VideoFrameBuffer: Make non-const data access explicit

webrtc/common_video/interface/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 24 matching lines @@
 
   // The resolution of the frame in pixels. For formats where some planes are
   // subsampled, this is the highest-resolution plane.
   virtual int width() const = 0;
   virtual int height() const = 0;
 
   // Returns pointer to the pixel data for a given plane. The memory is owned by
   // the VideoFrameBuffer object and must not be freed by the caller.
   virtual const uint8_t* data(PlaneType type) const = 0;
 
-  // Non-const data access is only allowed if |HasOneRef| is true.
-  virtual uint8_t* data(PlaneType type) = 0;
+  // Non-const data access is disallowed by default. You need to make sure you
+  // have exclusive access and a writable buffer before calling this function.
+  virtual uint8_t* MutableData(PlaneType type);
 
   // Returns the number of bytes between successive rows for a given plane.
   virtual int stride(PlaneType type) const = 0;
 
   // Return the handle of the underlying video frame. This is used when the
   // frame is backed by a texture.
   virtual void* native_handle() const = 0;
 
   // Returns a new memory-backed frame buffer converted from this buffer's
   // native handle.
   virtual rtc::scoped_refptr<VideoFrameBuffer> NativeToI420Buffer() = 0;
 
  protected:
   virtual ~VideoFrameBuffer();
 };
 
 // Plain I420 buffer in standard memory.
 class I420Buffer : public VideoFrameBuffer {
  public:
   I420Buffer(int width, int height);
   I420Buffer(int width, int height, int stride_y, int stride_u, int stride_v);
 
   int width() const override;
   int height() const override;
   const uint8_t* data(PlaneType type) const override;
-  uint8_t* data(PlaneType type) override;
+  // Non-const data access is only allowed if HasOneRef() is true to protect
+  // against unexpected overwrites.
+  uint8_t* MutableData(PlaneType type) override;
   int stride(PlaneType type) const override;
   void* native_handle() const override;
   rtc::scoped_refptr<VideoFrameBuffer> NativeToI420Buffer() override;
 
  protected:
   ~I420Buffer() override;
 
  private:
   const int width_;
   const int height_;
   const int stride_y_;
   const int stride_u_;
   const int stride_v_;
   const rtc::scoped_ptr<uint8_t, AlignedFreeDeleter> data_;
 };
 
 // Base class for native-handle buffer is a wrapper around a |native_handle|.
 // This is used for convenience as most native-handle implementations can share
 // many VideoFrame implementations, but need to implement a few others (such
 // as their own destructors or conversion methods back to software I420).
 class NativeHandleBuffer : public VideoFrameBuffer {
  public:
   NativeHandleBuffer(void* native_handle, int width, int height);
 
   int width() const override;
   int height() const override;
   const uint8_t* data(PlaneType type) const override;
-  uint8_t* data(PlaneType type) override;
   int stride(PlaneType type) const override;
   void* native_handle() const override;
 
  protected:
   void* native_handle_;
   const int width_;
   const int height_;
 };
 
 class WrappedI420Buffer : public webrtc::VideoFrameBuffer {
  public:
   WrappedI420Buffer(int width,
                     int height,
                     const uint8_t* y_plane,
                     int y_stride,
                     const uint8_t* u_plane,
                     int u_stride,
                     const uint8_t* v_plane,
                     int v_stride,
                     const rtc::Callback0<void>& no_longer_used);
   int width() const override;
   int height() const override;
 
   const uint8_t* data(PlaneType type) const override;
-  uint8_t* data(PlaneType type) override;
 
   int stride(PlaneType type) const override;
   void* native_handle() const override;
 
   rtc::scoped_refptr<VideoFrameBuffer> NativeToI420Buffer() override;
 
  private:
   friend class rtc::RefCountedObject<WrappedI420Buffer>;
   ~WrappedI420Buffer() override;
 
@@ skipping 11 matching lines @@
 // 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_VIDEO_FRAME_BUFFER_H_