Refreshing region outside client area.

[sjc]

I have a window, and as part of an internal diagnostic, I frame a region around it. I have a CRgn member, and whenever my window receives the WM_PAINT message, I create a CWindowDC given the Desktop window and call FrameRgn on it. This part works fine. However when my window goes away, I want to invalidate and repaint the region to remove the frame from the windows I painted over. I can't seem to figure out how to do this since the InvalidateRgn and Update API methods all take an HWND. In this case, I don't have an HWND, I just have an HRGN on the screen. What's the best way to invalidate this region without knowing what windows intersect it? Thanks!

[sjc]

I was able to find a way to do it by enumerating all top-level windows (EnumWindows) and seeing if the region intersected with each window. If so, invalidate and redraw that window (as long as its visible). While this seems to work, it's not ideal. Is there a better way?

[ProgramArtist]

What is wrong with this solution?

What should be better?

[sjc]

I was hoping you could just pass NULL as the 'hWnd' into InvalidateRgn or something, and the Win32API would invalidate all windows that intersect the given region. It just seems like there should be a single API for doing this rather than having to enumerate all the top-level windows. Seems like a hack to me.

[ProgramArtist]

The MSDN says:

A handle to the window whose update region has changed. If this parameter is NULL, the system invalidates and redraws all windows, not just the windows for this application, and sends the WM_ERASEBKGND and WM_NCPAINT messages before the function returns. Setting this parameter to NULL is not recommended.

To try it out I did the following:

    HWND hWnd = ::GetDesktopWindow();
    if (hWnd)
    {
        ::InvalidateRect(hWnd, NULL, TRUE);
        ::SendMessage(hWnd, WM_PAINT, 0, 0);
    }

and it didn't work (no flickering of my great IDE occured)

But the MSDN indeed is right:

        ::InvalidateRect(NULL, NULL, TRUE);

worked.

So you shouldn't set the HWND param of InvalidateRect to the handle of the desktop window, but instead set it to NULL.

I don't knwo exactly how mean I'm since I'm doing something "not recommended"..., but it worked.

regards
PA

[sjc]

I do lots of things that aren't recommended, so what's one more? =) Thanks for your assistance, ProgramArtist.

[Eri523]

So it looks like the appilication windows aren't all children of the desktop window. Instead, the desktop is just some sort of another application window, invariably lying below all the others in the Z order.