首先引用一段关于拖动，缩放，剪切的基础代码

 /*

 *    作者：http://cloudgamer.cnblogs.com/

 *

 *    改进与增强

 *    作者：http://yoker.sc0826.com/

 *    时间：2008年11月09日

 *    功能：远程web图片在线裁剪，图片预加载比例缩放，裁剪参数个性设置，裁剪比例缩放等。

 */

 /* -------------这里定义一些环境变量--------------- */

 //获取dom对象的方法

 var $ = function(id) {

     return "string" == typeof id ? document.getElementById(id) : id;

 };

 //判断是否ie

 var isIE = (document.all) ? true : false;

 //添加事件

 function addEventHandler(oTarget, sEventType, fnHandler) {

     if (oTarget.addEventListener) {

         oTarget.addEventListener(sEventType, fnHandler, false);

     } else if (oTarget.attachEvent) {

         oTarget.attachEvent("on" + sEventType, fnHandler);

     } else {

         oTarget["on" + sEventType] = fnHandler;

     }

 };

 //移除事件

 function removeEventHandler(oTarget, sEventType, fnHandler) {

     if (oTarget.removeEventListener) {

         oTarget.removeEventListener(sEventType, fnHandler, false);

     } else if (oTarget.detachEvent) {

         oTarget.detachEvent("on" + sEventType, fnHandler);

     } else {

         oTarget["on" + sEventType] = null;

     }

 };

 //这相当于一个类工厂。

 //js中函数即是类，new function()就是用该函数作为构造函数生成一个对象

 //当然，默认的该对象需自定义一个initialize方法

 var Class = {

     create: function() {

         return function() {

             this.initialize.apply(this, arguments);

         }

     }

 }

 //这是对象拷贝函数

 Object.extend = function(destination, source) {

     for (var property in source) {

         destination[property] = source[property];

     }

     return destination;

 }

环境变量

这里定义了几个环境变量，包括挂载/卸载事件方法，根据id获取dom对象方法。比较有意思的是

var Class = {
create: function() {
return function() {
this.initialize.apply(this, arguments);
}
}
}

的写法。网上说prototype.js是这么写的。

看起来这样写实现了某种标准化，比如能产生一批受约束的类，这些类看起来是从某个抽象类中继承而来，然后更方便的用propertype定义方法。

整个编程看起来更加面向对象而不是面向函数。

除此之外没什么好处。

js的prototype相当于c#的直接初始化字段，function相当于在构造函数中初始化字段，无形中都生成对象。js中的this应是某个对象，

 //拖放程序

 var Drag = Class.create();

 Drag.prototype = {

     //拖放对象,触发对象

     initialize: function(obj, drag, options) {

         var oThis = this;

         this._obj = $(obj); //拖放对象

         this.Drag = $(drag); //触发对象

         this._x = this._y = 0; //记录鼠标相对拖放对象的位置

         //事件对象(用于移除事件)

         this._fM = function(e) { oThis.Move(window.event || e); }

         this._fS = function() { oThis.Stop(); }

         this.SetOptions(options);

         this.Limit = !!this.options.Limit;

         this.mxLeft = parseInt(this.options.mxLeft);

         this.mxRight = parseInt(this.options.mxRight);

         this.mxTop = parseInt(this.options.mxTop);

         this.mxBottom = parseInt(this.options.mxBottom);

         this.onMove = this.options.onMove;

         this._obj.style.position = "absolute";

         addEventHandler(this.Drag, "mousedown", function(e) { oThis.Start(window.event || e); });

     },

     //设置默认属性

     SetOptions: function(options) {

         this.options = {//默认值

             Limit: false, //是否设置限制(为true时下面参数有用,可以是负数)

             mxLeft: 0, //左边限制

             mxRight: 0, //右边限制

             mxTop: 0, //上边限制

             mxBottom: 0, //下边限制

             onMove: function() { } //移动时执行

         };

         Object.extend(this.options, options || {});

     },

     //准备拖动

     Start: function(oEvent) {

         //记录鼠标相对拖放对象的位置

         this._x = oEvent.clientX - this._obj.offsetLeft;

         this._y = oEvent.clientY - this._obj.offsetTop;

         //mousemove时移动 mouseup时停止

         addEventHandler(document, "mousemove", this._fM);

         addEventHandler(document, "mouseup", this._fS);

         //使鼠标移到窗口外也能释放

         if (isIE) {

             addEventHandler(this.Drag, "losecapture", this._fS);

             this.Drag.setCapture();

         } else {

             addEventHandler(window, "blur", this._fS);

         }

     },

     //拖动

     Move: function(oEvent) {

         //清除选择(ie设置捕获后默认带这个)

         window.getSelection && window.getSelection().removeAllRanges();

         //当前鼠标位置减去相对拖放对象的位置得到offset位置

         var iLeft = oEvent.clientX - this._x, iTop = oEvent.clientY - this._y;

         //设置范围限制

         if (this.Limit) {

             //获取超出长度

             var iRight = iLeft + this._obj.offsetWidth - this.mxRight, iBottom = iTop + this._obj.offsetHeight - this.mxBottom;

             //这里是先设置右边下边再设置左边上边,可能会不准确

             if (iRight > 0) iLeft -= iRight;

             if (iBottom > 0) iTop -= iBottom;

             if (this.mxLeft > iLeft) iLeft = this.mxLeft;

             if (this.mxTop > iTop) iTop = this.mxTop;

         }

         //设置位置

         this._obj.style.left = iLeft + "px";

         this._obj.style.top = iTop + "px";

         //附加程序

         this.onMove();

     },

     //停止拖动

     Stop: function() {

         //移除事件

         removeEventHandler(document, "mousemove", this._fM);

         removeEventHandler(document, "mouseup", this._fS);

         if (isIE) {

             removeEventHandler(this.Drag, "losecapture", this._fS);

             this.Drag.releaseCapture();

         } else {

             removeEventHandler(window, "blur", this._fS);

         }

     }

 };

拖放类

拖放类的基本思路是给一个参照的dom对象，一个移动的dom对象，捕捉鼠标相对参照对象的变化，赋值给移动对象。

另外两个功能，其一允许用户自定义onmove,把移动中x,y值传出去，其二给移动对象定义mouseclik确保鼠标按下时记录相关参数，做好拖放准备。

总之是拖放功能的总管秘书。

缩放类

与拖放类思路基本相同。

document.defaultView.getComputedStyle用于获取所有dom元素的style对象。

 //图片切割

 var ImgCropper = Class.create();

 ImgCropper.prototype = {

     //容器对象,拖放缩放对象,图片地址,宽度,高度

     initialize: function(container, drag, url, width, height, options) {

         var oThis = this;

         //容器对象

         this.Container = $(container);

         this.Container.style.position = "relative";

         this.Container.style.overflow = "hidden";

         //拖放对象

         this.Drag = $(drag);

         this.Drag.style.cursor = "move";

         this.Drag.style.zIndex = 200;

         if (isIE) {

             //设置overflow解决ie6的渲染问题(缩放时填充对象高度的问题)

             this.Drag.style.overflow = "hidden";

             //ie下用一个透明的层填充拖放对象 不填充的话onmousedown会失效(未知原因)

             (function(style) {

                 style.width = style.height = "100%";

                 style.backgroundColor = "#fff";

                 style.opacity = 0;

                 style.filter = 'alpha(opacity = 0)';

             })(this.Drag.appendChild(document.createElement("div")).style)

         }

         this._cropper = this.Container.appendChild(document.createElement("img")); //切割对象

         this._pic = this.Container.appendChild(document.createElement("img")); //图片对象

         this._pic.style.position = "absolute";

         this._cropper.style.position = "absolute";

         this._pic.style.top = this._pic.style.left = this._cropper.style.top = this._cropper.style.left = "0"; //对齐

         this._pic.style.zIndex = 100;

         this._cropper.style.zIndex = 150;

         this._cropper.onload = function() { oThis.SetPos(); }

         this.Url = url; //图片地址

         this.Width = parseInt(width); //宽度

         this.Height = parseInt(height); //高度

         this.SetOptions(options);

         this.Opacity = parseInt(this.options.Opacity);

         this.dragTop = parseInt(this.options.dragTop);

         this.dragLeft = parseInt(this.options.dragLeft);

         this.dragWidth = parseInt(this.options.dragWidth);

         this.dragHeight = parseInt(this.options.dragHeight);

         //设置预览对象

         this.View = $(this.options.View) || null; //预览对象

         this.viewWidth = parseInt(this.options.viewWidth);

         this.viewHeight = parseInt(this.options.viewHeight);

         this._view = null; //预览图片对象

         if (this.View) {

             this.View.style.position = "relative";

             this.View.style.overflow = "hidden";

             this._view = this.View.appendChild(document.createElement("img"));

             this._view.style.position = "absolute";

         }

         this.Scale = parseInt(this.options.Scale);

         //设置拖放

         this._drag = new Drag(this.Drag, this.Drag, { Limit: true, onMove: function() { oThis.SetPos(); } });

         //设置缩放

         this._resize = this.GetResize();

         this.Init();

     },

     //设置默认属性

     SetOptions: function(options) {

         this.options = {//默认值

             Opacity: 50, //透明度(0到100)

             //拖放位置和宽高

             dragTop: 0,

             dragLeft: 0,

             dragWidth: 100,

             dragHeight: 100,

             //缩放触发对象

             Right: "",

             Left: "",

             Up: "",

             Down: "",

             RightDown: "",

             LeftDown: "",

             RightUp: "",

             LeftUp: "",

             Scale: false, //是否按比例缩放

             //预览对象设置

             View: "", //预览对象

             viewWidth: 100, //预览宽度

             viewHeight: 100//预览高度

         };

         Object.extend(this.options, options || {});

     },

     //初始化对象

     Init: function() {

         var oThis = this;

         //设置拖放对象

         this.Drag.style.top = this.dragTop + "px";

         this.Drag.style.left = this.dragLeft + "px";

         this.Drag.style.width = this.dragWidth + "px";

         this.Drag.style.height = this.dragHeight + "px";

         //Yoker.Wu前台缩放效果改善，图片加载完成后，得到缩放大小再初始化显示

         var trueImg = new Image();

         trueImg.src = this.Url;

         //图片已经加载并缓存

         if (trueImg.complete) {

             if (trueImg.width > oThis.Width || trueImg.height > oThis.Height) {

                 if (this.Width / this.Height > trueImg.width / trueImg.height) {

                     this.Width = parseInt(trueImg.width * this.Height / trueImg.height);

                 } else {

                     this.Height = parseInt(trueImg.height * this.Width / trueImg.width);

                 }

             } else {

                 this.Width = trueImg.width;

                 this.Height = trueImg.height;

             }

             //设置容器

             this.Container.style.width = this.Width + "px";

             this.Container.style.height = this.Height + "px";

             //设置切割对象

             this._cropper.src = this.Url;

             this._pic.src = this.Url;

             this._pic.style.width = this._cropper.style.width = this.Width + "px";

             this._pic.style.height = this._cropper.style.height = this.Height + "px";

             if (isIE) {

                 if (navigator.appVersion.indexOf("MSIE 6.0") != -1

                 || navigator.appVersion.indexOf("MSIE 7.0") != -1

                 || navigator.appVersion.indexOf("MSIE 8.0") != -1) {

                     this._pic.style.filter = "alpha(opacity:" + this.Opacity + ")";

                 }

                 else if (navigator.appVersion.indexOf("MSIE 9.0") != -1) {

                     this._pic.style.filter = "alpha(opacity:" + this.Opacity + ")";

                     this._pic.style.opacity = this.Opacity / 100;

                 }

                 else {

                     this._pic.style.opacity = this.Opacity / 100;

                 }

             } else {

                 this._pic.style.opacity = this.Opacity / 100;

             }

             this._cropper.style.filter = "alpha(opacity:100)";

             this._cropper.style.opacity = 1;

             //设置预览对象

             if (this.View) { this._view.src = this.Url; }

             //设置拖放

             this._drag.mxRight = this.Width; this._drag.mxBottom = this.Height;

             //设置缩放

             if (this._resize) { this._resize.mxRight = this.Width; this._resize.mxBottom = this.Height; this._resize.Scale = this.Scale; }

         }

         //新加载的情况

         trueImg.onload = function() {

             if (this.width > oThis.Width || this.height > oThis.Height) {

                 if (oThis.Width / oThis.Height > this.width / this.height) {

                     oThis.Width = parseInt(this.width * oThis.Height / this.height);

                 } else {

                     oThis.Height = parseInt(this.height * oThis.Width / this.width);

                 }

             } else {

                 oThis.Width = this.width;

                 oThis.Height = this.height;

             }

             //设置容器

             oThis.Container.style.width = oThis.Width + "px";

             oThis.Container.style.height = oThis.Height + "px";

             //设置切割对象

             oThis._cropper.src = oThis.Url;

             oThis._pic.src = oThis.Url;

             oThis._pic.style.width = oThis._cropper.style.width = oThis.Width + "px";

             oThis._pic.style.height = oThis._cropper.style.height = oThis.Height + "px";

             if (isIE) {

                 if (navigator.appVersion.indexOf("MSIE 6.0") != -1

                 || navigator.appVersion.indexOf("MSIE 7.0") != -1

                 || navigator.appVersion.indexOf("MSIE 8.0") != -1) {

                     oThis._pic.style.filter = "alpha(opacity:" + oThis.Opacity + ")";

                 }

                 else if (navigator.appVersion.indexOf("MSIE 9.0") != -1) {

                     oThis._pic.style.filter = "alpha(opacity:" + oThis.Opacity + ")";

                     oThis._pic.style.opacity = oThis.Opacity / 100;

                 }

                 else {

                     oThis._pic.style.opacity = oThis.Opacity / 100;

                 }

             } else {

                 oThis._pic.style.opacity = oThis.Opacity / 100;

             }

             oThis._cropper.style.filter = "alpha(opacity:100)";

             oThis._cropper.style.opacity = 1;

             //设置预览对象

             if (oThis.View) { oThis._view.src = oThis.Url; }

             //设置拖放

             oThis._drag.mxRight = oThis.Width; oThis._drag.mxBottom = oThis.Height;

             //设置缩放

             if (oThis._resize) { oThis._resize.mxRight = oThis.Width; oThis._resize.mxBottom = oThis.Height; oThis._resize.Scale = oThis.Scale; }

         }

     },

     //设置获取缩放对象

     GetResize: function() {

         var op = this.options;

         //有触发对象时才设置

         if (op.RightDown || op.LeftDown || op.RightUp || op.LeftUp || op.Right || op.Left || op.Up || op.Down) {

             var oThis = this, _resize = new Resize(this.Drag, { Limit: true, onResize: function() { oThis.SetPos(); } });

             //设置缩放触发对象

             if (op.RightDown) { _resize.Set(op.RightDown, "right-down"); }

             if (op.LeftDown) { _resize.Set(op.LeftDown, "left-down"); }

             if (op.RightUp) { _resize.Set(op.RightUp, "right-up"); }

             if (op.LeftUp) { _resize.Set(op.LeftUp, "left-up"); }

             if (op.Right) { _resize.Set(op.Right, "right"); }

             if (op.Left) { _resize.Set(op.Left, "left"); }

             if (op.Up) { _resize.Set(op.Up, "up"); }

             if (op.Down) { _resize.Set(op.Down, "down"); }

             return _resize;

         } else { return null; }

     },

     //设置切割

     SetPos: function() {

         var o = this.Drag;

         //按拖放对象的参数进行切割

         this._cropper.style.clip = "rect(" + o.offsetTop + "px " + (o.offsetLeft + o.offsetWidth) + "px " + (o.offsetTop + o.offsetHeight) + "px " + o.offsetLeft + "px)";

         //切割预览

         if (this.View) this.PreView();

     },

     //切割预览

     PreView: function() {

         //按比例设置宽度和高度

         var o = this.Drag, h = this.viewWidth, w = h * o.offsetWidth / o.offsetHeight;

         if (w > this.viewHeight) { w = this.viewHeight; h = w * o.offsetHeight / o.offsetWidth; }

         //获取对应比例尺寸

         var scale = h / o.offsetHeight, ph = this.Height * scale, pw = this.Width * scale, pt = o.offsetTop * scale, pl = o.offsetLeft * scale, styleView = this._view.style;

         //设置样式

         styleView.width = pw + "px"; styleView.height = ph + "px";

         styleView.top = -pt + "px "; styleView.left = -pl + "px";

         //切割预览图

         styleView.clip = "rect(" + pt + "px " + (pl + w) + "px " + (pt + h) + "px " + pl + "px)";

     }

 }

切割类

拖放中 window.getSelection && window.getSelection().removeAllRanges();用途不明，待查。

缩放中防止冒泡用户不明。

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