Microsoft KB Archive/77702

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INFO: Processing WM_PALETTECHANGED and WM_QUERYNEWPALETTE

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Q77702

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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

Keywords : kbOSWinNT350 kbOSWinNT351 kbOSWinNT400 kbOSWin95 kbSDKWin16

Issue type : kbinfo

Technology : kbAudDeveloper kbSDKSearch kbWin32sSearch kbWin32API kbWinSDKSearch