static void vnc_rect_updated(VncDisplay *vd, int x, int y, struct timeval * tv)
{
    VncRectStat *rect;

    rect = vnc_stat_rect(vd, x, y);
    if (rect->updated) {
        return ;
    }
    rect->times[rect->idx] = *tv;
    rect->idx = (rect->idx + 1) % ARRAY_SIZE(rect->times);
    rect->updated = true;
}