Detailed explanation of JavaScript implementation of proportional drag and zoom method of selection box-JS Tutorial-php.cn

本文实例讲述了JavaScript实现选择框按比例拖拉缩放的方法。分享给大家供大家参考。具体如下：
这里通过javascript实现可以像PS一样拉出一个选择框的效果。里面的很多方法都是我们值得学习的。
运行效果如下图所示：
具体代码如下：
&lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
&lt;html xmlns="http://www.w3.org/1999/xhtml">
&lt;head>
&lt;meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
&lt;title>JavaScript拖拉缩放效果&lt;/title>
&lt;/head>
&lt;body>
&lt;script>
var isIE = (document.all) ? true : false;
var $ = function (id) {
  return "string" == typeof id ? document.getElementById(id) : id;
};
var Class = {
  create: function() {
    return function() { this.initialize.apply(this, arguments); }
  }
}
var Extend = function(destination, source) {
  for (var property in source) {
    destination[property] = source[property];
  }
}
var Bind = function(object, fun) {
  return function() {
    return fun.apply(object, arguments);
  }
}
var BindAsEventListener = function(object, fun) {
  var args = Array.prototype.slice.call(arguments).slice(2);
  return function(event) {
    return fun.apply(object, [event || window.event].concat(args));
  }
}
var CurrentStyle = function(element){
  return element.currentStyle || document.defaultView.getComputedStyle(element, null);
}
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;
  }
};
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;
 }
};
//缩放程序
var Resize = Class.create();
Resize.prototype = {
//缩放对象
initialize: function(obj, options) {
  this._obj = $(obj);//缩放对象  
  this._styleWidth = this._styleHeight = this._styleLeft = this._styleTop = 0;//样式参数
  this._sideRight = this._sideDown = this._sideLeft = this._sideUp = 0;//坐标参数
  this._fixLeft = this._fixTop = 0;//定位参数
  this._scaleLeft = this._scaleTop = 0;//定位坐标
  this._mxSet = function(){};//范围设置程序
  this._mxRightWidth = this._mxDownHeight = this._mxUpHeight = this._mxLeftWidth = 0;//范围参数
  this._mxScaleWidth = this._mxScaleHeight = 0;//比例范围参数
  this._fun = function(){};//缩放执行程序
  //获取边框宽度
  var _style = CurrentStyle(this._obj);
  this._borderX = (parseInt(_style.borderLeftWidth) || 0) + (parseInt(_style.borderRightWidth) || 0);
  this._borderY = (parseInt(_style.borderTopWidth) || 0) + (parseInt(_style.borderBottomWidth) || 0);
  //事件对象(用于绑定移除事件)
  this._fR = BindAsEventListener(this, this.Resize);
  this._fS = Bind(this, this.Stop);
  this.SetOptions(options);
  //范围限制
  this.Max = !!this.options.Max;
  this._mxContainer = $(this.options.mxContainer) || null;
  this.mxLeft = Math.round(this.options.mxLeft);
  this.mxRight = Math.round(this.options.mxRight);
  this.mxTop = Math.round(this.options.mxTop);
  this.mxBottom = Math.round(this.options.mxBottom);
  //宽高限制
  this.Min = !!this.options.Min;
  this.minWidth = Math.round(this.options.minWidth);
  this.minHeight = Math.round(this.options.minHeight);
  //按比例缩放
  this.Scale = !!this.options.Scale;
  this.Ratio = Math.max(this.options.Ratio, 0);
  this.onResize = this.options.onResize;
  this._obj.style.position = "absolute";
  !this._mxContainer || CurrentStyle(this._mxContainer).position == "relative" || (this._mxContainer.style.position = "relative");
 },
 //设置默认属性
 SetOptions: function(options) {
 this.options = {//默认值
    Max:    false,//是否设置范围限制(为true时下面mx参数有用)
    mxContainer:"",//指定限制在容器内
    mxLeft:    0,//左边限制
    mxRight:  9999,//右边限制
    mxTop:    0,//上边限制
    mxBottom:  9999,//下边限制
    Min:    false,//是否最小宽高限制(为true时下面min参数有用)
    minWidth:  50,//最小宽度
    minHeight:  50,//最小高度
    Scale:    false,//是否按比例缩放
    Ratio:    0,//缩放比例(宽/高)
    onResize:  function(){}//缩放时执行
 };
 Extend(this.options, options || {});
 },
 //设置触发对象
 Set: function(resize, side) {
  var resize = $(resize), fun;
  if(!resize) return;
  //根据方向设置
  switch (side.toLowerCase()) {
  case "up" :
    fun = this.Up;
    break;
  case "down" :
    fun = this.Down;
    break;
  case "left" :
    fun = this.Left;
    break;
  case "right" :
    fun = this.Right;
    break;
  case "left-up" :
    fun = this.LeftUp;
    break;
  case "right-up" :
    fun = this.RightUp;
    break;
  case "left-down" :
    fun = this.LeftDown;
    break;
  case "right-down" :
  default :
    fun = this.RightDown;
  };
  //设置触发对象
  addEventHandler(resize, "mousedown", BindAsEventListener(this, this.Start, fun));
 },
 //准备缩放
 Start: function(e, fun, touch) {  
  //防止冒泡(跟拖放配合时设置)
  e.stopPropagation ? e.stopPropagation() : (e.cancelBubble = true);
  //设置执行程序
  this._fun = fun;
  //样式参数值
  this._styleWidth = this._obj.clientWidth;
  this._styleHeight = this._obj.clientHeight;
  this._styleLeft = this._obj.offsetLeft;
  this._styleTop = this._obj.offsetTop;
  //四条边定位坐标
  this._sideLeft = e.clientX - this._styleWidth;
  this._sideRight = e.clientX + this._styleWidth;
  this._sideUp = e.clientY - this._styleHeight;
  this._sideDown = e.clientY + this._styleHeight;
  //top和left定位参数
  this._fixLeft = this._styleLeft + this._styleWidth;
  this._fixTop = this._styleTop + this._styleHeight;
  //缩放比例
  if(this.Scale){
    //设置比例
    this.Ratio = Math.max(this.Ratio, 0) || this._styleWidth / this._styleHeight;
    //left和top的定位坐标
    this._scaleLeft = this._styleLeft + this._styleWidth / 2;
    this._scaleTop = this._styleTop + this._styleHeight / 2;
  };
  //范围限制
  if(this.Max){
    //设置范围参数
    var mxLeft = this.mxLeft, mxRight = this.mxRight, mxTop = this.mxTop, mxBottom = this.mxBottom;
    //如果设置了容器，再修正范围参数
    if(!!this._mxContainer){
      mxLeft = Math.max(mxLeft, 0);
      mxTop = Math.max(mxTop, 0);
      mxRight = Math.min(mxRight, this._mxContainer.clientWidth);
      mxBottom = Math.min(mxBottom, this._mxContainer.clientHeight);
    };
    //根据最小值再修正
    mxRight = Math.max(mxRight, mxLeft + (this.Min ? this.minWidth : 0) + this._borderX);
    mxBottom = Math.max(mxBottom, mxTop + (this.Min ? this.minHeight : 0) + this._borderY);
    //由于转向时要重新设置所以写成function形式
    this._mxSet = function(){
      this._mxRightWidth = mxRight - this._styleLeft - this._borderX;
      this._mxDownHeight = mxBottom - this._styleTop - this._borderY;
      this._mxUpHeight = Math.max(this._fixTop - mxTop, this.Min ? this.minHeight : 0);
      this._mxLeftWidth = Math.max(this._fixLeft - mxLeft, this.Min ? this.minWidth : 0);
    };
    this._mxSet();
    //有缩放比例下的范围限制
    if(this.Scale){
      this._mxScaleWidth = Math.min(this._scaleLeft - mxLeft, mxRight - this._scaleLeft - this._borderX) * 2;
      this._mxScaleHeight = Math.min(this._scaleTop - mxTop, mxBottom - this._scaleTop - this._borderY) * 2;
    };
  };
  //mousemove时缩放 mouseup时停止
  addEventHandler(document, "mousemove", this._fR);
  addEventHandler(document, "mouseup", this._fS);
  if(isIE){
    addEventHandler(this._obj, "losecapture", this._fS);
    this._obj.setCapture();
  }else{
    addEventHandler(window, "blur", this._fS);
    e.preventDefault();
  };
 },
 //缩放
 Resize: function(e) {
  //清除选择
  window.getSelection ? window.getSelection().removeAllRanges() : document.selection.empty();
  //执行缩放程序
  this._fun(e);
  //设置样式，变量必须大于等于0否则ie出错
  with(this._obj.style){
    width = this._styleWidth + "px"; height = this._styleHeight + "px";
    top = this._styleTop + "px"; left = this._styleLeft + "px";
  }
  //附加程序
  this.onResize();
 },
 //缩放程序
 //上
 Up: function(e) {
  this.RepairY(this._sideDown - e.clientY, this._mxUpHeight);
  this.RepairTop();
  this.TurnDown(this.Down);
 },
 //下
 Down: function(e) {
  this.RepairY(e.clientY - this._sideUp, this._mxDownHeight);
  this.TurnUp(this.Up);
 },
 //右
 Right: function(e) {
  this.RepairX(e.
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