DOC: SetBkColor() Does Not Support Dithered Colors

• Microsoft Windows Software Development Kit (SDK) for Windows versions 3.1, 3.0
• Microsoft Win32 Application Programming Interface (API) included with:

      - Microsoft Windows NT versions 3.5, 3.51
      - Microsoft Windows 95
  

SUMMARY

The syntax for the SetBkColor function is documented in the Microsoft Windows Software Development Kit (SDK) as follows:

   DWORD SetBkColor(HDC hDC, COLORREF crColor);

MORE INFORMATION

This behavior can cause unexpected results for an application that changes the background color of a control to a color that cannot be represented by a color provided by the display device.

Specifically, when an application specifies a dithered color for the background of an edit control, and specifies the same color for the text background, Windows paints the control in two distinct colors.

For example, using the standard VGA display driver, the following call, in which COLOR_INACTIVEBORDER is a green/gray specified by RGB(64, 128, 128), sets the background color to gray (RGB(128, 128, 128)) rather than the dithered green/gray that is desired:

   SetBkColor(wParam, GetSysColor(COLOR_INACTIVEBORDER));

This behavior can also occur with other controls such as option buttons and list boxes. However, an application can avoid this problem by using the SetBkMode function to set the background mode to TRANSPARENT. This allows the dithered brush pattern to show through beneath the text to achieve the desired results. That solution is not practical with a multiline edit control because if text is inserted, and the background mode has been set to TRANSPARENT, the text that is pushed to the right by the inserted text leaves its image behind. The result is text superimposed on top of other text, which quickly becomes unreadable.

To partially work around this situation for a multiline edit control, use the GetNearestColor function to determine the nearest physical color to the desired color, as in the code fragment below. In this case, the entire edit control is gray:

   case WM_CREATE:
      {
      HDC hDC;
      hDC = GetDC(hWnd);
      hGrayBrush = CreateSolidBrush(GetNearestColor(hDC,
            RGB(64, 128, 128)));
      ReleaseDC(hWnd, hDC);
      hWndEdit = CreateWindow( ... ES_MULTILINE ... );
      }
      break;

   case WM_CTLCOLOR:
         if (HIWORD(lParam) == CTLCOLOR_EDIT)
         // Use the following line instead of the two above for
         // 32-bit Windows
         // case WM_CTLCOLOREDIT:
         {
         // The following call creates the nearest physical
         // color; therefore, it will be the same as the
         // hGrayBrush created above.
         SetBkColor(wParam, RGB(64, 128, 128));
         SetTextColor(wParam, RGB(255, 0, 0)); // red text
         return (DWORD)hGrayBrush;
         }
      else
        return DefWindowProc(hWnd, identifier, wParam, lParam);
      break;