skia: Add support for CHROMIUM_image backed textures.

include/gpu/GrTypes.h

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrTypes_DEFINED
 #define GrTypes_DEFINED
 
@@ skipping 392 matching lines @@
     /**
      * Indicates that all allocations (color buffer, FBO completeness, etc)
      * should be verified.
      */
     kCheckAllocation_GrSurfaceFlag  = 0x4,
 };
 
 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
  * to BottomLeft.
  */
 
 enum GrSurfaceOrigin {
     kDefault_GrSurfaceOrigin,         // DEPRECATED; to be removed
     kTopLeft_GrSurfaceOrigin,
     kBottomLeft_GrSurfaceOrigin,
 };
 
 /**
  * Describes a surface to be created.
  */
 struct GrSurfaceDesc {
     GrSurfaceDesc()
     : fFlags(kNone_GrSurfaceFlags)
     , fOrigin(kDefault_GrSurfaceOrigin)
     , fWidth(0)
     , fHeight(0)
     , fConfig(kUnknown_GrPixelConfig)
-    , fSampleCnt(0) {
+    , fSampleCnt(0)
+    , fTextureStorageAllocator(nullptr) {
     }
 
     GrSurfaceFlags         fFlags;  //!< bitfield of TextureFlags
     GrSurfaceOrigin        fOrigin; //!< origin of the texture
     int                    fWidth;  //!< Width of the texture
     int                    fHeight; //!< Height of the texture
 
     /**
      * Format of source data of the texture. Not guaranteed to be the same as
      * internal format used by 3D API.
      */
     GrPixelConfig          fConfig;
 
     /**
      * The number of samples per pixel or 0 to disable full scene AA. This only
      * applies if the kRenderTarget_GrSurfaceFlag is set. The actual number
      * of samples may not exactly match the request. The request will be rounded
      * up to the next supported sample count, or down if it is larger than the
      * 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
 typedef GrSurfaceDesc GrTextureDesc;
 
 /**
  * Clips are composed from these objects.
  */
 enum GrClipType {
     kRect_ClipType,
@@ skipping 59 matching lines @@
     /**
      * If the render target flag is set and sample count is greater than 0
      * then Gr will create an MSAA buffer that resolves to the texture.
      */
     int                             fSampleCnt;
     /**
      * Handle to the 3D API object.
      * 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. 

 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
 /**
  * Gr can wrap an existing render target created by the client in the 3D API
  * with a GrRenderTarget object. The client is responsible for ensuring that the
  * underlying 3D API object lives at least as long as the GrRenderTarget object
  * wrapping it. We require the client to explicitly provide information about
  * the target, such as width, height, and pixel config rather than querying the
@@ skipping 72 matching lines @@
             return 4 * width * height;
     }
 }
 
 /**
  * This value translates to reseting all the context state for any backend.
  */
 static const uint32_t kAll_GrBackendState = 0xffffffff;
 
 #endif