https://github.com/SDL-mirror/SDL/blob/master/src/video/x11/SDL_x11events.c#L949-L956

SDL receiving UnmapNotify event assumes that window has been iconified. This assumption seems wrong... For example UnmapNotify event is also sent when window is reparented, see https://tronche.com/gui/x/xlib/window-and-session-manager/XReparentWindow.html.

This causes problems when using SDL applications with Metacity 3.36+. Metacity now removes decorations when windows are fullscreen.

Perhaps SDL could check if next event is ReparentNotify and not dispatch UnmapNotify in that case? Something like this:

XEvent ev;
if (X11_XCheckIfEvent(display, &ev, &isReparentNotify, (XPointer)&xevent.xunmap))
  X11_XCheckIfEvent(display, &ev, &isMapNotify, (XPointer)&xevent.xunmap);
else
  X11_DispatchUnmapNotify(data);


static Bool isMapNotify(Display *dpy, XEvent *ev, XPointer unmap)
{
    XUnmapEvent *event;

    event = (XUnmapEvent*) unmap;

    return ev->type == MapNotify &&
        ev->xmap.window == event->window &&
        ev->xmap.serial == event->serial;
}

static Bool isReparentNotify(Display *dpy, XEvent *ev, XPointer unmap)
{
    XUnmapEvent *event;

    event = (XUnmapEvent*) unmap;

    return ev->type == ReparentNotify &&
        ev->xreparent.window == event->window &&
        ev->xreparent.serial == event->serial;
}