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
}
}