc/basic_widgets/w/feat/keyboard_handler.hpp
@@ -1,6 +1,7 @@
-#ifndef BWIDGETS_KEYBOARD_HANDLER
-#define BWIDGETS_KEYBOARD_HANDLER
+#ifndef BWIDGETS_KEYBOARD_HANDLER_HPP
+#define BWIDGETS_KEYBOARD_HANDLER_HPP
 
+#include <basic_widgets/w/feat/event_handler.hpp>
 #include <basic_widgets/w/feat/focus_handler.hpp>
 
 struct SDL_KeyboardEvent;
@@ -8,26 +9,22 @@ struct SDL_TextInputEvent;
 
 namespace bwidgets
 {
-    class KeyboardHandler : public virtual FocusHandler
+    class KeyboardHandler : public virtual EventHandler,
+                            public virtual FocusHandler
     {
     protected:
-        virtual void _handle_key(const SDL_KeyboardEvent&)         = 0;
-        virtual void _handle_text_input(const SDL_TextInputEvent&) = 0;
+        using EventHandler::EventHandler;
 
     public:
-        virtual inline auto handle_keyboard(const SDL_KeyboardEvent& ev)
-          -> KeyboardHandler* final
-        {
-            if (_has_focus) _handle_key(ev);
-            return this;
-        }
-
-        virtual inline auto handle_keyboard(const SDL_TextInputEvent& ev)
-          -> KeyboardHandler* final
-        {
-            if (_has_focus) _handle_text_input(ev);
-            return this;
-        }
+        // Disable keyboard event handling.
+        virtual void disable_keyboard_handler()                                 = 0;
+        // Enable keyboard event handling.
+        virtual void enable_keyboard_handler()                                  = 0;
+        // Set the handler for key press events.
+        virtual void key_handler(std::function<void(const SDL_KeyboardEvent&)>) = 0;
+        // Set the handler for text input events.
+        virtual void
+        text_input_handler(std::function<void(const SDL_TextInputEvent&)>) = 0;
     };
 }
 
diff --git a/inc/basic_widgets/w/feat/keyboard_handler_impl.hpp b/inc/basic_widgets/w/feat/keyboard_handler_impl.hpp
new file mode 100644
index 0000000..98eee31
--- /dev/null
+++ b/inc/basic_widgets/w/feat/keyboard_handler_impl.hpp
@@ -0,0 +1,31 @@
+#ifndef BWIDGETS_KEYBOARD_HANDLER_IMPL_HPP
+#define BWIDGETS_KEYBOARD_HANDLER_IMPL_HPP
+
+#include <basic_widgets/w/feat/event_handler_impl.hpp>
+#include <basic_widgets/w/feat/focus_handler_impl.hpp>
+#include <basic_widgets/w/feat/keyboard_handler.hpp>
+
+namespace bwidgets
+{
+    class KeyboardHandlerImpl : public virtual KeyboardHandler,
+                                public virtual EventHandlerImpl,
+                                public virtual FocusHandlerImpl
+    {
+        std::function<void(const SDL_KeyboardEvent&)>  _key_handler {[](auto) {}};
+        std::function<void(const SDL_TextInputEvent&)> _input_handler {[](auto) {}};
+
+    public:
+        void disable_keyboard_handler() override;
+        void enable_keyboard_handler() override;
+        void key_handler(decltype(_key_handler) handler) override
+        {
+            _key_handler = std::move(handler);
+        }
+        void text_input_handler(decltype(_input_handler) handler) override
+        {
+            _input_handler = std::move(handler);
+        }
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/w/feat/mouse_handler.hpp b/inc/basic_widgets/w/feat/mouse_handler.hpp
index 7236e83..1328bd4 100644
--- a/inc/basic_widgets/w/feat/mouse_handler.hpp
+++ b/inc/basic_widgets/w/feat/mouse_handler.hpp
@@ -1,8 +1,7 @@
 #ifndef BWIDGETS_MOUSE_HANDLER_HPP
 #define BWIDGETS_MOUSE_HANDLER_HPP
 
-#include <functional>
-
+#include <basic_widgets/w/feat/event_handler.hpp>
 #include <basic_widgets/w/feat/focus_handler.hpp>
 
 struct SDL_MouseButtonEvent;
@@ -10,27 +9,28 @@ struct SDL_MouseMotionEvent;
 
 namespace bwidgets
 {
-    class MouseHandler : public virtual FocusHandler
+    class MouseHandler : public virtual FocusHandler,
+                         public virtual EventHandler
     {
     protected:
-        const SDL_Rect* _click_area = nullptr;
-        bool            _is_hovered = false;
-        bool            _is_pushed  = false;
-
-        virtual void _handle_mouse_button(const SDL_MouseButtonEvent&,
-                                          const SDL_Rect&) {};
-        virtual void _handle_mouse_motion(const SDL_MouseMotionEvent&,
-                                          const SDL_Rect&) {};
-        virtual void _on_push(bool) {};
+        using EventHandler::EventHandler;
 
     public:
-        std::function<void(const SDL_MouseButtonEvent&)> click_handler = nullptr;
-
-        virtual auto handle_mouse(const SDL_MouseButtonEvent&, const SDL_Rect&)
-          -> MouseHandler* final;
-        virtual auto handle_mouse(const SDL_MouseMotionEvent&, const SDL_Rect&)
-          -> MouseHandler* final;
-        virtual auto push(bool) -> MouseHandler* final;
+        // Set click handler.
+        virtual void click_handler(std::function<void(const SDL_MouseButtonEvent&)>) = 0;
+        // Disable mouse event handling.
+        virtual void disable_mouse_handler()                                         = 0;
+        // Enable mouse event handling.
+        virtual void enable_mouse_handler(const SDL_Rect&, const SDL_Rect&)          = 0;
+        // Called on hover state changes.
+        virtual void hover_handler(std::function<void(bool)>)                        = 0;
+        // Get current hover state.
+        [[nodiscard]] virtual bool hovered() const                                   = 0;
+        // Set mouse motion handler.
+        virtual void
+        mouse_motion_handler(std::function<void(const SDL_MouseMotionEvent&)>) = 0;
+        // Get current push state (mouse button down)
+        [[nodiscard]] virtual bool pushed() const                              = 0;
     };
 }
 
diff --git a/inc/basic_widgets/w/feat/mouse_handler_impl.hpp b/inc/basic_widgets/w/feat/mouse_handler_impl.hpp
new file mode 100644
index 0000000..58a8f1c
--- /dev/null
+++ b/inc/basic_widgets/w/feat/mouse_handler_impl.hpp
@@ -0,0 +1,59 @@
+#ifndef BWIDGETS_MOUSE_HANDLER_IMPL_HPP
+#define BWIDGETS_MOUSE_HANDLER_IMPL_HPP
+
+#include <basic_widgets/w/feat/event_handler_impl.hpp>
+#include <basic_widgets/w/feat/focus_handler_impl.hpp>
+#include <basic_widgets/w/feat/mouse_handler.hpp>
+
+namespace bwidgets
+{
+    class MouseHandlerImpl : public virtual MouseHandler,
+                             public virtual EventHandlerImpl,
+                             public virtual FocusHandlerImpl
+    {
+        bool _hovered {false};
+        bool _pushed {false};
+
+        std::function<void(const SDL_MouseButtonEvent&)> _click_handler {[](auto) {}};
+        std::function<void(bool)>                        _hover_handler {[](auto) {}};
+        std::function<void(const SDL_MouseMotionEvent&)> _motion_handler {[](auto) {}};
+
+    public:
+        void click_handler(decltype(_click_handler) handler) override
+        {
+            _click_handler = std::move(handler);
+        }
+
+        void disable_mouse_handler() override;
+
+        void enable_mouse_handler(const SDL_Rect&, const SDL_Rect&) override;
+
+        [[nodiscard]] bool hovered() const override
+        {
+            return _hovered;
+        }
+
+        void hover_handler(decltype(_hover_handler) handler) override
+        {
+            _hover_handler = std::move(handler);
+        }
+
+        void mouse_motion_handler(decltype(_motion_handler) handler) override
+        {
+            _motion_handler = std::move(handler);
+        }
+
+        [[nodiscard]] bool pushed() const override
+        {
+            return _pushed;
+        }
+
+    protected:
+        using MouseHandler::MouseHandler;
+
+        // Called on push state changes.
+        virtual void _on_push(bool) {}
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/w/feat/texture_handler.hpp b/inc/basic_widgets/w/feat/texture_handler.hpp
index b780bff..1d70960 100644
--- a/inc/basic_widgets/w/feat/texture_handler.hpp
+++ b/inc/basic_widgets/w/feat/texture_handler.hpp
@@ -1,5 +1,5 @@
-#ifndef BWIDGETS_TEXTURE_HANDLER
-#define BWIDGETS_TEXTURE_HANDLER
+#ifndef BWIDGETS_TEXTURE_HANDLER_HPP
+#define BWIDGETS_TEXTURE_HANDLER_HPP
 
 namespace bwidgets
 {
@@ -11,10 +11,17 @@ namespace bwidgets
     class TextureHandler
     {
     protected:
+        TextureHandler() noexcept             = default;
+        // (Re)render textures.
         virtual void _handle_texture_update() = 0;
 
     public:
-        virtual ~TextureHandler() noexcept = default;
+        TextureHandler(const TextureHandler&) = delete;
+        TextureHandler(TextureHandler&&)      = delete;
+        virtual ~TextureHandler() noexcept    = default;
+
+        auto operator=(const TextureHandler&) = delete;
+        auto operator=(TextureHandler&&) = delete;
     };
 }
 
diff --git a/inc/basic_widgets/w/numeric_input.hpp b/inc/basic_widgets/w/numeric_input.hpp
index 8d7c029..1cb5b3b 100644
--- a/inc/basic_widgets/w/numeric_input.hpp
+++ b/inc/basic_widgets/w/numeric_input.hpp
@@ -1,175 +1,26 @@
 #ifndef BWIDGETS_NUMERIC_INPUT_HPP
 #define BWIDGETS_NUMERIC_INPUT_HPP
 
-#include <limits>
-
-#include <basic_widgets/core/math.hpp>
 #include <basic_widgets/core/type/concepts.hpp>
 #include <basic_widgets/w/base/input.hpp>
-#include <basic_widgets/w/button.hpp>
-
-#include <type_traits>
 
 namespace bwidgets
 {
     template<Numeric T>
-    class NumericInput : public Input<T>
+    class NumericInput : public virtual Input<T>
     {
     protected:
-        Button          _increment_button;
-        SDL_Rect        _increment_button_area {};
-        Button          _decrement_button;
-        SDL_Rect        _decrement_button_area {};
-        std::pair<T, T> _value_range {std::numeric_limits<T>::lowest(),
-                                      std::numeric_limits<T>::max()};
-
-        void _handle_font_change(Font* f) override
-        {
-            _decrement_button.font(f);
-            _increment_button.font(f);
-            Input<T>::_handle_font_change(f);
-        }
-
-        void _handle_font_color_change(const Color& fg,
-                                       const Color& bg) override
-        {
-            Input<T>::_handle_font_color_change(fg, bg);
-            _decrement_button.font_color_bg(bg)->font_color_fg(fg);
-            _increment_button.font_color_bg(bg)->font_color_fg(fg);
-        }
-
-        void _handle_geometry_change(const SDL_Rect& vp) override
-        {
-            Input<T>::_handle_geometry_change(vp);
-
-            const int widest_button     = _increment_button.size().w != 0
-                                          ? _increment_button.size().w
-                                          : _decrement_button.size().w;
-            const int button_area_width = 2 * widest_button;
-            const int spacing           = center_line(button_area_width, widest_button);
-            const int field_width       = vp.w - 2 * button_area_width;
-
-            Widget::_widget_area.x = Widget::_widget_area.x + button_area_width;
-            Widget::_widget_area.w = field_width;
-
-            Input<T>::_input_caption.viewport(
-              rect_offset(rect_margin(Widget::_widget_area,
-                                      {Input<T>::border_width, Input<T>::border_width}),
-                          vp));
-            _decrement_button_area = {spacing, Widget::_widget_area.y,
-                                      _decrement_button.size().w,
-                                      _decrement_button.size().h};
-
-            _increment_button_area = {vp.w - spacing - _increment_button.size().w,
-                                      Widget::_widget_area.y, _increment_button.size().w,
-                                      _increment_button.size().h};
-
-            _increment_button.viewport(rect_offset(_increment_button_area, vp));
-            _decrement_button.viewport(rect_offset(_decrement_button_area, vp));
-        }
-
-        void _handle_renderer_change(Renderer* r) override
-        {
-            Input<T>::_handle_renderer_change(r);
-            _decrement_button.renderer(r);
-            _increment_button.renderer(r);
-        }
-
-        void _handle_rendering() override
-        {
-            Input<T>::_handle_rendering();
-            _increment_button.render();
-            _decrement_button.render();
-        }
+        using Input<T>::Input;
 
     public:
+        // Button increment/decrement step.
         T button_step = 1;
 
-        NumericInput(Widget* parent = nullptr)
-          : Input<T>(parent), _increment_button(this), _decrement_button(this)
-        {
-            Input<T>::_input_caption.alignment = Caption::Alignment::RIGHT;
-
-            Input<T>::input_min_width  = 10; // NOLINT(readability-magic-numbers)
-            Input<T>::input_width_unit = '0';
-
-            _increment_button.text("+");
-
-            _increment_button.click_handler = [this](const SDL_MouseButtonEvent&) {
-                T new_value = this->value + button_step;
-                if (_value_range.second - this->value < button_step)
-                    new_value = _value_range.second;
-
-                this->value = new_value;
-                this->input_text(this->value_to_string(new_value));
-            };
-
-            _decrement_button.text("-");
-
-            _decrement_button.click_handler = [this](const SDL_MouseButtonEvent&) {
-                T new_value = this->value - button_step;
-                if (this->value - _value_range.first < button_step)
-                    new_value = _value_range.first;
-
-                this->value = new_value;
-                this->input_text(this->value_to_string(new_value));
-            };
-        }
-
-        auto handle_event(const SDL_Event& ev) -> Widget* override
-        {
-            Input<T>::handle_event(ev);
-            _increment_button.handle_event(ev);
-            _decrement_button.handle_event(ev);
-            return this;
-        }
-
-        [[nodiscard]] auto is_valid_input(const std::string& input) const noexcept
-          -> bool override
-        {
-            bool valid = false;
-
-            if (input[0] >= '0' && input[0] <= '9') valid = true;
-            if constexpr (std::is_floating_point_v<T>)
-                if (input[0] == '.'
-                    && Input<T>::input_text().find('.') == std::string::npos)
-                    valid = true;
-            if constexpr (std::is_signed_v<T>) {
-                std::string displayed_value = Input<T>::input_text();
-                if (input[0] == '-' && displayed_value.empty()) valid = true;
-            }
-            return valid;
-        }
-
-        [[nodiscard]] auto process_value(T x) const noexcept -> T override
-        {
-            T value = x;
-            if (x < _value_range.first) value = _value_range.first;
-            else if (x > _value_range.second) value = _value_range.second;
-
-            return value;
-        }
-
-        [[nodiscard]] inline auto size() const noexcept -> Size override
-        {
-            const auto base       = Input<T>::size();
-            const auto btns_width = 4 * _increment_button.size().w;
-            return {base.w + btns_width, base.h};
-        }
-
-        [[nodiscard]] virtual auto value_range() const noexcept -> const std::pair<T, T>&
-        {
-            return _value_range;
-        }
-
-        virtual auto value_range(T min, T max) -> NumericInput<T>*
-        {
-            if (min > max) throw std::invalid_argument("min cannot be greater than max");
-            _value_range    = {min, max};
-            Input<T>::value = process_value(Input<T>::value);
-            Input<T>::input_text(Input<T>::value_to_string(Input<T>::value));
-            return this;
-        }
+        // Get allowed value range.
+        [[nodiscard]] virtual auto value_range() const noexcept
+          -> const std::pair<T, T>&            = 0;
+        // Set allowed value range.
+        virtual void value_range(T min, T max) = 0;
     };
 }
 
diff --git a/inc/basic_widgets/w/numeric_input_impl.hpp b/inc/basic_widgets/w/numeric_input_impl.hpp
new file mode 100644
index 0000000..8a751c2
--- /dev/null
+++ b/inc/basic_widgets/w/numeric_input_impl.hpp
@@ -0,0 +1,196 @@
+#ifndef BWIDGETS_NUMERIC_INPUT_IMPL_HPP
+#define BWIDGETS_NUMERIC_INPUT_IMPL_HPP
+
+#include <basic_widgets/w/base/input_impl.hpp>
+#include <basic_widgets/w/numeric_input.hpp>
+
+namespace bwidgets
+{
+    template<Numeric T>
+    class NumericInputImpl : public virtual NumericInput<T>,
+                             public virtual InputImpl<T>
+    {
+        using Self = NumericInputImpl;
+
+    public:
+        NumericInputImpl(Widget* parent = nullptr)
+          : InputImpl<T>(parent),
+            _increment_button(create_button(this)),
+            _decrement_button(create_button(this))
+        {
+            Self::_input_caption->alignment = Caption::Alignment::RIGHT;
+
+            Self::input_min_width  = 10; // NOLINT(readability-magic-numbers)
+            Self::input_width_unit = '0';
+
+            // +/- buttons click handler. op is the operation (+/-) to apply on current
+            // value.
+            const auto button_action = [this](const std::function<T(T, T)> op) {
+                const T new_value = [this, &op]() {
+                    auto _new_value = op(this->value, NumericInput<T>::button_step);
+                    if (_new_value < this->value) {
+                        // if value - button_step is out of allowed range
+                        // set value to the smallest allowed value.
+                        if (std::abs(_value_range.first - this->value)
+                            < std::abs(NumericInput<T>::button_step))
+                            return _value_range.first;
+                        return _new_value;
+                    }
+                    // if value + button_step exceeds maximal allowed value
+                    // set value to max allowed value.
+                    if (std::abs(_value_range.second - this->value)
+                        < std::abs(NumericInput<T>::button_step))
+                        return _value_range.second;
+                    return _new_value;
+                }();
+
+                this->value = new_value;
+                this->input_text(this->value_to_string(new_value));
+            };
+
+            _increment_button->text("+");
+            _increment_button->click_handler(
+              [button_action](const SDL_MouseButtonEvent&) {
+                  button_action([](const T a, const T b) { return a + b; });
+              });
+
+            _decrement_button->text("-");
+
+            _decrement_button->click_handler(
+              [button_action](const SDL_MouseButtonEvent&) {
+                  button_action([](const T a, const T b) { return a - b; });
+              });
+        }
+
+        void handle_event(const SDL_Event& ev) override
+        {
+            InputImpl<T>::handle_event(ev);
+            _increment_button->handle_event(ev);
+            _decrement_button->handle_event(ev);
+        }
+
+        [[nodiscard]] auto is_valid_input(const std::string_view input) const noexcept
+          -> bool override
+        {
+            bool valid = [input, this]() {
+                // Allow 0-9 chars.
+                if (input[0] >= '0' && input[0] <= '9') return true;
+                // Allow one point for float types.
+                if constexpr (std::is_floating_point_v<T>)
+                    if (input[0] == '.'
+                        && Self::input_text().find('.') == std::string::npos)
+                        return true;
+                // Allow "-" as first input char for signed types.
+                if constexpr (std::is_signed_v<T>) {
+                    std::string_view displayed_value = Self::input_text();
+                    if (input[0] == '-' && displayed_value.empty()) return true;
+                }
+                return false;
+            }();
+            return valid;
+        }
+
+        [[nodiscard]] auto process_value(const T x) const noexcept -> T override
+        {
+            // If value is out of allowed range return either min or max allowed
+            // value.
+            T value = [x, this]() {
+                if (x < _value_range.first) return _value_range.first;
+                if (x > _value_range.second) return _value_range.second;
+                return x;
+            }();
+
+            return value;
+        }
+
+        [[nodiscard]] auto size() const noexcept -> Size override
+        {
+            const auto base       = InputImpl<T>::size();
+            const auto btns_width = 4 * _increment_button->size().w;
+            return {base.w + btns_width, base.h};
+        }
+
+        [[nodiscard]] auto value_range() const noexcept
+          -> const std::pair<T, T>& override
+        {
+            return _value_range;
+        }
+
+        void value_range(const T min, const T max) override
+        {
+            if (min > max) throw std::invalid_argument("min cannot be greater than max");
+            _value_range = {min, max};
+            Self::value  = process_value(Self::value);
+            Self::input_text(Self::value_to_string(Self::value));
+        }
+
+    protected:
+        std::unique_ptr<Button> _increment_button;
+        SDL_Rect                _increment_button_area {};
+        std::unique_ptr<Button> _decrement_button;
+        SDL_Rect                _decrement_button_area {};
+        std::pair<T, T>         _value_range {std::numeric_limits<T>::lowest(),
+                                      std::numeric_limits<T>::max()};
+
+        void _handle_font_change(const std::shared_ptr<Font>& f) override
+        {
+            _decrement_button->font(f);
+            _increment_button->font(f);
+            InputImpl<T>::_handle_font_change(f);
+        }
+
+        void _handle_font_color_change(const Color fg, const Color bg) override
+        {
+            InputImpl<T>::_handle_font_color_change(fg, bg);
+            _decrement_button->font_color_bg(bg);
+            _decrement_button->font_color_fg(fg);
+            _increment_button->font_color_bg(bg);
+            _increment_button->font_color_fg(fg);
+        }
+
+        void _handle_geometry_change(const SDL_Rect& vp) override
+        {
+            InputImpl<T>::_handle_geometry_change(vp);
+
+            const int widest_button     = _increment_button->size().w != 0
+                                          ? _increment_button->size().w
+                                          : _decrement_button->size().w;
+            const int button_area_width = 2 * widest_button;
+            const int spacing           = center_line(button_area_width, widest_button);
+            const int field_width       = vp.w - 2 * button_area_width;
+
+            Self::_widget_area.x = Self::_widget_area.x + button_area_width;
+            Self::_widget_area.w = field_width;
+
+            Self::_input_caption->viewport(rect_offset(
+              rect_margin(Self::_widget_area, {Self::border_width, Self::border_width}),
+              vp));
+            _decrement_button_area = {spacing, Self::_widget_area.y,
+                                      _decrement_button->size().w,
+                                      _decrement_button->size().h};
+
+            _increment_button_area = {vp.w - spacing - _increment_button->size().w,
+                                      Self::_widget_area.y, _increment_button->size().w,
+                                      _increment_button->size().h};
+
+            _increment_button->viewport(rect_offset(_increment_button_area, vp));
+            _decrement_button->viewport(rect_offset(_decrement_button_area, vp));
+        }
+
+        void _handle_renderer_change(const std::shared_ptr<Renderer>& r) override
+        {
+            InputImpl<T>::_handle_renderer_change(r);
+            _decrement_button->renderer(r);
+            _increment_button->renderer(r);
+        }
+
+        void _handle_rendering() override
+        {
+            InputImpl<T>::_handle_rendering();
+            _increment_button->render();
+            _decrement_button->render();
+        }
+    };
+}
+
+#endif
diff --git a/inc/basic_widgets/w/widget_factory.hpp b/inc/basic_widgets/w/widget_factory.hpp
new file mode 100644
index 0000000..7777c29
--- /dev/null
+++ b/inc/basic_widgets/w/widget_factory.hpp
@@ -0,0 +1,19 @@
+#ifndef BWIDGETS_WIDGET_FACTORY_HPP
+#define BWIDGETS_WIDGET_FACTORY_HPP
+
+#include <basic_widgets/w/aligned_layout.hpp>
+#include <basic_widgets/w/button.hpp>
+#include <basic_widgets/w/caption.hpp>
+#include <basic_widgets/w/numeric_input.hpp>
+
+namespace bwidgets
+{
+    auto create_button(Widget* p = nullptr) -> std::unique_ptr<Button>;
+    auto create_caption(Widget* p = nullptr) -> std::unique_ptr<Caption>;
+    auto create_horizontal_layout(Widget* p = nullptr) -> std::unique_ptr<AlignedLayout>;
+    auto create_input_float(Widget* p = nullptr) -> std::unique_ptr<NumericInput<float>>;
+    auto create_input_int(Widget* p = nullptr) -> std::unique_ptr<NumericInput<int>>;
+    auto create_vertical_layout(Widget* p = nullptr) -> std::unique_ptr<AlignedLayout>;
+}
+
+#endif
diff --git a/meson.build b/meson.build
index ec64ee7..99a5a5e 100644
--- a/meson.build
+++ b/meson.build
@@ -1,16 +1,19 @@
 project('sdl2_basic_widgets', 'cpp',
-    version : '0.1pre',
+    version : '0.9.0',
     default_options : [
         'b_lundef=false',
-        'b_sanitize=address,undefined',
+        'b_sanitize=undefined',
         'cpp_std=c++20',
-        'd_ndebug=if-release',
         'optimization=g',
         'warning_level=3',
     ],
     license: 'EUPL-1.2')
 
-add_project_arguments('-pedantic', '-Winline', language: 'cpp')
+add_project_arguments('-Wconversion', '-pedantic', language: 'cpp')
+
+if (get_option('buildtype').startswith('debug'))
+    add_project_arguments('-DBWIDGETS_DEBUG', language: 'cpp')
+endif
 
 sdl = [
     dependency('sdl2', version: '>=2.0.5'),
@@ -25,12 +28,14 @@ libbasic_widgets = static_library('basic_widgets',
     'src/core/font.cpp',
     'src/core/renderer.cpp',
     'src/core/texture.cpp',
-    'src/w/aligned_layout.cpp',
-    'src/w/base/layout.cpp',
-    'src/w/base/widget.cpp',
-    'src/w/button.cpp',
-    'src/w/caption.cpp',
-    'src/w/feat/mouse_handler.cpp',
+    'src/w/base/layout_impl.cpp',
+    'src/w/base/widget_impl.cpp',
+    'src/w/button_impl.cpp',
+    'src/w/caption_impl.cpp',
+    'src/w/feat/event_handler_impl.cpp',
+    'src/w/feat/keyboard_handler_impl.cpp',
+    'src/w/feat/mouse_handler_impl.cpp',
+    'src/w/widget_factory.cpp',
     dependencies : [sdl, fontconfig],
     include_directories : pub_api,
     install : true)
@@ -42,24 +47,28 @@ libbasic_widgets_dep = declare_dependency(
 
 executable('button_demo',
     'examples/button_example.cpp',
+    dependencies: [sdl],
     include_directories : pub_api,
     link_with : libbasic_widgets,
     install : false)
 
 executable('caption_demo',
     'examples/caption_example.cpp',
+    dependencies: [sdl],
     include_directories : pub_api,
     link_with : libbasic_widgets,
     install : false)
 
 executable('example_demo',
     'examples/example_example.cpp',
+    dependencies: [sdl],
     include_directories : pub_api,
     link_with : libbasic_widgets,
     install : false)
 
 executable('input_demo',
     'examples/input_example.cpp',
+    dependencies: [sdl],
     include_directories : pub_api,
     link_with : libbasic_widgets,
     install : false)
diff --git a/src/core/draw.cpp b/src/core/draw.cpp
index b57153f..2447ec5 100644
--- a/src/core/draw.cpp
+++ b/src/core/draw.cpp
@@ -2,7 +2,7 @@
 #include <cmath>
 #include <vector>
 
-#include <SDL2/SDL_render.h>
+#include <SDL_render.h>
 
 #include <basic_widgets/core/draw.hpp>
 #include <basic_widgets/core/math.hpp>
@@ -10,26 +10,27 @@
 
 namespace bwidgets
 {
-    auto aa(const Color& base_color, const int aa_pixels, const float d) noexcept
-      -> Color
+    auto aa(const Color base_color, const int aa_pixels, const float d) noexcept -> Color
     {
-        Color c(base_color);
-        if (aa_pixels == 0) {
-            if (d > 0) c().a = 0;
-        }
-        else {
+        Color c = [aa_pixels, base_color, d]() -> Color {
+            const auto [r, g, b, a] = base_color();
+            // AA disabled, returns fully opaque or fully transparent colors
+            if (aa_pixels == 0) {
+                if (d > 0) return {r, g, b, 0};
+                return {r, g, b, a};
+            }
             const auto factor = 1.0 - smoothstep<float>(d, (float)-aa_pixels, 0.);
-            c().a             = (uint8_t)((float)c().a * factor);
-        }
+            return {r, g, b, (uint8_t)((float)base_color().a * factor)};
+        }();
 
         return c;
     }
 
-    auto filled_circle(const Color& c, const int resolution, Renderer* r,
-                       const int aa_pixels) -> Texture*
+    auto filled_circle(const Color c, const int resolution, const Renderer& r,
+                       const int aa_pixels) -> std::shared_ptr<Texture>
     {
         // clang-format off
-        auto*           texture {new Texture(
+        auto           texture {std::make_shared<Texture>(
                                  r,
                                  SDL_PIXELFORMAT_RGBA32,
                                  SDL_TEXTUREACCESS_STATIC,
@@ -39,16 +40,15 @@ namespace bwidgets
         const auto      radius {resolution / 2};
         const SDL_Point center {radius, radius};
 
-        set_pixels_color(
-          texture,
-          [aa_pixels, c, center, radius](const SDL_Point&       p,
-                                         const SDL_PixelFormat* format) -> uint32_t {
-              const auto d_delta  = distance(center, p) - (float)radius;
-              const auto aa_color = aa(c, aa_pixels, d_delta);
+        set_pixels_color(texture.get(),
+                         [aa_pixels, c, center, radius](
+                           SDL_Point p, const SDL_PixelFormat& format) -> uint32_t {
+                             const auto d_delta  = distance(center, p) - (float)radius;
+                             const auto aa_color = aa(c, aa_pixels, d_delta);
 
-              return SDL_MapRGBA(format, aa_color().r, aa_color().g, aa_color().b,
-                                 aa_color().a);
-          });
+                             return SDL_MapRGBA(&format, aa_color().r, aa_color().g,
+                                                aa_color().b, aa_color().a);
+                         });
         texture->blend_mode(SDL_BLENDMODE_BLEND);
         texture->scale_mode(SDL_ScaleModeNearest);
 
@@ -56,21 +56,21 @@ namespace bwidgets
     }
 
     void set_pixels_color(
-      Texture* t,
-      const std::function<uint32_t(const SDL_Point&, const SDL_PixelFormat*)>&
-        pixel_color)
+      Texture&                                                          t,
+      const std::function<uint32_t(SDL_Point, const SDL_PixelFormat&)>& pixel_color)
     {
-        auto attr  = t->attributes();
+        auto attr  = t.attributes();
         auto pitch = attr.w * attr.format->BytesPerPixel;
 
         std::vector<uint32_t> pixels;
         pixels.reserve(attr.h * (std::vector<uint32_t>::size_type)pitch);
+        // TODO parallel algo
         for (auto y = 0; y < attr.h; y++) {
             for (auto x = 0; x < attr.w; x++) {
-                pixels.emplace_back(pixel_color({x, y}, attr.format));
+                pixels.emplace_back(pixel_color({x, y}, *attr.format));
             }
         }
 
-        t->update(nullptr, (const void*)pixels.data(), pitch);
+        t.update(nullptr, (const void*)pixels.data(), pitch);
     }
 }
diff --git a/src/core/font.cpp b/src/core/font.cpp
index 5368d58..a7a6bed 100644
--- a/src/core/font.cpp
+++ b/src/core/font.cpp
@@ -1,161 +1,145 @@
 #include <functional>
+#include <memory>
 #include <stack>
+#include <stdexcept>
 
 #include <fontconfig/fontconfig.h>
 
+#include <basic_widgets/core/error_helper.hpp>
 #include <basic_widgets/core/font.hpp>
 #include <basic_widgets/core/type/fc_error.hpp>
-#include <basic_widgets/core/type/sdl_error.hpp>
 
-namespace bwidgets
+using namespace bwidgets;
+
+const Color Font::default_color_bg {255, 255, 255, SDL_ALPHA_OPAQUE};
+const Color Font::default_color_fg {0, 0, 0, SDL_ALPHA_OPAQUE};
+
+Font::Font(TTF_Font* f)
+  : _data {ptr_or_throw<SDLError>(f)},
+    ascent {TTF_FontAscent(f)},
+    descent {TTF_FontDescent(f)},
+    faces {TTF_FontFaces(f)},
+    family_name {TTF_FontFaceFamilyName(f)},
+    fixed_width {TTF_FontFaceIsFixedWidth(f) != 0},
+    height {TTF_FontHeight(f)},
+    line_skip {TTF_FontLineSkip(f)},
+    style_name {TTF_FontFaceStyleName(f)}
+{}
+
+Font::Font(const std::string_view file, const int size)
+  : Font {TTF_OpenFont(file.data(), size)}
+{}
+
+auto Font::hinting() const noexcept -> Font::Hinting
 {
-    Font::Font(TTF_Font* f)
-      : OpaqueStruct(f),
-        ascent(TTF_FontAscent(f)),
-        descent(TTF_FontDescent(f)),
-        faces(TTF_FontFaces(f)),
-        family_name(TTF_FontFaceFamilyName(f)),
-        fixed_width(TTF_FontFaceIsFixedWidth(f) != 0),
-        height(TTF_FontHeight(f)),
-        line_skip(TTF_FontLineSkip(f)),
-        style_name(TTF_FontFaceStyleName(f))
-    {}
+    return static_cast<Hinting>(TTF_GetFontHinting(_data.get()));
+}
 
-    Font::Font(const std::string& file, const int size)
-      : Font(ptr_or_throw<FCError>(TTF_OpenFont(file.c_str(), size), __FILE__,
-                                   __FUNCTION__, __LINE__, "failed to open font"))
-    {}
+auto Font::hinting(const Font::Hinting h) noexcept -> Font*
+{
+    TTF_SetFontHinting(_data.get(), static_cast<int>(h));
+    return this;
+}
 
-    Font::~Font() noexcept
-    {
-        TTF_CloseFont(_c_pod);
-    }
+auto Font::kerning() const noexcept -> bool
+{
+    return TTF_GetFontKerning(_data.get()) != 0;
+}
 
-    auto Font::hinting() const noexcept -> Font::Hinting
-    {
-        return (Hinting)TTF_GetFontHinting(_c_pod);
-    }
+auto Font::kerning(const bool allowed) noexcept -> Font*
+{
+    TTF_SetFontKerning(_data.get(), static_cast<int>(allowed));
+    return this;
+}
 
-    auto Font::hinting(const Font::Hinting h) noexcept -> Font*
-    {
-        TTF_SetFontHinting(_c_pod, (int)h);
-        return this;
-    }
+auto Font::outline() const noexcept -> int
+{
+    return TTF_GetFontOutline(_data.get());
+}
 
-    auto Font::kerning() const noexcept -> bool
-    {
-        return TTF_GetFontKerning(_c_pod) != 0;
-    }
-
-    auto Font::kerning(const bool allowed) noexcept -> Font*
-    {
-        TTF_SetFontKerning(_c_pod, static_cast<int>(allowed));
-        return this;
-    }
-
-    auto Font::outline() const noexcept -> int
-    {
-        return TTF_GetFontOutline(_c_pod);
-    }
-
-    auto Font::outline(const int size) noexcept -> Font*
-    {
-        TTF_SetFontOutline(_c_pod, size);
-        return this;
-    }
-
-    auto Font::render(const RenderMode m, const std::string& str, const Color& fg,
-                      const Color& bg) -> SDL_Surface*
-    {
-        std::function<SDL_Surface*()> renderer;
-        const char*                   c_str = str.empty() ? " " : str.c_str();
+auto Font::outline(const int size) noexcept -> Font*
+{
+    TTF_SetFontOutline(_data.get(), size);
+    return this;
+}
 
+auto Font::render(const RenderMode m, const std::string_view str, const Color fg,
+                  const Color bg) -> std::unique_ptr<SDL_Surface, Deleter>
+{
+    const char* const c_str = str.empty() ? " " : str.data();
+    auto renderer = [bg, c_str, fg, m, this]() -> std::function<SDL_Surface*()> {
         switch (m) {
             case RenderMode::BLENDED:
-                renderer = [&fg, c_str, this]() {
-                    return TTF_RenderUTF8_Blended(_c_pod, c_str, fg());
+                return [fg, c_str, this]() {
+                    return TTF_RenderUTF8_Blended(_data.get(), c_str, fg());
                 };
-                break;
             case RenderMode::SHADED:
-                renderer = [&bg, &fg, c_str, this]() {
-                    return TTF_RenderUTF8_Shaded(_c_pod, c_str, fg(), bg());
+                return [bg, fg, c_str, this]() {
+                    return TTF_RenderUTF8_Shaded(_data.get(), c_str, fg(), bg());
                 };
-                break;
             case RenderMode::SOLID:
-                renderer = [&fg, c_str, this]() {
-                    return TTF_RenderUTF8_Solid(_c_pod, c_str, fg());
+                return [fg, c_str, this]() {
+                    return TTF_RenderUTF8_Solid(_data.get(), c_str, fg());
                 };
-                break;
+            default:
+                throw std::logic_error("missing switch case.");
         }
+    }();
 
-        return ptr_or_throw<SDLError>(renderer(), __FILE__, __FUNCTION__, __LINE__);
-    }
-
-    auto Font::style() const noexcept -> uint8_t
-    {
-        return TTF_GetFontStyle(_c_pod);
-    }
-
-    auto Font::style(const uint8_t s) noexcept -> Font*
-    {
-        TTF_SetFontStyle(_c_pod, s);
-        return this;
-    }
-
-    auto Font::text_size(const std::string& str) const noexcept -> Size
-    {
-        Size s {};
-        TTF_SizeUTF8(_c_pod, str.c_str(), &s.w, &s.h);
-        return s;
-    }
-
-    auto Font::find(const std::string& pat) -> std::string
-    {
-        std::stack<std::function<void()>> cleaners;
-
-        FcConfig* conf = ptr_or_throw<FCError>(FcInitLoadConfigAndFonts(), __FILE__,
-                                               __FUNCTION__, __LINE__, "init failed");
-        cleaners.emplace([conf]() { FcConfigDestroy(conf); });
-
-        FcPattern* pattern = nullptr;
-        try {
-            pattern =
-              ptr_or_throw<FCError>(FcNameParse((FcChar8*)pat.c_str()), __FILE__,
-                                    __FUNCTION__, __LINE__, "pattern parsing failed");
-            cleaners.emplace([pattern]() { FcPatternDestroy(pattern); });
-
-            if (FcConfigSubstitute(conf, pattern, FcMatchPattern) == FcFalse)
-                throw FCError {__FILE__, __FUNCTION__, __LINE__,
-                               "FcConfigSubstitute failed"};
-        } catch (const std::exception& e) {
-            while (!cleaners.empty()) {
-                cleaners.top()();
-                cleaners.pop();
-            }
-            throw e;
-        }
-
-        FcDefaultSubstitute(pattern);
-
-        std::string file_path;
-        FcResult    res {};
-        FcPattern*  font = FcFontMatch(conf, pattern, &res);
-        if (font != nullptr) {
-            FcChar8* file = nullptr;
-            if (FcPatternGetString(font, FC_FILE, 0, &file) == FcResultMatch) {
-                file_path = (char*)file;
-            }
-            FcPatternDestroy(font);
-        }
-
-        while (!cleaners.empty()) {
-            cleaners.top()();
-            cleaners.pop();
-        }
-
-        if (file_path.empty())
-            throw FCError {__FILE__, __FUNCTION__, __LINE__, "no font found"};
-
-        return file_path;
-    }
+    return std::unique_ptr<SDL_Surface, Deleter>(ptr_or_throw<SDLError>(renderer()));
+}
+
+auto Font::style() const noexcept -> uint8_t
+{
+    return TTF_GetFontStyle(_data.get());
+}
+
+auto Font::style(const uint8_t s) noexcept -> Font*
+{
+    TTF_SetFontStyle(_data.get(), s);
+    return this;
+}
+
+auto Font::text_size(const std::string_view str) const noexcept -> Size
+{
+    Size s {};
+    TTF_SizeUTF8(_data.get(), str.data(), &s.w, &s.h);
+    return s;
+}
+
+auto Font::find(const std::string_view pat) -> std::string
+{
+    const auto conf = std::unique_ptr<FcConfig, Deleter>(
+      ptr_or_throw<FCError>(FcInitLoadConfigAndFonts(), "fontconfig init failed."));
+
+    const auto pattern = [&conf, pat]() {
+        auto pattern = std::unique_ptr<FcPattern, Deleter>(ptr_or_throw<FCError>(
+          FcNameParse(reinterpret_cast<const FcChar8*>(pat.data())),
+          "pattern parsing failed"));
+
+        success_or_throw<FCError, FcBool>(
+          FcConfigSubstitute(conf.get(), pattern.get(), FcMatchPattern),
+          "FcConfigSubstitute failed", [](auto code) { return code == FcTrue; });
+        return pattern;
+    }();
+
+    FcDefaultSubstitute(pattern.get());
+
+    std::string file_path = [&conf, &pattern]() {
+        FcResult   res {};
+        const auto font = std::unique_ptr<FcPattern, Deleter>(ptr_or_throw<FCError>(
+          FcFontMatch(conf.get(), pattern.get(), &res), "no font found."));
+
+        if (FcChar8* file = nullptr;
+            FcPatternGetString(font.get(), FC_FILE, 0, &file) == FcResultMatch)
+        {
+            // "I know what I'm doing"
+            // NOLINTNEXTLINE
+            std::string _file_path {reinterpret_cast<char*>(file)};
+            return _file_path;
+        }
+        throw FCError("no font found.");
+    }();
+
+    return file_path;
 }
diff --git a/src/core/renderer.cpp b/src/core/renderer.cpp
index c24fd86..bda2961 100644
--- a/src/core/renderer.cpp
+++ b/src/core/renderer.cpp
@@ -3,47 +3,39 @@
 
 using namespace bwidgets;
 
-Renderer::Renderer(SDL_Renderer* r) : OpaqueStruct(r), info(_info(r)) {}
-
-Renderer::Renderer(SDL_Window* w, const int index, const uint32_t flags = 0)
-  : Renderer(ptr_or_throw<SDLError>(SDL_CreateRenderer(w, index, flags), __FILE__,
-                                    __FUNCTION__, __LINE__))
+Renderer::Renderer(SDL_Renderer* r) : _data {ptr_or_throw<SDLError>(r)}, info {_info(r)}
 {}
 
-Renderer::~Renderer() noexcept
-{
-    SDL_DestroyRenderer(_c_pod);
-}
+Renderer::Renderer(SDL_Window* w, const int index, const uint32_t flags = 0)
+  : Renderer {SDL_CreateRenderer(w, index, flags)}
+{}
 
 auto Renderer::blend_mode() -> SDL_BlendMode
 {
     SDL_BlendMode mode {};
-    SDLError::success_or_throw(SDL_GetRenderDrawBlendMode(_c_pod, &mode), __FILE__,
-                               __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_GetRenderDrawBlendMode(_data.get(), &mode));
 
     return mode;
 }
 
 auto Renderer::blend_mode(const SDL_BlendMode mode) -> Renderer*
 {
-    SDLError::success_or_throw(SDL_SetRenderDrawBlendMode(_c_pod, mode), __FILE__,
-                               __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_SetRenderDrawBlendMode(_data.get(), mode));
 
     return this;
 }
 
 auto Renderer::clear() -> Renderer*
 {
-    SDLError::success_or_throw(SDL_RenderClear(_c_pod), __FILE__, __FUNCTION__,
-                               __LINE__);
+    success_or_throw<SDLError>(SDL_RenderClear(_data.get()));
 
     return this;
 }
 
-auto Renderer::copy(Texture* t, const SDL_Rect* src, const SDL_Rect* dst) -> Renderer*
+auto Renderer::copy(const Texture& t, const SDL_Rect* const src,
+                    const SDL_Rect* const dst) -> Renderer*
 {
-    SDLError::success_or_throw(SDL_RenderCopy(_c_pod, (*t)(), src, dst), __FILE__,
-                               __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_RenderCopy(_data.get(), t._data.get(), src, dst));
 
     return this;
 }
@@ -51,55 +43,51 @@ auto Renderer::copy(Texture* t, const SDL_Rect* src, const SDL_Rect* dst) -> Ren
 auto Renderer::draw_color() -> Color
 {
     Color c;
-    SDLError::success_or_throw(
-      SDL_GetRenderDrawColor(_c_pod, &c().r, &c().g, &c().b, &c().a), __FILE__,
-      __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(
+      SDL_GetRenderDrawColor(_data.get(), &c().r, &c().g, &c().b, &c().a));
 
     return c;
 }
 
-auto Renderer::draw_color(const Color& c) -> Renderer*
+auto Renderer::draw_color(const Color c) -> Renderer*
 {
-    SDLError::success_or_throw(
-      SDL_SetRenderDrawColor(_c_pod, c().r, c().g, c().b, c().a), __FILE__, __FUNCTION__,
-      __LINE__);
+    success_or_throw<SDLError>(
+      SDL_SetRenderDrawColor(_data.get(), c().r, c().g, c().b, c().a));
 
     return this;
 }
 
-auto Renderer::draw_line(const SDL_Point& a, const SDL_Point& b) -> Renderer*
+auto Renderer::draw_line(const SDL_Point a, const SDL_Point b) -> Renderer*
 {
-    SDLError::success_or_throw(SDL_RenderDrawLine(_c_pod, a.x, a.y, b.x, b.y), __FILE__,
-                               __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_RenderDrawLine(_data.get(), a.x, a.y, b.x, b.y));
 
     return this;
 }
 
-auto Renderer::draw_lines(const std::vector<SDL_Point>& pts) -> Renderer*
+auto Renderer::draw_lines(const std::span<SDL_Point> pts) -> Renderer*
 {
-    SDLError::success_or_throw(SDL_RenderDrawLines(_c_pod, pts.data(), (int)pts.size()),
-                               __FILE__, __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(
+      SDL_RenderDrawLines(_data.get(), pts.data(), (int)pts.size()));
 
     return this;
 }
 
-auto Renderer::draw_point(const SDL_Point& p) -> Renderer*
+auto Renderer::draw_point(const SDL_Point p) -> Renderer*
 {
-    SDLError::success_or_throw(SDL_RenderDrawPoint(_c_pod, p.x, p.y), __FILE__,
-                               __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_RenderDrawPoint(_data.get(), p.x, p.y));
 
     return this;
 }
 
-auto Renderer::draw_points(const std::vector<SDL_Point>& pts) -> Renderer*
+auto Renderer::draw_points(const std::span<SDL_Point> pts) -> Renderer*
 {
-    SDLError::success_or_throw(SDL_RenderDrawPoints(_c_pod, pts.data(), (int)pts.size()),
-                               __FILE__, __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(
+      SDL_RenderDrawPoints(_data.get(), pts.data(), (int)pts.size()));
 
     return this;
 }
 
-auto Renderer::draw_rect(const SDL_Rect* r) -> Renderer*
+auto Renderer::draw_rect(const SDL_Rect* const r) -> Renderer*
 {
     auto vp = viewport();
     // Has glitch at top-left and bottom-right corner.
@@ -107,37 +95,35 @@ auto Renderer::draw_rect(const SDL_Rect* r) -> Renderer*
     // The second corner is missing a pixel.
     if (r != nullptr)
         viewport({vp.x + r->x, vp.y + r->y, r->w - 1, r->h - 1}); // crop extra pixel
-    SDLError::success_or_throw(SDL_RenderDrawRect(_c_pod, nullptr), __FILE__,
-                               __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_RenderDrawRect(_data.get(), nullptr));
     // add missing pixel. works sometimes…
     if (r != nullptr) draw_point({r->w - 1, r->h - 1});
     else draw_point({vp.w - 1, vp.h - 1});
 
-    viewport(vp);
+    viewport(&vp);
 
     return this;
 }
 
-auto Renderer::draw_rects(const std::vector<SDL_Rect>& rs) -> Renderer*
+auto Renderer::draw_rects(const std::span<SDL_Rect> rs) -> Renderer*
 {
-    SDLError::success_or_throw(SDL_RenderDrawRects(_c_pod, rs.data(), (int)rs.size()),
-                               __FILE__, __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(
+      SDL_RenderDrawRects(_data.get(), rs.data(), (int)rs.size()));
 
     return this;
 }
 
-auto Renderer::fill_rect(const SDL_Rect* r) -> Renderer*
+auto Renderer::fill_rect(const SDL_Rect* const r) -> Renderer*
 {
-    SDLError::success_or_throw(SDL_RenderFillRect(_c_pod, r), __FILE__, __FUNCTION__,
-                               __LINE__);
+    success_or_throw<SDLError>(SDL_RenderFillRect(_data.get(), r));
 
     return this;
 }
 
-auto Renderer::fill_rects(const std::vector<SDL_Rect>& rs) -> Renderer*
+auto Renderer::fill_rects(const std::span<SDL_Rect> rs) -> Renderer*
 {
-    SDLError::success_or_throw(SDL_RenderFillRects(_c_pod, rs.data(), (int)rs.size()),
-                               __FILE__, __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(
+      SDL_RenderFillRects(_data.get(), rs.data(), (int)rs.size()));
 
     return this;
 }
@@ -145,29 +131,27 @@ auto Renderer::fill_rects(const std::vector<SDL_Rect>& rs) -> Renderer*
 auto Renderer::output_size() -> Size
 {
     Size s {};
-    SDLError::success_or_throw(SDL_GetRendererOutputSize(_c_pod, &s.w, &s.h), __FILE__,
-                               __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_GetRendererOutputSize(_data.get(), &s.w, &s.h));
 
     return s;
 }
 
 void Renderer::present() noexcept
 {
-    SDL_RenderPresent(_c_pod);
+    SDL_RenderPresent(_data.get());
 }
 
 auto Renderer::viewport() noexcept -> SDL_Rect
 {
     SDL_Rect vp;
-    SDL_RenderGetViewport(_c_pod, &vp);
+    SDL_RenderGetViewport(_data.get(), &vp);
 
     return vp;
 }
 
-auto Renderer::viewport(const SDL_Rect* vp) -> Renderer*
+auto Renderer::viewport(const SDL_Rect* const vp) -> Renderer*
 {
-    SDLError::success_or_throw(SDL_RenderSetViewport(_c_pod, vp), __FILE__, __FUNCTION__,
-                               __LINE__);
+    success_or_throw<SDLError>(SDL_RenderSetViewport(_data.get(), vp));
 
     return this;
 }
diff --git a/src/core/texture.cpp b/src/core/texture.cpp
index ed2ffac..07aa213 100644
--- a/src/core/texture.cpp
+++ b/src/core/texture.cpp
@@ -3,43 +3,36 @@
 
 using namespace bwidgets;
 
-Texture::Texture(SDL_Texture* t) : OpaqueStruct(t)
-{
-    _attributes = attributes(t);
-}
-
-Texture::Texture(Renderer* r, const SDL_PixelFormatEnum f, const SDL_TextureAccess a,
-                 int w, int h)
-  : Texture(ptr_or_throw<SDLError>(SDL_CreateTexture((*r)(), f, a, w, h), __FILE__,
-                                   __FUNCTION__, __LINE__))
+Texture::Texture(SDL_Texture* t)
+  : _attributes(attributes(t)), _data {ptr_or_throw<SDLError>(t)}
 {}
 
-Texture::Texture(Renderer* r, SDL_Surface* s)
-  : OpaqueStruct(ptr_or_throw<SDLError>(SDL_CreateTextureFromSurface((*r)(), s),
-                                        __FILE__, __FUNCTION__, __LINE__))
-{
-    _attributes = attributes(_c_pod);
-}
+Texture::Texture(const Renderer& r, const SDL_PixelFormatEnum f,
+                 const SDL_TextureAccess a, int w, int h)
+  : Texture {SDL_CreateTexture(r._data.get(), f, a, w, h)}
+{}
+
+Texture::Texture(const Renderer& r, SDL_Surface* const s)
+  : Texture {SDL_CreateTextureFromSurface(r._data.get(), s)}
+{}
 
 Texture::~Texture() noexcept
 {
-    SDL_DestroyTexture(_c_pod);
-    _c_pod = nullptr;
+    // Idk why but freeing the format in ~Attr gives memory errors (valgrind)
+    SDL_FreeFormat(_attributes.format);
 }
 
 auto Texture::alpha_mode() -> uint8_t
 {
     uint8_t mode = 0;
-    SDLError::success_or_throw(SDL_GetTextureAlphaMod(_c_pod, &mode), __FILE__,
-                               __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_GetTextureAlphaMod(_data.get(), &mode));
 
     return mode;
 }
 
 auto Texture::alpha_mode(const uint8_t m) -> Texture*
 {
-    SDLError::success_or_throw(SDL_SetTextureAlphaMod(_c_pod, m), __FILE__, __FUNCTION__,
-                               __LINE__);
+    success_or_throw<SDLError>(SDL_SetTextureAlphaMod(_data.get(), m));
 
     return this;
 }
@@ -47,16 +40,14 @@ auto Texture::alpha_mode(const uint8_t m) -> Texture*
 auto Texture::blend_mode() -> SDL_BlendMode
 {
     SDL_BlendMode mode {};
-    SDLError::success_or_throw(SDL_GetTextureBlendMode(_c_pod, &mode), __FILE__,
-                               __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_GetTextureBlendMode(_data.get(), &mode));
 
     return mode;
 }
 
 auto Texture::blend_mode(const SDL_BlendMode m) -> Texture*
 {
-    SDLError::success_or_throw(SDL_SetTextureBlendMode(_c_pod, m), __FILE__,
-                               __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_SetTextureBlendMode(_data.get(), m));
 
     return this;
 }
@@ -64,17 +55,15 @@ auto Texture::blend_mode(const SDL_BlendMode m) -> Texture*
 auto Texture::color_mode() -> Color
 {
     Color mode;
-    SDLError::success_or_throw(
-      SDL_GetTextureColorMod(_c_pod, &mode().r, &mode().g, &mode().b), __FILE__,
-      __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(
+      SDL_GetTextureColorMod(_data.get(), &mode().r, &mode().g, &mode().b));
 
     return mode;
 }
 
-auto Texture::color_mode(const Color& m) -> Texture*
+auto Texture::color_mode(Color m) -> Texture*
 {
-    SDLError::success_or_throw(SDL_SetTextureColorMod(_c_pod, m().r, m().g, m().b),
-                               __FILE__, __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_SetTextureColorMod(_data.get(), m().r, m().g, m().b));
 
     return this;
 }
@@ -82,24 +71,22 @@ auto Texture::color_mode(const Color& m) -> Texture*
 auto Texture::scale_mode() -> SDL_ScaleMode
 {
     SDL_ScaleMode mode {};
-    SDLError::success_or_throw(SDL_GetTextureScaleMode(_c_pod, &mode), __FILE__,
-                               __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_GetTextureScaleMode(_data.get(), &mode));
 
     return mode;
 }
 
 auto Texture::scale_mode(const SDL_ScaleMode m) -> Texture*
 {
-    SDLError::success_or_throw(SDL_SetTextureScaleMode(_c_pod, m), __FILE__,
-                               __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_SetTextureScaleMode(_data.get(), m));
 
     return this;
 }
 
-auto Texture::update(SDL_Rect* r, const void* pixels, const int pitch) -> Texture*
+auto Texture::update(const SDL_Rect* const r, const void* const pixels, const int pitch)
+  -> Texture*
 {
-    SDLError::success_or_throw(SDL_UpdateTexture(_c_pod, r, pixels, pitch), __FILE__,
-                               __FUNCTION__, __LINE__);
+    success_or_throw<SDLError>(SDL_UpdateTexture(_data.get(), r, pixels, pitch));
 
     return this;
 }
diff --git a/src/w/aligned_layout.cpp b/src/w/aligned_layout.cpp
deleted file mode 100644
index 7c2d56a..0000000
--- a/src/w/aligned_layout.cpp
+++ /dev/null
@@ -1,57 +0,0 @@
-#include <basic_widgets/core/math.hpp>
-#include <basic_widgets/w/aligned_layout.hpp>
-
-using namespace bwidgets;
-
-auto AlignedLayout::size() const noexcept -> Size
-{
-    Size min_size {0, 0};
-
-    if (alignment == Alignment::HORIZONTAL) {
-        for (const auto* w : _widgets) {
-            if (w->size().w > min_size.w) min_size.w = w->size().w;
-            if (w->size().h > min_size.h) min_size.h = w->size().h;
-        }
-
-        return {(int)_widgets.size() * min_size.w
-                  + ((int)_widgets.size() + 1) * margins.w,
-                min_size.h + 2 * margins.h};
-    }
-
-    for (const auto* w : _widgets) {
-        if (w->size().w > min_size.w) min_size.w = w->size().w;
-
-        min_size.h += w->size().h;
-    }
-
-    return {min_size.w + 2 * margins.w,
-            min_size.h + ((int)_widgets.size() + 1) * margins.h};
-}
-
-void AlignedLayout::_update_layout(const SDL_Rect& vp)
-{
-    if (alignment == Alignment::HORIZONTAL) {
-        int widget_width =
-          (vp.w - ((int)_widgets.size() + 1) * margins.w) / (int)_widgets.size();
-
-        for (std::vector<Widget*>::size_type i = 0; i < _widgets.size(); i++) {
-            auto* w = _widgets[i];
-            w->viewport({vp.x + margins.w + (int)i * (widget_width + margins.w),
-                         vp.y + center_line(vp.h, w->size().h), widget_width,
-                         w->size().h});
-        }
-    }
-    else {
-        int offset = 0;
-        for (std::vector<Widget*>::size_type i = 0; i < _widgets.size(); i++) {
-            auto* w = _widgets[i];
-            w->viewport({
-              vp.x,
-              vp.y + ((int)i + 1) * margins.h + offset,
-              vp.w,
-              w->size().h,
-            });
-            offset += w->size().h;
-        }
-    }
-}
diff --git a/src/w/base/layout.cpp b/src/w/base/layout.cpp
deleted file mode 100644
index da8124f..0000000
--- a/src/w/base/layout.cpp
+++ /dev/null
@@ -1,42 +0,0 @@
-#include <basic_widgets/w/base/layout.hpp>
-
-using namespace bwidgets;
-
-Layout::~Layout()
-{
-    for (auto* widget_ptr : _widgets) delete widget_ptr;
-}
-
-auto Layout::add_widget(Widget* widget_ptr) -> Layout*
-{
-    widget_ptr->renderer(_renderer);
-    _widgets.emplace_back(widget_ptr);
-    _update_layout(_viewport);
-    return this;
-}
-
-void Layout::for_widgets(const std::function<void(Widget*)>& f)
-{
-    for (auto* w : _widgets) f(w);
-}
-
-auto Layout::handle_event(const SDL_Event& ev) -> Layout*
-{
-    for (auto* widget_ptr : _widgets) widget_ptr->handle_event(ev);
-    return this;
-}
-
-void Layout::_handle_geometry_change(const SDL_Rect& vp)
-{
-    _update_layout(vp);
-}
-
-void Layout::_handle_renderer_change(Renderer* r)
-{
-    for (auto* w : _widgets) w->renderer(r);
-}
-
-void Layout::_handle_rendering()
-{
-    for (auto* widget_ptr : _widgets) widget_ptr->render();
-}
diff --git a/src/w/base/layout_impl.cpp b/src/w/base/layout_impl.cpp
new file mode 100644
index 0000000..5eb8022
--- /dev/null
+++ b/src/w/base/layout_impl.cpp
@@ -0,0 +1,36 @@
+#include <basic_widgets/w/base/layout_impl.hpp>
+
+using namespace bwidgets;
+
+void LayoutImpl::add_widget(std::unique_ptr<Widget> widget_ptr)
+{
+    if (_renderer) widget_ptr->renderer(_renderer);
+    _widgets.emplace_back(std::move(widget_ptr));
+    _update_layout(_viewport);
+}
+
+void LayoutImpl::for_widgets(const std::function<void(Widget*)>& f)
+{
+    for (const auto& w : _widgets) f(w.get());
+}
+
+void LayoutImpl::handle_event(const SDL_Event& ev)
+{
+    EventHandlerImpl::handle_event(ev);
+    for (const auto& w : _widgets) w->handle_event(ev);
+}
+
+void LayoutImpl::_handle_geometry_change(const SDL_Rect& vp)
+{
+    _update_layout(vp);
+}
+
+void LayoutImpl::_handle_renderer_change(const std::shared_ptr<Renderer>& r)
+{
+    for (const auto& w : _widgets) w->renderer(r);
+}
+
+void LayoutImpl::_handle_rendering()
+{
+    for (const auto& w : _widgets) w->render();
+}
diff --git a/src/w/base/widget.cpp b/src/w/base/widget.cpp
deleted file mode 100644
index 3453a64..0000000
--- a/src/w/base/widget.cpp
+++ /dev/null
@@ -1,77 +0,0 @@
-#include <SDL2/SDL_assert.h>
-#include <SDL2/SDL_events.h>
-
-#include <basic_widgets/w/base/widget.hpp>
-#include <basic_widgets/w/feat/keyboard_handler.hpp>
-#include <basic_widgets/w/feat/mouse_handler.hpp>
-
-using namespace bwidgets;
-
-auto Widget::handle_event(const SDL_Event& ev) -> Widget*
-{
-    if (auto* handler = dynamic_cast<KeyboardHandler*>(this); handler) {
-        switch (ev.type) {
-            case SDL_KEYDOWN:
-            case SDL_KEYUP:
-                handler->handle_keyboard(ev.key);
-                break;
-            case SDL_TEXTINPUT:
-                handler->handle_keyboard(ev.text);
-                break;
-        }
-    }
-
-    if (auto* handler = dynamic_cast<MouseHandler*>(this); handler) {
-        switch (ev.type) {
-            case SDL_MOUSEBUTTONDOWN:
-            case SDL_MOUSEBUTTONUP:
-                handler->handle_mouse(ev.button, _viewport);
-                break;
-            case SDL_MOUSEMOTION:
-                handler->handle_mouse(ev.motion, _viewport);
-                break;
-        }
-    }
-
-    return this;
-}
-
-auto Widget::render() -> Widget*
-{
-    if (_renderer == nullptr) return this;
-
-#ifndef _NDEBUG
-    _renderer
-      ->draw_color({
-  // NOLINTNEXTLINE(readability-magic-numbers)
-        {0, 255, 0, SDL_ALPHA_TRANSPARENT}
-    })
-      ->draw_rect(nullptr);
-#endif
-
-    _renderer->viewport(_viewport);
-    _handle_rendering();
-
-    return this;
-}
-
-auto Widget::renderer(Renderer* r) -> Widget*
-{
-    if (r != _renderer) {
-        _handle_renderer_change(r);
-        _renderer = r;
-    }
-    return this;
-}
-
-auto Widget::viewport(const SDL_Rect& vp) -> Widget*
-{
-    _handle_geometry_change(vp);
-    _viewport = vp;
-    return this;
-}
-
-auto Widget::viewport() const -> const SDL_Rect&
-{
-    return _viewport;
-}
diff --git a/src/w/base/widget_impl.cpp b/src/w/base/widget_impl.cpp
new file mode 100644
index 0000000..5b71e42
--- /dev/null
+++ b/src/w/base/widget_impl.cpp
@@ -0,0 +1,40 @@
+#include <basic_widgets/w/base/widget_impl.hpp>
+
+using namespace bwidgets;
+
+void WidgetImpl::render()
+{
+    if (!_renderer) return;
+
+#ifdef BWIDGETS_DEBUG
+    // Render a debug outline of widget viewport.
+    _renderer
+      ->draw_color({
+  // NOLINTNEXTLINE(readability-magic-numbers)
+        {0, 255, 0, SDL_ALPHA_OPAQUE}
+    })
+      ->draw_rect(nullptr);
+#endif
+
+    _renderer->viewport(&_viewport);
+    _handle_rendering();
+}
+
+void WidgetImpl::renderer(std::shared_ptr<Renderer> r)
+{
+    if (r != _renderer) {
+        _handle_renderer_change(r);
+        _renderer = std::move(r);
+    }
+}
+
+void WidgetImpl::viewport(const SDL_Rect& vp)
+{
+    _handle_geometry_change(vp);
+    _viewport = vp;
+}
+
+auto WidgetImpl::viewport() const -> const SDL_Rect&
+{
+    return _viewport;
+}
diff --git a/src/w/button.cpp b/src/w/button.cpp
deleted file mode 100644
index ad4ab08..0000000
--- a/src/w/button.cpp
+++ /dev/null
@@ -1,108 +0,0 @@
-#include <cmath>
-
-#include <SDL2/SDL_render.h>
-
-#include <basic_widgets/core/math.hpp>
-#include <basic_widgets/w/button.hpp>
-
-using namespace bwidgets;
-
-Button::Button(Widget* parent) noexcept : Widget(parent), _caption(this)
-{
-    _focus_area = _click_area = &_widget_area;
-    _caption.alignment        = Caption::Alignment::CENTER;
-
-    _caption.render_mode(Font::RenderMode::BLENDED);
-
-    border_gradient = [this](int len, int pos) -> Color {
-        const auto& end_color   = _is_hovered ? color_bg_hover : color_bg;
-        const auto  start_color = end_color / 2;
-        const auto  factor      = linear(pos, 0, len);
-        return lerp(start_color, end_color, factor);
-    };
-
-    border_gradient_pushed = [this](int len, int pos) -> Color {
-        const auto& end_color   = _is_hovered ? color_bg_hover : color_bg;
-        const Color start_color = end_color / 1.5;
-        const auto  factor      = linear(pos, 0, len);
-        return lerp(start_color, end_color, factor);
-    };
-}
-
-auto Button::size() const noexcept -> Size
-{
-    return _caption.size() + border_size * 2;
-}
-
-auto Button::text() const noexcept -> const std::string&
-{
-    return _caption.text();
-}
-
-auto Button::text(const std::string& txt) -> Button*
-{
-    _caption.text(txt);
-    _handle_geometry_change(_viewport);
-    return this;
-}
-
-void Button::_handle_font_change(Font* f)
-{
-    _caption.font(f);
-    _handle_geometry_change(_viewport);
-}
-
-void Button::_handle_font_color_change(const Color& fg, const Color&)
-{
-    _caption.font_color_fg(fg);
-}
-
-void Button::_handle_geometry_change(const SDL_Rect& vp)
-{
-    const auto h = _caption.size().h + 2 * border_size.h;
-
-    _widget_area = {0, center_line(vp.h, _caption.size().h) - border_size.h, vp.w, h};
-
-    const auto txt_size = _caption.size();
-
-    _caption_area = {center_line(vp.w, txt_size.w), center_line(vp.h, txt_size.h),
-                     txt_size.w, txt_size.h};
-    _caption.viewport(rect_offset(_caption_area, vp));
-}
-
-void Button::_handle_renderer_change(Renderer* r)
-{
-    _caption.renderer(r);
-}
-
-void Button::_handle_rendering()
-{
-    const Color& c        = _is_hovered ? color_bg_hover : color_bg;
-    const auto&  gradient = _is_pushed ? border_gradient_pushed : border_gradient;
-    auto         x        = 0;
-    auto         y        = 0;
-    const auto   biggest = border_size.w > border_size.h ? border_size.w : border_size.h;
-    while (x < border_size.w || y < border_size.h) {
-        const auto max    = x > y ? x : y;
-        const auto margin = Size({x, y});
-        _renderer->draw_color(gradient(biggest, max)())
-          ->draw_rect(rect_margin(_widget_area, margin));
-        if (x < border_size.w) x++;
-        if (y < border_size.h) y++;
-    }
-
-    _renderer->draw_color(c())->fill_rect(rect_margin(_widget_area, border_size));
-    _caption.font_color_bg(c());
-    _caption.render();
-}
-
-void Button::_on_push(bool state)
-{
-    SDL_Point offset {_viewport.x, _viewport.y};
-    if (state) {
-        offset.x += 1;
-        offset.y += 1;
-    }
-
-    _caption.viewport(rect_offset(_caption_area, offset));
-}
diff --git a/src/w/button_impl.cpp b/src/w/button_impl.cpp
new file mode 100644
index 0000000..899182c
--- /dev/null
+++ b/src/w/button_impl.cpp
@@ -0,0 +1,102 @@
+#include <cmath>
+
+#include <basic_widgets/core/math.hpp>
+#include <basic_widgets/w/button_impl.hpp>
+#include <basic_widgets/w/widget_factory.hpp>
+
+using namespace bwidgets;
+
+ButtonImpl::ButtonImpl(Widget* parent) noexcept
+  : WidgetImpl {parent}, _caption {create_caption(this)}
+{
+    enable_mouse_handler(_widget_area, _viewport);
+
+    _caption->alignment = Caption::Alignment::CENTER;
+    _caption->render_mode(Font::RenderMode::BLENDED);
+
+    border_gradient = [this](const int len, const int pos,
+                             const float divider) -> Color {
+        const auto& end_color = hovered() ? color_bg_hover : color_bg;
+        return lerp(end_color / divider, end_color, linear(pos, 0, len));
+    };
+}
+
+auto ButtonImpl::size() const noexcept -> Size
+{
+    return _caption->size() + border_size * 2;
+}
+
+auto ButtonImpl::text() const noexcept -> std::string_view
+{
+    return _caption->text();
+}
+
+void ButtonImpl::text(std::string txt)
+{
+    _caption->text(std::move(txt));
+    _handle_geometry_change(_viewport);
+}
+
+void ButtonImpl::_handle_font_change(const std::shared_ptr<Font>& f)
+{
+    _caption->font(f);
+    _handle_geometry_change(_viewport);
+}
+
+void ButtonImpl::_handle_font_color_change(const Color fg, Color)
+{
+    _caption->font_color_fg(fg);
+}
+
+void ButtonImpl::_handle_geometry_change(const SDL_Rect& vp)
+{
+    const auto h = _caption->size().h + 2 * border_size.h;
+    _widget_area = {0, center_line(vp.h, _caption->size().h) - border_size.h, vp.w, h};
+
+    const auto txt_size = _caption->size();
+    _caption_area       = {center_line(vp.w, txt_size.w), center_line(vp.h, txt_size.h),
+                     txt_size.w, txt_size.h};
+
+    _caption->viewport(rect_offset(_caption_area, vp));
+}
+
+void ButtonImpl::_handle_renderer_change(const std::shared_ptr<Renderer>& r)
+{
+    _caption->renderer(r);
+}
+
+void ButtonImpl::_handle_rendering()
+{
+    const Color& c       = hovered() ? color_bg_hover : color_bg;
+    const auto   divider = pushed() ? 1.5F : 2.F;
+    auto         x       = 0;
+    auto         y       = 0;
+    const auto   biggest_dimension =
+      border_size.w > border_size.h ? border_size.w : border_size.h;
+    const auto& max_xy = border_size.w > border_size.h ? x : y;
+
+    // Render button borders.
+    while (x < border_size.w || y < border_size.h) {
+        _renderer->draw_color(border_gradient(biggest_dimension, max_xy, divider))
+          ->draw_rect(rect_margin(_widget_area, {x, y}));
+        if (x < border_size.w) x++;
+        if (y < border_size.h) y++;
+    }
+
+    _renderer->draw_color(c)->fill_rect(rect_margin(_widget_area, border_size));
+    _caption->font_color_bg(c);
+    _caption->render();
+}
+
+void ButtonImpl::_on_push(const bool state)
+{
+    // Move slightly the caption position to give a push effect.
+    const auto offset = [state, this]() -> SDL_Point {
+        if (state) {
+            return {_viewport.x + 1, _viewport.y + 1};
+        }
+        return {_viewport.x, _viewport.y};
+    }();
+
+    _caption->viewport(rect_offset(_caption_area, offset));
+}
diff --git a/src/w/caption.cpp b/src/w/caption.cpp
deleted file mode 100644
index b6dff1e..0000000
--- a/src/w/caption.cpp
+++ /dev/null
@@ -1,121 +0,0 @@
-#include <SDL2/SDL_assert.h>
-
-#include <basic_widgets/core/math.hpp>
-#include <basic_widgets/core/texture.hpp>
-#include <basic_widgets/w/caption.hpp>
-#include <basic_widgets/w/numeric_input.hpp>
-
-using namespace bwidgets;
-
-Caption::Caption(Widget* parent) noexcept : Widget(parent)
-{
-    _font_color_bg = default_font_color_bg;
-    _font_color_fg = default_font_color_fg;
-}
-
-Caption::~Caption() noexcept
-{
-    discard(_text_texture);
-}
-
-auto Caption::render_mode(Font::RenderMode m) -> Caption*
-{
-    if (m != _render_mode) {
-        discard(_text_texture);
-        _render_mode = m;
-    }
-    return this;
-}
-
-auto Caption::size() const noexcept -> Size
-{
-    if (_font == nullptr) return {0, 0};
-
-    const Size size = _font->text_size(_text);
-
-    return {size.w + 2 * margins.w, size.h + 2 * margins.h};
-}
-
-auto Caption::text() const noexcept -> const std::string&
-{
-    return _text;
-}
-
-auto Caption::text(const std::string& t) -> Caption*
-{
-    if (t != _text) {
-        discard(_text_texture);
-        _text = t;
-    }
-    return this;
-}
-
-void Caption::_handle_font_change(Font*)
-{
-    discard(_text_texture);
-}
-
-void Caption::_handle_font_color_change(const Color& fg, const Color& bg)
-{
-    if (fg != _font_color_fg
-        || (bg != _font_color_bg && _font_render_mode == Font::RenderMode::SHADED))
-    {
-        discard(_text_texture);
-        _font_color_bg = bg;
-    }
-}
-
-void Caption::_handle_geometry_change(const SDL_Rect& vp)
-{
-    if (vp.w != _viewport.w || vp.h != _viewport.h) {
-        _widget_area = rect_margin({0, 0, vp.w, vp.h}, margins);
-    }
-}
-
-void Caption::_handle_renderer_change(Renderer*)
-{
-    discard(_text_texture);
-}
-
-void Caption::_handle_rendering()
-{
-    if (_text_texture == nullptr) _handle_texture_update();
-
-    if (_render_mode == Font::RenderMode::SHADED) {
-        _renderer->draw_color(_font_color_bg)
-          ->fill_rect({0, 0, _viewport.w, _viewport.h});
-    }
-
-    const Size size_dst {
-      (int)((float)_text_texture->attributes().w / (float)_text_texture->attributes().h
-            * (float)_widget_area.h),
-      _widget_area.h};
-    SDL_Rect texture_dst {margins.w, margins.h, size_dst.w, size_dst.h};
-    switch (alignment) {
-        case Alignment::CENTER:
-            texture_dst.x = center_line(_widget_area.w, texture_dst.w) + _widget_area.x;
-            break;
-        case Alignment::LEFT:
-            break;
-        case Alignment::RIGHT:
-            texture_dst.x = _widget_area.w - texture_dst.w - margins.w + _widget_area.x;
-            break;
-    }
-    _renderer->copy(_text_texture, nullptr, texture_dst);
-}
-
-void Caption::_handle_texture_update()
-{
-    SDL_assert_release(_font != nullptr && _text_texture == nullptr); // NOLINT
-    SDL_Surface* s;
-    switch (_render_mode) {
-        case Font::RenderMode::SHADED:
-            s = _font->render(_render_mode, _text, _font_color_fg, _font_color_bg);
-            break;
-        default:
-            s = _font->render(_render_mode, _text, _font_color_fg);
-            break;
-    }
-    _text_texture = new Texture(_renderer, s);
-    SDL_FreeSurface(s);
-}
diff --git a/src/w/caption_impl.cpp b/src/w/caption_impl.cpp
new file mode 100644
index 0000000..c47ad22
--- /dev/null
+++ b/src/w/caption_impl.cpp
@@ -0,0 +1,124 @@
+#include <basic_widgets/core/math.hpp>
+#include <basic_widgets/core/texture.hpp>
+#include <basic_widgets/w/caption_impl.hpp>
+#include <basic_widgets/w/numeric_input.hpp>
+
+using namespace bwidgets;
+
+CaptionImpl::CaptionImpl(Widget* parent) noexcept : WidgetImpl {parent}
+{
+    _font_color_bg = default_font_color_bg;
+    _font_color_fg = default_font_color_fg;
+}
+
+void CaptionImpl::render_mode(const Font::RenderMode m)
+{
+    if (m != _render_mode) {
+        _text_texture.reset();
+        _render_mode = m;
+    }
+}
+
+auto CaptionImpl::size() const noexcept -> Size
+{
+    if (!_font) return {0, 0};
+
+    const auto [w, h] = _font->text_size(_text);
+    return {w + 2 * margins.w, h + 2 * margins.h};
+}
+
+auto CaptionImpl::text() const noexcept -> std::string_view
+{
+    return _text;
+}
+
+void CaptionImpl::text(std::string t)
+{
+    if (t != _text) {
+        _text_texture.reset();
+        _text = std::move(t);
+    }
+}
+
+void CaptionImpl::_handle_font_change(const std::shared_ptr<Font>&)
+{
+    _text_texture.reset();
+}
+
+void CaptionImpl::_handle_font_color_change(const Color fg, const Color bg)
+{
+    if (fg != _font_color_fg) {
+        _text_texture.reset();
+        _font_color_fg = fg;
+    }
+    if (bg != _font_color_bg && _font_render_mode == Font::RenderMode::SHADED) {
+        _text_texture.reset();
+        _font_color_bg = fg;
+    }
+}
+
+void CaptionImpl::_handle_geometry_change(const SDL_Rect& vp)
+{
+    if (vp.w != _viewport.w) {
+        _widget_area = rect_margin({0, 0, vp.w, vp.h}, margins);
+    }
+    else if (vp.h != _viewport.h) {
+        _widget_area = rect_margin({0, 0, vp.w, vp.h}, margins);
+        _text_texture.reset();
+    }
+}
+
+void CaptionImpl::_handle_renderer_change(const std::shared_ptr<Renderer>&)
+{
+    _text_texture.reset();
+}
+
+void CaptionImpl::_handle_rendering()
+{
+    if (!_text_texture) _handle_texture_update();
+
+    // fill caption viewport with background color when using
+    // shaded text rendering mode.
+    if (_render_mode == Font::RenderMode::SHADED) {
+        _renderer->draw_color(_font_color_bg)
+          ->fill_rect({0, 0, _viewport.w, _viewport.h});
+    }
+
+    const Size size_dst {
+      (int)((float)_text_texture->attributes().w / (float)_text_texture->attributes().h
+            * (float)_widget_area.h),
+      _widget_area.h};
+
+    const auto texture_dst = [size_dst, this]() -> SDL_Rect {
+        switch (alignment) {
+            case Alignment::CENTER:
+                return {center_line(_widget_area.w, size_dst.w) + _widget_area.x,
+                        margins.h, size_dst.w, size_dst.h};
+            case Alignment::LEFT:
+                return {margins.w, margins.h, size_dst.w, size_dst.h};
+            case Alignment::RIGHT:
+                return {_widget_area.w - size_dst.w - margins.w + _widget_area.x,
+                        margins.h, size_dst.w, size_dst.h};
+            default:
+                throw std::logic_error("missing switch case.");
+        }
+    }();
+    _renderer->copy(*_text_texture, nullptr, texture_dst);
+}
+
+void CaptionImpl::_handle_texture_update()
+{
+    if (!_font) return;
+    _text_texture.reset();
+
+    auto s = [this]() {
+        switch (_render_mode) {
+            case Font::RenderMode::SHADED:
+                return _font->render(_render_mode, _text, _font_color_fg,
+                                     _font_color_bg);
+            default:
+                return _font->render(_render_mode, _text, _font_color_fg);
+        }
+    }();
+    _text_texture = std::make_shared<Texture>(*_renderer, s.get());
+}
diff --git a/src/w/feat/event_handler_impl.cpp b/src/w/feat/event_handler_impl.cpp
new file mode 100644
index 0000000..5353a1f
--- /dev/null
+++ b/src/w/feat/event_handler_impl.cpp
@@ -0,0 +1,32 @@
+#include <basic_widgets/w/feat/event_handler_impl.hpp>
+
+using namespace bwidgets;
+
+void EventHandlerImpl::handle_event(const SDL_Event& ev)
+{
+    auto type = static_cast<SDL_EventType>(ev.type);
+    if (!_event_handlers.contains(type)) return;
+
+    _event_handlers[type](ev);
+}
+
+auto EventHandlerImpl::_add_event_handler(handler_t event_handler) -> bool
+{
+    if (_event_handlers.contains(event_handler.first)) return false;
+
+    _event_handlers.emplace(std::move(event_handler));
+    return true;
+}
+
+auto EventHandlerImpl::_remove_event_handler(const SDL_EventType ev_type)
+  -> std::pair<handler_t, bool>
+{
+    handler_t handler;
+    auto      pos = _event_handlers.find(ev_type);
+    if (pos == _event_handlers.end()) return {handler, false};
+
+    handler = {ev_type, _event_handlers[ev_type]};
+    _event_handlers.erase(pos);
+
+    return {handler, true};
+}
diff --git a/src/w/feat/keyboard_handler_impl.cpp b/src/w/feat/keyboard_handler_impl.cpp
new file mode 100644
index 0000000..4aa8e5a
--- /dev/null
+++ b/src/w/feat/keyboard_handler_impl.cpp
@@ -0,0 +1,23 @@
+#include <basic_widgets/w/feat/keyboard_handler_impl.hpp>
+
+using namespace bwidgets;
+
+void KeyboardHandlerImpl::disable_keyboard_handler()
+{
+    _remove_event_handler(SDL_KEYDOWN);
+    _remove_event_handler(SDL_KEYUP);
+    _remove_event_handler(SDL_TEXTINPUT);
+}
+
+void KeyboardHandlerImpl::enable_keyboard_handler()
+{
+    const auto keyboard_handler = [this](const SDL_Event& ev) {
+        if (focus()) _key_handler(ev.key);
+    };
+
+    _add_event_handler({SDL_KEYDOWN, keyboard_handler});
+    _add_event_handler({SDL_KEYUP, keyboard_handler});
+    _add_event_handler({SDL_TEXTINPUT, [this](const SDL_Event& ev) {
+                            if (focus()) _input_handler(ev.text);
+                        }});
+}
diff --git a/src/w/feat/mouse_handler.cpp b/src/w/feat/mouse_handler.cpp
deleted file mode 100644
index 437042c..0000000
--- a/src/w/feat/mouse_handler.cpp
+++ /dev/null
@@ -1,60 +0,0 @@
-#include <SDL2/SDL_events.h>
-#include <SDL2/SDL_rect.h>
-
-#include <basic_widgets/core/math.hpp>
-#include <basic_widgets/w/feat/mouse_handler.hpp>
-
-using namespace bwidgets;
-
-auto MouseHandler::handle_mouse(const SDL_MouseButtonEvent& ev, const SDL_Rect& orig)
-  -> MouseHandler*
-{
-    if (_click_area == nullptr) return this;
-
-    const SDL_Point p {ev.x, ev.y};
-    const SDL_Rect  vp {rect_offset(*_click_area, orig)};
-
-    if (ev.type == SDL_MOUSEBUTTONDOWN) {
-        if (SDL_PointInRect(&p, &vp) == SDL_TRUE) {
-            push(true);
-            _handle_mouse_button(ev, vp);
-        }
-        else focus(false);
-    }
-    else {
-        if (_is_pushed) {
-            if (SDL_PointInRect(&p, &vp) == SDL_TRUE) {
-                focus(true);
-
-                if (click_handler != nullptr) click_handler(ev);
-            }
-            push(false);
-            _handle_mouse_button(ev, vp);
-        }
-    }
-
-    return this;
-}
-
-auto MouseHandler::handle_mouse(const SDL_MouseMotionEvent& ev, const SDL_Rect& orig)
-  -> MouseHandler*
-{
-    if (_click_area == nullptr) return this;
-
-    const SDL_Point p {ev.x, ev.y};
-    const SDL_Rect  vp {rect_offset(*_click_area, orig)};
-
-    _is_hovered = SDL_PointInRect(&p, &vp) != 0;
-
-    if (_is_hovered) _handle_mouse_motion(ev, orig);
-
-    return this;
-}
-
-auto MouseHandler::push(bool state) -> MouseHandler*
-{
-    _on_push(state);
-    _is_pushed = state;
-
-    return this;
-}
diff --git a/src/w/feat/mouse_handler_impl.cpp b/src/w/feat/mouse_handler_impl.cpp
new file mode 100644
index 0000000..ee8d73f
--- /dev/null
+++ b/src/w/feat/mouse_handler_impl.cpp
@@ -0,0 +1,48 @@
+#include <basic_widgets/core/math.hpp>
+#include <basic_widgets/w/feat/mouse_handler_impl.hpp>
+
+using namespace bwidgets;
+
+void MouseHandlerImpl::disable_mouse_handler()
+{
+    _remove_event_handler(SDL_MOUSEBUTTONDOWN);
+    _remove_event_handler(SDL_MOUSEBUTTONUP);
+    _remove_event_handler(SDL_MOUSEMOTION);
+}
+
+// NOLINTNEXTLINE(readability-function-cognitive-complexity)
+void MouseHandlerImpl::enable_mouse_handler(const SDL_Rect& rel_area,
+                                            const SDL_Rect& origin)
+{
+    const auto mouse_in_rect = [&rel_area, &origin](const SDL_Point p) {
+        const auto area = rect_offset(rel_area, origin);
+        return SDL_PointInRect(&p, &area) == SDL_TRUE;
+    };
+
+    _add_event_handler({SDL_MOUSEBUTTONDOWN, [this, mouse_in_rect](const SDL_Event& ev) {
+                            if (!mouse_in_rect({ev.button.x, ev.button.y})) {
+                                focus(false);
+                                return;
+                            }
+                            _on_push(_pushed = true);
+                        }});
+    _add_event_handler({SDL_MOUSEBUTTONUP, [this, mouse_in_rect](const SDL_Event& ev) {
+                            if (_pushed) {
+                                _on_push(_pushed = false);
+                                // Only execute handler and give focus if mouse button
+                                // has been pushed and released over the widget.
+                                if (mouse_in_rect({ev.button.x, ev.button.y})) {
+                                    focus(true);
+                                    _click_handler(ev.button);
+                                }
+                            }
+                        }});
+    _add_event_handler({SDL_MOUSEMOTION, [this, mouse_in_rect](const SDL_Event& ev) {
+                            if (!mouse_in_rect({ev.motion.x, ev.motion.y})) {
+                                if (_hovered) _hover_handler(_hovered = false);
+                                return;
+                            }
+                            if (!_hovered) _hover_handler(_hovered = true);
+                            _motion_handler(ev.motion);
+                        }});
+}
diff --git a/src/w/widget_factory.cpp b/src/w/widget_factory.cpp
new file mode 100644
index 0000000..0d79c0f
--- /dev/null
+++ b/src/w/widget_factory.cpp
@@ -0,0 +1,37 @@
+#include <basic_widgets/w/aligned_layout_impl.hpp>
+#include <basic_widgets/w/button_impl.hpp>
+#include <basic_widgets/w/caption_impl.hpp>
+#include <basic_widgets/w/numeric_input_impl.hpp>
+#include <basic_widgets/w/widget_factory.hpp>
+
+auto bwidgets::create_horizontal_layout(Widget* parent) -> std::unique_ptr<AlignedLayout>
+{
+    return std::unique_ptr<AlignedLayout>(
+      new AlignedLayoutImpl<LayoutAlignment::HORIZONTAL>(parent));
+}
+
+auto bwidgets::create_vertical_layout(Widget* parent) -> std::unique_ptr<AlignedLayout>
+{
+    return std::unique_ptr<AlignedLayout>(
+      new AlignedLayoutImpl<LayoutAlignment::VERTICAL>(parent));
+}
+
+auto bwidgets::create_button(Widget* parent) -> std::unique_ptr<Button>
+{
+    return std::unique_ptr<Button>(new ButtonImpl(parent));
+}
+
+auto bwidgets::create_caption(Widget* parent) -> std::unique_ptr<Caption>
+{
+    return std::unique_ptr<Caption>(new CaptionImpl(parent));
+}
+
+auto bwidgets::create_input_float(Widget* parent) -> std::unique_ptr<NumericInput<float>>
+{
+    return std::unique_ptr<NumericInput<float>>(new NumericInputImpl<float>(parent));
+}
+
+auto bwidgets::create_input_int(Widget* parent) -> std::unique_ptr<NumericInput<int>>
+{
+    return std::unique_ptr<NumericInput<int>>(new NumericInputImpl<int>(parent));
+}