BUG: MCIWndClass Popup Window Palette Flashes

The information in this article applies to:

• Microsoft Windows Software Development Kit (SDK) for Windows version 3.1
• Microsoft Video for Windows, version 1.1

SYMPTOMS

An MCIWndClass popup window realizes its logical palette in the foreground instead of the background as requested in a call to MCIWndRealize() with the fBkgnd flag set to TRUE. The foreground palette realization is seen as a flash.

The following code demonstrates the setting that results in the flash. The flash occurs when the popup window receives the input focus from another application using a different logical palette.

   hwndPanel = MCIWndCreate(hwndParent, hInst,
      MCIWNDF_NOAUTOSIZEMOVIE | MCIWNDF_NOMENU |
      WS_OVERLAPPED | WS_BORDER | WS_CAPTION |
      WS_SYSMENU | WS_POPUP, NULL);
   MCIWndOpen(hwndPanel, fname, 0);
   MCIWndRealize(hwndPanel, TRUE);
   SetWindowPos(hwndPanel, HWND_TOP, X, Y, 0, 0,
      SWP_NOSIZE | SWP_DRAWFRAME | SWP_SHOWWINDOW);
   MCIWndPlay(hwndPanel);

CAUSE

When the MCIWndClass popup window receives the input focus from another application that uses a different logical palette, the popup window receives a WM_QUERYNEWPALETTE message that is processed for the popup window by the MCIWndProc() procedure. In the MCIWndProc() procedure, the "case WM_QUERYNEWPALETTE:" results in a call to MCIWndRealize() with the flag fBkgnd set to FALSE. This occurs even if the popup window's palette was originally realized in the background.

STATUS

Microsoft has confirmed this to be a bug in Microsoft Video for Windows Version 1.1. We are researching this problem and will post new information as it becomes available in the Microsoft Knowledge Base.

MORE INFORMATION

The problem described in the SYMPTOMS section occurs only with popup windows. It does not arise when the window style is WS_CHILD. When the window is a child window, the WM_QUERYNEWPALETTE messages are processed by the parent window's callback procedure instead of the MCIWndProc() procedure.

When the window involved is a popup window, you can avoid the flash by subclassing the MCIWndProc() procedure and allowing the subclassing application to process the WM_QUERYNEWPALETTE message directly by calling MCIWndRealize() with the fBkgnd flag set to TRUE. The following code demonstrates this workaround:

// MakeProcInstance() is called once in a convenient place such
// as the application's InitInstance() procedure. RealizeProc()
// is the procedure that subclasses MCIWndProc(). RealizeProc()
// will process WM_QUERYNEWPALETTE messages on behalf of
// MCIWndProc(). In the Module Definition File, list the
// RealizeProc() procedure under EXPORTS.

   lpfnRealizeProc = MakeProcInstance((FARPROC)
      RealizeProc, hinstCurrent);

// In the application's MainWndProc() under "case WM_DESTROY:",
// call FreeProcInstance().

   FreeProcInstance(lpfnRealizeProc);

// Add the next two function calls to the code shown in the
// Symptoms section just after the call to MCIWndCreate(). The
// GetWindowLong() call returns a pointer to the popup window's
// original window procedure, namely MCIWndProc(). The
// SetWindowLong() procedure specifies that the RealizeProc()
// procedure is the new window procedure for the popup window.

   lpfnOldRealizeProc = (FARPROC)GetWindowLong(hwndPanel,
      GWL_WNDPROC);

   SetWindowLong(hwndPanel, GWL_WNDPROC, (LONG)
      lpfnRealizeProc);

// The following procedure subclasses MCIWndProc(). It processes
// the WM_QUERYNEWPALETTE messages. All other messages
// are sent to MCIWndProc(), which is pointed to by the
// parameter lpfnOldRealizeProc.

               wParam, LPARAM lParam)
{
   switch (message)
   {
      case WM_QUERYNEWPALETTE:
         return (MCIWndRealize(hwndPanel, TRUE));

      default:
          return (CallWindowProc((WNDPROC)lpfnOldRealizeProc,
            hwndPanel, message, wParam, lParam));
   }
}