缓动动画表达式

freq = 3;

decay = 5;

n = 0;

if (numKeys > 0){

  n = nearestKey(time).index;

  if (key(n).time > time) n--;

}

if (n > 0){

  t = time - key(n).time;

  amp = velocityAtTime(key(n).time - .001);

  w = freq*Math.PI*2;

  value + amp*(Math.sin(t*w)/Math.exp(decay*t)/w);

}else

  value