[WebRTC] Add ScreenCapturerDifferWrapper to share Differ across ScreenCapturers

webrtc/modules/desktop_capture/differ_block.h

 /*
  *  Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_MODULES_DESKTOP_CAPTURE_DIFFER_BLOCK_H_
 #define WEBRTC_MODULES_DESKTOP_CAPTURE_DIFFER_BLOCK_H_
 
 #include <stdint.h>
 
 namespace webrtc {
 
 // Size (in pixels) of each square block used for diffing. This must be a
 // multiple of sizeof(uint64)/8.
 const int kBlockSize = 32;
 
 // Format: BGRA 32 bit.
 const int kBytesPerPixel = 4;
 
+// Low level function to compare 2 vectors of pixels of size kBlockSize. Returns
+// whether the blocks differ.
+bool VectorDifference(const uint8_t* image1, const uint8_t* image2);
+
+// Low level function to compare 2 blocks of pixels of size
+// (kBlockSize, |height|).  Returns whether the blocks differ.
+bool BlockDifference(const uint8_t* image1,
+                     const uint8_t* image2,
+                     int height,
+                     int stride);
+
 // Low level function to compare 2 blocks of pixels of size
 // (kBlockSize, kBlockSize).  Returns whether the blocks differ.
 bool BlockDifference(const uint8_t* image1,
                      const uint8_t* image2,
                      int stride);
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_DIFFER_BLOCK_H_