• Adobe After Effects Expressions

  Making the opacity to switch on and off – should be easy.

  Posted by Thor Hansvik on January 19, 2013 at 9:56 am

  Yes, I am new to this…

  I have a precomp I want to switch the opacity to 0 and 100 for every e.g. 10th frame. That is, 0% for the 10 first frames, then 100% for the next 10 frames and back to 0% for the next 10 frames and so on…

  I tried the following expression but I guess that the state variable is initialized for every new frame. Thus, the opacity stays at 100% for 10 frames, switching to 0% for one frame, and then switching back to 100% for the next 10 frames and so on.

  How (if possible) do I prevent the state variable to be initialized for every new frame, or solve this problem?

  
frames = timeToFrames() % 10;
state = 1;

  if (frames == 0)
  state = state * -1;

  if (state == 1)
  f = 1;
  else
  f = 0;

  transform.opacity = 100*f;

  Dan Ebberts replied 13 years, 7 months ago 2 Members · 3 Replies
• 3 Replies

• 

  Dan Ebberts

  January 19, 2013 at 5:37 pm

  This should work:

  f = timeToFrames(time-inPoint);
  Math.floor(f/10)%2 ? 100 : 0

  Dan
• 

  Thor Hansvik

  January 20, 2013 at 11:31 am

  Thanks, it works!

  Do I understand this right; The intire expression code is executed for each frame? Is it possible to define a variable that is initialized at “start up” (frame 0 or -1) ?
• 

  Dan Ebberts

  January 20, 2013 at 5:18 pm

  >The intire expression code is executed for each frame?

  Yes.

  > Is it possible to define a variable that is initialized at “start up” (frame 0 or -1) ?

  No, variables can’t persist between frames.

  Dan

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