I only get VisibilityNotify events at window mapping

[Lucas de Sena]

Hi,

I'm trying to get VisibilityNotify events to check whether a given
window is obscured.

However, I only get VisibilityNotify events after mapping the window.
Obscuring it with any other window (be it a sibling or not) does not
trigger a VisibilityNotify event, nor when I unobscure it.

And when I get such event, the value of `ev.xvisibility.state` is always
`VisibilityUnobscured`, even when mapping the window below others.

Here's a sample program:

        #include <stdio.h>
        #include <X11/Xlib.h>
        
        int
        main(void)
        {
                Display *dpy;
                Window win;
                XEvent ev;
        
                if ((dpy = XOpenDisplay(NULL)) == NULL)
                        return 1;
                win = XCreateWindow(
                        dpy,
                        XDefaultRootWindow(dpy),
                        0, 0,
                        100, 100,
                        0,
                        CopyFromParent, InputOutput, CopyFromParent,
                        CWEventMask | CWBackPixel,
                        &(XSetWindowAttributes){
                                .event_mask = VisibilityChangeMask,
                                .background_pixel = BlackPixel(dpy, 
DefaultScreen(dpy)),
                        }
                );
                XMapWindow(dpy, win);
                while (!XNextEvent(dpy, &ev))
                        if (ev.type == VisibilityNotify)
                                printf("visibility: %d\n", 
ev.xvisibility.state);
                return 0;
        }

Is that how VisibilityNotify is supposed to work?