Question

I’m wondering if it’s possible to toggle back and forth between fullscreen mode and windowed mode in an OpenGL window(I’m writing for Windows using C++ and win32), without destroying the OpenGL context, and thus having to reload assets(Textures, VBOs, etc) in the process?

This is undesirable because it introduces a delay in switching between fullscreen and windowed mode, potentially a long one, as well as making it easier to screw things up by forgetting to reinitialize something.

As a followup to that, are there certain visual effects that are broken by managing to do this?

I’ve done a fair bit of searching and reading for the past few days, and despite a lot of flaming of SDL and other frameworks for having the same problem(I’m not using them anyway, but…), the best I’ve managed to find is a possible lead on opening a 1×1 window in the background to retain the context while a secondary window is destroyed or created at whim. And that’s seeming unreliable from the comments I found regarding it, and seems very kludgey regardless.

Is there a proper way to do this, or is the proper way the often-given-as-an-example method of destroying your window, and recreating it, including destroying your OpenGL context and recreating it?

Answer 1

Basically it’s just resizing the window and specifying flags that the border is invisible.

SetWindowLongPtr(hWnd, GWL_STYLE, 
    WS_SYSMENU | WS_POPUP | WS_CLIPCHILDREN | WS_CLIPSIBLINGS | WS_VISIBLE);
MoveWindow(hWnd, 0, 0, width, height, TRUE);

to set it back:

RECT rect;
rect.left = 0;
rect.top = 0;
rect.right = width;
rect.bottom = height;
SetWindowLongPtr(hWnd, GWL_STYLE, WS_OVERLAPPEDWINDOW | WS_VISIBLE);
AdjustWindowRect(&rect, WS_OVERLAPPEDWINDOW, FALSE);
MoveWindow(hWnd, 0, 0, rect.right-rect.left, rect.bottom-rect.top, TRUE);

or for a not-resizable window:

SetWindowLongPtr(hWnd, GWL_STYLE, WS_CAPTION | WS_POPUPWINDOW | WS_VISIBLE);
AdjustWindowRect(&rect, WS_CAPTION | WS_POPUPWINDOW, FALSE);
MoveWindow(hWnd, 0, 0, rect.right-rect.left, rect.bottom-rect.top, TRUE);

and then just resize your OpenGL viewport settings.

If you want to set the display mode too, use this:

// change display mode if destination mode is fullscreen
if (fullscreen) {
    DEVMODE dm;
    dm.dmSize = sizeof(DEVMODE);
    dm.dmPelsWidth = width;
    dm.dmPelsHeight = height;
    dm.dmBitsPerPel = bitsPerPixel;
    dm.dmFields = DM_PELSWIDTH | DM_PELSHEIGHT | DM_BITSPERPEL;
    success = ChangeDisplaySettings(&dm, 0) == DISP_CHANGE_SUCCESSFUL;
}

// reset display mode if destination mode is windowed
if (!fullscreen)
    success = ChangeDisplaySettings(0, 0) == DISP_CHANGE_SUCCESSFUL;