Useful animation expressions

animation-expressions.js

// Link with expression
l = thisComp.layer("Layer Name");
p = l.toWorld(l.anchorPoint)

// Opacity jittering in
transitionTime = 1;
if (time < transitionTime) {
  (random() < 0.5 ? 0 : 100);
} else {
  100;
}

// Keyframe Bounce Back
// Source: http://www.motionscript.com/articles/bounce-and-overshoot.html#kf-bounce-back
e = .7;
g = 4000;
nMax = 9;

n = 0;
if (numKeys > 0){
  n = nearestKey(time).index;
  if (key(n).time > time) n--;
}
if (n > 0){
  t = time - key(n).time;
  v = -velocityAtTime(key(n).time - .001)*e;
  vl = length(v);
  if (value instanceof Array){
    vu = (vl > 0) ? normalize(v) : [0,0,0];
  }else{
    vu = (v < 0) ? -1 : 1;
  }
  tCur = 0;
  segDur = 2*vl/g;
  tNext = segDur;
  nb = 1; // number of bounces
  while (tNext < t && nb <= nMax){
    vl *= e;
    segDur *= e;
    tCur = tNext;
    tNext += segDur;
    nb++
  }
  if(nb <= nMax){
    delta = t - tCur;
    value +  vu*delta*(vl - g*delta/2);
  }else{
    value
  }
}else
  value


// Source: http://www.motion-graphics-exchange.com/after-effects/Wiggle-rubber-bounce-throw-inertia-expressions/4ad0f32a944ad

// Jumpy Wiggle 1 makes wiggle skip and hold rather than move fluidly.
// Jumpy Wiggle 1 (moves at a random FPS)
v=wiggle(5,50);
if(v < 50)v=0;
if(v > 50)v=100;
v


// Jumpy Wiggle 2 is similar to 1, but works at a defined FPS so your "jump" will happen at a regular pace.
// Jumpy Wiggle 2 (moves at a defined FPS)
fps=5; //frequency
amount=50; //amplitude
wiggle(fps,amount,octaves = 1, amp_mult = 0.5,(Math.round(time*fps))/fps);


// Inertial Bounce is like making your moves "rubbery." Layers will overextend, then settle into place on position and rotation keyframes.
// Inertial Bounce (moves settle into place after bouncing around a little)
n = 0;
if (numKeys > 0){
  n = nearestKey(time).index;
  if (key(n).time > time){
    n--;
  }
}
if (n == 0){
  t = 0;
}else{
  t = time - key(n).time;
}

if (n > 0){
  v = velocityAtTime(key(n).time - thisComp.frameDuration/10);
  amp = .05;
  freq = 4.0;
  decay = 2.0;
  value + v*amp*Math.sin(freq*t*2*Math.PI)/Math.exp(decay*t);
}else{
  value;
}


// Sometimes you just want something to move constantly without keyframing it. Use throw.
// Throw (move at a constant speed without keyframes)
veloc = -10; //horizontal velocity (pixels per second)
x = position[0] + (time - inPoint) *veloc;
y = position[1];
[x,y]


// Same as throw, but for rotation.
// Spin (rotate at a constant speed without keyframes)
veloc = 360; //rotational velocity (degrees per second)
r = rotation + (time - inPoint) *veloc;
[r] 

// By Chris Wright


// Flip anchor point side according to keyframe value
// Transform anchor point
[-content("Rectangle Path 1").size[0] / 2, value[1]] * (effect("Flip")("Checkbox") == 1 ? -1 : 1)

// Transform position
x = (effect("Flip")("Checkbox") == 1 ? effect("Width")("Slider").valueAtTime(effect("Width")("Slider").key(2).time) : 0);
value + [x, ];