[2023.2][URP] Improvement on downsampled SSAO (UUM-49557)

Backport of #42246.
Fixes UUM-49557.

Packages/com.unity.render-pipelines.universal/ShaderLibrary/SSAO.hlsl

@@ -211,9 +211,14 @@ half3 PickSamplePoint(float2 uv, int sampleIndex, half sampleIndexHalf, half rcp
     return v;
 }
 
+// For Downsampled SSAO we need to adjust the UV coordinates
+// so it hits the center of the pixel inside the depth texture.
+// The texelSize multiplier is 1.0 when DOWNSAMPLE is enabled, otherwise 0.0
+#define ADJUSTED_DEPTH_UV(uv) uv.xy + ((_CameraDepthTexture_TexelSize.xy * 0.5) * (1.0 - (DOWNSAMPLE - 0.5) * 2.0))
+
 float SampleDepth(float2 uv)
 {
-    return SampleSceneDepth(uv.xy);
+    return SampleSceneDepth(ADJUSTED_DEPTH_UV(uv.xy));
 }
 
 float GetLinearEyeDepth(float rawDepth)

Tests/SRPTests/Projects/UniversalGraphicsTest_Foundation/Assets/CommonAssets/URPAssets/200_SSAOURPAsset.asset

@@ -21,6 +21,7 @@ MonoBehaviour:
   - {fileID: 11400000, guid: 590f3c2dabc9147698f7027e50b2ecd6, type: 2}
   - {fileID: 11400000, guid: 33768f1904a5640658411475990e6a10, type: 2}
   - {fileID: 11400000, guid: da4df2f1951704ee7aa560ed78d91c24, type: 2}
+  - {fileID: 11400000, guid: 3818ca301fb764854bfe2ed63d85c4a8, type: 2}
   m_DefaultRendererIndex: 0
   m_RequireDepthTexture: 1
   m_RequireOpaqueTexture: 1

Tests/SRPTests/Projects/UniversalGraphicsTest_Foundation/Assets/Scenes/200_Assets/Renderers/SSAO_DepthRenderer_Downsample.asset

@@ -0,0 +1,96 @@
+%YAML 1.1
+%TAG !u! tag:unity3d.com,2011:
+--- !u!114 &11400000
+MonoBehaviour:
+  m_ObjectHideFlags: 0
+  m_CorrespondingSourceObject: {fileID: 0}
+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
+  m_GameObject: {fileID: 0}
+  m_Enabled: 1
+  m_EditorHideFlags: 0
+  m_Script: {fileID: 11500000, guid: de640fe3d0db1804a85f9fc8f5cadab6, type: 3}
+  m_Name: SSAO_DepthRenderer_Downsample
+  m_EditorClassIdentifier: 
+  debugShaders:
+    debugReplacementPS: {fileID: 4800000, guid: cf852408f2e174538bcd9b7fda1c5ae7,
+      type: 3}
+    hdrDebugViewPS: {fileID: 4800000, guid: 573620ae32aec764abd4d728906d2587, type: 3}
+    probeVolumeSamplingDebugComputeShader: {fileID: 7200000, guid: 53626a513ea68ce47b59dc1299fe3959,
+      type: 3}
+  probeVolumeResources:
+    probeVolumeDebugShader: {fileID: 4800000, guid: e5c6678ed2aaa91408dd3df699057aae,
+      type: 3}
+    probeVolumeFragmentationDebugShader: {fileID: 4800000, guid: 03cfc4915c15d504a9ed85ecc404e607,
+      type: 3}
+    probeVolumeOffsetDebugShader: {fileID: 4800000, guid: 53a11f4ebaebf4049b3638ef78dc9664,
+      type: 3}
+    probeVolumeSamplingDebugShader: {fileID: 4800000, guid: 8f96cd657dc40064aa21efcc7e50a2e7,
+      type: 3}
+    probeSamplingDebugMesh: {fileID: -3555484719484374845, guid: 57d7c4c16e2765b47a4d2069b311bffe,
+      type: 3}
+    probeSamplingDebugTexture: {fileID: 2800000, guid: 24ec0e140fb444a44ab96ee80844e18e,
+      type: 3}
+    probeVolumeBlendStatesCS: {fileID: 7200000, guid: b9a23f869c4fd45f19c5ada54dd82176,
+      type: 3}
+  m_RendererFeatures:
+  - {fileID: 339116797255187971}
+  m_RendererFeatureMap: 037ec32deec8b404
+  m_UseNativeRenderPass: 0
+  xrSystemData: {fileID: 11400000, guid: 60e1133243b97e347b653163a8c01b64, type: 2}
+  postProcessData: {fileID: 0}
+  m_AssetVersion: 2
+  m_OpaqueLayerMask:
+    serializedVersion: 2
+    m_Bits: 4294967295
+  m_TransparentLayerMask:
+    serializedVersion: 2
+    m_Bits: 4294967295
+  m_DefaultStencilState:
+    overrideStencilState: 0
+    stencilReference: 0
+    stencilCompareFunction: 8
+    passOperation: 2
+    failOperation: 0
+    zFailOperation: 0
+  m_ShadowTransparentReceive: 0
+  m_RenderingMode: 0
+  m_DepthPrimingMode: 0
+  m_CopyDepthMode: 1
+  m_AccurateGbufferNormals: 0
+  m_IntermediateTextureMode: 1
+--- !u!114 &339116797255187971
+MonoBehaviour:
+  m_ObjectHideFlags: 0
+  m_CorrespondingSourceObject: {fileID: 0}
+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
+  m_GameObject: {fileID: 0}
+  m_Enabled: 1
+  m_EditorHideFlags: 0
+  m_Script: {fileID: 11500000, guid: f62c9c65cf3354c93be831c8bc075510, type: 3}
+  m_Name: SSAO
+  m_EditorClassIdentifier: 
+  m_Active: 1
+  m_Settings:
+    AOMethod: 1
+    Downsample: 1
+    AfterOpaque: 0
+    Source: 0
+    NormalSamples: 1
+    Intensity: 14.41
+    DirectLightingStrength: 1
+    Radius: 0.2
+    Samples: 0
+    BlurQuality: 2
+    Falloff: 100
+    SampleCount: -1
+  m_BlueNoise256Textures:
+  - {fileID: 2800000, guid: 36f118343fc974119bee3d09e2111500, type: 3}
+  - {fileID: 2800000, guid: 4b7b083e6b6734e8bb2838b0b50a0bc8, type: 3}
+  - {fileID: 2800000, guid: c06cc21c692f94f5fb5206247191eeee, type: 3}
+  - {fileID: 2800000, guid: cb76dd40fa7654f9587f6a344f125c9a, type: 3}
+  - {fileID: 2800000, guid: e32226222ff144b24bf3a5a451de54bc, type: 3}
+  - {fileID: 2800000, guid: 3302065f671a8450b82c9ddf07426f3a, type: 3}
+  - {fileID: 2800000, guid: 56a77a3e8d64f47b6afe9e3c95cb57d5, type: 3}
+  m_Shader: {fileID: 4800000, guid: 0849e84e3d62649e8882e9d6f056a017, type: 3}