Allow Windows to return a monitor out of the first quadrant

webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.h

 /*
  *  Copyright (c) 2016 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 140 matching lines @@
   bool DoDuplicateAll(Context* context, SharedDesktopFrame* target);
 
   // Captures one monitor.
   bool DoDuplicateOne(Context* context,
                       int monitor_id,
                       SharedDesktopFrame* target);
 
   // The minimum GetNumFramesCaptured() returned by |duplicators_|.
   int64_t GetNumFramesCaptured() const;
 
-  // Returns a DesktopSize to cover entire desktop_rect. This may be different
-  // than desktop_rect().size(), since top-left of the screen does not need to
-  // be started from (0, 0).
+  // Returns a DesktopSize to cover entire |desktop_rect_|.
   DesktopSize desktop_size() const;
 
   // Returns the size of one screen. |id| should be >= 0. If system does not
   // support DXGI based capturer, or |id| is greater than the total screen count
   // of all the Duplicators, this function returns an empty DesktopRect.
   DesktopRect ScreenRect(int id) const;
 
   int ScreenCountUnlocked() const;
 
   // Returns the desktop size of the selected screen |monitor_id|. Setting
   // |monitor_id| < 0 to return the entire screen size.
   DesktopSize SelectedDesktopSize(int monitor_id) const;
 
   // Retries DoDuplicateAll() for several times until GetNumFramesCaptured() is
   // large enough. Returns false if DoDuplicateAll() returns false, or
   // GetNumFramesCaptured() has never reached the requirement.
   // According to http://crbug.com/682112, dxgi capturer returns a black frame
   // during first several capture attempts.
   bool EnsureFrameCaptured(Context* context, SharedDesktopFrame* target);
 
+  // Moves |desktop_rect_| and all underlying |duplicators_| to (0, 0).
+  // DXGI_OUTPUT_DESC may return negative values in DesktopCoordinate, which is
+  // not consistent with the requirement of DesktopFrame. But we cannot get the
+  // size of desktop without initializing all the DxgiAdapterDuplicator and
+  // DxgiOutputDuplicator instances. So this is a helper function to "move" the
+  // entire screen from any quadrant to (0, 0). This function is expected to be
+  // executed in DoInitialize() only.

[Sergey Ulanov, 2017/04/28 01:15:02]

Suggest rewording it a bit to simplify:

  // Moves |desktop_rect_| and all underlying |duplicators_|, putting top
  // left corner of the desktop at (0, 0). This is necessary because
  // DXGI_OUTPUT_DESC may return negative desktop coordinates.
  // Called from DoInitialize() after all DxgiAdapterDuplicator and 
  // DxgiOutputDuplicator instances are initialized.

[Hzj_jie, 2017/04/28 01:58:32]

Done.

+  // This comment makes this piece of logic deserve a standalone function.

[Sergey Ulanov, 2017/04/28 01:15:02]

I don't think you need this sentence.

[Hzj_jie, 2017/04/28 01:58:32]

Done.

+  void Translate();

[Sergey Ulanov, 2017/04/28 01:15:02]

TranslateDesktopRect()?

[Hzj_jie, 2017/04/28 01:58:32]

Done.

+
   // This lock must be locked whenever accessing any of the following objects.
   rtc::CriticalSection lock_;
 
   // A self-incremented integer to compare with the one in Context. It ensures
   // a Context instance is always initialized after DxgiDuplicatorController.
   int identity_ = 0;
   DesktopRect desktop_rect_;
   DesktopVector dpi_;
   std::vector<DxgiAdapterDuplicator> duplicators_;
   D3dInfo d3d_info_;
   ResolutionChangeDetector resolution_change_detector_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_WIN_DXGI_DUPLICATOR_CONTROLLER_H_