text: // 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 MEDIA_VIDEO_CAPTURE_SCREEN_SCREEN_CAPTURER_HELPER_H_
  #define MEDIA_VIDEO_CAPTURE_SCREEN_SCREEN_CAPTURER_HELPER_H_
  
  #include "base/memory/scoped_ptr.h"
  #include "base/synchronization/lock.h"
  #include "media/base/media_export.h"
  #include "third_party/skia/include/core/SkRegion.h"
  #include "third_party/webrtc/modules/desktop_capture/desktop_geometry.h"
  #include "third_party/webrtc/modules/desktop_capture/desktop_region.h"
  
  namespace media {
  
  // ScreenCapturerHelper is intended to be used by an implementation of the
  // ScreenCapturer interface. It maintains a thread-safe invalid region, and
  // the size of the most recently captured screen, on behalf of the
  // ScreenCapturer that owns it.
  class MEDIA_EXPORT ScreenCapturerHelper {
   public:
    ScreenCapturerHelper();
    ~ScreenCapturerHelper();
  
    // Clear out the invalid region.
    void ClearInvalidRegion();
  
    // Invalidate the specified region.
    void InvalidateRegion(const webrtc::DesktopRegion& invalid_region);
  
    // Invalidate the entire screen, of a given size.
    void InvalidateScreen(const webrtc::DesktopSize& size);
  
    // Copies current invalid region to |invalid_region| clears invalid region
    // storage for the next frame.
    void TakeInvalidRegion(webrtc::DesktopRegion* invalid_region);
  
    // Access the size of the most recently captured screen.
    const webrtc::DesktopSize& size_most_recent() const;
    void set_size_most_recent(const webrtc::DesktopSize& size);
  
    // Lossy compression can result in color values leaking between pixels in one
    // block. If part of a block changes, then unchanged parts of that block can
    // be changed in the compressed output. So we need to re-render an entire
    // block whenever part of the block changes.
    //
    // If |log_grid_size| is >= 1, then this function makes TakeInvalidRegion()
    // produce an invalid region expanded so that its vertices lie on a grid of
    // size 2 ^ |log_grid_size|. The expanded region is then clipped to the size
    // of the most recently captured screen, as previously set by
    // set_size_most_recent().
    // If |log_grid_size| is <= 0, then the invalid region is not expanded.
    void SetLogGridSize(int log_grid_size);
  
    // Expands a region so that its vertices all lie on a grid.
    // The grid size must be >= 2, so |log_grid_size| must be >= 1.
    static scoped_ptr<SkRegion> ExpandToGrid(const SkRegion& region,
                                             int log_grid_size);
  
   private:
    // A region that has been manually invalidated (through InvalidateRegion).
    // These will be returned as dirty_region in the capture data during the next
    // capture.
    SkRegion invalid_region_;
  
    // A lock protecting |invalid_region_| across threads.
    base::Lock invalid_region_lock_;
  
    // The size of the most recently captured screen.
    webrtc::DesktopSize size_most_recent_;
  
    // The log (base 2) of the size of the grid to which the invalid region is
    // expanded.
    // If the value is <= 0, then the invalid region is not expanded to a grid.
    int log_grid_size_;
  
    DISALLOW_COPY_AND_ASSIGN(ScreenCapturerHelper);
  };
  
  }  // namespace media
  
  #endif  // MEDIA_VIDEO_CAPTURE_SCREEN_SCREEN_CAPTURER_HELPER_H_
  