• Adobe After Effects Expressions

  Random Lightining Strikes

  Posted by Pat Bray on June 18, 2011 at 12:14 pm

  Hi

  I was hoping to create lightning strikes from one element and wondered if there was a way to write an expression so when that element’s opacity = 0% it would reposition randomly , say 20-30 pixels? (the lightning is flickering using a simple wiggle expression at the moment).

  Any suggestions?

  Pat Bray replied 14 years, 10 months ago 2 Members · 2 Replies
• 2 Replies

• 

  Dan Ebberts

  June 18, 2011 at 4:48 pm

  This should give you a new random position every time the opacity goes below 1%:

  
p = transform.opacity;
threshold = 1;
trig = false;
for (f = timeToFrames(); f >= timeToFrames(inPoint); f--){
tCur = framesToTime(f);
v = p.valueAtTime(tCur);
if (trig && (v > threshold)) break;
if (v <= threshold) trig = true;
}
seedRandom(f,true);
offset = random([-20,-20],[20,20])
value + offset


  Dan
• 

  Pat Bray

  June 21, 2011 at 9:09 am

  Thank you! Wish I knew expression coding more thoroughly, it’s such a time saver and my workflow is so much tidier, unlike my desk… 😛

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