• Adobe After Effects Expressions

  force a var to stop updating every frame

  Posted by Christian Labuska on April 29, 2010 at 3:11 pm

  hi there,

  is there a way to store the current time in a variable, when a specific event happens. or in other words: can i force a var to stop updating every frame?

  in detail:
  i have a keyframed slider control (1900 … 2000)
  i have a bunch of layer which names goes like that: 1902_…/1904_../…

  with the following expression i set the opacity:

  n = thisLayer.name;
  a = n.split(“_”);
  e = a[0];
  if(e<=thisComp.layer("SLIDER").effect("SLIDER")("Slider Control")) 100; else 0;

  so far so good.

  now i want that, if the layer’s opacity jumps to 100, the layer scales from 0 to 100 which would look like this:

  ease(time, timeAtEvent, timeAtEvent+20, 0, 100)

  tried to store the time in a variable in different ways (if else/while,…) but couldn’t get the variable to stop updating when the event shown above happens.

  somebody got an idea?
  thanks a lot

  Christian Labuska replied 16 years, 3 months ago 2 Members · 2 Replies
• 2 Replies

• 

  Dan Ebberts

  April 29, 2010 at 8:09 pm

  Variables don’t survive from one frame to the next, so your scale expression needs to figure out how long it’s been since the event. It will look something like this:

  if (transform.opacity >= 100){
  eventTime = time – thisComp.frameDuration;
  while (transform.opacity.valueAtTime(eventTime) >= 100) eventTime -= thisComp.frameDuration;
  t = time – eventTime;

  // calculate scale here based on t

  }else{
  value
  }

  This expression assumes that opacity starts out at less than 100%. If you have it set so that it’s always 100%, the expression will time out looking for the transition, so don’t apply the expression until you’ve keyframed the opacity (or modify the expression to check for that condition).

  Dan
• 

  Christian Labuska

  May 3, 2010 at 12:36 pm

  Thanks a lot Dan.

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