前兩天面試，讓我現場用css3做一個圓環加載的進度條，沒寫出來，尷尬了。抽空參考了些網上的例子，做了下面這個demo。
效果圖：
當時的要求是讓進度條以扇形漸變的效果加載。我想了半天，好像只有用border-img來做漸變圖了，還有一個超笨的方法就是寫50個長方形分佈在進度條上。css3提供的漸變有線性漸變，徑向漸變和重複漸變，想不出來怎樣實現扇形漸變。不說了，上代碼：
<!DOCTYPE html>
<html lang="cn">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
*{
margin: 0;
padding: 0;
}
.wrap,.circle,.percent{
position: absolute;
width: 200px;
height: 200px;
border-radius: 50%;
}
.wrap{
top:50px;
left:50px;
background-color: #ccc;
}
.circle{
box-sizing: border-box;
border:20px solid #ccc;
clip:rect(0,200px,200px,100px);
}
.clip-auto{
clip:rect(auto, auto, auto, auto);
}
.percent{
box-sizing: border-box;
top:-20px;
left:-20px;
}
.left{
transition:transform ease;
border:20px solid blue;
clip: rect(0,100px,200px,0);
}
.right{
border:20px solid blue;
clip: rect(0,200px,200px,100px);
}
.wth0{
width:0;
}
.num{
position: absolute;
box-sizing: border-box;
width: 160px;
height: 160px;
line-height: 160px;
text-align: center;
font-size: 40px;
left: 20px;
top: 20px;
border-radius: 50%;
background-color: #fff;
z-index: 1;
}
</style>
<script src="http://apps.bdimg.com/libs/zepto/1.1.4/zepto.min.js"></script>
</head>
<body>
<div class="wrap">
<div class="circle">
<div class="percent left"></div>
<div class="percent right wth0"></div>
</div>
<div class="num"><span>0</span>%</div>
</div>
</body>
<script>
var percent=0;
var loading=setInterval(function(){
if(percent>100){
percent=0;
$('.circle').removeClass('clip-auto');
$('.right').addClass('wth0');
}else if(percent>50){
$('.circle').addClass('clip-auto');
$('.right').removeClass('wth0');
}
$('.left').css("-webkit-transform","rotate("+(18/5)*percent+"deg)");
$('.num>span').text(percent);
percent++;
},200);
</script>
</html>