• Adobe After Effects Expressions

  Dan Ebberts—questions regarding expressions from motionscript.com

  Posted by John Cuevas on March 30, 2006 at 6:25 pm

  First off I want to take the time to thank you for spending your time creating such a valuable learning tool & all of the help you give us javaphobes.

  Finally decided to start exploring the power of java, but I’m a little confused by the mathematical order in this expression. Also have a quick secondary question

  veloc = 40; //horizontal velocity (pixels per second)
  amp =12; //sine wave amplitude (pixels)
  freq = 2.4; //oscillations per second

  x = time*veloc;
  y = amp*time*(Math.sin(freq*time*2*Math.PI) – 1)/2 + thisComp.height/2;
  [x,y]

  In the array here, “veloc = 40; //horizontal velocity (pixels per second)” Everything after the “;” are just notes correct?

  y = amp*time*(Math.sin(freq*time*2*Math.PI) – 1)/2 + thisComp.height/2;
  [x,y]

  (freq*time*2*math.pi) is calculated first, then multiplied by Sin, then -1, /2

  Thank you
  Johnny Cuevas
  Editor
  Ck&Co

  John Cuevas replied 20 years, 4 months ago 2 Members · 2 Replies
• 2 Replies

• 

  Dan Ebberts

  March 30, 2006 at 6:35 pm

  >Finally decided to start exploring the power of java,

  Actually, AE’s expression and scripting languages are based on JavaScript.

  >Everything after the “;” are just notes correct?

  Yes. Javascript considers everything on a line after “//” to be a comment.

  >(freq*time*2*math.pi) is calculated first, then multiplied by Sin, then -1, /2

  Actually, freq*time*2*math.pi becomes the argument to the Math.sin trig function. The range of that function is +1 to -1. So subtracting one makes the range 0 to -2. Then, dividing by two makes the range 0 to -1 (which is what the expression needs).

  Dan
• 

  John Cuevas

  March 30, 2006 at 7:03 pm

  Thank you Dan

  I’m only about 16 years removed from the last time I used trig fuctions and basic alegebra. Took me a bit to wrap my head around exactly how it worked out.

  I feel for you having to deal with students like me. Again, I really appreciate you taking the time to put up motionscripts.com. Been using AE since Cosa 3.0, it’s about time I start fully taking advatage of the program.

  Johnny

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