Fixing invalid mip <-> roughness mapping for reflection environment sampling

Data/Raw/Engine/Includes/ReflectionCubemapCommon.bslinc

@@ -32,22 +32,29 @@ Technique : base("ReflectionCubemapCommon") =
 			 * @param	numMips		Total number of mip-map levels in the texture we'll be sampling from.
 			 * @return				Index of the mipmap level to sample.
 			 */					
-			float mapRoughnessToMipLevel(float roughness, uint numMips)
+			float mapRoughnessToMipLevel(float roughness, int numMips)
 			{
 				// We use the following equation:
 				//    mipLevel = log10(roughness) / log10(dropPercent)
 				//
 				// Where dropPercent represent by what % to drop the roughness with each mip level.
 				// We convert to log2 and a assume a drop percent value of 0.6. This gives us:
-				//    mipLevel = -1.35692 * log2(roughness);
-				
-				return max(0, numMips - 1 - (-1.35692 * log2(roughness)));
+				//    mipLevel = -1.35692 * log2( roughness);
+
+				return max(0, (float)numMips - 1.0f - (-1.35692f * log2(roughness)));
 			}
 			
-			float mapMipLevelToRoughness(uint mipLevel)
+			/**
+			 * Calculates a roughness value from the provided mip level.
+			 *
+			 * @param 	mipLevel	Mip level to determine roughness for.
+			 * @param	numMips		Total number of mip-map levels in the texture we'll be sampling from.
+			 * @return				Roughness value for the specific mip level.
+			 */				
+			float mapMipLevelToRoughness(int mipLevel, int numMips)
 			{
 				// mapRoughnessToMipLevel() solved for roughness
-				return 1.0f - exp2(-0.7369655941662063 * mipLevel);
+				return saturate(exp2(((float)mipLevel - (float)numMips + 1.0f) / 1.35692));
 			}	
 		};
 	};

Data/Raw/Engine/Shaders/ReflectionCubeImportanceSample.bsl

@@ -52,7 +52,7 @@ Technique
 				// See GGXImportanceSample.nb for derivation (essentially, take base GGX, normalize it,
 				// generate PDF, split PDF into marginal probability for theta and conditional probability
 				// for phi. Plug those into the CDF, invert it.)				
-				float cosTheta = sqrt((1.0f - e.x) / (1.0f + (roughness4 - 1.0f) * e.y));
+				float cosTheta = sqrt((1.0f - e.x) / (1.0f + (roughness4 - 1.0f) * e.x));
 				float phi = 2.0f * PI * e.y;
 				
 				return float2(cosTheta, phi);
@@ -78,6 +78,7 @@ Technique
 			{
 				int gCubeFace;
 				int gMipLevel;
+				int gNumMips;
 				float gPrecomputedMipFactor;
 			}	
 		
@@ -94,7 +95,7 @@ Technique
 				// Determine which mip level to sample from depending on PDF and cube -> sphere mapping distortion
 				float distortion = rcp(pow(N.x * N.x + N.y * N.y + N.z * N.z, 3.0f/2.0f));
 				
-				float roughness = mapMipLevelToRoughness(gMipLevel);
+				float roughness = mapMipLevelToRoughness(gMipLevel, gNumMips);
 				float roughness2 = roughness * roughness;
 				float roughness4 = roughness2 * roughness2;
 				
@@ -107,7 +108,7 @@ Technique
 					float cosTheta = sphericalH.x;
 					float phi = sphericalH.y;
 					
-					float sinTheta = sqrt(1.0f - cosTheta);
+					float sinTheta = sqrt(1.0f - cosTheta * cosTheta);
 					
 					float3 H = sphericalToCartesian(cosTheta, sinTheta, phi);
 					float PDF = pdfGGX(cosTheta, sinTheta, roughness4);
@@ -126,7 +127,7 @@ Technique
 					mipLevel++;
 					
 					// sum += H * GGX / PDF. In GGX/PDF most factors cancel out and we're left with 1/sin*cos
-					sum += gInputTex.SampleLevel(gInputSamp, H, mipLevel) / (cosTheta * sinTheta);
+					sum += gInputTex.SampleLevel(gInputSamp, H, mipLevel) * cosTheta;
 				}
 				
 				return sum / NUM_SAMPLES;