目的：
利用html5，css實現(xiàn)鐘擺效果
知識點：
1） 利用position/left/top和calc()實現(xiàn)元素的水平和垂直居中；
2） 利用CSS3的animation/transform/transform-origin屬性定義動畫；
3） 利用transform-origin實現(xiàn)旋轉(zhuǎn)原點的圓心調(diào)整
廢話不多說了，直接看代碼吧，具體代碼如下所示：
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style>
li{
list-style:none;
}
#box{
width: 400px;
height: 400px;
position: absolute;
top:calc(50% - 200px);
left:calc(50% - 200px);
border: 2px solid palegoldenrod;
}
#dial{
width: 200px;
height: 200px;
position: absolute;
top:calc(50% - 100px);
left:calc(50% - 100px);
border: 2px solid cyan;
border-radius: 50%;
}
.scaleIndex{
width: 4px;
height: 12px;
position: absolute;
top: 0;
left: calc(50% - 2px);
background-color: gray;
transform-origin: 2px 100px;
}
.angle30{transform : rotate(30deg);}
.angle60{transform : rotate(60deg);}
.angle90{transform : rotate(90deg);}
.angle120{transform : rotate(120deg);}
.angle150{transform : rotate(150deg);}
.angle180{transform : rotate(180deg);}
.angle210{transform : rotate(210deg);}
.angle240{transform : rotate(240deg);}
.angle270{transform : rotate(270deg);}
.angle300{transform : rotate(300deg);}
.angle330{transform : rotate(330deg);}
#fixPoint{
width: 10px;
height: 10px;
position: absolute;
top:calc(50% - 5px);
left:calc(50% - 5px);
background-color: cadetblue;
border-radius: 50%;
}
#hourHand{
width: 6px;
height: 70px;
position:absolute;
top: 40px;
left: calc(50% - 3px);
background-color: darkblue;
transform-origin: 50% 60px;
}
#minuteHand{
width: 4px;
height: 75px;
position:absolute;
top: 35px;
left: calc(50% - 2px);
background-color: yellow;
transform-origin: 50% 65px;
}
#secondHand{
width: 2px;
height: 90px;
position:absolute;
top: 20px;
left: calc(50% - 1px);
background-color: red;
transform-origin: 50% 80px;
}
</style>
</head>
<body>
<div id = "box">
<div id = 'dial'>
<ul id = "scale">
<li class = "scaleIndex"></li>
<li class = "scaleIndex angle30"></li>
<li class = "scaleIndex angle60"></li>
<li class = "scaleIndex angle90"></li>
<li class = "scaleIndex angle120"></li>
<li class = "scaleIndex angle150"></li>
<li class = "scaleIndex angle180"></li>
<li class = "scaleIndex angle210"></li>
<li class = "scaleIndex angle240"></li>
<li class = "scaleIndex angle270"></li>
<li class = "scaleIndex angle300"></li>
<li class = "scaleIndex angle330"></li>
</ul>
<div id = "fixPoint"></div>
<div id = "hourHand"></div>
<div id = "minuteHand"></div>
<div id = "secondHand"></div>
</div>
</div>
<script type = 'text/javascript' src = 'js/jquery-3.2.1.js'></script>
<script type = "text/javascript">
window.onload = function(){
var hourHand = document.getElementById('hourHand');
var minuteHand = document.getElementById('minuteHand');
var secondHand = document.getElementById('secondHand');
setInterval(function(){
var currentTime = new Date();
var hourValue = currentTime.getHours();
var hourAngle = hourValue / 24 * 360 + 'deg';
var minuteValue = currentTime.getMinutes();
var minuteAngle = minuteValue / 60 * 360 + 'deg';
var secondValue = currentTime.getSeconds();
var secondAngle = secondValue / 60 * 360 + 'deg';
console.log(hourAngle);
// 方法一：利用jquery的css()增加屬性
var cmdHour = 'rotate('+ hourAngle +')';
$('#hourHand').css({transform:'rotate('+ hourAngle +')'});
var cmdMinute = 'rotate('+ minuteAngle +')';
$('#minuteHand').css({transform:cmdMinute});
var cmdSecond = 'rotate('+ secondAngle +')';
$('#secondHand').css({transform:cmdSecond});
// 方法二：利用DOM元素的style屬性設(shè)置
// hourHand.style.transform = 'rotate('+ hourAngle + ')';
// minuteHand.style.transform = 'rotate('+ minuteAngle + ')';
// secondHand.style.transform = 'rotate('+ secondAngle + ')';
},1000);
}
</script>
</body>
</html>
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