• Adobe After Effects Expressions

  Using Sine to drive Opacity, but between a range of values

  Posted by Alex Barnet on June 29, 2017 at 7:47 am

  I basically have a shadow underneath a hovering object that I want to increase and decrease in opacity as a function of a sin wave. The hovering object already has this expression on it’s y position:

  amp = 5;
freq = .75;

  y = amp*Math.sin(time*freq*Math.PI*2);
value + [0,y,0]

  The tricky part is, getting the max and min values to fall between something like 20 and 50. I understand it might be done with something like a clamp, but I don’t understand the syntax.

  Thanks

  Dan Ebberts replied 9 years, 2 months ago 2 Members · 3 Replies
• 3 Replies

• 

  Dan Ebberts

  June 29, 2017 at 1:13 pm

  This is probably the simplest:

  freq = .75;
  s = Math.sin(time*freq*Math.PI*2);
  linear(s,-1,1,50,20)

  You might have to swap the 50 and the 20.

  Dan
• 

  Alex Barnet

  June 29, 2017 at 11:22 pm

  Brilliant.

  Thanks Dan!

  p.s. my colleagues and I are trying to figure out what the purpose of the Math*PI function is?
• 

  Dan Ebberts

  June 30, 2017 at 12:23 am

  Math.PI*2 is the number of radians in one complete cycle of the sine wav. Including it lets the freq variable specify the frequency in complete cycles per second.

  Dan

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