简单的碰撞运动

//碰撞运动
//对运动的方向以及临界值的处理
function bumpMove(obj) {
    clearInterval(obj.timer);
    var speedX = 10;
    var speedY = 10;
    timer = setInterval(function() {
        var L = obj.offsetLeft + speedX;
        var T = obj.offsetTop + speedY;

        if(T > document.documentElement.clientHeight - obj.offsetHeight) {
            T = document.documentElement.clientHeight - obj.offsetHeight;
            speedY *= -1;
        } else if(T < 0) {
            T = 0;
            speedY *= -1;
        }
        if(L > document.documentElement.clientWidth - obj.offsetWidth) {
            L = document.documentElement.clientWidth - obj.offsetWidth;
            speedX *= -1;
        } else if(L < 0) {
            L = 0;
            speedX *= -1;
        }

        obj.style.left = L + ‘px‘;
        obj.style.top = T + ‘px‘;
    }, 30);

}