From 0b61b7a60bf014c60261f50e581fcffbe8ba3d38 Mon Sep 17 00:00:00 2001
From: Vovanium <vovanium@protonmail.ch>
Date: Thu, 19 Jan 2023 00:50:39 +0300
Subject: [PATCH] * Changed the profile of the line draw procedure

---
 source/video-algorithms-generic_line.adb | 28 ++++++++++++++----------
 source/video-algorithms-generic_line.ads |  8 +++++--
 2 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/source/video-algorithms-generic_line.adb b/source/video-algorithms-generic_line.adb
index b511fd5..c41c089 100644
--- a/source/video-algorithms-generic_line.adb
+++ b/source/video-algorithms-generic_line.adb
@@ -2,42 +2,46 @@ with Video.Integer_Geometry;
 use type Video.Integer_Geometry.Point;
 
 procedure Video.Algorithms.Generic_Line (
-	A, B   : in     Integer_Geometry.Point;
-	Offset : in     Integer := 0)
+	A,      B      : in     Integer_Geometry.Point;
+	A_Clip, B_Clip : in     Integer_Geometry.Point)
 is
-	D    : constant Integer_Geometry.Point := B - A;
+	D    : constant Integer_Geometry.Point := B - A; -- Direction vector
 	S    : constant Integer_Geometry.Point := (
 		X => (if D.X >= 0 then 1 else -1),
-		Y => (if D.Y >= 0 then 1 else -1));
-	N, M : Integer;
+		Y => (if D.Y >= 0 then 1 else -1)); -- Signs of directions
+	N, M : Integer; -- Denominator and numerator
+	NC   : Integer; -- Number of steps
 	E    : Integer;
-	P    : Integer_Geometry.Point := A;
+	P    : Integer_Geometry.Point := A_Clip;
 begin
 	if abs D.X > abs D.Y then -- Nearly horizontal
 		N := abs D.X;
 		M := abs D.Y;
-		E := -N / 2 + Offset;
-		for I in 1 .. N loop
+		E := -N / 2 + M * abs (A_Clip.X - A.X) - N * abs (A_Clip.Y - A.Y);
+		 -- May need extended precision here
+		NC := abs (B_Clip.X - A_Clip.X);
+		for I in 0 .. NC loop
+			Put_Pixel (P);
 			E := E + M;
 			if E >= 0 then
 				E := E - N;
 				P.Y := P.Y + S.Y;
 			end if;
 			P.X := P.X + S.X;
-			Put_Pixel (P);
 		end loop;
 	else -- Nearly vertical
 		N := abs D.Y;
 		M := abs D.X;
-		E := -N / 2 + Offset;
-		for I in 1 .. N loop
+		E := -N / 2 + M * abs (A_Clip.Y - A.Y) - N * abs (A_Clip.X - A.X);
+		NC := abs (B_Clip.Y - A_Clip.Y);
+		for I in 0 .. NC loop
+			Put_Pixel (P);
 			E := E + M;
 			if E >= 0 then
 				E := E - N;
 				P.X := P.X + S.X;
 			end if;
 			P.Y := P.Y + S.Y;
-			Put_Pixel (P);
 		end loop;
 	end if;
 
diff --git a/source/video-algorithms-generic_line.ads b/source/video-algorithms-generic_line.ads
index d4b8774..24894a9 100644
--- a/source/video-algorithms-generic_line.ads
+++ b/source/video-algorithms-generic_line.ads
@@ -2,5 +2,9 @@ with Video.Integer_Geometry;
 generic
 	with procedure Put_Pixel (Location : Integer_Geometry.Point);
 procedure Video.Algorithms.Generic_Line (
-	A, B   : in     Integer_Geometry.Point;
-	Offset : in     Integer := 0);
+	A,      B      : in     Integer_Geometry.Point;  -- Virtual line ends (possibly out of clip area)
+	A_Clip, B_Clip : in     Integer_Geometry.Point); -- Actual first and last points to draw
+
+-- A_Clip and B_Clip could be the same as A and B when no clipping is done
+-- A_Clip is the closest to A and B_Clip is the closest to B to draw.
+-- If order is not met algorighm could refuse to draw
\ No newline at end of file