PBR: Fixed noise in IBL irradiance cube map (close #200)

DiligentGraphics · May 14, 2024 · 1224607 · 1224607
1 parent ee0295b
commit 1224607
Show file tree

Hide file tree

Showing 3 changed files with 25 additions and 14 deletions.
diff --git a/Shaders/PBR/private/ComputeIrradianceMap.psh b/Shaders/PBR/private/ComputeIrradianceMap.psh
@@ -57,18 +57,17 @@ float3 IrradianceMap(float3 N)
         // Solid angle of current smple
         float OmegaS = 1.0 / (float(g_NumSamples) * pdf);
 
-        float NumPixels = g_EnvMapWidth * g_EnvMapHeight;
+        // Solid angle of 1 pixel across all cube faces
 #if ENV_MAP_TYPE == ENV_MAP_TYPE_CUBE
-        NumPixels *= 6.0;
+        float OmegaP = ComputeCubeMapPixelSolidAngle(g_EnvMapWidth, g_EnvMapHeight);
+#else
+        // Solid angle of 1 pixel on sphere
+        float OmegaP = ComputeSphereMapPixelSolidAngle(g_EnvMapWidth, g_EnvMapHeight, acos(L.y), 0.5);
 #endif
-
-        // Solid angle of 1 pixel across all cube faces
-        float OmegaP = 4.0 * PI / NumPixels;
-
         // Applying mip bias produces better results, especially for environments maps with
         // very bright spots.
         float MipBias = 1.0;
-        float MipLevel = max(0.5 * log2(OmegaS / OmegaP) + MipBias, 0.0);
+        float MipLevel = max(0.5 * (log2(OmegaS) - log2(OmegaP)) + MipBias, 0.0);
 #else
         float MipLevel = 0.0;
 #endif

diff --git a/Shaders/PBR/private/PBR_PrecomputeCommon.fxh b/Shaders/PBR/private/PBR_PrecomputeCommon.fxh
@@ -39,4 +39,16 @@ float3 ImportanceSampleGGX(float2 Xi, float PerceptualRoughness, float3 N)
     return TangentX * H.x + TangentY * H.y + N * H.z;
 }
 
+float ComputeCubeMapPixelSolidAngle(float Width, float Height)
+{
+    return 4.0 * PI / (6.0 * Width * Height);
+} 
+
+float ComputeSphereMapPixelSolidAngle(float Width, float Height, float Theta, float Gamma)
+{
+    float dTheta = PI / Width;
+    float dPhi = 2.0 * PI / Height;
+    return dPhi * (cos(Theta - 0.5 * dTheta * Gamma) - cos(Theta + 0.5 * dTheta * Gamma));
+}
+
 #endif // _PBR_PRECOMPUTE_COMMON_FXH_
diff --git a/Shaders/PBR/private/PrefilterEnvMap.psh b/Shaders/PBR/private/PrefilterEnvMap.psh
@@ -71,17 +71,17 @@ float3 PrefilterEnvMap( float PerceptualRoughness, float3 R )
             // Solid angle of current smple
             float OmegaS = 1.0 / (float(g_NumSamples) * pdf);
 
-            float NumPixels = g_EnvMapWidth * g_EnvMapHeight;
+            // Solid angle of 1 pixel across all cube faces
 #if ENV_MAP_TYPE == ENV_MAP_TYPE_CUBE
-            NumPixels *= 6.0;
+            float OmegaP = ComputeCubeMapPixelSolidAngle(g_EnvMapWidth, g_EnvMapHeight);
+#else
+            // Solid angle of 1 pixel on sphere
+            float OmegaP = ComputeSphereMapPixelSolidAngle(g_EnvMapWidth, g_EnvMapHeight, acos(L.y), 1.0);
 #endif
-
-            // Solid angle of 1 pixel across all cube faces
-            float OmegaP = 4.0 * PI / NumPixels;
             // Applying mip bias produces better results, especially for environments maps with
             // very bright spots.
-            float MipBias = 1.0; 
-            float MipLevel = (AlphaRoughness == 0.0) ? 0.0 : max(0.5 * log2(OmegaS / OmegaP) + MipBias, 0.0);
+            float MipBias = 1.0;
+            float MipLevel = (AlphaRoughness == 0.0) ? 0.0 : max(0.5 * (log2(OmegaS) - log2(OmegaP)) + MipBias, 0.0);
 #else
             float MipLevel = 0.0;
 #endif