After Effect - Triangle Wave (JavaScript)

Question

I'm trying to control a parameter with AE expressions and I need a triangle wave. I've got this so far:

freq = 20;
amplitude = 8; 

m = amplitude;
i = time*freq;

m - (i % (2*m) - m);

Unfortunately this gives a saw wave (see below) and my math's a bit rusty, any takers?

Thanks!

PJ

http://i25.photobucket.com/albums/c73/pjburnhill/Screenshot2010-04-09at153815.png

score 2 · Accepted Answer · answered Apr 09 '10 at 15:12

2

An easy way to get a triangle wave from here would be to subtract m/2 and take the absolute value. Alternatively, use f = m - abs(i % (2*m) - m).

answered Apr 09 '10 at 15:12

John Feminella

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See above, AE doesn't seem to allow abs... Am I missing out something here? – PJ Palomaki Apr 09 '10 at 15:23
Use `Math.abs()`. It's in the Javascript pulldown, I think. – John Feminella Apr 09 '10 at 16:08
Thanks John! That's it, got it working. Much appreciated. – PJ Palomaki Apr 09 '10 at 16:31
Just a (hopefully) final question, how can I get the triangle wave to give me negative values as well? So oscillating between i.e. 16 and -16? The line is currently like this: x = m - Math.abs(i % (2*m) - m); – PJ Palomaki Apr 09 '10 at 16:38
What's it oscillating between right now? – John Feminella Apr 09 '10 at 17:09
Whis this code it oscillates between 0 and 8: freq = 20;nd amplitude = 8; m = amplitude; i = time*freq; m - Math.abs(i % (2*m) - m); How can I get it to go to -8? Thanks! – PJ Palomaki Apr 11 '10 at 11:43
Make it `2 * Math.abs(...) - m`. – John Feminella Apr 11 '10 at 12:23
Hmm... still doesn't give negative values.. now oscillates between 0 and 16. Code: `2 * Math.abs(i % (2*m) - m);` – PJ Palomaki Apr 11 '10 at 15:38
You didn't write what I said. Keep the part in the `abs` the same as in post, but make it `2 * Math.abs(...) - m`. – John Feminella Apr 11 '10 at 16:01
Ahhh... my bad! So finally this code works: `2 * Math.abs(i % (2*m) - m) - m;` Thanks John, very much appreciated! – PJ Palomaki Apr 11 '10 at 16:14
Erhm... and how would I get the wave to start from negative value instead of a positive? – PJ Palomaki Apr 11 '10 at 16:26
Shift `i` accordingly (e.g. by making `i +/- [something]`). – John Feminella Apr 11 '10 at 21:00

After Effect - Triangle Wave (JavaScript)

1 Answers1