Anybody knows how to get MaskBlt to work ?

Hello,

i would like to do a MaskBlt operation, but for some reason i can't get
it to do anything but copying nothing. Here's a fragment of code i
tried.

procedure TForm1.Button1Click(Sender: TObject);
var
  RasterOP: Integer;
begin
    RasterOP := DWORD(((SrcCopy shl 8) and $FF000000) or SrcCopy);

    MaskBlt(Dest.Canvas.Handle, 0, 0, Dest.Width, Dest.Height,
      Source.Canvas.Handle, 0, 0, Mask.Canvas.Handle, 0,0, RasterOP);
    Dest.Refresh;
end;

any suggestion would be welcome.