jQuery实现前端图片裁剪与预览功能详解

jQuery图片裁剪功能概述

在研究PHP GD库处理图片裁剪时，发现前端同样可以实现类似功能。实际上，利用JavaScript和jQuery实现图片裁剪并不复杂，下面将展示具体的实现方式。

前端实现版本

 
HTML结构与CSS样式定义<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Resize</title>
<style type="text/css">
*{ padding:0; margin:0;}
ul{ list-style-type:none; overflow:hidden; zoom:1; width:1000px; margin:30px auto; }
li{ float:left; width:500px;}
#container{width:480px; height:480px; margin:0 auto; border:1px solid #999; position:relative;background:url(http://images.cnblogs.com/cnblogs_com/wtcsy/192373/r_xx.jpg);}
#container .block{height:100px; width:100px; border:1px solid #000000; position:absolute; left:50px; top:50px; background:#fff;filter:alpha(opacity=30);opacity:0.3; cursor:move;}
.rRightDown,.rLeftDown,.rLeftUp,.rRightUp,.rRight,.rLeft,.rUp,.rDown{
position:absolute;background:#f00;width:6px;height:6px;z-index:5;font-size:0;}
.rLeftDown,.rRightUp{cursor:ne-resize;}
.rRightDown,.rLeftUp{cursor:nw-resize;}
.rRight,.rLeft{cursor:e-resize;}
.rUp,.rDown{cursor:n-resize;}
.rRightDown{ bottom:-3px; right:-3px;}
.rLeftDown{ bottom:-3px; left:-3px;}
.rRightUp{ top:-3px; right:-3px;}
.rLeftUp{ top:-3px; left:-3px;}
.rRight{ right:-3px; top:50%}
.rLeft{ left:-3px; top:50%}
.rUp{ top:-3px; left:50%}
.rDown{ bottom:-3px; left:50%}
#imgC{ border:1px solid #CCC; width:0; height:0; margin:0 auto;background:url(http://images.cnblogs.com/cnblogs_com/wtcsy/192373/r_xx.jpg);}
</style>
</head>
<body>
<ul>
<li>
<div id="container"></div>
</li>
<li>
<div id="imgC"></div>
</li>
</ul>
<script type="text/javascript" src="http://common.cnblogs.com/script/jquery.js"></script>
JavaScript核心逻辑实现<script type="text/javascript">
(function(){
var dBody = document.body,
dDoc = document.documentElement;
var clip = function(options){
this.init.call(this,options);
} 
clip.prototype = {
options :{
moveCallBack : function(){},
className : "block"
}, 
init : function(options){
$.extend(this,this.options,options||{});
if(!this.container || !this.imgC){
return;
} 
this.container = $(this.container);
var self = this;
this.block = $('<div class="'+this.className+'">\
<div action="rightDown" class="rRightDown"></div>\
<div action="leftDown" class="rLeftDown"></div>\
<div action="rightUp" class="rRightUp"></div>\
<div action="leftUp" class="rLeftUp"></div>\
<div action="right" class="rRight"></div>\
<div action="left" class="rLeft"></div>\
<div action="up" class="rUp"></div>\
<div action="down" class="rDown" ></div>\
</div>')
.bind("mousedown.r",function(e){self.start(e)})
.appendTo(this.container[0]);
this.setImg();
}, 
setImg : function(){
var block = this.block;
this.imgC.css({
height: block.height(),
width : block.width(),
"background-position" : "-"+block.css("left")+" -"+block.css("top")
}); 
}, 
start : function(e){
var $elem = $(e.target),
block = this.block,
self = this,
move = false,
container = this.container,
action = $elem.attr("action");
//这个 每次都要计算 基本dom结构的改变 浏览器的缩放 都会让里面的值发生改变
this.offset = $.extend({height:container.height(),width:container.width()},container.offset());
this.blockOriginal = {height:block.height(),width:block.width(),left:parseInt(block.css("left")),top:parseInt(block.css("top"))};
if(action){
this.fun = this[action];
}else{
this.x = e.clientX - this.offset.left - this.blockOriginal.left ;
this.y = e.clientY - this.offset.top - this.blockOriginal.top;
move = true;
} 
$(document)
.bind("mousemove.r",function(e){self.move(e,move)})
.bind("mouseup.r",function(){self.end()});
}, 
end : function(){
$(document)
.unbind("mousemove.r")
.unbind("mouseup.r");
}, 
move : function(e,isMove){
window.getSelection
? window.getSelection().removeAllRanges()
: document.selection.empty();
var block = this.block;
if(isMove){
var left = Math.max(0,e.clientX - this.offset.left - this.x);
left = Math.min(left,this.offset.width - this.blockOriginal.width);
var top = Math.max(0,e.clientY - this.offset.top - this.y);
top = Math.min(top,this.offset.height - this.blockOriginal.height);
block.css({left:left,top:top});
}else{
var offset = this.fun(e);
block.css(offset);
} 
this.setImg();
this.moveCallBack();
}, 
down : function(e){
var blockOriginal = this.blockOriginal,
sTop = Math.max(dBody.scrollTop,dDoc.scrollTop), //出现垂直方向滚动条时候 要计算这个
offset = this.offset;
if(e.clientY-offset.top>=blockOriginal.top-sTop){
var height = Math.min(offset.height - blockOriginal.top,e.clientY-offset.top-blockOriginal.top+sTop),
top = blockOriginal.top;
}else{
var height = Math.min(offset.top+blockOriginal.top-e.clientY-sTop,blockOriginal.top),
top = Math.max(e.clientY - offset.top+sTop,0);
} 
return {height:height, top:top};
}, 
up : function(e){
var blockOriginal = this.blockOriginal,
sTop = Math.max(dBody.scrollTop,dDoc.scrollTop),
offset = this.offset;
if(e.clientY-offset.top-blockOriginal.height<=blockOriginal.top-sTop){
var top = Math.max(e.clientY-offset.top+sTop,0),
maxHeight = blockOriginal.top + blockOriginal.height,
height = Math.min(maxHeight,blockOriginal.top + blockOriginal.height -(e.clientY-offset.top)-sTop);
}else{
var height = Math.min(e.clientY-offset.top-blockOriginal.top-blockOriginal.height+sTop,offset.height-blockOriginal.top-blockOriginal.height),
top = blockOriginal.top+blockOriginal.height;
} 
return {height:height, top:top};
}, 
left : function(e){
var blockOriginal = this.blockOriginal,
offset = this.offset;
if(e.clientX - offset.left - blockOriginal.width - blockOriginal.left<=0){
var left = Math.max(e.clientX - offset.left,0),
width = Math.min(blockOriginal.left + blockOriginal.width,blockOriginal.left + blockOriginal.width -(e.clientX-offset.left));
}else{
var width = Math.min(e.clientX-offset.left-blockOriginal.left-blockOriginal.width,offset.width-blockOriginal.left-blockOriginal.width),
left = blockOriginal.left + blockOriginal.width;
} 
return {left : left, width : width};
}, 
right : function(e){
var blockOriginal = this.blockOriginal,
offset = this.offset;
if(e.clientX-offset.left>=blockOriginal.left){
var width = Math.min(offset.width - blockOriginal.left,e.clientX - offset.left - blockOriginal.left),
left = blockOriginal.left;
}else{
var width = Math.min(offset.left + blockOriginal.left - e.clientX,blockOriginal.left),
left = Math.max(e.clientX - offset.left,0);
} 
return {left : left, width : width};
}, 
rightDown : function(e){
return $.extend(this.right(e),this.down(e));
}, 
leftDown : function(e){
return $.extend(this.left(e),this.down(e));
}, 
rightUp : function(e){
return $.extend(this.right(e),this.up(e));
}, 
leftUp : function(e){
return $.extend(this.left(e),this.up(e));
}, 
getValue : function(){
var block = this.block;
return {
left : parseInt(block.css("left")),
top : parseInt(block.css("top")),
width : block.width(),
height : block.height()
} 
} 
} 
$.fn.clip = function(options){
options.container = this;
return new clip(options);
} 
})(); 
$("#container").clip({
imgC : $("#imgC")
}) 
</script>
</body>
</html>