Use prefiltered radiance

3 files changed, 51 insertions, 20 deletions

diff --git a/servers/rendering/renderer_rd/shaders/cubemap_roughness.glsl b/servers/rendering/renderer_rd/shaders/cubemap_roughness.glsl
index 28f4dc59ec..1d46f59408 100644
--- a/servers/rendering/renderer_rd/shaders/cubemap_roughness.glsl
+++ b/servers/rendering/renderer_rd/shaders/cubemap_roughness.glsl
@@ -21,24 +21,38 @@ void main() {
 	vec2 uv = ((vec2(id.xy) * 2.0 + 1.0) / (params.face_size) - 1.0);
 	vec3 N = texelCoordToVec(uv, id.z);
 
-	//vec4 color = color_interp;
-
 	if (params.use_direct_write) {
 		imageStore(dest_cubemap, ivec3(id), vec4(texture(source_cube, N).rgb, 1.0));
 	} else {
 		vec4 sum = vec4(0.0, 0.0, 0.0, 0.0);
 
+		float solid_angle_texel = 4.0 * M_PI / (6.0 * params.face_size * params.face_size);
+		float roughness2 = params.roughness * params.roughness;
+		float roughness4 = roughness2 * roughness2;
+		vec3 UpVector = abs(N.z) < 0.999 ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0);
+		mat3 T;
+		T[0] = normalize(cross(UpVector, N));
+		T[1] = cross(N, T[0]);
+		T[2] = N;
+
 		for (uint sampleNum = 0u; sampleNum < params.sample_count; sampleNum++) {
 			vec2 xi = Hammersley(sampleNum, params.sample_count);
 
-			vec3 H = ImportanceSampleGGX(xi, params.roughness, N);
-			vec3 V = N;
-			vec3 L = (2.0 * dot(V, H) * H - V);
+			vec3 H = T * ImportanceSampleGGX(xi, roughness4);
+			float NdotH = dot(N, H);
+			vec3 L = (2.0 * NdotH * H - N);
 
 			float ndotl = clamp(dot(N, L), 0.0, 1.0);
 
 			if (ndotl > 0.0) {
-				sum.rgb += textureLod(source_cube, L, 0.0).rgb * ndotl;
+				float D = DistributionGGX(NdotH, roughness4);
+				float pdf = D * NdotH / (4.0 * NdotH) + 0.0001;
+
+				float solid_angle_sample = 1.0 / (float(params.sample_count) * pdf + 0.0001);
+
+				float mipLevel = params.roughness == 0.0 ? 0.0 : 0.5 * log2(solid_angle_sample / solid_angle_texel);
+
+				sum.rgb += textureLod(source_cube, L, mipLevel).rgb * ndotl;
 				sum.a += ndotl;
 			}
 		}
diff --git a/servers/rendering/renderer_rd/shaders/cubemap_roughness_inc.glsl b/servers/rendering/renderer_rd/shaders/cubemap_roughness_inc.glsl
index ce0a25e12f..1bee428a6f 100644
--- a/servers/rendering/renderer_rd/shaders/cubemap_roughness_inc.glsl
+++ b/servers/rendering/renderer_rd/shaders/cubemap_roughness_inc.glsl
@@ -47,12 +47,10 @@ vec3 texelCoordToVec(vec2 uv, uint faceID) {
 	return normalize(result);
 }
 
-vec3 ImportanceSampleGGX(vec2 Xi, float Roughness, vec3 N) {
-	float a = Roughness * Roughness; // DISNEY'S ROUGHNESS [see Burley'12 siggraph]
-
+vec3 ImportanceSampleGGX(vec2 xi, float roughness4) {
 	// Compute distribution direction
-	float Phi = 2.0 * M_PI * Xi.x;
-	float CosTheta = sqrt((1.0 - Xi.y) / (1.0 + (a * a - 1.0) * Xi.y));
+	float Phi = 2.0 * M_PI * xi.x;
+	float CosTheta = sqrt((1.0 - xi.y) / (1.0 + (roughness4 - 1.0) * xi.y));
 	float SinTheta = sqrt(1.0 - CosTheta * CosTheta);
 
 	// Convert to spherical direction
@@ -61,12 +59,15 @@ vec3 ImportanceSampleGGX(vec2 Xi, float Roughness, vec3 N) {
 	H.y = SinTheta * sin(Phi);
 	H.z = CosTheta;
 
-	vec3 UpVector = abs(N.z) < 0.999 ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0);
-	vec3 TangentX = normalize(cross(UpVector, N));
-	vec3 TangentY = cross(N, TangentX);
+	return H;
+}
+
+float DistributionGGX(float NdotH, float roughness4) {
+	float NdotH2 = NdotH * NdotH;
+	float denom = (NdotH2 * (roughness4 - 1.0) + 1.0);
+	denom = M_PI * denom * denom;
 
-	// Tangent to world space
-	return TangentX * H.x + TangentY * H.y + N * H.z;
+	return roughness4 / denom;
 }
 
 // https://graphicrants.blogspot.com.au/2013/08/specular-brdf-reference.html
diff --git a/servers/rendering/renderer_rd/shaders/cubemap_roughness_raster.glsl b/servers/rendering/renderer_rd/shaders/cubemap_roughness_raster.glsl
index 2570308816..c29accd8a7 100644
--- a/servers/rendering/renderer_rd/shaders/cubemap_roughness_raster.glsl
+++ b/servers/rendering/renderer_rd/shaders/cubemap_roughness_raster.glsl
@@ -42,17 +42,33 @@ void main() {
 	} else {
 		vec4 sum = vec4(0.0, 0.0, 0.0, 0.0);
 
+		float solid_angle_texel = 4.0 * M_PI / (6.0 * params.face_size * params.face_size);
+		float roughness2 = params.roughness * params.roughness;
+		float roughness4 = roughness2 * roughness2;
+		vec3 UpVector = abs(N.z) < 0.999 ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0);
+		mat3 T;
+		T[0] = normalize(cross(UpVector, N));
+		T[1] = cross(N, T[0]);
+		T[2] = N;
+
 		for (uint sampleNum = 0u; sampleNum < params.sample_count; sampleNum++) {
 			vec2 xi = Hammersley(sampleNum, params.sample_count);
 
-			vec3 H = ImportanceSampleGGX(xi, params.roughness, N);
-			vec3 V = N;
-			vec3 L = (2.0 * dot(V, H) * H - V);
+			vec3 H = T * ImportanceSampleGGX(xi, roughness4);
+			float NdotH = dot(N, H);
+			vec3 L = (2.0 * NdotH * H - N);
 
 			float ndotl = clamp(dot(N, L), 0.0, 1.0);
 
 			if (ndotl > 0.0) {
-				sum.rgb += textureLod(source_cube, L, 0.0).rgb * ndotl;
+				float D = DistributionGGX(NdotH, roughness4);
+				float pdf = D * NdotH / (4.0 * NdotH) + 0.0001;
+
+				float solid_angle_sample = 1.0 / (float(params.sample_count) * pdf + 0.0001);
+
+				float mipLevel = params.roughness == 0.0 ? 0.0 : 0.5 * log2(solid_angle_sample / solid_angle_texel);
+
+				sum.rgb += textureLod(source_cube, L, mipLevel).rgb * ndotl;
 				sum.a += ndotl;
 			}
 		}