• Adobe After Effects Expressions

  Check for shortest distance

  Posted by Klaus Hertweck on May 21, 2025 at 6:45 am

  I have shapes A and B. A is stationary and B is moving across the screen. I want to calculate the frame when B is closest to A. I guess it’s done with a For Loop and distance but I cannot figure out the expression.

  Brie Clayton

  

  replied 11 months, 4 weeks ago 3 Members · 4 Replies
• 4 Replies

• 

  Klaus Hertweck

  May 21, 2025 at 12:36 pm

  I figured out the correct expression myself.

  First, I set up a null with an expression controls Slider Control “check distance” (just to do some of the calculations).

  There, I calculated the distance:

  var posA = thisComp.layer(“Shape A”).transform.position;
  var posB = thisComp.layer(“Shape B”).transform.position;
  var distance = length(posA, posB);
  distance

  On another slider, I set up the frame expression:

  var distance = effect(“check distance”)(“Slider”);
  var compLength = thisComp.duration / thisComp.frameDuration;
  for (i = 0; i <= compLength; i++) {
  if (distance.valueAtTime(framesToTime(i+1)) >= distance.valueAtTime(framesToTime(i))) break
  }
  i

  
  

  I would have liked to put all the expressions onto a single slider. However, when I insert length(posA, posB).valueAtTime(framesToTime(i) into the expression, I get an error: This is not a function.

  Is there a way to get around this error?
• 

  Dan Ebberts

  May 21, 2025 at 12:50 pm

  This could get complicated, depending on what you’re after, but the simplest version would probably be something like this:

  posterizeTime(0);
  p1 = thisComp.layer("Shape Layer 1").content("Rectangle 1").transform.position;
  p2 = thisComp.layer("Shape Layer 1").content("Rectangle 2").transform.position;
  minD = length(p1.valueAtTime(0),p2.valueAtTime(0));
  for (i = 1; i < timeToFrames(thisComp.duration); i++){
    t = framesToTime(i);
    d = length(p1.valueAtTime(t),p2.valueAtTime(t));
    minD = Math.min(d, minD);
  }
  minD
• 

  Klaus Hertweck

  May 21, 2025 at 4:20 pm

  That helped me a lot!
  Thank you very much.
• 

  Brie Clayton

  May 21, 2025 at 9:52 pm

  Thank you for solving this, Dan!

  

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