on going work on input field rendering

input.hpp

@@ -1,18 +1,66 @@
 #ifndef INPUT_HPP
 #define INPUT_HPP
 
+#include <iostream>
+#include <sstream>
+#include <string>
+#include <type_traits>
+
 #include "widget.hpp"
 
+template<typename T>
+concept CanToString = requires(T value) { std::to_string(value); };
+
+template<typename T>
+concept Printable = requires(T value) { std::declval<std::ostream&>() << value; };
+
 template<typename T> class Input : public Widget
 {
 protected:
-    SDL_Rect _input_field_area;
+    SDL_Rect _input_field_area = {0, 0, 0, 0};
+    SDL_Rect _input_area = {0, 0, 0, 0};
     T _value;
 
     Input(SDL_Renderer* r) : Widget(r) {}
-    virtual void _update_drawing_areas() = 0;
+    virtual void _update_drawing_areas()
+    {
+        _input_area = {
+            _input_field_area.x + 2,
+            _input_field_area.y + 2,
+            _input_field_area.w - 4,
+            _input_field_area.h - 4
+        };
+    }
+
+    virtual std::string _value_to_string() const
+    {
+        std::string s;
+
+        if constexpr(std::is_same_v<std::string, T> || std::convertible_to<T, std::string>)
+        {
+            s = _value;
+        }
+        else if constexpr(CanToString<T>)
+        {
+            s = std::to_string(_value);
+        }
+        else if constexpr(Printable<T>)
+        {
+            std::stringstream ss;
+            ss << _value;
+            return std::move(ss).str();
+        }
+        else
+        {
+            static_assert(sizeof(T) && false, "_value cannot be converted to string.");
+        }
+
+        return s;
+    }
 
 public:
+    SDL_Color border_color = {200, 200, 200, SDL_ALPHA_OPAQUE};
+    SDL_Color background_color = {255, 255, 255, SDL_ALPHA_OPAQUE};
     virtual void viewport(SDL_Rect vp)
     {
         Widget::viewport(vp);
@@ -28,8 +76,30 @@ public:
         SDL_RenderGetViewport(_renderer, &old_vp);
         SDL_RenderSetViewport(_renderer, &_viewport);
 
-        SDL_SetRenderDrawColor(_renderer, 0, 0, 255, SDL_ALPHA_OPAQUE);
-        SDL_RenderDrawRect(_renderer, &_input_field_area);
+        for (int i = 2; i > 0; i--)
+        {
+            SDL_SetRenderDrawColor(
+                    _renderer,
+                    border_color.r / i,
+                    border_color.g / i,
+                    border_color.b / i,
+                    border_color.a
+                    );
+            SDL_Rect border_area = {
+                _input_field_area.x + 2 - i,
+                _input_field_area.y + 2 - i,
+                _input_field_area.w - 2 * (2 - i),
+                _input_field_area.h - 2 * (2 - i)
+            };
+        }
+        SDL_SetRenderDrawColor(
+                _renderer,
+                background_color.r,
+                background_color.g,
+                background_color.b,
+                background_color.a
+                );
+        SDL_RenderFillRect(_renderer, &_input_area);
 
         SDL_RenderSetViewport(_renderer, &old_vp);
     }

numeric_input.hpp

@@ -61,6 +61,8 @@ private:
             (int)(1.25 * widest_button / 2) + Widget::_viewport.w - widest_button - Widget::_viewport.x,
             heighest_button
         };
+
+        Input<T>::_update_drawing_areas();
     }
 
 public:

widget_test.cpp

@@ -27,12 +27,12 @@ int main()
 
     SDL_Rect layout_vp = {0, 0, width, height};
     Layout* layout = new Vertical_Layout(rend);
-    for (int i = 0; i < 4; i++)
+    for (int i = 0; i < 2; i++)
     {
         std::cerr << "Layout " << i << " Widget:";
         Layout* column = new Horizontal_Layout(rend);
         layout->add_widget(column);
-        for (int j = 0; j < 3; j++)
+        for (int j = 0; j < 2; j++)
         {
             Numeric_Input<int>* widget = new Numeric_Input<int>(rend);
             widget->font(font);