Tween function

tween

var Tween = {
	Linear:function (start,alter,curTime,dur) {return start+curTime/dur*alter;},//最简单的线性变化,即匀速运动
	Quad:{//二次方缓动
		easeIn:function (start,alter,curTime,dur) {
			return start+Math.pow(curTime/dur,2)*alter;
		},
		easeOut:function (start,alter,curTime,dur) {
			var progress =curTime/dur;
			return start-(Math.pow(progress,2)-2*progress)*alter;
		},
		easeInOut:function (start,alter,curTime,dur) {
			var progress =curTime/dur*2;
			return (progress<1?Math.pow(progress,2):-((--progress)*(progress-2) - 1))*alter/2+start;
		}
	},
	Cubic:{//三次方缓动
		easeIn:function (start,alter,curTime,dur) {
			return start+Math.pow(curTime/dur,3)*alter;
		},
		easeOut:function (start,alter,curTime,dur) {
			var progress =curTime/dur;
			return start-(Math.pow(progress,3)-Math.pow(progress,2)+1)*alter;
		},
		easeInOut:function (start,alter,curTime,dur) {
			var progress =curTime/dur*2;
			return (progress<1?Math.pow(progress,3):((progress-=2)*Math.pow(progress,2) + 2))*alter/2+start;
		}
	},
	Quart:{//四次方缓动
		easeIn:function (start,alter,curTime,dur) {
			return start+Math.pow(curTime/dur,4)*alter;
		},
		easeOut:function (start,alter,curTime,dur) {
			var progress =curTime/dur;
			return start-(Math.pow(progress,4)-Math.pow(progress,3)-1)*alter;
		},
		easeInOut:function (start,alter,curTime,dur) {
			var progress =curTime/dur*2;
			return (progress<1?Math.pow(progress,4):-((progress-=2)*Math.pow(progress,3) - 2))*alter/2+start;
		}
	},
	Quint:{//五次方缓动
		easeIn:function (start,alter,curTime,dur) {
			return start+Math.pow(curTime/dur,5)*alter;
		},
		easeOut:function (start,alter,curTime,dur) {
			var progress =curTime/dur;
			return start-(Math.pow(progress,5)-Math.pow(progress,4)+1)*alter;
		},
		easeInOut:function (start,alter,curTime,dur) {
			var progress =curTime/dur*2;
			return (progress<1?Math.pow(progress,5):((progress-=2)*Math.pow(progress,4) +2))*alter/2+start;
		}
	},
	Sine :{//正弦曲线缓动
		easeIn:function (start,alter,curTime,dur) {
			return start-(Math.cos(curTime/dur*Math.PI/2)-1)*alter;
		},
		easeOut:function (start,alter,curTime,dur) {
			return start+Math.sin(curTime/dur*Math.PI/2)*alter;
		},
		easeInOut:function (start,alter,curTime,dur) {
			return start-(Math.cos(curTime/dur*Math.PI/2)-1)*alter/2;
		}
	},
	Expo: {//指数曲线缓动
		easeIn:function (start,alter,curTime,dur) {
			return curTime?(start+alter*Math.pow(2,10*(curTime/dur-1))):start;
		},
		easeOut:function (start,alter,curTime,dur) {
			return (curTime==dur)?(start+alter):(start-(Math.pow(2,-10*curTime/dur)+1)*alter);
		},
		easeInOut:function (start,alter,curTime,dur) {
			if (!curTime) {return start;}
			if (curTime==dur) {return start+alter;}
			var progress =curTime/dur*2;
			if (progress < 1) {
				return alter/2*Math.pow(2,10* (progress-1))+start;
			} else {
				return alter/2* (-Math.pow(2, -10*--progress) + 2) +start;
			}
		}
	},
	Circ :{//圆形曲线缓动
		easeIn:function (start,alter,curTime,dur) {
			return start-alter*Math.sqrt(-Math.pow(curTime/dur,2));
		},
		easeOut:function (start,alter,curTime,dur) {
			return start+alter*Math.sqrt(1-Math.pow(curTime/dur-1));
		},
		easeInOut:function (start,alter,curTime,dur) {
			var progress =curTime/dur*2;
			return (progress<1?1-Math.sqrt(1-Math.pow(progress,2)):(Math.sqrt(1 - Math.pow(progress-2,2)) + 1))*alter/2+start;
		}
	},
	Elastic: {//指数衰减的正弦曲线缓动
		easeIn:function (start,alter,curTime,dur,extent,cycle) {
			if (!curTime) {return start;}
			if ((curTime==dur)==1) {return start+alter;}
			if (!cycle) {cycle=dur*0.3;}
			var s;
			if (!extent || extent< Math.abs(alter)) {
				extent=alter;
				s = cycle/4;
			} else {s=cycle/(Math.PI*2)*Math.asin(alter/extent);}
			return start-extent*Math.pow(2,10*(curTime/dur-1)) * Math.sin((curTime-dur-s)*(2*Math.PI)/cycle);
		},
		easeOut:function (start,alter,curTime,dur,extent,cycle) {
			if (!curTime) {return start;}
			if (curTime==dur) {return start+alter;}
			if (!cycle) {cycle=dur*0.3;}
			var s;
			if (!extent || extent< Math.abs(alter)) {
				extent=alter;
				s =cycle/4;
			} else {s=cycle/(Math.PI*2)*Math.asin(alter/extent);}
			return start+alter+extent*Math.pow(2,-curTime/dur*10)*Math.sin((curTime-s)*(2*Math.PI)/cycle);
		},
		easeInOut:function (start,alter,curTime,dur,extent,cycle) {
			if (!curTime) {return start;}
			if (curTime==dur) {return start+alter;}
			if (!cycle) {cycle=dur*0.45;}
			var s;
			if (!extent || extent< Math.abs(alter)) {
				extent=alter;
				s =cycle/4;
			} else {s=cycle/(Math.PI*2)*Math.asin(alter/extent);}
			var progress = curTime/dur*2;
			if (progress<1) {
				return start-0.5*extent*Math.pow(2,10*(progress-=1))*Math.sin( (progress*dur-s)*(2*Math.PI)/cycle);
			} else {
				return start+alter+0.5*extent*Math.pow(2,-10*(progress-=1)) * Math.sin( (progress*dur-s)*(2*Math.PI)/cycle);
			}
		}
	},
	Back:{
		easeIn: function (start,alter,curTime,dur,s){
			if (typeof s == "undefined") {s = 1.70158;}
			return start+alter*(curTime/=dur)*curTime*((s+1)*curTime - s);
		},
		easeOut: function (start,alter,curTime,dur,s) {
			if (typeof s == "undefined") {s = 1.70158;}
			return start+alter*((curTime=curTime/dur-1)*curTime*((s+1)*curTime + s) + 1);
		},
		easeInOut: function (start,alter,curTime,dur,s){
			if (typeof s == "undefined") {s = 1.70158;}
			if ((curTime/=dur/2) < 1) {
				return start+alter/2*(Math.pow(curTime,2)*(((s*=(1.525))+1)*curTime- s));
			}
			return start+alter/2*((curTime-=2)*curTime*(((s*=(1.525))+1)*curTime+ s)+2);
		}
	},
	Bounce:{
		easeIn: function(start,alter,curTime,dur){
			return start+alter-Tween.Bounce.easeOut(0,alter,dur-curTime,dur);
		},
		easeOut: function(start,alter,curTime,dur){
			if ((curTime/=dur) < (1/2.75)) {
				return alter*(7.5625*Math.pow(curTime,2))+start;
			} else if (curTime < (2/2.75)) {
				return alter*(7.5625*(curTime-=(1.5/2.75))*curTime + .75)+start;
			} else if (curTime< (2.5/2.75)) {
				return alter*(7.5625*(curTime-=(2.25/2.75))*curTime + .9375)+start;
			} else {
				return alter*(7.5625*(curTime-=(2.625/2.75))*curTime + .984375)+start;
			}
		},
		easeInOut: function (start,alter,curTime,dur){
			if (curTime< dur/2) {
				return Tween.Bounce.easeIn(0,alter,curTime*2,dur) *0.5+start;
			} else {
				return Tween.Bounce.easeOut(0,alter,curTime*2-dur,dur) *0.5 + alter*0.5 +start;
			}
		}
	}
};