Add wrapBackendTextureAsRenderTarget API

include/gpu/GrTextureProvider.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrTextureProvider_DEFINED
 #define GrTextureProvider_DEFINED
 
@@ skipping 80 matching lines @@
     GrTexture* wrapBackendTexture(const GrBackendTextureDesc& desc,
                                   GrWrapOwnership = kBorrow_GrWrapOwnership);
 
     /**
      * Wraps an existing render target with a GrRenderTarget object. It is
      * similar to wrapBackendTexture but can be used to draw into surfaces
      * that are not also textures (e.g. FBO 0 in OpenGL, or an MSAA buffer that
      * the client will resolve to a texture). Currently wrapped render targets
      * always use the kBorrow_GrWrapOwnership semantics.
      *
-     * @return GrTexture object or NULL on failure.
+     * @return GrRenderTarget object or NULL on failure.
      */
      GrRenderTarget* wrapBackendRenderTarget(const GrBackendRenderTargetDesc& desc);
 
+     /**
+      * Wraps an existing texture with a GrRenderTarget object. This is useful when the provided
+      * texture has a format that cannot be textured from by Skia, but we want to raster to it.
+      *
+      * @return GrRenderTarget object or NULL on failure.
+      */
+     GrRenderTarget* wrapBackendTextureAsRenderTarget(const GrBackendTextureDesc& desc,

[bsalomon, 2016/02/22 16:41:01]

Can we put this in GrResourceProvider (it's a derived private class of
TexturProvider)? I'd eventually like to hide wrapBackendRT and
wrapBackendTexture there as well and only expose these imports of foreign
textures through SkSurface and SkImage.

[ericrk, 2016/02/22 21:02:59]

I was planning on calling this directly from Chrome. I'm happy to use an
SkSurface/SkImage wrapper, but I think we currently need to get a GrSurface (not
an SkSurface) so we can call prepareForExternalIO on it... happy to re-work this
though. WDYT?

[bsalomon, 2016/02/23 02:25:27]

Gotcha, what if we added a prepareForExternalIO (or similar) to SkSurface?

[ericrk, 2016/02/24 00:39:53]

Added this function.

+                                                      GrWrapOwnership = kBorrow_GrWrapOwnership);
+
 protected:
     GrTextureProvider(GrGpu* gpu, GrResourceCache* cache, GrSingleOwner* singleOwner);
 
     /**
      * Assigns a unique key to a resource. If the key is associated with another resource that
      * association is removed and replaced by this resource.
      */
     void assignUniqueKeyToResource(const GrUniqueKey&, GrGpuResource*);
 
     /**
@@ skipping 39 matching lines @@
 
 private:
     GrResourceCache* fCache;
     GrGpu* fGpu;
 
     // In debug builds we guard against improper thread handling
     SkDEBUGCODE(mutable GrSingleOwner* fSingleOwner;)
 };
 
 #endif