Disable use of directly wrapping msaa RTs on Vulkan

Currently the Vulkan backend is set up to always treat the "resolve"
target as the main VkImage in a render target and the msaa is a side cart
image. This makes it difficult to just wrap an msaa image that we don't own.
However, unlike GL the equivalent FBO 0 will never be multisampled so there
isn't much use for the functionality. Once we find a need for it we can find
a way to refactor to make it work.

Bug: skia:
Change-Id: I121e9c72a70c2a6f1aaddba2dbae19d8bddc3998
Reviewed-on: https://skia-review.googlesource.com/13980
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/src/gpu/vk/GrVkGpu.cpp b/src/gpu/vk/GrVkGpu.cpp
index 12d98769cf..3d30e3585b 100644
--- a/src/gpu/vk/GrVkGpu.cpp
+++ b/src/gpu/vk/GrVkGpu.cpp
@@ -822,6 +822,13 @@ sk_sp<GrTexture> GrVkGpu::onWrapBackendTexture(const GrBackendTexture& backendTe
 }
 
 sk_sp<GrRenderTarget> GrVkGpu::onWrapBackendRenderTarget(const GrBackendRenderTargetDesc& wrapDesc){
+    // Currently the Vulkan backend does not support wrapping of msaa render targets directly. In
+    // general this is not an issue since swapchain images in vulkan are never multisampled. Thus if
+    // you want a multisampled RT it is best to wrap the swapchain images and then let Skia handle
+    // creating and owning the MSAA images.
+    if (wrapDesc.fSampleCnt) {
+        return nullptr;
+    }
 
     const GrVkImageInfo* info =
         reinterpret_cast<const GrVkImageInfo*>(wrapDesc.fRenderTargetHandle);
@@ -834,7 +841,7 @@ sk_sp<GrRenderTarget> GrVkGpu::onWrapBackendRenderTarget(const GrBackendRenderTa
     desc.fFlags = kCheckAllocation_GrSurfaceFlag | kRenderTarget_GrSurfaceFlag;
     desc.fWidth = wrapDesc.fWidth;
     desc.fHeight = wrapDesc.fHeight;
-    desc.fSampleCnt = SkTMin(wrapDesc.fSampleCnt, this->caps()->maxSampleCount());
+    desc.fSampleCnt = 0;
 
     desc.fOrigin = resolve_origin(wrapDesc.fOrigin);