Count up and down elegantly

Question

I'm trying to make a flashing object, i.e., increment it's alpha value from 0 to 255 (gradually) and then back down to 0, and repeat.

Is there a way I can do this without using some boolean? Getting it to increment is easy:

alpha = time.elapsed()%256;

But what's a nice way to get it to count back down again after that?

Answer 1

Maybe you could do it this way:

alpha = abs((time.elapsed() % 510) - 254);

Answer 2

abs(((x + 255) % 510) - 255) will go linearly from 0 to 255 for x between 0 and 255, and linearly from 255 to 0 for x between 255 and 510. Then it repeats (with period 510 of course).

Answer 3

How about using a sin function, that way the fading is more pleasant and you'll get what you want.