[WebRTC] A real ScreenCapturer test

webrtc/modules/desktop_capture/screen_drawer.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.
  */
 
 #ifndef WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_DRAWER_H_
 #define WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_DRAWER_H_
 
 #include <stdint.h>
 
 #include <memory>
 
 #include "webrtc/modules/desktop_capture/desktop_geometry.h"
 
 namespace webrtc {
 
-// A set of platform independent functions to draw various of shapes on the
-// screen. This class is for testing ScreenCapturer* implementations only, and
+// A set of basic platform dependent functions to draw various shapes on the
+// screen.
+// Usually ScreenPainter is preferred, instead of using this class directly. As
+// ScreenPainter provides more complex shapes by using ScreenDrawer for each
+// platform. This class is for testing ScreenCapturer* implementations only, and
 // should not be used in production logic.
 class ScreenDrawer {
  public:
-  // Creates a ScreenDrawer for the current platform.
+  // Creates a ScreenDrawer for the current platform, returns nullptr if no
+  // ScreenDrawer implementation available.
   static std::unique_ptr<ScreenDrawer> Create();
 
   ScreenDrawer() {}
   virtual ~ScreenDrawer() {}
 
-  // Returns a rect, on which this instance can draw.
+  // Returns a rectangle, on which this instance can draw. Note, this rectangle
+  // does not need to map to a physical monitor or a logic screen. ScreenDrawer
+  // does not guarantee drawing a point at (0, 0) means the point will be placed
+  // at (0, 0) of a monitor or a logic screen. But it guarantees points drawing
+  // at (0, 0) will eventually show up, top-left part of the drawable region
+  // should not be covered by another window, or out of display area. Refer to
+  // CalibrateScreenDrawerPosition() function in screen_capturer_unittest.cc to
+  // see how to calibrate the visible region of a ScreenDrawer.
   virtual DesktopRect DrawableRegion() = 0;
 
-  // Draws a rectangle to cover |rect| with color |rgba|. Note, rect.bottom()
+  // Draws a rectangle to cover |rect| with color |bgra|. Note, rect.bottom()
   // and rect.right() two lines are not included.
-  virtual void DrawRectangle(DesktopRect rect, uint32_t rgba) = 0;
+  virtual void DrawRectangle(DesktopRect rect, uint32_t bgra) = 0;
 
-  // Clears all content on the screen.
-  virtual void Clear() = 0;
+  // Blocks current thread until OS finishes previous Draw* actions.
+  // ScreenCapturer should be able to capture the changes after this function
+  // finish.
+  virtual void WaitForPendingPaintings() = 0;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_DRAWER_H_