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..23abad8be077fefb7330c88a280e9b941bf458f6 100644
--- a/include/gpu/GrTypes.h
+++ b/include/gpu/GrTypes.h
@@ -409,6 +409,37 @@ enum GrSurfaceFlags {
 
 GR_MAKE_BITFIELD_OPS(GrSurfaceFlags)
 
+// opaque type for 3D API object handles
+typedef intptr_t GrBackendObject;
+
+/**
+ * An abstract base class which consumers of Skia can subclass and pass to Skia
+ * to use custom storage allocation in place of TexImage2D.

[bsalomon, 2016/01/26 22:20:54]

Maybe say "in place of backend API texture creation function" as there will soon
be a non-GL backend.

[erikchen, 2016/01/27 21:55:14]

Done.

+ */
+class TextureStorageAllocator {

[bsalomon, 2016/01/26 22:20:54]

Should be GrTextureStorageAllocator

[erikchen, 2016/01/27 21:55:15]

Done.

+ public:
+  /*

[bsalomon, 2016/01/26 22:20:54]

nit, we use four space indents.

[erikchen, 2016/01/27 21:55:14]

Done.

+   * The required bind target for any texture with custom storage.
+   */
+  virtual unsigned textureStorageTarget() = 0;
+  /*
+   * 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
+   * WRAP_S and WRAP_T must be GL_CLAMP_TO_EDGE.
+   */
+  virtual bool allocateTextureStorage(GrBackendObject texture, unsigned width, 

[bsalomon, 2016/01/26 22:20:54]

Don't we also need to somehow tell the allocator the pixel format that we want
to use?

Also, wondering what we should do when the client is creating a compressed
texture. Should we ignore the allocator param, respect it, or fail? Or give the
allocator the option (ternary return value - success, fail, fallback to normal
allocation).

[erikchen, 2016/01/27 21:55:14]

CHROMIUM_image on Mac supports very few pixel formats, and does not support
compressed textures. I added a new method supportsPixelConfig(GrPixelConfig
config) that Skia can call to determine whether a given pixel format is
supported.

+                                      unsigned height) = 0;
+  /*
+   * Deallocate the storage for the given texture.
+   */
+  virtual void deallocateTextureStorage(GrBackendObject texture) = 0;

[bsalomon, 2016/01/26 22:20:54]

We have a method on GrContext called abandonContext(), it's called when the 3D
context behind the GrContext is no longer available (e.g. lost context on
chrome). When that happens we don't call glDeleteTextures() (or equivalent for
other resource types).

What's our contract in that case? Do we call the deallocate function? Should we
let it know that the context was lost?

[erikchen, 2016/01/27 21:55:15]

The consumer of Skia will be responsible for destroying all extant textures.
I've updated the documentation.

+
+ protected:
+  ~TextureStorageAllocator() {}

[bsalomon, 2016/01/26 22:20:54]

Who deletes the allocator, Skia? Should this be virtual?

[erikchen, 2016/01/27 21:55:14]

Skia does not delete the allocator, but this should still be virtual.

+};
+
 /**
  * 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
@@ -432,7 +463,8 @@ struct GrSurfaceDesc {
     , fWidth(0)
     , fHeight(0)
     , fConfig(kUnknown_GrPixelConfig)
-    , fSampleCnt(0) {
+    , fSampleCnt(0)
+    , fTextureStorageAllocator(nullptr) {
     }
 
     GrSurfaceFlags         fFlags;  //!< bitfield of TextureFlags
@@ -454,6 +486,13 @@ 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
@@ -469,9 +508,6 @@ enum GrClipType {
 
 ///////////////////////////////////////////////////////////////////////////////
 
-// opaque type for 3D API object handles
-typedef intptr_t GrBackendObject;
-
 
 /** Ownership rules for external GPU resources imported into Skia. */
 enum GrWrapOwnership {