[JIRA # UMM-64133] Fixing hardware DRS half res downsample.

* Fixing the wrong texture being set (due to resource name leaking) for half res downsample: instead of using _CameraDepthTexture which could be anything, using an new explicit name _SourceDownsampleDepth
* When hardware DRS is on, we can safely assume that the ratio between the input and output textures is 1 because the GPU hardware sizes are watertight.
Jira: https://jira.unity3d.com/browse/UUM-64133

Author: kecho

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

@@ -1456,6 +1456,7 @@ class DownsampleDepthForLowResPassData
             public float downsampleScale;
             public Material downsampleDepthMaterial;
             public TextureHandle depthTexture;
+            public TextureHandle depthPyramidTexture;
             public TextureHandle downsampledDepthBuffer;
             public Rect viewport;
 
@@ -1499,11 +1500,9 @@ void DownsampleDepthForLowResTransparency(RenderGraph renderGraph, HDCamera hdCa
                 passData.computesMip1OfAtlas = computeMip1OfPyramid;
                 passData.downsampleScale = hdCamera.lowResScale;
                 passData.viewport = hdCamera.lowResViewport;
-                passData.depthTexture = builder.ReadTexture(output.depthPyramidTexture);
+                passData.depthTexture = builder.ReadTexture(output.resolvedDepthBuffer);
                 if (computeMip1OfPyramid)
-                {
-                    passData.depthTexture = builder.WriteTexture(passData.depthTexture);
-                }
+                    passData.depthPyramidTexture = builder.WriteTexture(output.depthPyramidTexture);
 
                 passData.downsampledDepthBuffer = builder.UseDepthBuffer(renderGraph.CreateTexture(
                     new TextureDesc(Vector2.one * hdCamera.lowResScale, true, true) { depthBufferBits = DepthBits.Depth32, name = "LowResDepthBuffer" }), DepthAccess.Write);
@@ -1514,20 +1513,27 @@ void DownsampleDepthForLowResTransparency(RenderGraph renderGraph, HDCamera hdCa
                         if (data.computesMip1OfAtlas)
                         {
                             data.downsampleDepthMaterial.SetVector(HDShaderIDs._DstOffset, new Vector4(data.mip0Offset.x, data.mip0Offset.y, 0.0f, 0.0f));
-                            context.cmd.SetRandomWriteTarget(1, data.depthTexture);
+                            context.cmd.SetRandomWriteTarget(1, data.depthPyramidTexture);
                         }
 
                         if (data.useGatherDownsample)
                         {
                             float downsampleScaleInv = 1.0f / data.downsampleScale;
                             RenderTexture srcTexture = data.depthTexture;
                             RenderTexture destTexture = data.downsampledDepthBuffer;
-                            float uvScaleX = ((float)destTexture.width / (float)srcTexture.width) * downsampleScaleInv;
-                            float uvScaleY = ((float)destTexture.height / (float)srcTexture.height) * downsampleScaleInv;
+                            float uvScaleX = 1.0f;
+                            float uvScaleY = 1.0f;
+                            if (!DynamicResolutionHandler.instance.HardwareDynamicResIsEnabled())
+                            {
+                                uvScaleX = ((float)destTexture.width / (float)srcTexture.width) * downsampleScaleInv;
+                                uvScaleY = ((float)destTexture.height / (float)srcTexture.height) * downsampleScaleInv;
+                            }
+
                             data.downsampleDepthMaterial.SetVector(HDShaderIDs._ScaleBias, new Vector4(uvScaleX, uvScaleY, 0.0f, 0.0f));
                         }
 
                         context.cmd.SetViewport(data.viewport);
+                        context.cmd.SetGlobalTexture(HDShaderIDs._SourceDownsampleDepth, data.depthTexture);
                         context.cmd.DrawProcedural(Matrix4x4.identity, data.downsampleDepthMaterial, 0, MeshTopology.Triangles, 3, 1, null);
 
                         if (data.computesMip1OfAtlas)

Packages/com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/HDStringConstants.cs

@@ -521,6 +521,7 @@ static class HDShaderIDs
         public static readonly int _ComputeThicknessScale = Shader.PropertyToID("_ComputeThicknessScale");
         public static readonly int _ComputeThicknessShowOverlapCount = Shader.PropertyToID("_ComputeThicknessShowOverlapCount");
         public static readonly int _VolumetricCloudsDebugMode = Shader.PropertyToID("_VolumetricCloudsDebugMode");
+        public static readonly int _SourceDownsampleDepth = Shader.PropertyToID("_SourceDownsampleDepth");
 
         public static readonly int _InputCubemap = Shader.PropertyToID("_InputCubemap");
         public static readonly int _Mipmap = Shader.PropertyToID("_Mipmap");

Packages/com.unity.render-pipelines.high-definition/Runtime/ShaderLibrary/DownsampleDepth.shader

@@ -52,6 +52,8 @@ Shader "Hidden/HDRP/DownsampleDepth"
 #endif
         }
 
+        TEXTURE2D_X(_SourceDownsampleDepth);
+
 #ifdef OUTPUT_FIRST_MIP_OF_MIPCHAIN
     #ifdef SHADER_API_PSSL
         RW_TEXTURE2D_X(float, _OutputTexture) : register(u0);
@@ -67,15 +69,15 @@ Shader "Hidden/HDRP/DownsampleDepth"
         {
             UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(input);
 #ifdef GATHER_DOWNSAMPLE
-            float4 depths = GATHER_RED_TEXTURE2D_X(_CameraDepthTexture, s_linear_clamp_sampler, input.texcoord * _ScaleBias.xy + _ScaleBias.zw);
+            float4 depths = GATHER_RED_TEXTURE2D_X(_SourceDownsampleDepth, s_linear_clamp_sampler, input.texcoord * _ScaleBias.xy + _ScaleBias.zw);
             outputDepth = MinDepth(depths);
 #else
             uint2 fullResUpperCorner = uint2((((float2)input.positionCS.xy - 0.5f) * 2.0) + 0.5f);
             float4 depths;
-            depths.x = LoadCameraDepth(fullResUpperCorner);
-            depths.y = LoadCameraDepth(fullResUpperCorner + uint2(0, 1));
-            depths.z = LoadCameraDepth(fullResUpperCorner + uint2(1, 0));
-            depths.w = LoadCameraDepth(fullResUpperCorner + uint2(1, 1));
+            depths.x = LOAD_TEXTURE2D_X_LOD(_SourceDownsampleDepth, fullResUpperCorner, 0);
+            depths.y = LOAD_TEXTURE2D_X_LOD(_SourceDownsampleDepth, fullResUpperCorner + uint2(0, 1), 0);
+            depths.z = LOAD_TEXTURE2D_X_LOD(_SourceDownsampleDepth, fullResUpperCorner + uint2(1, 0), 0);
+            depths.w = LOAD_TEXTURE2D_X_LOD(_SourceDownsampleDepth, fullResUpperCorner + uint2(1, 1), 0);
 
             float minDepth = MinDepth(depths);
         #if MIN_DOWNSAMPLE