/*!
 * by zhangxinxu(.com) 2012-12-27
 * you can visit http://www.zhangxinxu.com/wordpress/?p=3855 to get more infomation
 * under MIT license
*/
var funParabola = function(element, target, options) {
 /*
 * 網(wǎng)頁模擬現(xiàn)實(shí)需要一個比例尺
 * 如果按照1像素就是1米來算，顯然不合適，因?yàn)轫撁鎰硬粍泳蛶装傧袼? * 頁面上，我們放兩個物體，200~800像素之間，我們可以映射為現(xiàn)實(shí)世界的2米到8米，也就是100:1
 * 不過，本方法沒有對此有所體現(xiàn)，因此不必在意
 */
 
 var defaults = {
 speed: 166.67, // 每幀移動的像素大小，每幀（對于大部分顯示屏）大約16~17毫秒
 curvature: 0.001, // 實(shí)際指焦點(diǎn)到準(zhǔn)線的距離，你可以抽象成曲率，這里模擬扔物體的拋物線，因此是開口向下的
 progress: function() {},
 complete: function() {}
 };
 
 var params = {}; options = options || {};
 
 for (var key in defaults) {
 params[key] = options[key] || defaults[key];
 }
 
 var exports = {
 mark: function() { return this; },
 position: function() { return this; },
 move: function() { return this; },
 init: function() { return this; }
 };
 
 /* 確定移動的方式 
 * IE6-IE8 是margin位移
 * IE9+使用transform
 */
 var moveStyle = "margin", testDiv = document.createElement("div");
 if ("oninput" in testDiv) {
 ["", "ms", "webkit"].forEach(function(prefix) {
 var transform = prefix + (prefix? "T": "t") + "ransform";
 if (transform in testDiv.style) {
 moveStyle = transform;
 }
 }); 
 }
 
 // 根據(jù)兩點(diǎn)坐標(biāo)以及曲率確定運(yùn)動曲線函數(shù)（也就是確定a, b的值）
 /* 公式： y = a*x*x + b*x + c;
 */
 var a = params.curvature, b = 0, c = 0;
 
 // 是否執(zhí)行運(yùn)動的標(biāo)志量
 var flagMove = true;
 
 if (element && target && element.nodeType == 1 && target.nodeType == 1) {
 var rectElement = {}, rectTarget = {};
 
 // 移動元素的中心點(diǎn)位置，目標(biāo)元素的中心點(diǎn)位置
 var centerElement = {}, centerTarget = {};
 
 // 目標(biāo)元素的坐標(biāo)位置
 var coordElement = {}, coordTarget = {};
 
 // 標(biāo)注當(dāng)前元素的坐標(biāo)
 exports.mark = function() {
 if (flagMove == false) return this;
 if (typeof coordElement.x == "undefined") this.position();
 element.setAttribute("data-center", [coordElement.x, coordElement.y].join());
 target.setAttribute("data-center", [coordTarget.x, coordTarget.y].join());
 return this;
 }
 
 exports.position = function() {
 if (flagMove == false) return this;
 
 var scrollLeft = document.documentElement.scrollLeft || document.body.scrollLeft,
 scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
 
 // 初始位置
 if (moveStyle == "margin") {
 element.style.marginLeft = element.style.marginTop = "0px";
 } else {
 element.style[moveStyle] = "translate(0, 0)";
 }
 
 // 四邊緣的坐標(biāo)
 rectElement = element.getBoundingClientRect();
 rectTarget = target.getBoundingClientRect();
 
 // 移動元素的中心點(diǎn)坐標(biāo)
 centerElement = {
 x: rectElement.left + (rectElement.right - rectElement.left) / 2 + scrollLeft,
 y: rectElement.top + (rectElement.bottom - rectElement.top) / 2 + scrollTop
 };
 
 // 目標(biāo)元素的中心點(diǎn)位置
 centerTarget = {
 x: rectTarget.left + (rectTarget.right - rectTarget.left) / 2 + scrollLeft,
 y: rectTarget.top + (rectTarget.bottom - rectTarget.top) / 2 + scrollTop 
 };
 
 // 轉(zhuǎn)換成相對坐標(biāo)位置
 coordElement = {
 x: 0,
 y: 0 
 };
 coordTarget = {
 x: -1 * (centerElement.x - centerTarget.x),
 y: -1 * (centerElement.y - centerTarget.y) 
 };
 
 /*
 * 因?yàn)榻?jīng)過(0, 0), 因此c = 0
 * 于是：
 * y = a * x*x + b*x;
 * y1 = a * x1*x1 + b*x1;
 * y2 = a * x2*x2 + b*x2;
 * 利用第二個坐標(biāo)：
 * b = (y2+ a*x2*x2) / x2
 */
 // 于是
 b = (coordTarget.y - a * coordTarget.x * coordTarget.x) / coordTarget.x; 
 
 return this;
 }; 
 
 // 按照這個曲線運(yùn)動
 exports.move = function() {
 // 如果曲線運(yùn)動還沒有結(jié)束，不再執(zhí)行新的運(yùn)動
 if (flagMove == false) return this;
 
 var startx = 0, rate = coordTarget.x > 0? 1: -1;
 
 var step = function() {
 // 切線 y'=2ax+b
 var tangent = 2 * a * startx + b; // = y / x
 // y*y + x*x = speed
 // (tangent * x)^2 + x*x = speed
 // x = Math.sqr(speed / (tangent * tangent + 1));
 startx = startx + rate * Math.sqrt(params.speed / (tangent * tangent + 1));
 
 // 防止過界
 if ((rate == 1 && startx > coordTarget.x) || (rate == -1 && startx < coordTarget.x)) {
 startx = coordTarget.x;
 }
 var x = startx, y = a * x * x + b * x;
 
 // 標(biāo)記當(dāng)前位置，這里有測試使用的嫌疑，實(shí)際使用可以將這一行注釋
 element.setAttribute("data-center", [Math.round(x), Math.round(y)].join());
 
 // x, y目前是坐標(biāo)，需要轉(zhuǎn)換成定位的像素值
 if (moveStyle == "margin") {
 element.style.marginLeft = x + "px";
 element.style.marginTop = y + "px";
 } else {
 element.style[moveStyle] = "translate("+ [x + "px", y + "px"].join() +")";
 }
 
 if (startx !== coordTarget.x) {
 params.progress(x, y);
 window.requestAnimationFrame(step); 
 } else {
 // 運(yùn)動結(jié)束，回調(diào)執(zhí)行
 params.complete();
 flagMove = true; 
 }
 };
 window.requestAnimationFrame(step);
 flagMove = false;
 
 return this;
 };
 
 // 初始化方法
 exports.init = function() {
 this.position().mark().move();
 };
 }
 
 return exports;
};
 
/*! requestAnimationFrame.js
 * by zhangxinxu 2013-09-30
*/
(function() {
 var lastTime = 0;
 var vendors = ['webkit', 'moz'];
 for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
 window.requestAnimationFrame = window[vendors[x] + 'RequestAnimationFrame'];
 window.cancelAnimationFrame = window[vendors[x] + 'CancelAnimationFrame'] || // name has changed in Webkit
 window[vendors[x] + 'CancelRequestAnimationFrame'];
 }
 
 if (!window.requestAnimationFrame) {
 window.requestAnimationFrame = function(callback, element) {
 var currTime = new Date().getTime();
 var timeToCall = Math.max(0, 16.7 - (currTime - lastTime));
 var id = window.setTimeout(function() {
 callback(currTime + timeToCall);
 }, timeToCall);
 lastTime = currTime + timeToCall;
 return id;
 };
 }
 if (!window.cancelAnimationFrame) {
 window.cancelAnimationFrame = function(id) {
 clearTimeout(id);
 };
 }
}());

/* 元素 */
var element = document.getElementById("element"), 
 target = document.getElementById("target");
// 拋物線元素的的位置標(biāo)記
var parabola = funParabola(element, target).mark();
// 拋物線運(yùn)動的觸發(fā)
document.body.onclick = function() {
 element.style.marginLeft = "0px";
 element.style.marginTop = "0px";
 parabola.init();
};

/* 本demo演示腳本基于ieBetter.js, 項(xiàng)目地址：https://github.com/zhangxinxu/ieBetter.js */
 
// 元素以及其他一些變量
var eleFlyElement = document.querySelector("#flyItem"), eleShopCart = document.querySelector("#shopCart");
var numberItem = 0;
// 拋物線運(yùn)動
var myParabola = funParabola(eleFlyElement, eleShopCart, {
 speed: 400,
 curvature: 0.002, 
 complete: function() {
 eleFlyElement.style.visibility = "hidden";
 eleShopCart.querySelector("span").innerHTML = ++numberItem;
 }
});
// 綁定點(diǎn)擊事件
if (eleFlyElement && eleShopCart) {
 [].slice.call(document.getElementsByClassName("btnCart")).forEach(function(button) {
 button.addEventListener("click", function() {
 // 滾動大小
 var scrollLeft = document.documentElement.scrollLeft || document.body.scrollLeft || 0,
 scrollTop = document.documentElement.scrollTop || document.body.scrollTop || 0;
 
 eleFlyElement.style.left = event.clientX + scrollLeft + "px";
 eleFlyElement.style.top = event.clientY + scrollTop + "px";
 eleFlyElement.style.visibility = "visible";
 
 // 需要重定位
 myParabola.position().move(); 
 });
 });
}