CURSORINFO.flags should be checked before capturing its bitmap

webrtc/modules/desktop_capture/mouse_cursor_monitor_win.cc

 /*
  *  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 74 matching lines @@
 void MouseCursorMonitorWin::Capture() {
   assert(callback_);
 
   CURSORINFO cursor_info;
   cursor_info.cbSize = sizeof(CURSORINFO);
   if (!GetCursorInfo(&cursor_info)) {
     LOG_F(LS_ERROR) << "Unable to get cursor info. Error = " << GetLastError();
     return;
   }
 
+  if (cursor_info.flags != CURSOR_SHOWING) {

[joedow, 2016/05/09 17:14:05]

Do any clients rely on receiving the bitmap when the cursor is hidden/suppressed
to determine whether to show/hide the cursor?  Perhaps the WebApp on Windows or
ChromeOS.

[Hzj_jie, 2016/05/10 00:40:58]

I believe other platform won't be impacted, they do not actively draw the cursor
themselves.

[Hzj_jie, 2016/05/10 18:15:22]

Done.

[Hzj_jie, 2016/05/10 18:15:22]

Done.

+    return;

[Sergey Ulanov, 2016/05/10 17:17:07]

I see two issues with this fix:
 1. This code is used for Desktop Capture API. For that API we want to capture
the screen and mouse exactly as the user sees it (DesktopAndCursorComposer is
used to render mouse cursor on captured frames). It means that if the cursor is
hidden we want to hide it from captured frames as well.
 2. If the cursor was shown and then then becomes hidden then the client will
keep showing the last cursor it received. The right behavior here is to default
to an arrow.

I suggest adding a flag in webrtc::MouseCursor to indicate that the cursor is
hidden and then handling that case in Chromoting by sending default arrow
cursor.
 

[Hzj_jie, 2016/05/10 18:15:22]

The following logic (after if (mode_ != SHAPE_AND_POSITION)) will eventually
draw the cursor out of the screen, if host hides it. But yes, I should not
return directly here. I have updated the code.

+  }
+
   if (last_cursor_ != cursor_info.hCursor) {
-    last_cursor_ = cursor_info.hCursor;
     // Note that |cursor_info.hCursor| does not need to be freed.
     std::unique_ptr<MouseCursor> cursor(
         CreateMouseCursorFromHCursor(desktop_dc_, cursor_info.hCursor));
-    if (cursor.get())
+    if (cursor) {
+      last_cursor_ = cursor_info.hCursor;
       callback_->OnMouseCursor(cursor.release());
+    } else {
+      last_cursor_ = NULL;
+    }
   }
 
   if (mode_ != SHAPE_AND_POSITION)
     return;
 
   DesktopVector position(cursor_info.ptScreenPos.x, cursor_info.ptScreenPos.y);
   bool inside = cursor_info.flags == CURSOR_SHOWING;
 
   if (window_) {
     DesktopRect original_rect;
@@ skipping 54 matching lines @@
   return new MouseCursorMonitorWin(reinterpret_cast<HWND>(window));
 }
 
 MouseCursorMonitor* MouseCursorMonitor::CreateForScreen(
     const DesktopCaptureOptions& options,
     ScreenId screen) {
   return new MouseCursorMonitorWin(screen);
 }
 
 }  // namespace webrtc