前言:在拿到一个需求之前，我们要先进行分析，再设计，最后实现代码的编写以及调试。
放大镜的原理分析
- 鼠标在小图片上移动时，通过捕获鼠标在小图片上的位置，定位大图片的相应位置
放大镜特效设计
- 页面元素
- 技术点：事件捕获、定位
- 难点：计算
代码编写,Github源码下载 [https://github.com/galyean-gong/function.git ]
<!DOCTYPE html>
<html>
<head>
<title>放大镜特效</title>
</head>
<style type="text/css">
* {
margin: 0;
padding: 0
}
#demo {
display: block;
width: 400px;
height: 255px;
margin: 50px;
position: relative;
border: 1px solid #ccc;
}
#small-box {
position: relative;
z-index: 1;
}
#float-box {
display: none;
width: 160px;
height: 120px;
position: absolute;
background: #ffffcc;
border: 1px solid #ccc;
filter: alpha(opacity=50);
opacity: 0.5;
}
#mark {
position: absolute;
display: block;
width: 400px;
height: 255px;
background-color: #fff;
filter: alpha(opacity=0);
opacity: 0;
z-index: 10;
}
#big-box {
display: none;
position: absolute;
top: 0;
left: 460px;
width: 400px;
height: 300px;
overflow: hidden;
border: 1px solid #ccc;
z-index: 1;;
}
#big-box img {
position: absolute;
z-index: 5
}
</style>
<body>
<div id="demo">
<div id="small-box">
<div id="mark"></div>
<div id="float-box"></div>
</div>
<div id="big-box">
</div>
</div>
<!-- offsetLeft 子元素想当父元素的左位移
offsetTop 子元素想当父元素的上位移
offsetWidth 盒子本身的宽高 不包括滚动条
event.clientX 鼠标的X，Y轴相对与整个页面，而非子元素
-->
<script type="text/javascript">
//页面加载完毕后执行
window.onload = function () {
var objDemo = document.getElementById("demo");
var objSmallBox = document.getElementById("small-box");
var objMark = document.getElementById("mark");
var objFloatBox = document.getElementById("float-box");
var objBigBox = document.getElementById("big-box");
var objBigBoxImage = objBigBox.getElementsByTagName("img")[0];
objMark.onmouseover = function () {
objFloatBox.style.display = "block"
objBigBox.style.display = "block"
}
objMark.onmouseout = function () {
objFloatBox.style.display = "none"
objBigBox.style.display = "none"
}
objMark.onmousemove = function (ev) {
var _event = ev || window.event; //兼容多个浏览器的event参数模式
var left = _event.clientX - objDemo.offsetLeft - objSmallBox.offsetLeft - objFloatBox.offsetWidth / 2;
var top = _event.clientY - objDemo.offsetTop - objSmallBox.offsetTop - objFloatBox.offsetHeight / 2;
if (left < 0) {
left = 0;
} else if (left > (objMark.offsetWidth - objFloatBox.offsetWidth)) {
left = objMark.offsetWidth - objFloatBox.offsetWidth;
}
if (top < 0) {
top = 0;
} else if (top > (objMark.offsetHeight - objFloatBox.offsetHeight)) {
top = objMark.offsetHeight - objFloatBox.offsetHeight;
}
objFloatBox.style.left = left + "px"; //oSmall.offsetLeft的值是相对什么而言
objFloatBox.style.top = top + "px";
var percentX = left / (objMark.offsetWidth - objFloatBox.offsetWidth);
var percentY = top / (objMark.offsetHeight - objFloatBox.offsetHeight);
objBigBoxImage.style.left = -percentX * (objBigBoxImage.offsetWidth - objBigBox.offsetWidth) + "px";
objBigBoxImage.style.top = -percentY * (objBigBoxImage.offsetHeight - objBigBox.offsetHeight) + "px";
}
}
</script>
</body>
</html>
