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..ed017c019316eaff059c3f8f636ba0cf1dc04807 100644
--- a/include/gpu/GrTypes.h
+++ b/include/gpu/GrTypes.h
@@ -409,6 +409,61 @@ enum GrSurfaceFlags {
 
 GR_MAKE_BITFIELD_OPS(GrSurfaceFlags)
 
+// opaque type for 3D API object handles
+typedef intptr_t GrBackendObject;
+
+/**
+ * An container of function pointers which consumers of Skia can fill in and
+ * pass to Skia. Skia will use these function pointers in place of its backend
+ * API texture creation function. Either all of the function pointers should be
+ * filled in, or they should all be nullptr.
+ */
+struct GrTextureStorageAllocator {
+    GrTextureStorageAllocator()
+    : fAllocateTextureStorage(nullptr)
+    , fDeallocateTextureStorage(nullptr) {
+    }
+
+    enum class Result {
+        kSucceededAndUploaded,
+        kSucceededWithoutUpload,
+        kFailed
+    };
+    typedef Result (*AllocateTextureStorageProc)(
+            void* ctx, GrBackendObject texture, unsigned width,
+            unsigned height, GrPixelConfig config, const void* srcData);
+    typedef void (*DeallocateTextureStorageProc)(void* ctx, GrBackendObject texture);
+
+    /*
+     * Generates and binds a texture to |textureStorageTarget()|. Allocates
+     * storage for the texture.
+     *
+     * The MIN and MAX filters for the created texture must be GL_LINEAR. The

[bsalomon, 2016/02/01 14:54:42]

In OpenGL, ...

[erikchen, 2016/02/01 22:58:32]

Done.

+     * WRAP_S and WRAP_T must be GL_CLAMP_TO_EDGE.
+     *
+     * If |srcData| is not nullptr, then the implementation of this function

[bsalomon, 2016/02/01 14:54:42]

I think we need an origin param as well. Also, maybe make the docs say that the
impl *may* attempt to upload. I think it's only worth implementing that if there
is a faster upload path.

[erikchen, 2016/02/01 22:58:32]

Done and done.

+     * should attempt to upload the data into the texture. On successful upload,
+     * or if |srcData| is nullptr, returns kSucceededAndUploaded.
+     */
+    AllocateTextureStorageProc fAllocateTextureStorage;
+
+    /*
+     * Deallocate the storage for the given texture.
+     *
+     * Skia does not always destroy its outstanding textures. See
+     * GrContext::abandonContext() for more details. The consumer of Skia is
+     * responsible for making sure that all textures are destroyed, even if this
+     * callback is not invoked.
+     */
+    DeallocateTextureStorageProc fDeallocateTextureStorage;
+
+    /*
+     * The context to use when invoking fAllocateTextureStorage and
+     * fDeallocateTextureStorage.
+     */
+    void* fCtx;
+};
+
 /**
  * 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
@@ -454,6 +509,13 @@ struct GrSurfaceDesc {
      * max supported count.
      */
     int                    fSampleCnt;
+
+    /**
+     * A custom platform-specific allocator to use in place of TexImage2D. All

[bsalomon, 2016/02/01 14:54:42]

...in place of the backend APIs usual texture creation method (e.g. TexImage2D
in OpenGL).

[erikchen, 2016/02/01 22:58:32]

Done.

+     * surfaces derived from the original surface will have the same value for

[bsalomon, 2016/02/01 14:54:42]

What exactly is meant here by surfaces derived from the original surface?

[erikchen, 2016/02/01 22:58:32]

I was referring to RenderTargets created by copy-on-write. I guess that's
probably implied, and I just removed that entire portion of the comment, because
apparently it was too confusing.

+     * fTextureStorageAllocator.
+     */
+    GrTextureStorageAllocator fTextureStorageAllocator;
 };
 
 // Legacy alias
@@ -469,9 +531,6 @@ enum GrClipType {
 
 ///////////////////////////////////////////////////////////////////////////////
 
-// opaque type for 3D API object handles
-typedef intptr_t GrBackendObject;
-
 
 /** Ownership rules for external GPU resources imported into Skia. */
 enum GrWrapOwnership {