enable fallback path

gpu/command_buffer/service/gles2_cmd_copy_texture_chromium.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef GPU_COMMAND_BUFFER_SERVICE_GLES2_CMD_COPY_TEXTURE_CHROMIUM_H_
 #define GPU_COMMAND_BUFFER_SERVICE_GLES2_CMD_COPY_TEXTURE_CHROMIUM_H_
 
 #include <vector>
 
 #include "base/containers/hash_tables.h"
 #include "base/macros.h"
 #include "gpu/command_buffer/service/feature_info.h"
 #include "gpu/command_buffer/service/gl_utils.h"
 #include "gpu/gpu_export.h"
 
 namespace gpu {
 namespace gles2 {
 
 class GLES2Decoder;
 
 enum CopyTextureMethod {
   // Use CopyTex{Sub}Image2D to copy from the source to the destination.
   DIRECT_COPY,
   // Draw from the source to the destination texture.
   DIRECT_DRAW,
   // Draw to an intermediate texture, and then copy to the destination texture.
   DRAW_AND_COPY,
+  // Draw to an intermediate texture in RGBA format, read back pixels in the
+  // intermediate texture from GPU to CPU, and then upload to the destination
+  // texture.
+  DRAW_AND_READBACK,
   // CopyTexture isn't available.
   NOT_COPYABLE
 };
 
 // TODOs(qiankun.miao@intel.com):
 // 1. Add readback path for RGB9_E5 and float formats (if extension isn't
 // available and they are not color-renderable).
-// 2. Support faces of cube map texture as valid dest target. The cube map
-// texture may be incomplete currently.
-// 3. Add support for levels other than 0.
-// 4. Support ALPHA, LUMINANCE and LUMINANCE_ALPHA formats on core profile.
-// 5. Update the extension doc after the whole work is done
-// in gpu/GLES2/extensions/CHROMIUM/CHROMIUM_copy_texture.txt. We probably
-// will need a ES2 version and a ES3 version.
+// 2. Support GL_TEXTURE_3D as valid dest_target.
+// 3. Support ALPHA, LUMINANCE and LUMINANCE_ALPHA formats on core profile.
 
 // This class encapsulates the resources required to implement the
 // GL_CHROMIUM_copy_texture extension.  The copy operation is performed
 // via glCopyTexImage2D() or a blit to a framebuffer object.
 // The target of |dest_id| texture must be GL_TEXTURE_2D.
 class GPU_EXPORT CopyTextureCHROMIUMResourceManager {
  public:
   CopyTextureCHROMIUMResourceManager();
   ~CopyTextureCHROMIUMResourceManager();
 
@@ skipping 151 matching lines @@
   GLuint buffer_id_;
   GLuint framebuffer_;
 
   DISALLOW_COPY_AND_ASSIGN(CopyTextureCHROMIUMResourceManager);
 };
 
 }  // namespace gles2
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_SERVICE_GLES2_CMD_COPY_TEXTURE_CHROMIUM_H_