Fix aliasing artifact in MultiScaleVolumetricObscurance (AmbientOcclusion)

com.unity.postprocessing/CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Fixed
 - Fixed FXAA artefact when trying to preserve alpha channel output.
+- Fixed MSVO aliasing artifact by using a z-Bias parameter. (case 1375337)
 
 ## [3.2.1] - 2022-01-12
 

com.unity.postprocessing/Documentation~/Ambient-Occlusion.md

@@ -63,5 +63,6 @@ This mode is optimized for consoles and desktop platforms. It has better graphic
 | Mode               | Select the type of **Ambient Occlusion** to use. |
 | Intensity          | Adjust the degree of darkness **Ambient Occlusion** produces. |
 | Thickness Modifier | Modify the thickness of occluders. This increases dark areas but can introduce dark halos around objects. |
+| Z Bias             | Modifies the z-bias to the depth buffer. This eliminates the banding aliasing artifact for MSVO. |
 | Color              | Set the tint color of the ambient occlusion. |
 | Ambient Only       | Enable this checkbox to make the **Ambient Occlusion** effect only affect ambient lighting. This option is only available with the Deferred rendering path and HDR rendering. |

com.unity.postprocessing/PostProcessing/Editor/Effects/AmbientOcclusionEditor.cs

@@ -11,6 +11,7 @@ internal sealed class AmbientOcclusionEditor : PostProcessEffectEditor<AmbientOc
         SerializedParameterOverride m_Color;
         SerializedParameterOverride m_AmbientOnly;
         SerializedParameterOverride m_ThicknessModifier;
+        SerializedParameterOverride m_ZBias;
         SerializedParameterOverride m_DirectLightingStrength;
         SerializedParameterOverride m_Quality;
         SerializedParameterOverride m_Radius;
@@ -22,6 +23,7 @@ public override void OnEnable()
             m_Color = FindParameterOverride(x => x.color);
             m_AmbientOnly = FindParameterOverride(x => x.ambientOnly);
             m_ThicknessModifier = FindParameterOverride(x => x.thicknessModifier);
+            m_ZBias = FindParameterOverride(x => x.zBias);
             m_DirectLightingStrength = FindParameterOverride(x => x.directLightingStrength);
             m_Quality = FindParameterOverride(x => x.quality);
             m_Radius = FindParameterOverride(x => x.radius);
@@ -51,6 +53,7 @@ public override void OnInspectorGUI()
                     EditorGUILayout.HelpBox("Multi-scale volumetric obscurance requires compute shader support.", MessageType.Warning);
 
                 PropertyField(m_ThicknessModifier);
+                PropertyField(m_ZBias);
 
                 if (RuntimeUtilities.scriptableRenderPipelineActive)
                     PropertyField(m_DirectLightingStrength);

com.unity.postprocessing/PostProcessing/Runtime/Effects/AmbientOcclusion.cs

@@ -127,6 +127,12 @@ public sealed class AmbientOcclusion : PostProcessEffectSettings
         [Range(1f, 10f), Tooltip("This modifies the thickness of occluders. It increases the size of dark areas and also introduces a dark halo around objects.")]
         public FloatParameter thicknessModifier = new FloatParameter { value = 1f };
 
+        /// <summary>
+        /// Add a bias distance to sampled depth in AO to reduce self-shadowing aliasing artifacts.
+        /// </summary>
+        [Range(0f, 0.001f), Tooltip("Add a bias distance to sampled depth in AO to reduce self-shadowing aliasing artifacts. ")]
+        public FloatParameter zBias = new FloatParameter { value = 0.0001f };
+
         // HDRP-only parameters
 
         /// <summary>

com.unity.postprocessing/PostProcessing/Runtime/Effects/MultiScaleVO.cs

@@ -388,7 +388,7 @@ void PushRenderCommands(CommandBuffer cmd, int source, int destination, Vector3
             cmd.SetComputeFloatParams(cs, "gInvThicknessTable", m_InvThicknessTable);
             cmd.SetComputeFloatParams(cs, "gSampleWeightTable", m_SampleWeightTable);
             cmd.SetComputeVectorParam(cs, "gInvSliceDimension", new Vector2(1f / sourceSize.x, 1f / sourceSize.y));
-            cmd.SetComputeVectorParam(cs, "AdditionalParams", new Vector2(-1f / m_Settings.thicknessModifier.value, m_Settings.intensity.value));
+            cmd.SetComputeVectorParam(cs, "AdditionalParams", new Vector3(-1f / m_Settings.thicknessModifier.value, m_Settings.intensity.value, m_Settings.zBias.value));
             cmd.SetComputeTextureParam(cs, kernel, "DepthTex", source);
             cmd.SetComputeTextureParam(cs, kernel, "Occlusion", destination);
 

com.unity.postprocessing/PostProcessing/Shaders/Builtins/MultiScaleVORender.compute

@@ -80,11 +80,12 @@ CBUFFER_START(CB1)
     float4 gInvThicknessTable[3];
     float4 gSampleWeightTable[3];
     float4 gInvSliceDimension;
-    float2 AdditionalParams;
+    float3 AdditionalParams;
 CBUFFER_END
 
 #define gRejectFadeoff AdditionalParams.x
 #define gIntensity AdditionalParams.y
+#define zBias AdditionalParams.z
 
 #ifdef MSAA
 float2 TestSamplePair(float frontDepth, float2 invRange, uint base, int offset)
@@ -249,10 +250,10 @@ void MAIN(uint3 Gid : SV_GroupID, uint GI : SV_GroupIndex, uint3 GTid : SV_Group
 #endif
 
 #ifdef MSAA
-    const float2 invThisDepth = float2(1.0 / DepthSamples[thisIdx].x, 1.0 / DepthSamples[thisIdx].y);
+    const float2 invThisDepth = float2(1.0 / (DepthSamples[thisIdx].x - zBias), 1.0 / (DepthSamples[thisIdx].y - zBias));
     float2 ao = 0.0;
 #else
-    const float invThisDepth = 1.0 / DepthSamples[thisIdx];
+    const float invThisDepth = 1.0 / (DepthSamples[thisIdx] - zBias);
     float ao = 0.0;
 #endif