Is there a graceful way to handle toggling between fullscreen and windowed mode in a Windows OpenGL application? - c++

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 1x1 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;

Answer 2

Here's the code I use, which uses SetWindowPos() rather than MoveWindow(), as discussed in the comments of the other answer.
void enter_fullscreen(application* App)
{
POINT Point = {0};
HMONITOR Monitor = MonitorFromPoint(Point, MONITOR_DEFAULTTONEAREST);
MONITORINFO MonitorInfo = { sizeof(MonitorInfo) };
if (GetMonitorInfo(Monitor, &MonitorInfo)) {
DWORD Style = WS_POPUP | WS_VISIBLE;
SetWindowLongPtr(App->Window, GWL_STYLE, Style);
SetWindowPos(App->Window, 0, MonitorInfo.rcMonitor.left, MonitorInfo.rcMonitor.top,
MonitorInfo.rcMonitor.right - MonitorInfo.rcMonitor.left, MonitorInfo.rcMonitor.bottom - MonitorInfo.rcMonitor.top,
SWP_FRAMECHANGED | SWP_SHOWWINDOW);
}
App->IsFullscreen = true;
}
void exit_fullscreen(application* App)
{
bool WasMaximized = App->IsMaximized;
DWORD Style = WS_OVERLAPPEDWINDOW | WS_VISIBLE | WS_CLIPCHILDREN;
if (WasMaximized) {
Style = Style | WS_MAXIMIZE;
}
ivec2 WindowPosition = WasMaximized ? App->WindowPosition : App->NormalWindowPosition;
ivec2 WindowSize = WasMaximized ? App->WindowSize : App->NormalWindowSize;
SetWindowLongPtr(App->Window, GWL_STYLE, Style);
SetWindowPos(App->Window, 0,
WindowPosition.X, WindowPosition.Y, WindowSize.X, WindowSize.Y,
SWP_FRAMECHANGED | SWP_SHOWWINDOW);
App->IsFullscreen = false;
}
I call it on F11, but also on WM_ACTIVATE. Otherwise the window would sometimes keep rendering on top on Windows 7, even if another application would receive all messages, including mouse and keyboard.