Updated env map prefiltering shader (requires less samples)

data/shaders/pbribl/prefilterenvmap.frag

@@ -8,7 +8,7 @@ layout (binding = 0) uniform samplerCube samplerEnv;
 layout(push_constant) uniform PushConsts {
 	layout (offset = 64) float roughness;
 	layout (offset = 68) uint numSamples;
-} pushConsts;
+} consts;
 
 const float PI = 3.1415926536;
 
@@ -69,14 +69,29 @@ vec3 prefilterEnvMap(vec3 R, float roughness)
 	vec3 V = R;
 	vec3 color = vec3(0.0);
 	float totalWeight = 0.0;
-	for(uint i = 0u; i < pushConsts.numSamples; i++) {
-		vec2 Xi = hammersley2d(i, pushConsts.numSamples);
+	float envMapDim = float(textureSize(samplerEnv, 0).s);
+	for(uint i = 0u; i < consts.numSamples; i++) {
+		vec2 Xi = hammersley2d(i, consts.numSamples);
 		vec3 H = importanceSample_GGX(Xi, roughness, N);
 		vec3 L = 2.0 * dot(V, H) * H - V;
 		float dotNL = clamp(dot(N, L), 0.0, 1.0);
 		if(dotNL > 0.0) {
-			color += texture(samplerEnv, L).rgb * dotNL;
+			// Filtering based on https://placeholderart.wordpress.com/2015/07/28/implementation-notes-runtime-environment-map-filtering-for-image-based-lighting/
+
+			float dotNH = clamp(dot(N, H), 0.0, 1.0);
+			float dotVH = clamp(dot(V, H), 0.0, 1.0);
+
+			// Probability Distribution Function
+			float pdf = D_GGX(dotNH, roughness) * dotNH / (4.0 * dotVH) + 0.0001;
+			// Slid angle of current smple
+			float omegaS = 1.0 / (float(consts.numSamples) * pdf);
+			// Solid angle of 1 pixel across all cube faces
+			float omegaP = 4.0 * PI / (6.0 * envMapDim * envMapDim);
+			// Biased (+1.0) mip level for better result
+			float mipLevel = roughness == 0.0 ? 0.0 : max(0.5 * log2(omegaS / omegaP) + 1.0, 0.0f);
+			color += textureLod(samplerEnv, L, mipLevel).rgb * dotNL;
 			totalWeight += dotNL;
+
 		}
 	}
 	return (color / totalWeight);
@@ -86,5 +101,5 @@ vec3 prefilterEnvMap(vec3 R, float roughness)
 void main()
 {		
 	vec3 N = normalize(inPos);
-	outColor = vec4(prefilterEnvMap(N, pushConsts.roughness), 1.0);
+	outColor = vec4(prefilterEnvMap(N, consts.roughness), 1.0);
 }