Clear DesktopFrame in DxgiFrame to avoid legacy image

webrtc/modules/desktop_capture/win/dxgi_frame.cc

 /*
  *  Copyright (c) 2017 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.
  */
 
 #include "webrtc/modules/desktop_capture/win/dxgi_frame.h"
 
+#include <string.h>
+
 #include <utility>
 
 #include "webrtc/base/checks.h"
 #include "webrtc/modules/desktop_capture/desktop_frame.h"
 #include "webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.h"
 
 namespace webrtc {
 
 DxgiFrame::DxgiFrame(SharedMemoryFactory* factory)
     : factory_(factory) {}
@@ skipping 16 matching lines @@
   if (!frame_) {
     std::unique_ptr<DesktopFrame> frame;
     if (factory_) {
       frame = SharedMemoryDesktopFrame::Create(size, factory_);
     } else {
       frame.reset(new BasicDesktopFrame(size));
     }
     if (!frame) {
       return false;
     }
+    // DirectX capturer won't paint each pixel in the frame due to its one
+    // capturer per monitor design. So once the new frame is created, we should
+    // clear it to avoid the legacy image to be remained on it. See
+    // http://crbug.com/708766.
+    RTC_DCHECK_EQ(frame->stride(),
+                  frame->size().width() * DesktopFrame::kBytesPerPixel);
+    memset(frame->data(), 0, frame->stride() * frame->size().height());
 
     frame_ = SharedDesktopFrame::Wrap(std::move(frame));
   }
 
   return !!frame_;
 }
 
 SharedDesktopFrame* DxgiFrame::frame() const {
   RTC_DCHECK(frame_);
   return frame_.get();
 }
 
 DxgiFrame::Context* DxgiFrame::context() {
   RTC_DCHECK(frame_);
   return &context_;
 }
 
 }  // namespace webrtc