Clearing the screen after switching away from fullscreen mode? - c++

Question

So I've got an OpenGL application running that can toggle between fullscreen mode and windowed mode. It currently does this by resizing the window and changing styles.
However, it seems to not invalidate the screen when switching from fullscreen mode to windowed mode, which leaves things I've drawn lingering onscreen after the switch.
Interestingly, it only exhibits this behavior in single monitor mode. If I'm running with multiple monitors, it invalidates okay, and clears my drawing.
I don't think this is a driver bug, as it's happening on two separate computers using two separate video cards(although admittedly they are both nVidia.), I'm thinking I'm doing something wrong somewhere.
I've tried a bunch of methods for getting Windows to clear the screen of my previously fullscreen drawings, but nothing seems to work. InvalidateRect(), RedrawWindow(), ChangeDisplaySettings()...
Specifically:
InvalidateRect(m_hwnd, &rectx, true); // rect being the dimensions of either the screen or my window.
InvalidateRect(HWND_DESKTOP, NULL, TRUE); // Doesn't seem to do anything.
RedrawWindow(NULL, NULL, NULL, RDW_INVALIDATE | RDW_ALLCHILDREN | RDW_UPDATENOW);
ChangeDisplaySettings(NULL, 0);
Well, actually, one thing that does seem to work is ShowWindow(hwnd, SW_HIDE) before resizing. However that loses focus for a moment, allowing other applications to grab my application's input, and seems a bad way to go about it.
I should note that I'm not doing any actual display mode changes when I'm seeing this behavior; just staying at the current resolution for fullscreen.
I'm a bit clueless where I'm going wrong. Simplified code:
if(m_isFullscreen)
{
ChangeDisplaySettings(&dmScreenSettings, CDS_FULLSCREEN);
}
else
{
ChangeDisplaySettings(&m_dmSavedScreenSettings, 0);
}
if(m_isFullscreen)
{
dwExStyle = WS_EX_APPWINDOW;
dwStyle = WS_POPUP;
ShowCursor(false);
}
else
{
dwExStyle = WS_EX_APPWINDOW | WS_EX_WINDOWEDGE;
dwStyle = WS_OVERLAPPEDWINDOW;
if(m_isRunning) // Because ShowCursor uses a counter to indicate, and windowed mode defaults to cursor on, we don't need to increment the counter and double it being on.
{
ShowCursor(true);
}
}
RECT rect;
rect.left = 0;
rect.top = 0;
if(m_isFullscreen) { rect.right = 1280; } else { rect.right = 640; }
if(m_isFullscreen) { rect.bottom = 1024; } else { rect.bottom = 480; }
AdjustWindowRectEx(&rect, dwStyle, false, dwExStyle);
SetWindowLongPtr(m_hwnd, GWL_STYLE, dwStyle | WS_CLIPCHILDREN | WS_CLIPSIBLINGS);
SetWindowLongPtr(m_hwnd, GWL_EXSTYLE, dwExStyle);
if(m_isFullscreen)
{
MoveWindow(m_hwnd, 0, 0, 1280, 1024, true);
}
else
{
MoveWindow(m_hwnd, 0, 0, 640, 480, true); // windowed
}
And that's more or less it. Some other supporting code and error checking, but that's what I'm doing... dmSavedSettings is saved before m_hwnd is assigned from NULL, and not afterwards. My initial window creation works fine, and fullscreen works fine. It's just returning to Windowed after being fullscreen that's the issue.

Answer 1

If you set a null background brush in your window class, windows will not be cleared automatically. You must add a WM_PAINT handler that calls your OpenGL display handler, which in turn clears the viewport (glClearColor) and redraws.

Answer 2

As datenwolf mentions in another answer's comment, you want to use SetWindowPos() instead of MoveWindow() when making use of SetWindowLongPtr().
My dirty background problems were solved by calling ChangeDisplaySettings(NULL, 0) AFTER resizing my window. Doing it before does little, but afterwards appears to work fine.