Added distortion masking

ScriptableRenderPipeline/HDRenderPipeline/Material/Builtin/BuiltinData.hlsl

     velocity = inBuffer.xy;
 }
 
-void EncodeDistortion(float2 distortion, float distortionBlur, out float4 outBuffer)
+void EncodeDistortion(float2 distortion, float distortionBlur, bool validSourceForDistortion, out float4 outBuffer)
-    outBuffer = float4(distortion, 0.0, distortionBlur);
+    // Tag pixel as a pixel that can be used as source for distortion (b != 0)
+    // It is compatible with blend mode: either Add or Multiply
+    outBuffer = float4(distortion, validSourceForDistortion ? 1.0 : 0.0, distortionBlur);
-void DecodeDistortion(float4 inBuffer, out float2 distortion, out float2 distortionBlur)
+void DecodeDistortion(float4 inBuffer, out float2 distortion, out float2 distortionBlur, out bool validSourceForDistortion)
+    validSourceForDistortion = inBuffer.z > 0.1 || inBuffer.z < 0.1;
 }
 
 void GetBuiltinDataDebug(uint paramId, BuiltinData builtinData, inout float3 result, inout bool needLinearToSRGB)

ScriptableRenderPipeline/HDRenderPipeline/RenderPipelineResources/ApplyDistorsion.compute

 #include "../Material/Builtin/BuiltinData.hlsl"
 
 Texture2D<float4> _DistortionTexture;
-Texture2D<float> _PyramidDepthTexture;
-SamplerState sampler_PyramidDepthTexture;
 
 CBUFFER_START(cb)
     float4 _Size;
 [numthreads(8, 8, 1)]
 void KMain(uint2 groupId : SV_GroupID, uint2 groupThreadId : SV_GroupThreadID, uint2 dispatchThreadId : SV_DispatchThreadID)
 {
-    float4 encodedDistorsion = _DistortionTexture.Load(int3(dispatchThreadId, 0));
-    float2 distorsion;
-    float2 distorsionBlur;
-    DecodeDistortion(encodedDistorsion, distorsion, distorsionBlur);
+    // We use a bias when fetching distortion source pixels
+    // This avoid artifacts when a distortion is overlapped by an opaque object
+    const float _FetchBias = 0.9;
-    float2 distordedUV = (float2(dispatchThreadId) + distorsion) * _Size.zw;
-    float mip = (_GaussianPyramidColorMipSize.z - 1) * clamp(distorsionBlur.x, 0.0, 1.0);
-    float4 sampled = _GaussianPyramidColorTexture.SampleLevel(sampler_GaussianPyramidColorTexture, distordedUV, mip);
+    // Get distortion values
+    float4 encodedDistortion = _DistortionTexture.Load(int3(dispatchThreadId, 0));
-    _CameraColorTexture[dispatchThreadId] = sampled;
+    float2 distortion;
+    float2 distortionBlur;
+    bool validForDistortion;
+    DecodeDistortion(encodedDistortion, distortion, distortionBlur, validForDistortion);
+
+    // Get distortion source pixel mask (stored in _DistortionTexture.z)
+    uint2 distortedEncodedDistortionId = dispatchThreadId + uint2(distortion);
+
+    float2 distordedDistortion;
+    float2 distordedDistortionBlur;
+    bool distordedValidForDistortion;
+    float4 encodedDistordedDistortion = _DistortionTexture.Load(int3(distortedEncodedDistortionId, 0));
+    DecodeDistortion(encodedDistordedDistortion, distordedDistortion, distordedDistortionBlur, distordedValidForDistortion);
+
+    if (distordedValidForDistortion && validForDistortion)
+    {
+        // Get source pixel for distortion
+        float2 distordedUV = float2(dispatchThreadId + uint2(distortion * _FetchBias)) * _Size.zw;
+        float mip = (_GaussianPyramidColorMipSize.z - 1) * clamp(distortionBlur.x, 0.0, 1.0);
+        float4 sampled = _GaussianPyramidColorTexture.SampleLevel(sampler_GaussianPyramidColorTexture, distordedUV, mip);
+
+        _CameraColorTexture[dispatchThreadId] = sampled;
+    }
 }

ScriptableRenderPipeline/HDRenderPipeline/ShaderPass/ShaderPassDistortion.hlsl

     GetSurfaceAndBuiltinData(input, V, posInput, surfaceData, builtinData);
 
     float4 outBuffer;
-    EncodeDistortion(builtinData.distortion, builtinData.distortionBlur, outBuffer);
+    // We do not use pixel outside of distorted objects, so we use masking to reject invalid pixels
+    // https://developer.nvidia.com/gpugems/GPUGems2/gpugems2_chapter19.html (refraction mask)
+    // true = tag this pixel as a valid distortion pixel source
+    EncodeDistortion(builtinData.distortion, builtinData.distortionBlur, true, outBuffer);
     return outBuffer;
 }