javascript每日一练（十）——运动二：缓冲运动

一、缓冲运动

　　实现原理：(目标距离-当前距离) / 基数 = 速度(运动距离越大速度越小，运动距离和速度成反比)　　(500 - oDiv.offsetLeft) / 7 = iSpeed;

　　需要注意：当计算出来的速度有小数时需要取整；

　　(500 - oDiv.offsetLeft) / 7 = iSpeed; iSpeed = iSpeed>0?Math.ceil(iSpeed):Math.floor(iSpeed);

例子1：

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>缓冲运动</title>
<style>
#div1{ width:100px; height:100px; background:red; position:absolute; top:50px; left:0;}
span{ width:1px; height:300px; background:black; position:absolute; left:300px; top:0; display:block;}
</style>
<script>
window.onload = function()
{
    var oBtn = document.getElementById('btn1');
    var oDiv = document.getElementById('div1');

    oBtn.onclick = function()
    {
        startMove(oDiv, 300);
    };
};

var timer = null;
function startMove(obj, iTarget)
{
    clearInterval(timer);

    timer = setInterval(function(){
        var iSpeed = (iTarget - obj.offsetLeft)/8;
        iSpeed = iSpeed>0?Math.ceil(iSpeed):Math.floor(iSpeed);

        if(iTarget==obj.offsetLeft){
            clearInterval(timer);
        }else{
            obj.style.left = obj.offsetLeft + iSpeed + 'px';
        }
    }, 30);
}
</script>
</head>

<body>
<input id="btn1" type="button" value="移动" />
<div id="div1"></div>
<span></span>
</body>
</html>

例子2：侧边栏滑动

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>侧边栏滑动</title>
<style>
#div1{ width:100px; height:100px; background:red; position:absolute; right:0; top:0;}
</style>
<script>
window.onload = window.onscroll = function()
{
    var oDiv = document.getElementById('div1');
    var iScrollTop = document.documentElement.scrollTop || document.body.scrollTop;
    var clientHeight = document.documentElement.clientHeight;
    var iH = (clientHeight - oDiv.offsetHeight)/2 + iScrollTop;

    //oDiv.style.top = iH + 'px';
    startMove(oDiv, parseInt(iH));

};
var timer = null;

function startMove(obj, iTarget)
{
    clearInterval(timer);

    timer = setInterval(function(){
        var iSpeed = (iTarget - obj.offsetTop) / 8;
        iSpeed = iSpeed>0?Math.ceil(iSpeed):Math.floor(iSpeed);

        if(obj.offsetTop == iTarget){
            clearInterval(timer);
        }else{
            obj.style.top = obj.offsetTop + iSpeed + 'px';
        }
    }, 30);
}
</script>
</head>

<body style="height:2000px;">
<div id="div1"></div>
</body>
</html>