Update I420Buffer to new VideoFrameBuffer interface

webrtc/api/video/i420_buffer.h

Index: webrtc/api/video/i420_buffer.h
diff --git a/webrtc/api/video/i420_buffer.h b/webrtc/api/video/i420_buffer.h
index c849ab22c053dbb63dfa76bb2f3fac1785dba7f7..1f38e943104eebbeae1d869852287cb63001cae9 100644
--- a/webrtc/api/video/i420_buffer.h
+++ b/webrtc/api/video/i420_buffer.h
@@ -30,7 +30,11 @@ class I420Buffer : public I420BufferInterface {
                                                int stride_v);
 
   // Create a new buffer and copy the pixel data.
-  static rtc::scoped_refptr<I420Buffer> Copy(const VideoFrameBuffer& buffer);
+  static rtc::scoped_refptr<I420Buffer> Copy(const I420BufferInterface& buffer);
+  // Deprecated.
+  static rtc::scoped_refptr<I420Buffer> Copy(const VideoFrameBuffer& buffer) {
+    return Copy(*const_cast<VideoFrameBuffer&>(buffer).GetI420());

[nisse-webrtc, 2017/05/30 12:35:40]

Any reason we can't mark the GetI420 and GetI44 methods const? Then you wouldn't
need this const_cast (and the one below).

Hmm, they'd need to return scoped_refptr<const I420BufferInterface> then (or a
raw const ptr), is that a problem? Ref counts are mutable, I think.

Ideally, we shouldn't be using any non-const references using these interfaces;
frame buffers should only be modified close to creation, using a more specific
type like I420Buffer. 

But current code doesn't look like that, unfortunately.
If needed, we could have one const and one non-const version of GetI420 and
GetI444.

[magjed_webrtc, 2017/05/30 13:18:08]

Yes, the problem is the return type... I would love to have the Get functions
const, but I don't want to return a scoped_refptr<const I420BufferInterface>
since that would cause a lot of trouble with everything that wants a
scoped_refptr<I420BufferInterface>. I would be ok with returning a raw const
pointer from the Get functions like we discussed, but I need to remove the
I420Wrapper class in video_frame_buffer.cc first. I think we need to do this
incrementally, so how about we land this CL as is and clean up the Get functions
later? I hate const_cast, but hopefully I can remove these temporary functions
quickly.

[nisse-webrtc, 2017/05/30 13:28:21]

Is that a lot of places? Current version of this cl replaces
scoped_refptr<VideoFrameBuffer> by scoped_refptr<I420BufferInterface> in lots of
places, I was hoping it would be easy to change to scoped_refptr<const
I420bufferInterface> instead.

But if it's a lot of work, we can postpone it. Just add a TODO item on the
declarations of these methods saying they ought to be const (and possibly raw
pointers?), and briefly explaining why they aren't. 

[magjed_webrtc, 2017/05/30 14:25:21]

Not many places it seems like, done.

+  }
 
   static rtc::scoped_refptr<I420Buffer> Copy(
       int width, int height,
@@ -39,8 +43,13 @@ class I420Buffer : public I420BufferInterface {
       const uint8_t* data_v, int stride_v);
 
   // Returns a rotated copy of |src|.
-  static rtc::scoped_refptr<I420Buffer> Rotate(const VideoFrameBuffer& src,
+  static rtc::scoped_refptr<I420Buffer> Rotate(const I420BufferInterface& src,
                                                VideoRotation rotation);
+  // Deprecated.
+  static rtc::scoped_refptr<I420Buffer> Rotate(const VideoFrameBuffer& src,
+                                               VideoRotation rotation) {
+    return Rotate(*const_cast<VideoFrameBuffer&>(src).GetI420(), rotation);
+  }
 
   // Sets the buffer to all black.
   static void SetBlack(I420Buffer* buffer);
@@ -69,7 +78,7 @@ class I420Buffer : public I420BufferInterface {
 
   // Scale the cropped area of |src| to the size of |this| buffer, and
   // write the result into |this|.
-  void CropAndScaleFrom(const VideoFrameBuffer& src,
+  void CropAndScaleFrom(const I420BufferInterface& src,
                         int offset_x,
                         int offset_y,
                         int crop_width,
@@ -77,10 +86,10 @@ class I420Buffer : public I420BufferInterface {
 
   // The common case of a center crop, when needed to adjust the
   // aspect ratio without distorting the image.
-  void CropAndScaleFrom(const VideoFrameBuffer& src);
+  void CropAndScaleFrom(const I420BufferInterface& src);
 
   // Scale all of |src| to the size of |this| buffer, with no cropping.
-  void ScaleFrom(const VideoFrameBuffer& src);
+  void ScaleFrom(const I420BufferInterface& src);
 
  protected:
   I420Buffer(int width, int height);