skia: Add support for CHROMIUM_image backed textures.

include/gpu/GrTypes.h

Index: include/gpu/GrTypes.h
diff --git a/include/gpu/GrTypes.h b/include/gpu/GrTypes.h
index dbcb9a6583321d715a437a9982c7da7b5521066e..ffc5bf1e37a01a50bb8befbcd4a823c8251c7d72 100644
--- a/include/gpu/GrTypes.h
+++ b/include/gpu/GrTypes.h
@@ -410,6 +410,30 @@ enum GrSurfaceFlags {
 GR_MAKE_BITFIELD_OPS(GrSurfaceFlags)
 
 /**
+ * An abstract base class which consumers of Skia can subclass and pass to Skia
+ * to use custom storage allocation in place of TexImage2D.
+ */
+class TextureStorageAllocator {
+ public:
+  /*
+   * The required bind target for any texture with custom storage.
+   */
+  virtual unsigned textureStorageTarget() = 0;
+  /*
+   * Allocates storage for the texture. |textureId| must already be bound to
+   * |TextureTarget()|.
+   */
+  virtual bool allocateTextureStorage(unsigned textureId, unsigned width, unsigned height) = 0;

[bsalomon, 2016/01/25 20:51:09]

What do you think about

virtual bool allocateTextureStorage(GrBackendObject* allocatedTexture, int
width, int height)

?

The allocator then just tells Skia the texture ID and texture target rather than
having Skia create the ID. It could work with alternative backends that don't
use ints a texture IDs (e.g. Vulkan).

Also I can imagine that the allocator might want more context than the ID when
deallocate is called (e.g. pointer to GpuMemoryBuffer, ...). Wondering if
GrGLTextureInfo should have a void* fAllocatorContext?

[erikchen, 2016/01/26 18:36:16]

I went with your suggested API for allocateTextureStorage(). For deallocate, I
kept the current API. On a local branch, when I integrated this patch, the
allocator kept a hash map of texture ids : custom allocations. this way, the
allocator can also ASSERT that before it is destroyed, each of the custom
allocations has been destroyed. 

+  /*
+   * Deallocate the storage for the given texture.
+   */
+  virtual void deallocateTextureStorage(unsigned textureId) = 0;
+
+ protected:
+  ~TextureStorageAllocator() {}
+};
+
+/**
  * Some textures will be stored such that the upper and left edges of the content meet at the
  * the origin (in texture coord space) and for other textures the lower and left edges meet at
  * the origin. kDefault_GrSurfaceOrigin sets textures to TopLeft, and render targets
@@ -432,7 +456,8 @@ struct GrSurfaceDesc {
     , fWidth(0)
     , fHeight(0)
     , fConfig(kUnknown_GrPixelConfig)
-    , fSampleCnt(0) {
+    , fSampleCnt(0)
+    , fTextureStorageAllocator(nullptr) {
     }
 
     GrSurfaceFlags         fFlags;  //!< bitfield of TextureFlags
@@ -454,6 +479,13 @@ struct GrSurfaceDesc {
      * max supported count.
      */
     int                    fSampleCnt;
+
+    /**
+     * A custom platform-specific allocator to use in place of TexImage2D. All
+     * surfaces derived from the original surface will have the same value for
+     * fTextureStorageAllocator.
+     */
+    TextureStorageAllocator*      fTextureStorageAllocator; 
 };
 
 // Legacy alias
@@ -533,6 +565,10 @@ struct GrBackendTextureDesc {
      * OpenGL: Texture ID.
      */
     GrBackendObject                 fTextureHandle;
+    /**
+     * The custom allocator to use in place of TexImage2D.
+     */
+    TextureStorageAllocator*      fTextureStorageAllocator; 

[bsalomon, 2016/01/25 20:51:09]

We shouldn't need this here. This is used to import an already existing texture
into Skia.

[erikchen, 2016/01/26 18:36:16]

Done. 

 };
 
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