function circularIndex(start, delta, len) {
    var mod = (start + delta) % len;
    return ((mod >= 0) ? mod : mod + len);
}

function delta(oldIndex, newIndex) {
    if (oldIndex > newIndex)
        return 0 - (oldIndex - newIndex);
    else if (oldIndex < newIndex)
        return (newIndex - oldIndex);
    else
        return 0;
}

function Point(x, y) {
    this.x = x;
    this.y = y;
}