Refactor scaling.

webrtc/common_video/include/video_frame_buffer.h

Index: webrtc/common_video/include/video_frame_buffer.h
diff --git a/webrtc/common_video/include/video_frame_buffer.h b/webrtc/common_video/include/video_frame_buffer.h
index 984bd50d674e78d7e7aedfc252fcfef8810b6963..08b914321a944b400f9350575fc5cfa1786547a5 100644
--- a/webrtc/common_video/include/video_frame_buffer.h
+++ b/webrtc/common_video/include/video_frame_buffer.h
@@ -109,6 +109,23 @@ class I420Buffer : public VideoFrameBuffer {
   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;
 
@@ -186,13 +203,6 @@ class WrappedI420Buffer : public webrtc::VideoFrameBuffer {
   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_