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>

src/gpu/vk/GrVkGpu.cpp

diff --git a/src/gpu/vk/GrVkGpu.cpp b/src/gpu/vk/GrVkGpu.cpp
index 12d9876..3d30e35 100644
--- a/src/gpu/vk/GrVkGpu.cpp
+++ b/src/gpu/vk/GrVkGpu.cpp
@@ -822,6 +822,13 @@
 }
 
 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 @@
     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);
 

tools/viewer/sk_app/VulkanWindowContext.cpp

diff --git a/tools/viewer/sk_app/VulkanWindowContext.cpp b/tools/viewer/sk_app/VulkanWindowContext.cpp
index 0749978..831c7ae 100644
--- a/tools/viewer/sk_app/VulkanWindowContext.cpp
+++ b/tools/viewer/sk_app/VulkanWindowContext.cpp
@@ -6,6 +6,7 @@
  * found in the LICENSE file.
  */
 
+#include "GrBackendSurface.h"
 #include "GrContext.h"
 #include "GrRenderTarget.h"
 #include "SkAutoMalloc.h"
@@ -264,7 +265,6 @@
     for (uint32_t i = 0; i < fImageCount; ++i) {
         fImageLayouts[i] = VK_IMAGE_LAYOUT_UNDEFINED;
 
-        GrBackendRenderTargetDesc desc;
         GrVkImageInfo info;
         info.fImage = fImages[i];
         info.fAlloc = { VK_NULL_HANDLE, 0, 0, 0 };
@@ -272,17 +272,14 @@
         info.fImageTiling = VK_IMAGE_TILING_OPTIMAL;
         info.fFormat = format;
         info.fLevelCount = 1;
-        desc.fWidth = fWidth;
-        desc.fHeight = fHeight;
-        desc.fConfig = fPixelConfig;
-        desc.fOrigin = kTopLeft_GrSurfaceOrigin;
-        desc.fSampleCnt = fSampleCount;
-        desc.fStencilBits = fStencilBits;
-        desc.fRenderTargetHandle = (GrBackendObject) &info;
 
-        fSurfaces[i] = SkSurface::MakeFromBackendRenderTarget(fContext, desc,
-                                                              fDisplayParams.fColorSpace,
-                                                              &fSurfaceProps);
+        GrBackendTexture backendTex(fWidth, fHeight, &info);
+
+        fSurfaces[i] = SkSurface::MakeFromBackendTextureAsRenderTarget(fContext, backendTex,
+                                                                       kTopLeft_GrSurfaceOrigin,
+                                                                       fSampleCount,
+                                                                       fDisplayParams.fColorSpace,
+                                                                       &fSurfaceProps);
     }
 
     // create the command pool for the command buffers