From a6d4bfc748706cfbcfa6cc6468c4bd2579f13a8c Mon Sep 17 00:00:00 2001
From: Magnus Norddahl <dpjudas@users.noreply.github.com>
Date: Sun, 13 Aug 2017 13:49:02 +0200
Subject: [PATCH] - Added linear and nearest shadowmap filters (enabled with
 defines)

---
 wadsrc/static/shaders/glsl/main.fp | 55 ++++++++++++++++++++++++++----
 1 file changed, 48 insertions(+), 7 deletions(-)

diff --git a/wadsrc/static/shaders/glsl/main.fp b/wadsrc/static/shaders/glsl/main.fp
index cab4f5d9bc..83cabbd0d3 100644
--- a/wadsrc/static/shaders/glsl/main.fp
+++ b/wadsrc/static/shaders/glsl/main.fp
@@ -138,27 +138,57 @@ float R_DoomLightingEquation(float light)
 
 #ifdef SUPPORTS_SHADOWMAPS
 
-float sampleShadowmap(vec2 dir, float v)
+float shadowDirToU(vec2 dir)
 {
-	float u;
 	if (abs(dir.x) > abs(dir.y))
 	{
 		if (dir.x >= 0.0)
-			u = dir.y / dir.x * 0.125 + (0.25 + 0.125);
+			return dir.y / dir.x * 0.125 + (0.25 + 0.125);
 		else
-			u = dir.y / dir.x * 0.125 + (0.75 + 0.125);
+			return dir.y / dir.x * 0.125 + (0.75 + 0.125);
 	}
 	else
 	{
 		if (dir.y >= 0.0)
-			u = dir.x / dir.y * 0.125 + 0.125;
+			return dir.x / dir.y * 0.125 + 0.125;
 		else
-			u = dir.x / dir.y * 0.125 + (0.50 + 0.125);
+			return dir.x / dir.y * 0.125 + (0.50 + 0.125);
 	}
+}
+
+float sampleShadowmap(vec2 dir, float v)
+{
+	float u = shadowDirToU(dir);
 	float dist2 = dot(dir, dir);
 	return texture(ShadowMap, vec2(u, v)).x > dist2 ? 1.0 : 0.0;
 }
 
+float sampleShadowmapLinear(vec2 dir, float v)
+{
+	float u = shadowDirToU(dir);
+	float dist2 = dot(dir, dir);
+
+	vec2 isize = textureSize(ShadowMap, 0);
+	vec2 size = vec2(isize);
+
+	vec2 fetchPos = vec2(u, v) * size - vec2(0.5, 0.0);
+	if (fetchPos.x < 0.0)
+		fetchPos.x += size.x;
+
+	ivec2 ifetchPos = ivec2(fetchPos);
+	int y = ifetchPos.y;
+
+	float t = fract(fetchPos.x);
+	int x0 = ifetchPos.x;
+	int x1 = ifetchPos.x + 1;
+	if (x1 == isize.x)
+		x1 = 0;
+
+	float depth0 = texelFetch(ShadowMap, ivec2(x0, y), 0).x;
+	float depth1 = texelFetch(ShadowMap, ivec2(x1, y), 0).x;
+	return mix(step(dist2, depth0), step(dist2, depth1), t);
+}
+
 //===========================================================================
 //
 // Check if light is in shadow using Percentage Closer Filtering (PCF)
@@ -168,6 +198,9 @@ float sampleShadowmap(vec2 dir, float v)
 #define PCF_FILTER_STEP_COUNT 3
 #define PCF_COUNT (PCF_FILTER_STEP_COUNT * 2 + 1)
 
+// #define USE_LINEAR_SHADOW_FILTER
+#define USE_PCF_SHADOW_FILTER 1
+
 float shadowmapAttenuation(vec4 lightpos, float shadowIndex)
 {
 	if (shadowIndex >= 1024.0)
@@ -182,7 +215,11 @@ float shadowmapAttenuation(vec4 lightpos, float shadowIndex)
 
 	vec2 dir = ray / length;
 
-	ray -= dir * 2.0; // margin
+#if defined(USE_LINEAR_SHADOW_FILTER)
+	ray -= dir * 6.0; // Shadow acne margin
+	return sampleShadowmapLinear(ray, v);
+#elif defined(USE_PCF_SHADOW_FILTER)
+	ray -= dir * 2.0; // Shadow acne margin
 	dir = dir * min(length / 50.0, 1.0); // avoid sampling behind light
 
 	vec2 normal = vec2(-dir.y, dir.x);
@@ -194,6 +231,10 @@ float shadowmapAttenuation(vec4 lightpos, float shadowIndex)
 		sum += sampleShadowmap(ray + normal * x - bias * abs(x), v);
 	}
 	return sum / PCF_COUNT;
+#else // nearest shadow filter
+	ray -= dir * 6.0; // Shadow acne margin
+	return sampleShadowmap(ray, v);
+#endif
 }
 
 #endif