From 3f58b2ac3d25022d99d706a10b98119a971f8ebd Mon Sep 17 00:00:00 2001
From: martinfouilleul <martinfouilleul@gmail.com>
Date: Wed, 8 Feb 2023 20:36:39 +0100
Subject: [PATCH] glsl canvas shader: do cross products in 64 bits fixed point
 to avoid overflow

---
 examples/win_canvas/main.c                    | 12 +++++---
 src/gles_canvas_shaders/gles_canvas_draw.glsl | 30 +++++++++++--------
 src/gles_canvas_shaders/gles_canvas_tile.glsl |  4 ---
 3 files changed, 26 insertions(+), 20 deletions(-)

diff --git a/examples/win_canvas/main.c b/examples/win_canvas/main.c
index 3224366..9d02fa6 100644
--- a/examples/win_canvas/main.c
+++ b/examples/win_canvas/main.c
@@ -120,28 +120,28 @@ int main()
 						{
 							if(x - 200 > 0)
 							{
-								x-=1;
+								x-=5;
 							}
 						}
 						else if(event.key.code == MP_KEY_RIGHT)
 						{
 							if(x + 200 < contentRect.w)
 							{
-								x+=1;
+								x+=5;
 							}
 						}
 						else if(event.key.code == MP_KEY_UP)
 						{
 							if(y + 200 < contentRect.h)
 							{
-								y+=1;
+								y+=5;
 							}
 						}
 						else if(event.key.code == MP_KEY_DOWN)
 						{
 							if(y - 200 > 0)
 							{
-								y-=1;
+								y-=5;
 							}
 						}
 						//*/
@@ -155,18 +155,22 @@ int main()
 
 		if(x-200 < 0)
 		{
+			x = 200;
 			dx = speed;
 		}
 		if(x+200 > contentRect.w)
 		{
+			x = contentRect.w - 200;
 			dx = -speed;
 		}
 		if(y-200 < 0)
 		{
+			y = 200;
 			dy = speed;
 		}
 		if(y+200 > contentRect.h)
 		{
+			y = contentRect.h - 200;
 			dy = -speed;
 		}
 		x += dx;
diff --git a/src/gles_canvas_shaders/gles_canvas_draw.glsl b/src/gles_canvas_shaders/gles_canvas_draw.glsl
index 48a2b07..2d6743d 100644
--- a/src/gles_canvas_shaders/gles_canvas_draw.glsl
+++ b/src/gles_canvas_shaders/gles_canvas_draw.glsl
@@ -1,4 +1,5 @@
 #version 430
+#extension GL_ARB_gpu_shader_int64 : require
 layout(local_size_x = 16, local_size_y = 16, local_size_z = 1) in;
 
 precision mediump float;
@@ -52,11 +53,16 @@ bool is_top_left(ivec2 a, ivec2 b)
 	      ||(b.y < a.y));
 }
 
-int orient2d(ivec2 a, ivec2 b, ivec2 p)
+int64_t orient2d(i64vec2 a, i64vec2 b, i64vec2 p)
 {
 	return((b.x-a.x)*(p.y-a.y) - (b.y-a.y)*(p.x-a.x));
 }
 
+int64_t is_clockwise(i64vec2 p0, i64vec2 p1, i64vec2 p2)
+{
+	return((p1 - p0).x*(p2 - p0).y - (p1 - p0).y*(p2 - p0).x);
+}
+
 void main()
 {
 	ivec2 pixelCoord = ivec2(gl_WorkGroupID.xy*uvec2(16, 16) + gl_LocalInvocationID.xy);
@@ -79,10 +85,10 @@ void main()
 	                                                     centerPoint + ivec2(7, 7)*16);
 /*/
 	const int sampleCount = 4;
-	ivec2 samplePoints[sampleCount] = ivec2[sampleCount](centerPoint + ivec2(-2, 6)*16,
-	                                                     centerPoint + ivec2(6, 2)*16,
-	                                                     centerPoint + ivec2(-6, -2)*16,
-	                                                     centerPoint + ivec2(2, -6)*16);
+	ivec2 samplePoints[sampleCount] = ivec2[sampleCount](centerPoint + ivec2(-2, 6),
+	                                                     centerPoint + ivec2(6, 2),
+	                                                     centerPoint + ivec2(-6, -2),
+	                                                     centerPoint + ivec2(2, -6));
 //*/
 	//DEBUG
 /*
@@ -142,7 +148,7 @@ void main()
 		ivec4 clip = ivec4(round((shapeBuffer.elements[zIndex].clip * vec4(scaling, scaling) + vec4(0.5, 0.5, 0.5, 0.5)) * subPixelFactor));
 
 		//NOTE(martin): reorder triangle counter-clockwise and compute bias for each edge
-		int cw = (p1 - p0).x*(p2 - p0).y - (p1 - p0).y*(p2 - p0).x;
+		int64_t cw = is_clockwise(p0, p1, p2);
 		if(cw < 0)
 		{
 			uint tmpIndex = i1;
@@ -158,9 +164,9 @@ void main()
 		vec4 cubic1 = vertexBuffer.elements[i1].cubic;
 		vec4 cubic2 = vertexBuffer.elements[i2].cubic;
 
-		int bias0 = is_top_left(p1, p2) ? 0 : -1;
-		int bias1 = is_top_left(p2, p0) ? 0 : -1;
-		int bias2 = is_top_left(p0, p1) ? 0 : -1;
+		int64_t bias0 = is_top_left(p1, p2) ? 0 : -1;
+		int64_t bias1 = is_top_left(p2, p0) ? 0 : -1;
+		int64_t bias2 = is_top_left(p0, p1) ? 0 : -1;
 
 		for(int sampleIndex = 0; sampleIndex < sampleCount; sampleIndex++)
 		{
@@ -174,9 +180,9 @@ void main()
 				continue;
 			}
 
-			int w0 = orient2d(p1, p2, samplePoint);
-			int w1 = orient2d(p2, p0, samplePoint);
-			int w2 = orient2d(p0, p1, samplePoint);
+			int64_t w0 = orient2d(p1, p2, samplePoint);
+			int64_t w1 = orient2d(p2, p0, samplePoint);
+			int64_t w2 = orient2d(p0, p1, samplePoint);
 
 			if((w0+bias0) >= 0 && (w1+bias1) >= 0 && (w2+bias2) >= 0)
 			{
diff --git a/src/gles_canvas_shaders/gles_canvas_tile.glsl b/src/gles_canvas_shaders/gles_canvas_tile.glsl
index 96c03b1..3600ef4 100644
--- a/src/gles_canvas_shaders/gles_canvas_tile.glsl
+++ b/src/gles_canvas_shaders/gles_canvas_tile.glsl
@@ -66,10 +66,6 @@ void main()
 		             min(max(max(p0.x, p1.x), p2.x), clip.z),
 		             min(max(max(p0.y, p1.y), p2.y), clip.w));
 
-/*
-	fbox.xy = min(fbox.xy, clip.xy);
-	fbox.zw = max(fbox.zw, clip.zw);
-*/
 	uvec4 box = uvec4(floor(fbox))/tileSize;
 
 	uint xMin = max(0u, box.x);