ID Number: Q77702
3.00
WINDOWS
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.