/// <summary>
/// DefWndProcWrapper is a wrapper around DefWndProc. This is a workaround
/// for WindowsSE bugs 124461 and 124455, which affect Windows XP SP2, Luna theme.
///
/// HwndSubclass.SubclassWndProc is sometimes directly set as the window proc of a
/// Window (HwndWrapper's constructor does this). When this happens it subclasses
/// itself on the first message it receives. Since the old window proc is itself,
/// it saves off DefWndProc as the old window proc instead.
///
/// As described by the bugs and and KB article 319740, if we set DefWndProc
/// as the window proc of the window, we'll leak 6 GDI region objects
/// corresponding to the Luna-themed non-client area.
///
/// The reason for this is that the kernel will flag that window as a server-side
/// window. If the WndProc replacement happens in response to a WM_NCDESTROY message
/// (as it does in the case where Avalon is creating and closing windows), the Shell
/// won't clean up the regions.
///
/// The fix is slated for XP SP3, so for now WPF is implementing a workaround:
/// if we set the window proc to be a stub that calls into DefWndProc, the kernel
/// won't set us as a server-side window.
/// </summary>
private static IntPtr DefWndProcWrapper(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
{
return(UnsafeNativeMethods.CallWindowProc(DefWndProc, hwnd, msg, wParam, lParam));
}
/// <summary>
/// This method lets the user call the old WNDPROC, i.e
/// the next WNDPROC in the chain directly.
/// </summary>
/// <param name="oldWndProc">
/// The WndProc to call.
/// </param>
/// <param name="hwnd">
/// The window that this message was sent or posted to.
/// </param>
/// <param name="msg">
/// The message that was sent or posted.
/// </param>
/// <param name="wParam">
/// A parameter for the message that was sent or posted.
/// </param>
/// <param name="lParam">
/// A parameter for the message that was sent or posted.
/// </param>
/// <returns>
/// The value that is the result of processing the message.
/// </returns>
IntPtr CallOldWindowProc(IntPtr oldWndProc, IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam)
{
return(UnsafeNativeMethods.CallWindowProc(oldWndProc, hwnd, (int)msg, wParam, lParam));
}