Fix Volumetric Fog sampling to use the same code path for depth slices conversion

Source/Shaders/ExponentialHeightFog.hlsl

@@ -27,6 +27,8 @@ 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

@@ -46,7 +46,7 @@ float4 PS_Fog(Quad_VS2PS input) : SV_Target0
 
 #if VOLUMETRIC_FOG
     // Sample volumetric fog and mix it in
-	float4 volumetricFog = SampleVolumetricFog(VolumetricFogTexture, worldPos - GBuffer.ViewPos, ExponentialHeightFog.VolumetricFogMaxDistance, input.TexCoord);
+	float4 volumetricFog = SampleVolumetricFog(VolumetricFogTexture, ExponentialHeightFog.VolumetricFogGrid, worldPos - GBuffer.ViewPos, input.TexCoord);
 	fog = CombineVolumetricFog(fog, volumetricFog);
 #endif
 

Source/Shaders/VolumetricFog.hlsl

@@ -5,7 +5,7 @@
 
 #define VOLUMETRIC_FOG_GRID_Z_LINEAR 1
 
-float GetDepthFromSlice(float3 gridSliceParameters, float zSlice)
+float GetDepthFromSlice(float4 gridSliceParameters, float zSlice)
 {
 #if VOLUMETRIC_FOG_GRID_Z_LINEAR
 	return zSlice * gridSliceParameters.x;
@@ -14,7 +14,7 @@ float GetDepthFromSlice(float3 gridSliceParameters, float zSlice)
 #endif
 }
 
-float GetSliceFromDepth(float3 gridSliceParameters, float sceneDepth)
+float GetSliceFromDepth(float4 gridSliceParameters, float sceneDepth)
 {
 #if VOLUMETRIC_FOG_GRID_Z_LINEAR
     return sceneDepth * gridSliceParameters.y;
@@ -23,11 +23,10 @@ float GetSliceFromDepth(float3 gridSliceParameters, float sceneDepth)
 #endif
 }
 
-float4 SampleVolumetricFog(Texture3D volumetricFogTexture, float3 viewVector, float maxDistance, float2 uv)
+float4 SampleVolumetricFog(Texture3D volumetricFogTexture, float4 gridSliceParameters, float3 viewVector, float2 uv)
 {
     float sceneDepth = length(viewVector);
-    float zSlice = sceneDepth / maxDistance;
-    // TODO: use GetSliceFromDepth instead to handle non-linear depth distributions
+    float zSlice = GetSliceFromDepth(gridSliceParameters, sceneDepth) * gridSliceParameters.w;
     float3 volumeUV = float3(uv, zSlice);
     return volumetricFogTexture.SampleLevel(SamplerLinearClamp, volumeUV, 0);
 }

Source/Shaders/VolumetricFog.shader

@@ -52,8 +52,7 @@ float VolumetricFogMaxDistance;
 float InverseSquaredLightDistanceBiasScale;
 
 float4 FogParameters;
-float3 GridSliceParameters;
-float Dummy1;
+float4 GridSliceParameters;
 
 float4x4 PrevWorldToClip;