dcHandle:  begin
                   glWnd := ReadInteger(_Data,_data_Bitmap,0);
                   pDC := GetDC(glWnd);
                end;
     dcBitmap:  begin
                   bmp := ReadBitmap(_Data,_data_Bitmap,nil);
                   if (bmp <> nil) and (not bmp.Empty) then
                      pDC := bmp.Canvas.Handle
                   else
                      Result := false;
                end;
     dcContext: pDC := ReadInteger(_Data,_data_Bitmap,0);