[Fogbugz 1330769] Fixing bloom bicubic filtering for DRS

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

@@ -179,6 +179,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed contact shadows tile coordinates calculations.
 - Fixed issue with history buffer allocation for AOVs when the request does not come in first frame.
 - Fix Clouds on Metal or platforms that don't support RW in same shader of R11G11B10 textures.
+- Fixed blocky looking bloom when dynamic resolution scaling was used.
 
 ### Changed
 - Changed Window/Render Pipeline/HD Render Pipeline Wizard to Window/Rendering/HDRP Wizard

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/HDRenderPipeline.PostProcess.cs

@@ -3165,6 +3165,16 @@ void PrepareBloomData(RenderGraph renderGraph, in RenderGraphBuilder builder, Bl
             // the mip up 0 will be used by uber, so not allocated as transient.
             m_BloomBicubicParams = new Vector4(passData.bloomMipInfo[0].x, passData.bloomMipInfo[0].y, 1.0f / passData.bloomMipInfo[0].x, 1.0f / passData.bloomMipInfo[0].y);
             var mip0Scale = new Vector2(passData.bloomMipInfo[0].z, passData.bloomMipInfo[0].w);
+
+            // We undo the scale here, because bloom uses these parameters for its bicubic filtering offset.
+            // The bicubic filtering function is SampleTexture2DBicubic, and it requires the underlying texture's
+            // unscaled pixel sizes to compute the offsets of the samples.
+            // For more info please see the implementation of SampleTexture2DBicubic
+            m_BloomBicubicParams.x /= RTHandles.rtHandleProperties.rtHandleScale.x;
+            m_BloomBicubicParams.y /= RTHandles.rtHandleProperties.rtHandleScale.y;
+            m_BloomBicubicParams.z *= RTHandles.rtHandleProperties.rtHandleScale.x;
+            m_BloomBicubicParams.w *= RTHandles.rtHandleProperties.rtHandleScale.y;
+
             passData.mipsUp[0] = builder.WriteTexture(renderGraph.CreateTexture(new TextureDesc(mip0Scale, true, true)
             {
                 name = "Bloom final mip up",