js实现多张图片同时放大缩小相对位置不变

     项目要求需要用js实现同时放大多张图片相对位置不变，就和同事去一家国外网站的js文件中跟踪扒取了这一算法，

庆幸的是算法抠出来了并整理了出来，但遗憾的只知计算过程却弄不明白算法原理：

大体上是核心运算将图片的中心点和画布（外层div）中心点的差和放大倍数针对矩阵[1.0000000000000002,-0,-0,1.0000000000000002]

（这个矩阵是由[1,0,01]经过一系列计算得出的一个固定矩阵）做了两次运算：（如果大家懂得其中计算原理，希望能分享一下）

/// <reference path="Scripts/jquery-1.4.1.min.js" />

//参数：canvas画布的id,img图片外层div的class值）

function ZoomBig(canvasId,imgDivClass) {

    Canvas.zoom(canvasId,imgDivClass,1.25);

}

function ZoomSmall(canvasId, imgDivClass) {

    Canvas.zoom(canvasId,imgDivClass,0.8);

}

//--

function Canvas() {

}

//--入口函数：

Canvas.zoom = function (canvasId,imgDivClass,c) {

    //初始化

    //canvas

    cvW = TranNum($("#" + canvasId).css("width"));

    cvH = TranNum($("#"+ canvasId).css("height"));

    //Canvas

    _items = $("#" + canvasId).find("[class=‘"+imgDivClass+"‘]");

    //计算

    if (c == 1) {

        return

    }

    var b = this.getCanvasSize();

    var a = new Point(b.w / 2, b.h / 2);

    var d = new Point(c, c);

    $.each(_items, function (f) {

        //pro

        proW = TranNum($(this).css("width"));

        proH = TranNum($(this).css("height"));

        proT = TranNum($(this).css("top"));

        proL = TranNum($(this).css("left"));

        //pro中心点到pro四条边的距离left,bottom,right,top

        x1 = -1 * proW / 2;

        x2 = proW / 2;

        y1 = -1 * proH / 2;

        y2 = proH / 2;

        //中心点到画布的top.left值：

        translation = new Point(x2 + proL, y2 + proT);

        //

        setScale(d, a)//放大倍数坐标，画布中间点

        $(this).css({ "left": round(x1 + translation.x, 0.001).toString() + "px", "top": round(y1 + translation.y, 0.001).toString() + "px" });

        $(this).css({ "width": Math.abs((x1 * 2)).toString() + "px", "height": Math.abs((y1 * 2)).toString() + "px" });

        $(this).find("img").css({ "width": Math.abs((x1 * 2)).toString() + "px", "height": Math.abs((y1 * 2)).toString() + "px" });

    });

};

//--Tool

function TranNum(a) {

    return parseFloat(a.replace("px", ""));

}

//

function Point(a, b) {

    this.x = a;

    this.y = b

}

//

Canvas.getCanvasSize = function () {

    return new Dim(parseInt(cvW, 10), parseInt(cvH, 10))

};

//

function Dim(a, b) {

    this.w = Math.abs(a);

    this.h = Math.abs(b);

    this.aspect = b / a

}

//--

setScale = function (c, a) {//,倍数, 画布中心点

    beginResize();

    scale(c, a); //,倍数.画布中心点

   // return endResize()

};

//

beginResize = function () {

    this.rectStart = clone();

    this.translationStart = new Point(translation.x, translation.y);

};

//

clone = function () {

    return new Rect(x1,y1,x2,y2)

};

//

function Rect(b, d, a, c) {

    this.x1 = b || 0;

    this.y1 = d || 0;

    this.x2 = a || 0;

    this.y2 = c || 0

}

//

scale = function (c, a, d, b) {

    this._scale(c, a, b);

};

//

_scale = function (c, a, f) {////,倍数,画布中心点

    if (f === undefined) {

        f = true;

    }

    this.rect = clone();

    x1 *= c.x;

    y1 *= c.y;

    x2 *= c.x;

    y2 *= c.y;

    if (a) {

        _values=[1.0000000000000002,-0,-0,1.0000000000000002];//对[1,0,0,1]做了些计算得出的；

        var b = transform(a.x -translationStart.x, a.y -translationStart.y);

        var d =transform(c.x * -b.x, c.y * -b.y);

        translation.x = d.x + a.x;

        translation.y = d.y + a.y

    } else {

        translation.x = translationStart.x * c.x;

        translation.y = translationStart.y * c.y

    }

};

//

transform = function (b, d, a) {//两中心x差，两中心y差

    if (a) {

        b -= a.x;

        d -= a.y;

    }

    var c = new Point(_values[0] * b + _values[1] * d, _values[2] * b + _values[3] * d);

    if (a) {

        c.x += a.x;

        c.y += a.y

    }

    return c

};

function round(b, a) {

    a = a || 1;

    if (a > 1) {

        return Math.round(b / a) * a

    } else {

        a = 1 / a;

        return Math.round(b * a) / a

    }

}

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