Q77702: INFO: Processing WM_PALETTECHANGED and WM_QUERYNEWPALETTE

Article: Q77702
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1,95; winnt:3.5,3.51,4.0
Operating System(s): 
Keyword(s): kbOSWinNT350 kbOSWinNT351 kbOSWinNT400 kbOSWin95 kbSDKWin16
Last Modified: 11-MAY-2001

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) 3.1 
- Microsoft Win32 Application Programming Interface (API), used with:
   - Microsoft Windows NT Server versions 3.5, 3.51, 4.0 
   - Microsoft Windows NT Workstation versions 3.5, 3.51, 4.0 
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SUMMARY
=======

An application that manipulates the system palette should process the
WM_PALETTECHANGED and WM_QUERYNEWPALETTE messages to maintain its appearance
during system palette and input focus changes.

MORE INFORMATION
================

The WM_PALETTECHANGED message informs all windows that the window with input
focus has realized its logical palette, thereby changing the system palette.
This message allows a window without input focus that uses a color palette to
realize its logical palettes and update its client area.

This message is sent to all windows, including the one that changed the system
palette and caused this message to be sent. The wParam of this message contains
the handle of the window that caused the system palette to change. To avoid an
infinite loop, care must be taken to check that the wParam of this message does
not match the window's handle. The following sample code demonstrates how to
process WM_PALETTECHANGED:

     case WM_PALETTECHANGED:
         {
         HDC hDC;           // Handle to device context
         HPALETTE hOldPal;  // Handle to previous logical palette

         // If this application did not change the palette, select
         // and realize this application's palette
         if (wParam != hWnd)
            {
            // Need the window's DC for SelectPalette/RealizePalette
            hDC = GetDC(hWnd);

            // Select and realize hPalette
            hOldPal = SelectPalette(hDC, hPalette, FALSE);
            RealizePalette(hDC);

            // When updating the colors for an inactive window,
            // UpdateColors can be called because it is faster than
            // redrawing the client area (even though the results are
            // not as good)
            UpdateColors(hDC);

            // Clean up
            if (hOldPal)
               SelectPalette(hDC, hOldPal, FALSE);
            ReleaseDC(hWnd, hDC);
            }
         }
         break;

NOTE: The WM_PALETTECHANGED message is sent to all top-level and overlapped
windows; therefore, if any child window uses a color palette, this message must
be passed on to it.

The WM_QUERYNEWPALETTE message informs a window that it is about to receive input
focus. In response, the window receiving focus should realize its palette as a
foreground palette and update its client area. If the window realizes its
palette, it should return TRUE; otherwise, it should return FALSE. The following
sample code demonstrates processing WM_QUERYNEWPALETTE:

     case WM_QUERYNEWPALETTE:
         {
         HDC hDC;           // Handle to device context
         HPALETTE hOldPal;  // Handle to previous logical palette

         // Need the window's DC for SelectPalette/RealizePalette
         hDC = GetDC(hWnd);

         // Select and realize hPalette
         hOldPal = SelectPalette(hDC, hPalette, FALSE);
         RealizePalette(hDC);

         // Redraw the entire client area
         InvalidateRect(hWnd, NULL, TRUE);
         UpdateWindow(hWnd);

         // Clean up
         if (hOldPal)
            SelectPalette(hDC, hOldPal, FALSE);
         ReleaseDC(hWnd, hDC);

         // Message processed, return TRUE
         return TRUE;
         }

NOTE: The WM_QUERYNEWPALETTE message is sent to all top-level and overlapped
windows; therefore, if any child window uses a color palette, this message must
be passed on to it.

Additional query words: handtag

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Keywords          : kbOSWinNT350 kbOSWinNT351 kbOSWinNT400 kbOSWin95 kbSDKWin16 
Technology        : kbAudDeveloper kbSDKSearch kbWin32sSearch kbWin32API kbWinSDKSearch
Version           : WINDOWS:3.1,95; winnt:3.5,3.51,4.0
Issue type        : kbinfo

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