Implement CompositorCC::ReadPixels

ui/gfx/compositor/compositor.h

 // Copyright (c) 2011 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 UI_GFX_COMPOSITOR_COMPOSITOR_H_
 #define UI_GFX_COMPOSITOR_COMPOSITOR_H_
 #pragma once
 
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
@@ skipping 111 matching lines @@
   const Layer* root_layer() const { return root_layer_; }
   Layer* root_layer() { return root_layer_; }
   void SetRootLayer(Layer* root_layer);
 
   // Draws the scene created by the layer tree and any visual effects. If
   // |force_clear| is true, this will cause the compositor to clear before
   // compositing.
   void Draw(bool force_clear);
 
   // Reads the contents of the last rendered frame into the given bitmap.
-  virtual void ReadPixels(SkBitmap* bitmap) = 0;
+  // Returns false if the pixels could not be read.
+  virtual bool ReadPixels(SkBitmap* bitmap) = 0;
 
   // Notifies the compositor that the size of the widget that it is
   // drawing to has changed.
   void WidgetSizeChanged(const gfx::Size& size) {
     if (size.IsEmpty())
       return;
     size_ = size;
     OnWidgetSizeChanged();
   }
 
@@ skipping 25 matching lines @@
 
   // Notifies the compositor that compositing is complete.
   virtual void OnNotifyEnd() = 0;
 
   virtual void OnWidgetSizeChanged() = 0;
   virtual void OnRootLayerChanged();
   virtual void DrawTree();
 
   CompositorDelegate* delegate() { return delegate_; }
 
+  // When reading back pixel data we often get RGBA rather than BGRA pixels and
+  // and the image often needs to be flipped vertically.
+  static void SwizzleRGBAToBGRAAndFlip(unsigned char* pixels,
+                                       const gfx::Size& image_size);
+
  private:
   // Notifies the compositor that compositing is about to start. See Draw() for
   // notes about |force_clear|.
   void NotifyStart(bool force_clear);
 
   // Notifies the compositor that compositing is complete.
   void NotifyEnd();
 
   CompositorDelegate* delegate_;
   gfx::Size size_;
 
   // The root of the Layer tree drawn by this compositor.
   Layer* root_layer_;
 
   ObserverList<CompositorObserver> observer_list_;
 
   // Factory used to create Compositors. Settable by tests.
   // The delegate can be NULL if you don't wish to catch the ScheduleDraw()
   // calls to it.
   static ui::Compositor*(*compositor_factory_)(
       ui::CompositorDelegate* delegate);
 
   friend class base::RefCounted<Compositor>;
 };
 
 }  // namespace ui
 
 #endif  // UI_GFX_COMPOSITOR_COMPOSITOR_H_