L-system Local Variable (g vs t)

[kidsreturnjj]

I would like to get some advice about l-system,

- g : The age of the current rule, initially 0.

- t : The iteration count, initially 0.

I understood t is genertation of l-system.

What is different between g and t?

[riviera]

There is a subtle but important difference. There are probably better L-system experts than me, but hopefully I won't spread misinformation here...

First thing to know is that (at least this is what I concluded) for each letter in the generated L-system string, Houdini seems to store the number of iteration when the letter is added to the final string. So Houdini knows when each letter was generated.

Now, the difference between g and t is that one refers to this stored iteration value, the other refers to the current iteration value (I don't recall which is which, though).

I ran into this when I wanted to build a tree, where for the first few iterations only the trunk was created -- with letters in it that started to grow branches after a given generation count (so instead of growing a tree with shorter branches at the top, I wanted equal-length ones, hopefully I'm making some sense here...). In other words, I wrote a rule to expand the branch letters after the L-system ran for say 10 iterations (that allowed only the trunk to grow.)

It could be done using one of the letters (g/t) but not the other. Don't remember which but it takes only 2 tries to find out. L-systems can be mind-bending, and there are some features that not even documented or just hinted in the docs.

(I really wouldn't like to spread stupidity, though, so please anyone correct me if I'm wrong. This was quite some time ago.)

cheers,

imre