Tween公式

Tween公式 4个参数

t：current time（当前时间）

b：beginning value（初始值）

c： change in value（变化量）

d：duration（持续时间） return （目标点）

 var Tween = {
     linear: function (t, b, c, d){  //匀速
         return c*t/d + b;
     },
     easeIn: function(t, b, c, d){  //加速曲线
         return c*(t/=d)*t + b;
     },
     easeOut: function(t, b, c, d){  //减速曲线
         return -c *(t/=d)*(t-2) + b;
     },
     easeBoth: function(t, b, c, d){  //加速减速曲线
         if ((t/=d/2) <) {
             return c/2*t*t + b;
         }
         return -c/2 * ((--t)*(t-2) - 1) + b;
     },
     easeInStrong: function(t, b, c, d){  //加加速曲线
         return c*(t/=d)*t*t*t + b;
     },
     easeOutStrong: function(t, b, c, d){  //减减速曲线
         return -c * ((t=t/d-1)*t*t*t - 1) + b;
     },
     easeBothStrong: function(t, b, c, d){  //加加速减减速曲线
         if ((t/=d/2) < 1) {
             return c/2*t*t*t*t + b;
         }
         return -c/2 * ((t-=2)*t*t*t - 2) + b;
     },
     elasticIn: function(t, b, c, d, a, p){  //正弦衰减曲线（弹动渐入）
         if (t === 0) {
             return b;
         }
         if ( (t /= d) == 1 ) {
             return b+c;
         }
         if (!p) {
             p=d*0.3;
         }
         if (!a || a < Math.abs(c)) {
             a = c;
             var s = p/4;
         } else {
             var s = p/(2*Math.PI) * Math.asin (c/a);
         }
         return -(a*Math.pow(2,10*(t-=1)) * Math.sin( (t*d-s)*(2*Math.PI)/p )) + b;
     },
     elasticOut: function(t, b, c, d, a, p){    //正弦增强曲线（弹动渐出）
         if (t === 0) {
             return b;
         }
         if ( (t /= d) == 1 ) {
             return b+c;
         }
         if (!p) {
             p=d*0.3;
         }
         if (!a || a < Math.abs(c)) {
             a = c;
             var s = p / 4;
         } else {
             var s = p/(2*Math.PI) * Math.asin (c/a);
         }
         return a*Math.pow(2,-10*t) * Math.sin( (t*d-s)*(2*Math.PI)/p ) + c + b;
     },
     elasticBoth: function(t, b, c, d, a, p){
         if (t === 0) {
             return b;
         }
         if ( (t /= d/2) == 2 ) {
             return b+c;
         }
         if (!p) {
             p = d*(0.3*1.5);
         }
         if ( !a || a < Math.abs(c) ) {
             a = c;
             var s = p/4;
         }
         else {
             var s = p/(2*Math.PI) * Math.asin (c/a);
         }
         if (t < 1) {
             return - 0.5*(a*Math.pow(2,10*(t-=1)) *
                     Math.sin( (t*d-s)*(2*Math.PI)/p )) + b;
         }
         return a*Math.pow(2,-10*(t-=1)) *
                 Math.sin( (t*d-s)*(2*Math.PI)/p )*0.5 + c + b;
     },
     backIn: function(t, b, c, d, s){     //回退加速（回退渐入）
         if (typeof s == 'undefined') {
            s = 1.70158;
         }
         return c*(t/=d)*t*((s+1)*t - s) + b;
     },
     backOut: function(t, b, c, d, s){
         if (typeof s == 'undefined') {
             s = 3.70158;  //回缩的距离
         }
         return c*((t=t/d-1)*t*((s+1)*t + s) + 1) + b;
     },
     backBoth: function(t, b, c, d, s){
         if (typeof s == 'undefined') {
             s = 1.70158;
         }
         if ((t /= d/2 ) < 1) {
             return c/2*(t*t*(((s*=(1.525))+1)*t - s)) + b;
         }
         return c/2*((t-=2)*t*(((s*=(1.525))+1)*t + s) + 2) + b;
     },
     bounceIn: function(t, b, c, d){    //弹球减振（弹球渐出）
         return c - Tween['bounceOut'](d-t, 0, c, d) + b;
     },
     bounceOut: function(t, b, c, d){
         if ((t/=d) < (1/2.75)) {
             return c*(7.5625*t*t) + b;
         } else if (t < (2/2.75)) {
             return c*(7.5625*(t-=(1.5/2.75))*t + 0.75) + b;
         } else if (t < (2.5/2.75)) {
             return c*(7.5625*(t-=(2.25/2.75))*t + 0.9375) + b;
         }
         return c*(7.5625*(t-=(2.625/2.75))*t + 0.984375) + b;
     },
     bounceBoth: function(t, b, c, d){
         if (t < d/2) {
             return Tween['bounceIn'](t*2, 0, c, d) * 0.5 + b;
         }
         return Tween['bounceOut'](t*2-d, 0, c, d) * 0.5 + c*0.5 + b;
     }
 }