"Buttery Smooth" Tab Capture.

content/public/browser/render_widget_host_view_frame_subscriber.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 CONTENT_PORT_BROWSER_RENDER_WIDGET_HOST_VIEW_FRAME_SUBSCRIBER_H_
 #define CONTENT_PORT_BROWSER_RENDER_WIDGET_HOST_VIEW_FRAME_SUBSCRIBER_H_
 
 #include "base/callback.h"
 #include "base/time/time.h"
 
@@ skipping 26 matching lines @@
   // If |frame_captured| is true then frame provided contains valid content and
   // |timestamp| is the time when the frame was painted.
   //
   // If |frame_captured| is false then the content in frame provided is
   // invalid. There was an error during the process of frame capture or the
   // platform layer is shutting down. |timestamp| is also invalid in this case.
   typedef base::Callback<void(base::TimeTicks /* timestamp */,
                               bool /* frame_captured */)> DeliverFrameCallback;
 
   // Called when a new frame is going to be presented at time
-  // |present_time|. Implementation can decide whether the current frame should
-  // be captured or not.
+  // |present_time| with |damage_rect| being the region of the frame that has
+  // changed since the last frame. The implementation decides whether the
+  // current frame should be captured or not.
   //
   // Return true if the current frame should be captured. If so, |storage|
-  // should will be set to hold an appropriately sized and allocated buffer
-  // into which to copy the frame. The platform presenter will perform scaling
-  // and color space conversion to fit into the output frame.
+  // will be set to hold an appropriately sized and allocated buffer into which
+  // to copy the frame. The platform presenter will perform scaling and color
+  // space conversion to fit into the output frame.
   //
   // Destination format is determined by |storage|, currently only
   // media::VideoFrame::YV12 is supported. Platform layer will perform color
   // space conversion if needed.
   //
   // When the frame is available |callback| will be called. It is up to the
   // platform layer to decide when to deliver a captured frame.
   //
   // Return false if the current frame should not be captured.
-  virtual bool ShouldCaptureFrame(base::TimeTicks present_time,
+  virtual bool ShouldCaptureFrame(const gfx::Rect& damage_rect,
+                                  base::TimeTicks present_time,
                                   scoped_refptr<media::VideoFrame>* storage,
                                   DeliverFrameCallback* callback) = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PORT_BROWSER_RENDER_WIDGET_HOST_VIEW_FRAME_SUBSCRIBER_H_