From 36946a47febba47fd3c53e601bcf41476440da0c Mon Sep 17 00:00:00 2001
From: Magnus Norddahl <dpjudas@users.noreply.github.com>
Date: Thu, 4 Oct 2018 00:46:17 +0200
Subject: [PATCH] - fix diagonal linear shadow map artifact

---
 wadsrc/static/shaders/glsl/main.fp      | 10 ++++++----
 wadsrc/static/shaders/glsl/shadowmap.fp | 11 ++++++-----
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/wadsrc/static/shaders/glsl/main.fp b/wadsrc/static/shaders/glsl/main.fp
index c78bb0e02..219e01581 100644
--- a/wadsrc/static/shaders/glsl/main.fp
+++ b/wadsrc/static/shaders/glsl/main.fp
@@ -162,17 +162,19 @@ float shadowDirToU(vec2 dir)
 {
 	if (abs(dir.x) > abs(dir.y))
 	{
+		float v = dir.y / dir.x * 0.125;
 		if (dir.x >= 0.0)
-			return dir.y / dir.x * 0.125 + (0.25 + 0.125);
+			return (0.25 + 0.125) - v;
 		else
-			return dir.y / dir.x * 0.125 + (0.75 + 0.125);
+			return (0.75 + 0.125) - v;
 	}
 	else
 	{
+		float v = dir.x / dir.y * 0.125;
 		if (dir.y >= 0.0)
-			return dir.x / dir.y * 0.125 + 0.125;
+			return 0.125 + v;
 		else
-			return dir.x / dir.y * 0.125 + (0.50 + 0.125);
+			return (0.50 + 0.125) + v;
 	}
 }
 
diff --git a/wadsrc/static/shaders/glsl/shadowmap.fp b/wadsrc/static/shaders/glsl/shadowmap.fp
index fb2257b92..5e5438075 100644
--- a/wadsrc/static/shaders/glsl/shadowmap.fp
+++ b/wadsrc/static/shaders/glsl/shadowmap.fp
@@ -140,12 +140,13 @@ void main()
 	if (radius > 0.0)
 	{
 		vec2 pixelpos;
-		switch (int(gl_FragCoord.x) / int(ShadowmapQuality/4.0))
+		float u = gl_FragCoord.x / ShadowmapQuality * 4.0;
+		switch (int(u))
 		{
-		case 0: pixelpos = vec2((gl_FragCoord.x - float(ShadowmapQuality/8.0)) / float(ShadowmapQuality/8.0), 1.0); break;
-		case 1: pixelpos = vec2(1.0, (gl_FragCoord.x - float(ShadowmapQuality/4.0 + ShadowmapQuality/8.0)) / float(ShadowmapQuality/8.0)); break;
-		case 2: pixelpos = vec2(-(gl_FragCoord.x - float(ShadowmapQuality/2.0 + ShadowmapQuality/8.0)) / float(ShadowmapQuality/8.0), -1.0); break;
-		case 3: pixelpos = vec2(-1.0, -(gl_FragCoord.x - float(ShadowmapQuality*3.0/4.0 + ShadowmapQuality/8.0)) / float(ShadowmapQuality/8.0)); break;
+		case 0: pixelpos = vec2(u * 2.0 - 1.0, 1.0); break;
+		case 1: pixelpos = vec2(1.0, 1.0 - (u - 1.0) * 2.0); break;
+		case 2: pixelpos = vec2(1.0 - (u - 2.0) * 2.0, -1.0); break;
+		case 3: pixelpos = vec2(-1.0, (u - 3.0) * 2.0 - 1.0); break;
 		}
 		pixelpos = lightpos + pixelpos * radius;