1252021 - [WebRtc]Display black frame when screen sharing with layered window or minimized windows

Status: NEW

(Core :: WebRTC: Audio/Video, defect, P3)

Description

[xpeng]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/46.0.2486.0 Safari/537.36 Edge/13.10586

Steps to reproduce:

screen share with application's windows using webrtc.
1.Could not  enumerate  minimized windows with webrtc interface.
We found that the implement of  App capturer in Firefox source code :  
media\webrtc\trunk\webrtc\modules\desktop_capture\window_capturer_win.cc
// Skip windows that are invisible, minimized, have no title, or are owned,
  // unless they have the app window style set.
  int len = GetWindowTextLength(hwnd);
  HWND owner = GetWindow(hwnd, GW_OWNER);
  LONG exstyle = GetWindowLong(hwnd, GWL_EXSTYLE);
  if (len == 0 || IsIconic(hwnd) || !IsWindowVisible(hwnd) ||
      (owner && !(exstyle & WS_EX_APPWINDOW))) {
    return TRUE;
  }

2.Display black frame when screen sharing with layered window or minimized windows

media\webrtc\trunk\webrtc\modules\desktop_capture\window_capturer_win.cc
  // Return a 1x1 black frame if the window is minimized, to match the behavior
  // on Mac.
  if (IsIconic(window_)) {
    BasicDesktopFrame* frame = new BasicDesktopFrame(DesktopSize(1, 1));
    memset(frame->data(), 0, frame->stride() * frame->size().height());

    previous_size_ = frame->size();
    callback_->OnCaptureCompleted(frame);
    return;
  }
...
  if (!IsAeroEnabled() || !previous_size_.equals(frame->size())) {
    result = PrintWindow(window_, mem_dc, 0);
  }

  // Aero is enabled or PrintWindow() failed, use BitBlt.
  if (!result) {
    result = BitBlt(mem_dc, 0, 0, frame->size().width(), frame->size().height(),
                    window_dc,
                    cropped_rect.left() - original_rect.left(),
                    cropped_rect.top() - original_rect.top(),
                    SRCCOPY);
  }

I suppose to  use  SRCCOPY|CAPTUREBLT  option to bitblt layered windows.

 #define CAPTUREBLT                   (DWORD)0x40000000 /* Include layered windows */


Actual results:

1.Could not  enumerate  minimized windows with webrtc interface.
2.Display black frame when screen sharing with layered window or minimized windows


Expected results:

1.enumerate  minimized windows with webrtc interface
2.Display normal frame when screen sharing with layered window or minimized windows

Comment 1

[Randell Jesup [:jesup] (needinfo me)]

I suspect we can't capture minimized windows in any case.   It's worth trying number 2 (and verifying number 1).  Note that it's possible there's a difference between different versions of Windows we capture on, and if Aero is on (generally the default).

Comment 2

[Bulk Bug Changes for mreavy's org]

Mass change P2->P3 to align with new Mozilla triage process.

Comment 3

[xpeng]

the issue of the minimized window:
case 1). the window is in minimized state when capturing
solution: send a message to the window to restore the window and then capture the window

case 2). the user minimize the window which is being capturing
solution：send the image of the window which is captured before