Force allocate texture if no fallback is available (#5130)

Co-authored-by: sebastienlagarde <sebastien@unity3d.com>

com.unity.render-pipelines.core/Runtime/RenderGraph/RenderGraphBuilder.cs

@@ -55,19 +55,22 @@ public TextureHandle ReadTexture(in TextureHandle input)
 
             if (!m_Resources.IsRenderGraphResourceImported(input.handle) && m_Resources.TextureNeedsFallback(input))
             {
-                var texDimension = m_Resources.GetTextureResourceDesc(input.handle).dimension;
-                if (texDimension == TextureXR.dimension)
+                // If texture is read from but never written to, return a fallback black texture to have valid reads
+                // Return one from the preallocated default textures if possible
+                var desc = m_Resources.GetTextureResourceDesc(input.handle);
+                if (!desc.bindTextureMS)
                 {
-                    return m_RenderGraph.defaultResources.blackTextureXR;
-                }
-                else if (texDimension == TextureDimension.Tex3D)
-                {
-                    return m_RenderGraph.defaultResources.blackTexture3DXR;
-                }
-                else
-                {
-                    return m_RenderGraph.defaultResources.blackTexture;
+                    if (desc.dimension == TextureXR.dimension)
+                        return m_RenderGraph.defaultResources.blackTextureXR;
+                    else if (desc.dimension == TextureDimension.Tex3D)
+                        return m_RenderGraph.defaultResources.blackTexture3DXR;
+                    else
+                        return m_RenderGraph.defaultResources.blackTexture;
                 }
+                // If not, force a write to the texture so that it gets allocated, and ensure it gets initialized with a clear color
+                if (!desc.clearBuffer)
+                    m_Resources.ForceTextureClear(input.handle, Color.black);
+                WriteTexture(input);
             }
 
             m_RenderPass.AddResourceRead(input.handle);

com.unity.render-pipelines.core/Runtime/RenderGraph/RenderGraphResourceRegistry.cs

@@ -345,6 +345,12 @@ internal TextureDesc GetTextureResourceDesc(in ResourceHandle handle)
             return (m_RenderGraphResources[(int)RenderGraphResourceType.Texture].resourceArray[handle] as TextureResource).desc;
         }
 
+        internal void ForceTextureClear(in ResourceHandle handle, Color clearColor)
+        {
+            GetTextureResource(handle).desc.clearBuffer = true;
+            GetTextureResource(handle).desc.clearColor = clearColor;
+        }
+
         internal RendererListHandle CreateRendererList(in CoreRendererListDesc desc)
         {
             ValidateRendererListDesc(desc);

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

@@ -383,6 +383,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed issue with fading in SSR applying fade factor twice, resulting in darkening of the image in the transition areas.
 - Fixed path traced subsurface scattering for transmissive surfaces (case 1329403)
 - Fixed missing context menu for “Post Anti-Aliasing” in Camera (1357283)
+- Fixed error when disabling opaque objects on a camera with MSAA.
 
 ### Changed
 - Changed Window/Render Pipeline/HD Render Pipeline Wizard to Window/Rendering/HDRP Wizard