用JQuery仿造QQ头像裁剪功能
最近工作真心忙碌，几乎没时间写博客。今天趁有时间来仿一个QQ头像裁剪功能插件，效果如下：
原理：
主要是通过css的clip来裁剪图片可视区域，拖动剪裁窗口这里使用了JQ-UI的draggable插件（但是缩放没有，贪方便可以使用Resizable插件，但都用插件的话就没有研究的意义了）。
缩放功能原理其实很简单，不外乎获取剪裁框的offset()或position()，以及各容器宽高、鼠标位置，然后做个大杂侩计算。
只能说咱做前端的必须要认真耐心地去做计算，虽然过程颇为麻烦，但绝对不是“做不出来”。有的朋友在做某些功能前，可能会因为需要涉及较麻烦的计算就放弃，这是不靠谱的做法。
P.S.：像效果图中会存在图片被选中（变蓝色）的情况，是因为本章直接用的img，如果不喜欢这种图片被选中的情况，可以用一个div直接设置背景替换img即可（不过这里得使用background-size:100% 100%，如果不考虑IE8-的话，利用这种方法交互视觉上感觉会更好些）
下面贴出核心代码：
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-type" content="text/html; charset=utf-8">
<title>裁剪头像</title>
<script src="jq.js"></script>
<script src="draggable.js"></script>
<style type="text/css">
body {background-color: #333;}
.pic_wrap{ position:relative; float:left;margin:100px; width:320px; height:320px; background:black; }
.pic_wrap img{position:absolute;width:320px; height:320px;}
.pic1{opacity:0.5;}
.pic2{clip:rect(0 150px 150px 0);}
.clip_box{position:absolute; margin-left:-1px; margin-top:-1px;width:150px; height:150px; border:solid 1px white; cursor:move;}
.clip_box span{display:block; position:absolute; width:8px; height:9px; background:white; border-radius:4px;}
#lt{left:-4px; top:-4px; cursor:nw-resize;}
#rt{right:-4px; top:-4px; cursor:ne-resize}
#lb{left:-4px; bottom:-4px; cursor:sw-resize}
#rb{right:-4px; bottom:-4px; cursor:se-resize}
.preview{ margin-top:100px; position:relative; float:left;width:100px; height:100px; overflow:hidden;}
.pic3{ position:absolute;}
</style>
<script type="text/javascript">
$(function(){
var $picWrap = $("#pic_wrap");
var $rawPic = $picWrap.find("img:eq(0)");
var $clipPic = $picWrap.find("img:eq(1)");
var $clipBox = $("#clip_box");
var $prePic = $("#pic3"); //获取预览图
var prebox_w = $("#preview").width(); //获取预览图容器宽度/高度
var $lt = $("#lt");
var $rt = $("#rt");
var $lb = $("#lb");
var $rb = $("#rb");
var wrap_w = $picWrap.width();
var isResize = !1;
var flag = "";
$lt.mousedown(function(e){
e.stopPropagation();
isResize=!0;
flag = "leftTop";
})
$rt.mousedown(function(e){
e.stopPropagation();
isResize=!0;
flag = "rightTop";
})
$lb.mousedown(function(e){
e.stopPropagation();
isResize=!0;
flag = "leftDown";
})
$rb.mousedown(function(e){
e.stopPropagation();
isResize=!0;
flag = "rightDown";
})
$(window).mouseup(function(){
isResize=!1;
flag = "";
})
$clipBox.find("span").mousemove(function(e){
e.stopPropagation();
})
$clipBox.draggable({
containment: "#pic_wrap",
drag: function(){
setClip();
},
stop: function(){
var box_pl = $clipBox.position().left;
var box_pt = $clipBox.position().top;
var box_w = $clipBox.width();
if(box_pl+box_w>wrap_w){
var l = wrap_w - box_w;
$clipBox.css("left",l);
}
if(box_pt+box_w>wrap_w){
var t = wrap_w - box_w;
$clipBox.css("top",t);
}
setClip();
}
});
$picWrap.mousemove(function(e){
if(isResize){
var x = e.pageX;
var y = e.pageY;
switch(flag){
case "leftTop":leftTop(x);console.log("aa");break;
case "rightTop":rightTop(y);break;
case "leftDown":leftDown(x);break;
case "rightDown":rightDown(y);break;
default: break;
}
}
})
function leftTop(x){
var box_ol = $clipBox.offset().left;
var box_pl = $clipBox.position().left;
var box_pt = $clipBox.position().top;
var box_w = $clipBox.width();
var s = x - box_ol;
var newLeft = box_pl + s;
var newWidth = box_w - s;
var newTop = box_pt + s;
newLeft = newLeft<=0?0:newLeft;
newTop = newTop<=0?0:newTop;
if(newTop+newWidth>=wrap_w){
newWidth = newWidth<8?8:newWidth;
newLeft = newLeft+newWidth>wrap_w?newLeft-8:newLeft;
newTop = wrap_w - newWidth;
}
if(newLeft+newWidth>=wrap_w-8){
newWidth = newWidth<8?8:newWidth;
newLeft = wrap_w - newWidth;
}
$clipBox.css({"left":newLeft,"width":newWidth,"height":newWidth,"top":newTop});
setClip();
}
function rightTop(y){
var box_ot = $clipBox.offset().top;
var box_pt = $clipBox.position().top;
var box_pl = $clipBox.position().left;
var box_h = $clipBox.height();
var s = y - box_ot;
var newTop = box_pt + s;
var newHeight = box_h - s;
newTop = newTop<=0?0:newTop;
if(newHeight+box_pl>=wrap_w){
return false;
}
$clipBox.css({"top":newTop,"width":newHeight,"height":newHeight});
setClip();
}
function leftDown(x){
var box_ol = $clipBox.offset().left;
var box_pl = $clipBox.position().left;
var box_pt = $clipBox.position().top;
var box_w = $clipBox.width();
var s = x - box_ol;
var newLeft = box_pl + s;
var newWidth = box_w - s;
newLeft = newLeft<=0?0:newLeft;
if(newWidth+box_pt>=wrap_w){
return false;
}
$clipBox.css({"left":newLeft,"width":newWidth,"height":newWidth});
setClip();
}
function rightDown(y){
var box_ot = $clipBox.offset().top;
var box_pl = $clipBox.position().left;
var newHeight = y - box_ot;
if(newHeight+box_pl>=wrap_w){
return false;
}
$clipBox.css({"width":newHeight,"height":newHeight});
setClip();
}
function setClip(){
var t = $clipBox.position().top;
var r = $clipBox.position().left + $clipBox.width();
var b = $clipBox.position().top + $clipBox.height();
var l = $clipBox.position().left;
var rect = "rect("+t+"px "+r+"px "+b+"px "+l+"px)";
$clipPic.css("clip",rect);
//预览图设置
var w = $clipBox.width();
var pre_w = prebox_w / w * wrap_w ; //存在比例 prebox_w / pre_w = w / wrap_w
var pre_t = pre_w / wrap_w *t; //存在比例 pre_t / t = pre_w / wrap_w
var pre_r = pre_w / wrap_w *r; //存在比例 pre_r / r = pre_w / wrap_w
var pre_b = pre_w / wrap_w *b; //存在比例 pre_b / b = pre_w / wrap_w
var pre_l = pre_w / wrap_w *l; //存在比例 pre_l / l = pre_w / wrap_w
var prect = "rect("+pre_t+"px "+pre_r+"px "+pre_b+"px "+pre_l+"px)";
$prePic.css({"width":pre_w,"height":pre_w,"clip":prect,"left":-pre_l,"top":-pre_t});
}
setClip();
})
</script>
</head>
<body>
<div class="pic_wrap" id="pic_wrap">
<img class="pic1" src="logo.jpg" />
<img class="pic2" src="logo.jpg" />
<div class="clip_box" id="clip_box">
<span id="lt"></span>
<span id="rt"></span>
<span id="lb"></span>
<span id="rb"></span>
</div>
</div>
<div id="preview" class="preview">
<img class="pic3" id="pic3" src="logo.jpg" />
</div>
</body>
</html>
有兴趣的朋友可以拷贝到自己电脑上测试，jq.js和draggable.js大家自己百度下载，这里不提供下载地址了。