/usr/src/RPM/BUILD/ctwm-4.1.0/win_ring.c

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/*
 * Functions related to the window ring.
 *
 * Invariants:
 * - If a window is not on the ring, its TwmWindow::ring.next and .prev
 *   are both NULL.
 * - If a window is on the ring, they are both not NULL and point to a
 *   window which is also on the ring.
 * - Corollary: if a window is the only one on the ring, .next and .prev
 *   point to itself.
 * - Functions which act on the "current" ring window, i.e. the window
 *   that has most recently been entered and is on the ring, use
 *   Scr->RingLeader.
 * - If RingLeader is NULL, fall back to Scr->Ring.
 * - If Ring is NULL, the ring is empty (and RingLeader is also NULL).
 */
 
#include "ctwm.h"
 
#include <assert.h>
 
#include "screen.h"
#include "win_ring.h"
 
void
UnlinkWindowFromRing(TwmWindow *win)
{
    TwmWindow *prev = win->ring.prev;
    TwmWindow *next = win->ring.next;
 
    // We call this unconditionally at various window deletion times, and
    // if it's not on the ring, there's nothing to do.  e.g., if we don't
    // have any WindowRing config enabled...
    if(!WindowIsOnRing(win)) {
        return;
    }
 
    // But if it is, prev/next should always exist.
    assert(prev != NULL);
    assert(next != NULL);
 
    /*
    * 1. Unlink window
    * 2. If window was only thing in ring, null out ring
    * 3. If window was ring leader, set to next (or null)
    *
    * If the window is the only one in the ring, prev == next == win,
    * so the unlinking effectively is a NOP, but that doesn't matter.
    */
    prev->ring.next = next;
    next->ring.prev = prev;
 
    win->ring.next = win->ring.prev = NULL;
 
    if(Scr->Ring == win) {
        Scr->Ring = (next != win ? next : NULL);
    }
 
    if(!Scr->Ring || Scr->RingLeader == win) {
        Scr->RingLeader = Scr->Ring;
    }
}
 
static void
AddWindowToRingUnchecked(TwmWindow *win, TwmWindow *after)
{
    TwmWindow *before = after->ring.next;
 
    win->ring.next = before;
    win->ring.prev = after;
 
    after->ring.next = win;
    before->ring.prev = win;
}
 
void
AddWindowToRing(TwmWindow *win)
{
    assert(win->ring.next == NULL);
    assert(win->ring.prev == NULL);
 
    if(Scr->Ring) {
        AddWindowToRingUnchecked(win, Scr->Ring);
    }
    else {
        win->ring.next = win->ring.prev = Scr->Ring = win;
    }
}