Query the preferred readback config in CopyFromBackingStore

content/browser/media/capture/web_contents_video_capture_device.cc

 // 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.
 //
 // Implementation notes: This needs to work on a variety of hardware
 // configurations where the speed of the CPU and GPU greatly affect overall
 // performance. Spanning several threads, the process of capturing has been
 // split up into four conceptual stages:
 //
 //   1. Reserve Buffer: Before a frame can be captured, a slot in the client's
@@ skipping 648 matching lines @@
                    start_time, target, deliver_frame_cb));
   } else if (view->CanCopyToVideoFrame()) {
     view->CopyFromCompositingSurfaceToVideoFrame(
         gfx::Rect(view_size),
         target,
         base::Bind(&WebContentsCaptureMachine::
                         DidCopyFromCompositingSurfaceToVideoFrame,
                    weak_ptr_factory_.GetWeakPtr(),
                    start_time, deliver_frame_cb));
   } else {
+    SkBitmap::Config preffered_format = rwh->PreferredReadbackFormat();

[piman, 2014/03/10 18:27:20]

typo: preferred_format

[sivag, 2014/03/11 14:41:50]

Done.

     rwh->CopyFromBackingStore(
         gfx::Rect(),
         fitted_size,  // Size here is a request not always honored.
         base::Bind(&WebContentsCaptureMachine::DidCopyFromBackingStore,
                    weak_ptr_factory_.GetWeakPtr(),
-                   start_time, target, deliver_frame_cb));
+                   start_time,
+                   target,
+                   deliver_frame_cb),
+        preffered_format);

[piman, 2014/03/10 18:27:20]

The receiving code only accepts RGBA8888, see RenderVideoFrame. So we can't
blindly use the preferred format, we should force it to 8888.

[sivag, 2014/03/11 14:41:50]

Done.

   }
 }
 
 bool WebContentsCaptureMachine::StartObservingWebContents() {
   // Look-up the RenderViewHost and, from that, the WebContents that wraps it.
   // If successful, begin observing the WebContents instance.
   //
   // Why this can be unsuccessful: The request for mirroring originates in a
   // render process, and this request is based on the current RenderView
   // associated with a tab.  However, by the time we get up-and-running here,
@@ skipping 133 matching lines @@
     scoped_ptr<Client> client) {
   DVLOG(1) << "Allocating " << params.requested_format.frame_size.ToString();
   core_->AllocateAndStart(params, client.Pass());
 }
 
 void WebContentsVideoCaptureDevice::StopAndDeAllocate() {
   core_->StopAndDeAllocate();
 }
 
 }  // namespace content