vroot.h

/* -*- Mode: C; tab-width: 2 -*-                                             */
/*****************************************************************************/
/**                   Copyright 1991 by Andreas Stolcke                     **/
/**               Copyright 1990 by Solbourne Computer Inc.                 **/
/**                          Longmont, Colorado                             **/
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/*****************************************************************************/
/*
 * vroot.h -- Virtual Root Window handling header file
 *
 * This header file redefines the X11 macros RootWindow and DefaultRootWindow,
 * making them look for a virtual root window as provided by certain `virtual'
 * window managers like swm and tvtwm. If none is found, the ordinary root
 * window is returned, thus retaining backward compatibility with standard
 * window managers.
 * The function implementing the virtual root lookup remembers the result of
 * its last invocation to avoid overhead in the case of repeated calls
 * on the same display and screen arguments.
 * The lookup code itself is taken from Tom LaStrange's ssetroot program.
 *
 * Most simple root window changing X programs can be converted to using
 * virtual roots by just including
 *
 * #include <X11/vroot.h>
 *
 * after all the X11 header files.  It has been tested on such popular
 * X clients as xphoon, xfroot, xloadimage, and xaqua.
 * It also works with the core clients xprop, xwininfo, xwd, and editres
 * (and is necessary to get those clients working under tvtwm).
 * It does NOT work with xsetroot; get the xsetroot replacement included in
 * the tvtwm distribution instead.
 *
 * Andreas Stolcke <stolcke@ICSI.Berkeley.EDU>, 9/7/90
 * - replaced all NULL's with properly cast 0's, 5/6/91
 * - free children list (suggested by Mark Martin <mmm@cetia.fr>), 5/16/91
 * - include X11/Xlib.h and support RootWindowOfScreen, too 9/17/91
 *
 * Jamie Zawinski <jwz@jwz.org>, 28-Apr-1997
 * - use ANSI C
 *
 * Jamie Zawinski <jwz@jwz.org>, 3-Sep-2003
 * - if the environment variable "XSCREENSAVER_WINDOW" is set, use that
 *   as the root window instead of searching for __SWM_VROOT.
 *
 * Jamie Zawinski <jwz@jwz.org>, 14-Aug-2004
 * - changes to get gcc to stop whining about "type punning".
 *
 * Jamie Zawinski <jwz@jwz.org>, 16-Dec-2004
 * - fixed that last fix.
 */

#ifndef _VROOT_H_
#define _VROOT_H_
#define _XSCREENSAVER_VROOT_H_

#if !defined(lint) && !defined(SABER)
static const char vroot_rcsid[] =
 "#Id: vroot.h,v 1.8 2004/12/16 05:33:54 jwz Exp #" "\n"
 "#Id: vroot.h,v 1.4 1991/09/30 19:23:16 stolcke Exp stolcke #";
#endif

#include <X11/X.h>
#include <X11/Xatom.h>
#include <X11/Xlib.h>

static Window
#ifdef __STDC__ /* ANSIfication added by jwz, to avoid superfluous warnings. */
VirtualRootWindowOfScreen(Screen *screen)
#else /* !__STDC__ */
VirtualRootWindowOfScreen(screen) Screen *screen;
#endif /* !__STDC__ */
{
    static Screen *save_screen = (Screen *)0;
    static Window root = (Window)0;

    if (screen != save_screen) {
        Display *dpy = DisplayOfScreen(screen);
        Atom __SWM_VROOT = None;
        int i;
        Window rootReturn, parentReturn, *children;
        unsigned int numChildren;

    /* first check for a hex or decimal window ID in the environment */
    const char *xss_id = getenv("XSCREENSAVER_WINDOW");
    if (xss_id && *xss_id) {
      unsigned long id = 0;
      char c;
      if (1 == sscanf (xss_id, " 0x%lx %c", &id, &c) ||
          1 == sscanf (xss_id, " %lu %c",   &id, &c)) {
        root = (Window) id;
        save_screen = screen;
        return root;
      }
    }

        root = RootWindowOfScreen(screen);

        /* go look for a virtual root */
        __SWM_VROOT = XInternAtom(dpy, "__SWM_VROOT", False);
        if (XQueryTree(dpy, root, &rootReturn, &parentReturn,
                 &children, &numChildren)) {
            for (i = 0; i < numChildren; i++) {
                Atom actual_type;
                int actual_format;
                unsigned long nitems, bytesafter;
                unsigned char *newRoot = 0;

                if (XGetWindowProperty(dpy, children[i],
                    __SWM_VROOT, 0, 1, False, XA_WINDOW,
                    &actual_type, &actual_format,
                    &nitems, &bytesafter,
                    &newRoot) == Success
                    && newRoot) {
                    root = *((Window *) newRoot);
                    break;
                }
            }
            if (children)
                XFree((char *)children);
        }

        save_screen = screen;
    }

    return root;
}

#undef RootWindowOfScreen
#define RootWindowOfScreen(s) VirtualRootWindowOfScreen(s)

#undef RootWindow
#define RootWindow(dpy,screen) VirtualRootWindowOfScreen(ScreenOfDisplay(dpy,screen))

#undef DefaultRootWindow
#define DefaultRootWindow(dpy) VirtualRootWindowOfScreen(DefaultScreenOfDisplay(dpy))

#endif /* _VROOT_H_ */