• Adobe After Effects Expressions

  Move layer from fixed position to random position, within range

  Posted by Kyle Hamrick on May 26, 2010 at 4:03 am

  Hey all,

  Got an expression problem I can’t quite wrap my head around.

  I’ve got an animation where groups of people icons are multiplying exponentially. It’s getting complex very quickly, and I’d love to help automate my workflow a little and let the expressions do the heavy lifting. I’m close, but haven’t quite gotten it working. Figured I’d see if anyone else might be able to take a stab at this.

  The layers in question spawn at [0,35,0], then need to move, over 30 frames beginning at the layer’s in point, to [random (-30,30), 35, random (-20,-80)], where it will stay for the rest of the comp.

  I’ve gotten results somewhat close to what I need by adapting parts of this original expression from Motionscript:

  segMin = .3; //minimum segment duration
  segMax = .7; //maximum segment duration
  minVal = [0.1*thisComp.width, 0.1*thisComp.height];
  maxVal = [0.9*thisComp.width, 0.9*thisComp.height];

  seedRandom(index,true);
  segDur = random(segMin, segMax);
  seed = Math.floor(time/segDur);
  segStart = seed*segDur;
  seedRandom(seed,true);
  startVal = random(minVal,maxVal);
  seedRandom(seed+1,true);
  endVal = random(minVal,maxVal);
  ease(time,segStart,segStart + segDur, startVal, endVal);

  …But that’s designed to repeat. Expressions dealing with time have always somewhat tripped me up, and I can’t seem to figure out what I’m missing.

  I’d love to be able to tie each random min/max value to a respective master slider, allowing me to easily control the density of this crowd. I can’t imagine a way to build an expression without still having that pickwhip option, but thought I’d make it known, at least.

  Any suggestions?

  EDIT: I’ve got this ALMOST working, by using the “Separate XYZ Position” Preset, and applying this to one dimension:

  seedRandom(index,true);
  segDur = 1;
  seed = index;
  segStart = inPoint;
  seedRandom(seed,true);
  startVal = 0;
  seedRandom(seed+1,true);
  endVal = effect(“X value”)(“Slider”);
  ease(time,segStart,segStart + segDur, startVal, endVal);

  Being able to compile all dimensions into one position expression would be nice, though.

  ============================

  Kyle Hamrick

  Editor/Motion Graphics Artist

  http://www.kylehamrick.com

  Kyle Hamrick replied 15 years, 11 months ago 2 Members · 2 Replies
• 2 Replies

• 

  Dan Ebberts

  May 26, 2010 at 4:32 am

  Something like this maybe:

  
moveFrames = 30;
seedRandom(index,true);
startPos = [0,35,0];
endPos = random([-30,35,-20],[30,35,-80]);
ease(time,inPoint,inPoint+framesToTime(moveFrames),startPos,endPos)


  Tying the min and max x and z values to sliders should be pretty straight forward.

  Dan
• 

  Kyle Hamrick

  May 26, 2010 at 4:39 am

  Thanks for the response Dan. Definitely more elegant than my solution.

  Your post just barely beat me submitting my edit saying that I’d gotten it working. =)

  Mine is still using my earlier expression nested into the “Separate XYZ” effect, but it’s just as easy to copy/paste that. I was outlining my post a little more clearly in the hopes that it’d be helpful for someone else in the future.

  Between your answer and mine, I think this thread has now served its purpose in that respect.

  Thanks again!

  Kyle Hamrick

  Editor/Motion Graphics Artist

  http://www.kylehamrick.com

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