Halving the perf impact of film grain and sRGB dithering in Final pass

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -107,6 +107,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Rename Raytracing Node to Raytracing Quality Keyword and rename high and low inputs as default and raytraced. All raytracing effects now use the raytraced mode but path tracing.
 - Moved diffusion profile list to the HDRP default settings panel.
 - Skip biquadratic resampling of vbuffer when volumetric fog filtering is enabled.
+- Optimized Grain and sRGB Dithering.
 
 ## [10.0.0] - 2019-06-10
 

com.unity.render-pipelines.high-definition/Runtime/PostProcessing/PostProcessSystem.cs

@@ -3918,17 +3918,24 @@ static void DoFinalPass(    in FinalPassParameters  parameters,
                     if (parameters.filmGrainTexture != null) // Fail safe if the resources asset breaks :/
                     {
                         #if HDRP_DEBUG_STATIC_POSTFX
-                        int offsetX = 0;
-                        int offsetY = 0;
+                        float offsetX = 0;
+                        float offsetY = 0;
                         #else
-                        int offsetX = (int)(parameters.random.NextDouble() * parameters.filmGrainTexture.width);
-                        int offsetY = (int)(parameters.random.NextDouble() * parameters.filmGrainTexture.height);
+                        float offsetX = (float)(parameters.random.NextDouble());
+                        float offsetY = (float)(parameters.random.NextDouble());
                         #endif
 
                         finalPassMaterial.EnableKeyword("GRAIN");
                         finalPassMaterial.SetTexture(HDShaderIDs._GrainTexture, parameters.filmGrainTexture);
                         finalPassMaterial.SetVector(HDShaderIDs._GrainParams, new Vector2(parameters.filmGrainIntensity * 4f, parameters.filmGrainResponse));
-                        finalPassMaterial.SetVector(HDShaderIDs._GrainTextureParams, new Vector4(parameters.filmGrainTexture.width, parameters.filmGrainTexture.height, offsetX, offsetY));
+
+                        float uvScaleX = parameters.hdCamera.actualWidth / (float)parameters.filmGrainTexture.width;
+                        float uvScaleY = parameters.hdCamera.actualHeight / (float)parameters.filmGrainTexture.height;
+                        float scaledOffsetX = offsetX * uvScaleX;
+                        float scaledOffsetY = offsetY * uvScaleY;
+
+                        finalPassMaterial.SetVector(HDShaderIDs._GrainTextureParams, new Vector4(uvScaleX, uvScaleY, offsetX, offsetY));
+
                     }
                 }
 
@@ -3944,7 +3951,8 @@ static void DoFinalPass(    in FinalPassParameters  parameters,
 
                     finalPassMaterial.EnableKeyword("DITHER");
                     finalPassMaterial.SetTexture(HDShaderIDs._BlueNoiseTexture, blueNoiseTexture);
-                    finalPassMaterial.SetVector(HDShaderIDs._DitherParams, new Vector3(blueNoiseTexture.width, blueNoiseTexture.height, textureId));
+                    finalPassMaterial.SetVector(HDShaderIDs._DitherParams, new Vector3(parameters.hdCamera.actualWidth / blueNoiseTexture.width,
+                                                                                        parameters.hdCamera.actualHeight / blueNoiseTexture.height, textureId));
                 }
             }
 

com.unity.render-pipelines.high-definition/Runtime/PostProcessing/Shaders/FinalPass.shader

@@ -32,8 +32,8 @@ Shader "Hidden/HDRP/FinalPass"
         SAMPLER(sampler_LinearRepeat);
 
         float2 _GrainParams;            // x: intensity, y: response
-        float4 _GrainTextureParams;     // x: width, y: height, zw: random offset
-        float3 _DitherParams;           // x: width, y: height, z: texture_id
+        float4 _GrainTextureParams;     // xy: _ScreenSize.xy / GrainTextureSize.xy, zw: (random offset in UVs) *  _GrainTextureParams.xy
+        float3 _DitherParams;           // xy: _ScreenSize.xy / DitherTextureSize.xy, z: texture_id
         float4 _UVTransform;
         float  _KeepAlpha;
 
@@ -114,8 +114,7 @@ Shader "Hidden/HDRP/FinalPass"
             #if GRAIN
             {
                 // Grain in range [0;1] with neutral at 0.5
-                uint2 icoords = fmod(positionSS + _GrainTextureParams.zw, _GrainTextureParams.xy);
-                float grain = LOAD_TEXTURE2D(_GrainTexture, icoords).w;
+                float grain = SAMPLE_TEXTURE2D(_GrainTexture, s_linear_repeat_sampler, (positionNDC * _GrainTextureParams.xy) + _GrainTextureParams.zw).w;
 
                 // Remap [-1;1]
                 grain = (grain - 0.5) * 2.0;
@@ -132,14 +131,14 @@ Shader "Hidden/HDRP/FinalPass"
             // sRGB 8-bit dithering
             {
                 float3 ditherParams = _DitherParams;
-                uint2 icoords = fmod(positionSS, ditherParams.xy);
-
                 // Symmetric triangular distribution on [-1,1] with maximal density at 0
-                float noise = LOAD_TEXTURE2D_ARRAY(_BlueNoiseTexture, icoords, ditherParams.z).a * 2.0 - 1.0;
+                float noise = SAMPLE_TEXTURE2D_ARRAY(_BlueNoiseTexture, s_linear_repeat_sampler, positionNDC * ditherParams.xy, ditherParams.z).a;
+                float3 sRGBColor = LinearToSRGB(outColor.xyz);
+                noise = noise * 2.0 - 1.0;
                 noise = FastSign(noise) * (1.0 - sqrt(1.0 - abs(noise)));
 
                 //outColor += noise / 255.0;
-                outColor.xyz = SRGBToLinear(LinearToSRGB(outColor.xyz) + noise / 255.0);
+                outColor.xyz = SRGBToLinear(sRGBColor + noise / 255.0);
             }
             #endif