Black painted if SetLayeredWindowAttributes is called.

[guitz]

Hi,

well I have a usual dialog based application with a resizable dialog. Because I have some regions which gonna be transparent, I make in the OnInitDialog the following call:

  const COLORREF crTransparent  = RGB( 255,   0,   0 );
  LONG dwNewLong = GetWindowLong(m_hWnd, GWL_EXSTYLE) | WS_EX_LAYERED;
  SetWindowLong(m_hWnd, GWL_EXSTYLE, dwNewLong);
  SetLayeredWindowAttributes( crTransparent, 0, LWA_COLORKEY);

The MFC (or whoever) makes a not so funny black painting of the region which will be bigger then the initial dialog. Without calling 'SetLayeredWindowAttributes' the black painting is not happend.

I tried to override the erase of background like this:

BOOL CBlaBlaTestDlg::OnEraseBkgnd(CDC* pDC)
{
      CRect rect;
      GetWindowRect(&rect);     // Erase the area needed
      ScreenToClient(&rect);
      pDC->FillSolidRect(&rect, RGB(0,255,0));
      return TRUE;
}

but ... no chance, they are ... almighty. First apears the black painting, then my green solid rect.
Has anyone, any idea how can I avoid this black painting ???
Thanks in advance!

Best regards,
Emil

[Marc G]

You mean you see the window temporary being drawn in black and then in the right color? If so, I'm afraid there is not much you can do. Are you calling SetLayeredWindowAttributes before the window is shown?

[Bornish]

Try:

SetWindowLong(m_hWnd, GetWindowLong(m_hWnd, GWL_EXSTYLE) | WS_EX_LAYERED);
const COLORREF crTransparent = RGB( 0,   0,   0 );
SetLayeredWindowAttributes(crTransparent, 0, LWA_COLORKEY);

Also in OnEraseBkgnd, make sure you paint your "transparent" region of the window with "crTransparent". Still, you may repaint the client area in OnPaint, or parts of it if you have child windows (ex: MDI client is also a child of MDI frame), but otherwise, you should get transparency wherever your window has pixel values equal to crTransparent.