Add dithering to Volumetric Fog to reduce aliasing

Source/Shaders/ExponentialHeightFog.hlsl

@@ -27,8 +27,6 @@ struct ExponentialHeightFogData
     float VolumetricFogMaxDistance;
     float DirectionalInscatteringStartDistance;
     float StartDistance;
-
-    float4 VolumetricFogGrid;
 };
 
 float4 GetExponentialHeightFog(ExponentialHeightFogData exponentialHeightFog, float3 posWS, float3 camWS, float skipDistance, float sceneDistance)

Source/Shaders/Fog.shader

@@ -16,6 +16,8 @@
 META_CB_BEGIN(0, Data)
 GBufferData GBuffer;
 ExponentialHeightFogData ExponentialHeightFog;
+VolumetricFogData VolumetricFog;
+float4 TemporalAAJitter;
 META_CB_END
 
 DECLARE_GBUFFERDATA_ACCESS(GBuffer)
@@ -46,7 +48,7 @@ float4 PS_Fog(Quad_VS2PS input) : SV_Target0
 
 #if VOLUMETRIC_FOG
     // Sample volumetric fog and mix it in
-	float4 volumetricFog = SampleVolumetricFog(VolumetricFogTexture, ExponentialHeightFog.VolumetricFogGrid, worldPos - GBuffer.ViewPos, input.TexCoord);
+	float4 volumetricFog = SampleVolumetricFog(VolumetricFogTexture, VolumetricFog, worldPos - GBuffer.ViewPos, input.TexCoord, TemporalAAJitter);
 	fog = CombineVolumetricFog(fog, volumetricFog);
 #endif
 

Source/Shaders/VolumetricFog.hlsl

@@ -3,8 +3,18 @@
 #ifndef __VOLUMETRIC_FOG__
 #define __VOLUMETRIC_FOG__
 
+#include "./Flax/Noise.hlsl"
+
 #define VOLUMETRIC_FOG_GRID_Z_LINEAR 1
 
+// Structure that contains information about volumetric fog
+struct VolumetricFogData
+{
+    float4 GridSliceParameters;
+    float2 ScreenSize;
+    float2 VolumeTexelSize; // Scaled for dithering
+};
+
 float GetDepthFromSlice(float4 gridSliceParameters, float zSlice)
 {
 #if VOLUMETRIC_FOG_GRID_Z_LINEAR
@@ -23,11 +33,19 @@ float GetSliceFromDepth(float4 gridSliceParameters, float sceneDepth)
 #endif
 }
 
-float4 SampleVolumetricFog(Texture3D volumetricFogTexture, float4 gridSliceParameters, float3 viewVector, float2 uv)
+float4 SampleVolumetricFog(Texture3D volumetricFogTexture, VolumetricFogData volumetricFogData, float3 viewVector, float2 uv, float4 temporalAAJitter = 0)
 {
+    // Project view vector to get 3D frustum UVW coordinates
     float sceneDepth = length(viewVector);
-    float zSlice = GetSliceFromDepth(gridSliceParameters, sceneDepth) * gridSliceParameters.w;
+    float zSlice = GetSliceFromDepth(volumetricFogData.GridSliceParameters, sceneDepth) * volumetricFogData.GridSliceParameters.w;
     float3 volumeUV = float3(uv, zSlice);
+
+    // Dither to reduce banding artifacts
+    float2 noiseUV = volumeUV.xy + temporalAAJitter.xy;
+    float2 noise = rand2dTo2d(noiseUV * volumetricFogData.ScreenSize) * 2.0f - 1.0f;
+    volumeUV.xy += noise * volumetricFogData.VolumeTexelSize;
+
+    // Sample 3D texture
     return volumetricFogTexture.SampleLevel(SamplerLinearClamp, volumeUV, 0);
 }