DesktopRect::UnionWith() to extend current rect to cover the input rect

webrtc/modules/desktop_capture/desktop_geometry.h

 /*
  *  Copyright (c) 2013 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 120 matching lines @@
   // Enlarges current DesktopRect by subtracting |left_offset| and |top_offset|
   // from |left_| and |top_|, and adding |right_offset| and |bottom_offset| to
   // |right_| and |bottom_|. This function does not normalize the result, so
   // |left_| and |top_| may be less than zero or larger than |right_| and
   // |bottom_|.
   void Extend(int32_t left_offset,
               int32_t top_offset,
               int32_t right_offset,
               int32_t bottom_offset);
 
+  // Finds the minimum area to cover both |this| and |rect|. If |this| is empty,
+  // replaces |this| with |rect|.

[jamiewalch, 2017/05/02 22:18:11]

This is not symmetric w.r.t |this| and |rect|. Specifically, if |rect| is empty,
|this| will be extended to include it. This might be the behaviour you want, but
I think it's worth calling it out explicitly one way or the other here.

Also, since this method is complementary to IntersectionWith(), maybe move it to
immediately after that method in both header and implementation.

[Hzj_jie, 2017/05/02 23:28:28]

A good point, I failed to notice it. I believe a correct behavior is to ignore
|rect| if it's empty. In DirectX capturer, the |rect| won't be empty. In
desktop_configuration.mm, I do not believe believe pixel_bounds may be empty,
otherwise we would have bug for a long time.

+  void UnionWith(const DesktopRect& rect);
+
  private:
   DesktopRect(int32_t left, int32_t top, int32_t right, int32_t bottom)
       : left_(left), top_(top), right_(right), bottom_(bottom) {
   }
 
   int32_t left_;
   int32_t top_;
   int32_t right_;
   int32_t bottom_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_DESKTOP_GEOMETRY_H_