Refactor scaling.

webrtc/common_video/include/video_frame_buffer.h

 /*
  *  Copyright (c) 2015 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.
  */
 
@@ skipping 91 matching lines @@
   int StrideU() const override;
   int StrideV() const override;
 
   void* native_handle() const override;
   rtc::scoped_refptr<VideoFrameBuffer> NativeToI420Buffer() override;
 
   // Create a new buffer and copy the pixel data.
   static rtc::scoped_refptr<I420Buffer> Copy(
       const rtc::scoped_refptr<VideoFrameBuffer>& buffer);
 
+  // Only the most generally useful operations should be methods on
+  // this class, for more specialized operations, use
+  // MutableDataY(,U,V) to get write access.
+
+  // Crop the input buffer, then scale it to the size of this buffer.
+  void CropAndScale(const rtc::scoped_refptr<VideoFrameBuffer>& buffer,

[pbos-webrtc, 2016/05/31 14:14:01]

const VideoFrameBuffer& src?

[nisse-webrtc, 2016/06/01 09:15:17]

I had a brief discussion with Magnus and Tommi, and Tommi favored using refptr
everywhere.

The case where we really need refptr is where we might return the input object,
e.g., QualityScaler::GetScaledFrame.
 
But I'd really like if input parameters could be properly const, i.e.,

const rtc::scoped_refptr<const VideoFrameBuffer>& buffer
                         ^^^^^

Does that work, or need some silly conversion operator in the scoped_reftpr
template machinery?

Maybe we should discuss this face-to-face, I'm happy to change to raw pointers
anywhere people agree it is appropriate.

+                    int offset_x,
+                    int offset_y,
+                    int crop_width,
+                    int crop_height);
+
+  // The common case of a center crop, when needed to maintain the
+  // same aspect ratio.
+  static void CenterCropAndScale(
+      const rtc::scoped_refptr<I420Buffer>& dst,

[pbos-webrtc, 2016/05/31 14:14:01]

Should this be a I420Buffer* dst and const VideoFrameBuffer& src? No need to
have the refptrs in the interface, is there?

+      const rtc::scoped_refptr<VideoFrameBuffer>& src);
+
  protected:
   ~I420Buffer() override;
 
  private:
   const int width_;
   const int height_;
   const int stride_y_;
   const int stride_u_;
   const int stride_v_;
   const std::unique_ptr<uint8_t, AlignedFreeDeleter> data_;
@@ skipping 57 matching lines @@
   const int height_;
   const uint8_t* const y_plane_;
   const uint8_t* const u_plane_;
   const uint8_t* const v_plane_;
   const int y_stride_;
   const int u_stride_;
   const int v_stride_;
   rtc::Callback0<void> no_longer_used_cb_;
 };
 
-// Helper function to crop |buffer| without making a deep copy. May only be used
-// for non-native frames.
-rtc::scoped_refptr<VideoFrameBuffer> ShallowCenterCrop(
-    const rtc::scoped_refptr<VideoFrameBuffer>& buffer,
-    int cropped_width,
-    int cropped_height);
-
 }  // namespace webrtc
 
 #endif  // WEBRTC_COMMON_VIDEO_INCLUDE_VIDEO_FRAME_BUFFER_H_