效果預覽：
一、模擬抽獎的實現過程
旋轉原理：當支持CSS3屬性採用transform: rotate（角度deg）設置,當角度為正數時順時針旋轉，當為負數時逆時針旋轉。如果是IE8及其以下，採用採用絕對定位設置top和left，模擬角度旋轉。
run方法，參數angle指角度
複製代碼代碼如下:
function run(angle) {
if (isIE) {
cosDeg = Math.cos(angle * Math.PI / 180);
sinDeg = Math.sin(angle * Math.PI / 180);
with (target.filters.item(0)) {
M11 = M22 = cosDeg; M12 = -(M21 = sinDeg);
}
target.style.top = (orginH - target.offsetHeight) / 2 + "px";
target.style.left = (orginW - target.offsetWidth) / 2 + "px";
} else if (target.style.MozTransform !== undefined) {
target.style.MozTransform = "rotate(" + angle + "deg)";
} else if (target.style.OTransform !== undefined) {
target.style.OTransform = "rotate(" + angle + "deg)";
} else if (target.style.webkitTransform !== undefined) {
target.style.webkitTransform = "rotate(" + angle + "deg)";
} else {
target.style.transform = "rotate(" + angle + "deg)";
}
}
模擬轉盤加速，勻速和減速。當角度小於某個數值時，讓其處於加速此處採用1.01的係數作為加速度，當大於某個數值時處於高速勻速狀態，當角度大於設置的最大數值時，讓其減速採用係數為0.99。設置負數作為減速的值（即變量tmp），隨即獲取負360中的值（即變量m），當大於這個值時，轉盤停止。
複製代碼代碼如下:
var tmp = -900;
var m = -parseInt(Math.random() * 360);
timer = setInterval(function () {
if (i > 3000) {
tmp = parseInt(tmp * 0.99);
if (tmp > m) {
tmp = m;
clearInterval(timer);
msg(m);
}
run(tmp);
}
else if (i > 1000) {
i = i + 45;
run(i);
}
else {
i = parseInt((i + 1) * 1.01);
run(i);
}
}, 50);
啟動抽獎和重新設置抽獎
複製代碼代碼如下:
<input id="test" type="button" value="抽獎" />
<input id="restart" style="display: none;" type="button" value="再抽一次" />
m$('test').onclick = function () {
m$('test').style.display = "none";
showMsg();
}
m$('restart').onclick = function () {
m$('restart').style.display = "none";
if (isIE) {
m$("demo").style.top = "0px";
m$("demo").style.left = "0px";
} else if (m$("demo").style.MozTransform !== undefined) {
m$("demo").style.MozTransform = 'rotate(0deg)';
} else if (m$("demo").style.OTransform !== undefined) {
m$("demo").style.OTransform = 'rotate(0deg)';
} else if (m$("demo").style.webkitTransform !== undefined) {
m$("demo").style.webkitTransform = 'rotate(0deg)';
} else {
m$("demo").style.transform = 'rotate(0deg)';
}
m$('test').style.display = "block";
i = 0;
}
二、完整代碼demo:
複製代碼代碼如下:<!DOCTYPE html>
<html>
<head>
<title>抽獎</title>
<style type="text/css">
#container{width: 400px;height: 400px;position: relative;margin: 0 auto;}
#demo{position: absolute;filter: progid:DXImageTransform.Microsoft.Matrix(sizingmethod="auto expand");}
</style>
</head>
<body style="height: 1000px;">
<div id="container">
<div id="demo">
<img src="//files.VeVB.COm/file_images/article/201406/20146394819279.png" />
</div>
</div>
<input id="test" type="button" value="抽獎" />
<input id="restart" style="display: none;" type="button" value="再抽一次" />
<div id="msg">
</div>
<script type="text/javascript">
var m$ = function (id) { return document.getElementById(id); }
var ua = navigator.userAgent;
var isIE = /msie/i.test(ua) && !window.opera;
var i = 1, sinDeg = 0, cosDeg = 0, timer = null;
var mRotate = function () {
var rotate = function (target, msg) {
target = m$(target);
var orginW = target.clientWidth, orginH = target.clientHeight;
clearInterval(timer);
function run(angle) {
if (isIE) {
cosDeg = Math.cos(angle * Math.PI / 180);
sinDeg = Math.sin(angle * Math.PI / 180);
with (target.filters.item(0)) {
M11 = M22 = cosDeg; M12 = -(M21 = sinDeg);
}
target.style.top = (orginH - target.offsetHeight) / 2 + "px";
target.style.left = (orginW - target.offsetWidth) / 2 + "px";
} else if (target.style.MozTransform !== undefined) {
target.style.MozTransform = "rotate(" + angle + "deg)";
} else if (target.style.OTransform !== undefined) {
target.style.OTransform = "rotate(" + angle + "deg)";
} else if (target.style.webkitTransform !== undefined) {
target.style.webkitTransform = "rotate(" + angle + "deg)";
} else {
target.style.transform = "rotate(" + angle + "deg)";
}
}
var tmp = -900;
var m = -parseInt(Math.random() * 360);
timer = setInterval(function () {
if (i > 3000) {
tmp = parseInt(tmp * 0.99);
if (tmp > m) {
tmp = m;
clearInterval(timer);
msg(m);
}
run(tmp);
}
else if (i > 1000) {
i = i + 45;
run(i);
}
else {
i = parseInt((i + 1) * 1.01);
run(i);
}
}, 50);
}
return { rotate: rotate }
} ();
function showMsg() {
mRotate.rotate("demo", function msg(m) {
if (m > -90 && m < -30) {
m$("msg").innerHTML += "22222222";
}
else if (m > -150 && m < -90) {
m$("msg").innerHTML += "333333333";
}
else if (m > -210 && m < -150) {
m$("msg").innerHTML += "444444";
}
else if (m > -270 && m < -210) {
m$("msg").innerHTML += "5555555";
}
else if (m > -330 && m < -270) {
m$("msg").innerHTML += "6666666";
} else {
m$("msg").innerHTML += "111111111";
}
m$('restart').style.display = "block";
});
}
window.onload = function () {
m$('test').onclick = function () {
m$('test').style.display = "none";
showMsg();
}
m$('restart').onclick = function () {
m$('restart').style.display = "none";
if (isIE) {
m$("demo").style.top = "0px";
m$("demo").style.left = "0px";
} else if (m$("demo").style.MozTransform !== undefined) {
m$("demo").style.MozTransform = 'rotate(0deg)';
} else if (m$("demo").style.OTransform !== undefined) {
m$("demo").style.OTransform = 'rotate(0deg)';
} else if (m$("demo").style.webkitTransform !== undefined) {
m$("demo").style.webkitTransform = 'rotate(0deg)';
} else {
m$("demo").style.transform = 'rotate(0deg)';
}
m$('test').style.display = "block";
i = 0;
}
}
</script>
</body>
</html>