js抛物线动画——加入购物车动效

参考文章：http://www.zhangxinxu.com/wordpress/2013/12/javascript-js-元素-抛物线-运动-动画/

parapola.js

/*!
 * 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) {
    /*
     * 网页模拟现实需要一个比例尺
     * 如果按照1像素就是1米来算，显然不合适，因为页面动不动就几百像素
     * 页面上，我们放两个物体，200~800像素之间，我们可以映射为现实世界的2米到8米，也就是100:1
     * 不过，本方法没有对此有所体现，因此不必在意
    */
    
    var defaults = {
        speed: 166.67, // 每帧移动的像素大小，每帧（对于大部分显示屏）大约16~17毫秒
        curvature: 0.001,  // 实际指焦点到准线的距离，你可以抽象成曲率，这里模拟扔物体的抛物线，因此是开口向下的
        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; }
    };
    
    /* 确定移动的方式 
     * 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;
            }
        });        
    }
    
    // 根据两点坐标以及曲率确定运动曲线函数（也就是确定a, b的值）
    /* 公式： y = a*x*x + b*x + c;
    */
    var a = params.curvature, b = 0, c = 0;
    
    // 是否执行运动的标志量
    var flagMove = true;
    
    if (element && target && element.nodeType == 1 && target.nodeType == 1) {
        var rectElement = {}, rectTarget = {};
        
        // 移动元素的中心点位置，目标元素的中心点位置
        var centerElement = {}, centerTarget = {};
        
        // 目标元素的坐标位置
        var coordElement = {}, coordTarget = {};
        
        // 标注当前元素的坐标
        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)";
            }
            
            // 四边缘的坐标
            rectElement = element.getBoundingClientRect();
            rectTarget = target.getBoundingClientRect();
            
            // 移动元素的中心点坐标
            centerElement = {
                x: rectElement.left + (rectElement.right - rectElement.left) / 2 + scrollLeft,
                y: rectElement.top + (rectElement.bottom - rectElement.top) / 2    + scrollTop
            };
            
            // 目标元素的中心点位置
            centerTarget = {
                x: rectTarget.left + (rectTarget.right - rectTarget.left) / 2 + scrollLeft,
                y: rectTarget.top + (rectTarget.bottom - rectTarget.top) / 2 + scrollTop        
            };
            
            // 转换成相对坐标位置
            coordElement = {
                x: 0,
                y: 0    
            };
            coordTarget = {
                x: -1 * (centerElement.x - centerTarget.x),
                y:  -1 * (centerElement.y - centerTarget.y)    
            };
            
            /*
             * 因为经过(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;
             * 利用第二个坐标：
             * b = (y2+ a*x2*x2) / x2
            */
            // 于是
            b = (coordTarget.y - a * coordTarget.x * coordTarget.x) / coordTarget.x;    
            
            return this;
        };        
        
        // 按照这个曲线运动
        exports.move = function() {
            // 如果曲线运动还没有结束，不再执行新的运动
            if (flagMove == false) return this;
            
            var startx = 0, rate = coordTarget.x > 0? 1: -1;

            var step = function() {
                // 切线 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));
                
                // 防止过界
                if ((rate == 1 && startx > coordTarget.x) || (rate == -1 && startx < coordTarget.x)) {
                    startx = coordTarget.x;
                }
                var x = startx, y = a * x * x + b * x;
                
                // 标记当前位置，这里有测试使用的嫌疑，实际使用可以将这一行注释
                element.setAttribute("data-center", [Math.round(x), Math.round(y)].join());
                
                // x, y目前是坐标，需要转换成定位的像素值
                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 {
                    // 运动结束，回调执行
                    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);
        };
    }
}());

使用：

/* 元素 */
var element = document.getElementById("element"), 
    target = document.getElementById("target");
// 抛物线元素的的位置标记
var parabola = funParabola(element, target).mark();
// 抛物线运动的触发
document.body.onclick = function() {
    element.style.marginLeft = "0px";
    element.style.marginTop = "0px";
    parabola.init();
};

加入购物车实战：

/* 本demo演示脚本基于ieBetter.js, 项目地址：https://github.com/zhangxinxu/ieBetter.js */

// 元素以及其他一些变量
var eleFlyElement = document.querySelector("#flyItem"), eleShopCart = document.querySelector("#shopCart");
var numberItem = 0;
// 抛物线运动
var myParabola = funParabola(eleFlyElement, eleShopCart, {
    speed: 400,
    curvature: 0.002,    
    complete: function() {
        eleFlyElement.style.visibility = "hidden";
        eleShopCart.querySelector("span").innerHTML = ++numberItem;
    }
});
// 绑定点击事件
if (eleFlyElement && eleShopCart) {
    [].slice.call(document.getElementsByClassName("btnCart")).forEach(function(button) {
        button.addEventListener("click", function() {
            // 滚动大小
            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();  
        });
    });
}