[Quest][URP] Added multiview support for the XR Occlusion Mesh pass.

Jira: https://jira.unity3d.com/browse/GFXFOUND-481
- Added multview C# occlusion mesh draw call
- Added multiview handling to occlusion pass shader
- yflip handling through model matrix when rendering to intermediate texture/eye texture (need test)

Author: thomas-zeng

Packages/com.unity.render-pipelines.core/Runtime/XR/XROcclusionMesh.cs

@@ -39,25 +39,35 @@ internal bool hasValidOcclusionMesh
             }
         }
 
-        internal void RenderOcclusionMesh(CommandBuffer cmd, float occlusionMeshScale)
+        internal void RenderOcclusionMesh(CommandBuffer cmd, float occlusionMeshScale, bool yFlip = false)
         {
             if (IsOcclusionMeshSupported())
             {
                 using (new ProfilingScope(cmd, k_OcclusionMeshProfilingSampler))
                 {
                     if (m_Pass.singlePassEnabled)
                     {
-                        if (m_CombinedMesh != null && SystemInfo.supportsRenderTargetArrayIndexFromVertexShader)
+                        // Prefer multiview draw
+                        if (m_CombinedMesh != null && SystemInfo.supportsMultiview) 
+                        {
+                            // For the multiview code path, keep the multiview state on to propagate geometries to all eye texture slices
+                            cmd.EnableShaderKeyword("XR_OCCLUSION_MESH_COMBINED");
+                            Vector3 scale = new Vector3(occlusionMeshScale, yFlip? occlusionMeshScale : -occlusionMeshScale, 1.0f);
+                            cmd.DrawMesh(m_CombinedMesh, Matrix4x4.Scale(scale), m_Material);
+                            cmd.DisableShaderKeyword("XR_OCCLUSION_MESH_COMBINED");
+                        }
+                        else if (m_CombinedMesh != null && SystemInfo.supportsRenderTargetArrayIndexFromVertexShader)
                         {
                             m_Pass.StopSinglePass(cmd);
 
                             cmd.EnableShaderKeyword("XR_OCCLUSION_MESH_COMBINED");
-                            Vector3 scale = new Vector3(occlusionMeshScale, occlusionMeshScale, 1.0f);
+                            Vector3 scale = new Vector3(occlusionMeshScale, yFlip ? occlusionMeshScale : -occlusionMeshScale, 1.0f);
                             cmd.DrawMesh(m_CombinedMesh, Matrix4x4.Scale(scale), m_Material);
                             cmd.DisableShaderKeyword("XR_OCCLUSION_MESH_COMBINED");
 
                             m_Pass.StartSinglePass(cmd);
                         }
+
                     }
                     else
                     {

Packages/com.unity.render-pipelines.core/Runtime/XR/XRPass.cs

@@ -326,10 +326,11 @@ public void StopSinglePass(BaseCommandBuffer cmd)
         /// "XR_OCCLUSION_MESH_COMBINED" is also enabled when rendering the combined mesh.
         /// </summary>
         /// <param name="cmd">CommandBuffer to modify</param>
-        public void RenderOcclusionMesh(CommandBuffer cmd)
+        /// <param name="renderIntoTexture">Set to true when rendering into a render texture. Used for handling Unity yflip.</param>
+        public void RenderOcclusionMesh(CommandBuffer cmd, bool renderIntoTexture = false)
         {
             if(occlusionMeshScale > 0)
-                m_OcclusionMesh.RenderOcclusionMesh(cmd, occlusionMeshScale);
+                m_OcclusionMesh.RenderOcclusionMesh(cmd, occlusionMeshScale, renderIntoTexture);
         }
 
         /// <summary>
@@ -339,10 +340,11 @@ public void RenderOcclusionMesh(CommandBuffer cmd)
         /// "XR_OCCLUSION_MESH_COMBINED" is also enabled when rendering the combined mesh.
         /// </summary>
         /// <param name="cmd">RasterCommandBuffer to modify</param>
-        public void RenderOcclusionMesh(RasterCommandBuffer cmd)
+        /// <param name="renderIntoTexture">Set to true when rendering into a render texture. Used for handling Unity yflip.</param>
+        public void RenderOcclusionMesh(RasterCommandBuffer cmd, bool renderIntoTexture = false)
         {
             if (occlusionMeshScale > 0)
-                m_OcclusionMesh.RenderOcclusionMesh(cmd.m_WrappedCommandBuffer, occlusionMeshScale);
+                m_OcclusionMesh.RenderOcclusionMesh(cmd.m_WrappedCommandBuffer, occlusionMeshScale, renderIntoTexture);
         }
 
         /// <summary>

Packages/com.unity.render-pipelines.universal/Runtime/Passes/XROcclusionMeshPass.cs

@@ -33,7 +33,7 @@ private static void ExecutePass(RasterCommandBuffer cmd, PassData data)
                 if (data.isActiveTargetBackBuffer)
                     cmd.SetViewport(data.xr.GetViewport());
 
-                data.xr.RenderOcclusionMesh(cmd);
+                data.xr.RenderOcclusionMesh(cmd, renderIntoTexture: !data.isActiveTargetBackBuffer);
             }
         }
 

Packages/com.unity.render-pipelines.universal/Shaders/XR/XROcclusionMesh.shader

@@ -7,7 +7,11 @@ Shader "Hidden/Universal Render Pipeline/XR/XROcclusionMesh"
 
         // Not all platforms properly support SV_RenderTargetArrayIndex
         #if defined(SHADER_API_D3D11) || defined(SHADER_API_VULKAN) || defined(SHADER_API_GLCORE) || defined(SHADER_API_GLES3) || defined(SHADER_API_PSSL)
-            #define USE_XR_OCCLUSION_MESH_COMBINED XR_OCCLUSION_MESH_COMBINED
+            #if defined (UNITY_STEREO_MULTIVIEW_ENABLED)
+                #define USE_XR_OCCLUSION_MESH_COMBINED_MULTIVIEW XR_OCCLUSION_MESH_COMBINED
+            #else
+                #define USE_XR_OCCLUSION_MESH_COMBINED_RT_ARRAY_INDEX XR_OCCLUSION_MESH_COMBINED
+            #endif
         #endif
 
         struct Attributes
@@ -19,7 +23,7 @@ Shader "Hidden/Universal Render Pipeline/XR/XROcclusionMesh"
         {
             float4 vertex : SV_POSITION;
 
-        #if USE_XR_OCCLUSION_MESH_COMBINED
+        #if USE_XR_OCCLUSION_MESH_COMBINED_RT_ARRAY_INDEX
             uint rtArrayIndex : SV_RenderTargetArrayIndex;
         #endif
         };
@@ -29,7 +33,12 @@ Shader "Hidden/Universal Render Pipeline/XR/XROcclusionMesh"
             Varyings output;
             output.vertex = mul(UNITY_MATRIX_M, float4(input.vertex.xy * float2(2.0f, -2.0f) + float2(-1.0f, 1.0f), UNITY_NEAR_CLIP_VALUE, 1.0f));
 
-        #if USE_XR_OCCLUSION_MESH_COMBINED
+        #if USE_XR_OCCLUSION_MESH_COMBINED_MULTIVIEW
+            if (unity_StereoEyeIndex != uint(input.vertex.z))
+            {
+                output.vertex = float4(0.0f, 0.0f, 0.0f, 0.0f);
+            }
+        #elif USE_XR_OCCLUSION_MESH_COMBINED_RT_ARRAY_INDEX
             output.rtArrayIndex = input.vertex.z;
         #endif