[URP] make the Vulkan RenderTexture MSAA support fallback work in the same way as the swapchain backend implementation (#6180)

* made the Vulkan MSAA support fallback behaviour behave in the same way as the swapchain's backend code

* added comments to the Vulkan MSAA fallback code

* Added changelog entry

Co-authored-by: Felipe Lira <[email protected]>

Author: manuele-bonanno

com.unity.render-pipelines.universal/CHANGELOG.md

@@ -35,6 +35,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fix for rendering thumbnails. [case 1348209](https://issuetracker.unity3d.com/issues/preview-of-assets-do-not-show-in-the-project-window)
 - Fixed a regression bug where XR camera postion can not be modified in beginCameraRendering [case 1365000]
 - Fixed an issue in where installing the Adaptive Performance package caused errors to the inspector UI [1368161](https://issuetracker.unity3d.com/issues/urp-package-throws-compilation-error-cs1525-when-imported-together-with-adaptive-performance-package)
+- Fixed an issue with MSAA falling back to the incorrect value when sample count 2 is not supported on some Android GPUs
 - Fixed decals to work with native render pass [case 1353141](https://issuetracker.unity3d.com/issues/urp-decals-are-not-visible-in-game-view-after-modifying-urp-asset-properties)
 - Fixed decals to work with render scale [1353885](https://issuetracker.unity3d.com/issues/urp-builtin-to-urp-render-pipeline-converter-freezes-the-editor-when-converting-rendering-settings)
 - Fixed a regression where filtering the scene view yielded incorrect visual results [1360233](https://issuetracker.unity3d.com/product/unity/issues/guid/1360233)

com.unity.render-pipelines.universal/Runtime/UniversalRenderPipelineCore.cs

@@ -572,6 +572,19 @@ static RenderTextureDescriptor CreateRenderTextureDescriptor(Camera camera, floa
             desc.bindMS = false;
             desc.useDynamicScale = camera.allowDynamicResolution;
 
+            // The way RenderTextures handle MSAA fallback when an unsupported sample count of 2 is requested (falling back to numSamples = 1), differs fom the way
+            // the fallback is handled when setting up the Vulkan swapchain (rounding up numSamples to 4, if supported). This caused an issue on Mali GPUs which don't support
+            // 2x MSAA.
+            // The following code makes sure that on Vulkan the MSAA unsupported fallback behaviour is consistent between RenderTextures and Swapchain.
+            // TODO: we should review how all backends handle MSAA fallbacks and move these implementation details in engine code.
+            if (SystemInfo.graphicsDeviceType == GraphicsDeviceType.Vulkan)
+            {
+                // if the requested number of samples is 2, and the supported value is 1x, it means that 2x is unsupported on this GPU.
+                // Then we bump up the requested value to 4.
+                if (desc.msaaSamples == 2 && SystemInfo.GetRenderTextureSupportedMSAASampleCount(desc) == 1)
+                    desc.msaaSamples = 4;
+            }
+
             // check that the requested MSAA samples count is supported by the current platform. If it's not supported,
             // replace the requested desc.msaaSamples value with the actual value the engine falls back to
             desc.msaaSamples = SystemInfo.GetRenderTextureSupportedMSAASampleCount(desc);

com.unity.render-pipelines.universal/Runtime/UniversalRenderer.cs

@@ -1127,7 +1127,7 @@ bool CanCopyDepth(ref CameraData cameraData)
 
             // copying depth on GLES3 is giving invalid results. Needs investigation (Fogbugz issue 1339401)
             if (SystemInfo.graphicsDeviceType == GraphicsDeviceType.OpenGLES3)
-                msaaDepthResolve = false;
+                return false;
 
             return supportsDepthCopy || msaaDepthResolve;
         }