• Adobe After Effects Expressions

  Set random value + keyframes

  Posted by Jeff Murchison on October 2, 2012 at 9:00 pm

  It’s been a while since I’ve worked with keyframes, so I’m having a bit of trouble nailing this one down.

  I’ve got an object in 3D space. X and Z coords are fine and shouldn’t change from their set value.

  For the Y value, I want it to be assigned a random number (between, say, -100 and -200) only once, at the beginning. Then it needs to go up to 0 over the course of 20 frames. I’d also like to set the frame that it starts that transition on as a random frame between 0 and 10.

  I’ve got some jumbled up code that I’ve been working on, but I don’t believe it’s worth posting. The part I’m having the issue with is the going up to 0 over the course of 20 frames, and getting the random values to only change once instead of once every frame.

  Edit: Actually, here’s some code:

  seedRandom(30,true);

  posY = random(-85, -385);

  startFrame = Math.floor(random(0,10));
  endFrame = startFrame+20;

  [value[0], posY, value[2]]

  Jeff Murchison replied 13 years, 10 months ago 2 Members · 2 Replies
• 2 Replies

• 

  Dan Ebberts

  October 2, 2012 at 10:21 pm

  Something like this, probably:

  maxDelayFrames = 11;
  minY = -200;
  maxY = -100;
  rampFrames = 20;

  seedRandom(index,true);
  f = Math.floor(random(maxDelayFrames));
  startY = random(minY,maxY);

  t1 = inPoint + framesToTime(f);
  t2 = t1 + framesToTime(rampFrames);
  y = linear(time,t1,t2,startY,0);
  [value[0],y,value[2]]

  Dan

  Dan
• 

  Jeff Murchison

  October 3, 2012 at 4:00 pm

  I adjusted it to do easy ease instead of linear and it works excellently. I’ll probably add an offset (slider effect) just in case I need to add a bit of manual control as well, but otherwise it’s perfect. Thanks Dan!

Reply to this Discussion! Login or Sign Up