using a channel with a ramp

[sanostol]

i use the ch("parameterpath", t) in vex to evaluate different channels per point, but instead of a keyframed anim I would like to use a ramp

is there a way?

Martin

[Adam Ferestad]

I am not sure how to answer your question, though it really does seem like a useful concept. I have a question for you though. What does the ", t" do in the ch() exactly? I have never seen a second argument to that expression, though I will confess that I haven't looked at the help card. Seems like it could be useful to know.

[anim]

...I will confess that I haven't looked at the help card....

you probably should

but it's not ch() expression, but ch() VEX function

http://www.sidefx.com/docs/houdini11.1/vex/functions/ch

[Adam Ferestad]

Well that answers that question. I haven't gotten into vex coding at all yet, so it tends to catch me a little off guard. Thanks for clarifying though. This program can be a little deep at times and i know I have only scratched the surface.

[sanostol]

indeed I need it in vex. but I found a work around. I created a expression ( chramp() )on a second parameter that evaluates the ramp in a certain range and query this second parmater with the ch() vex command. I first thought this would slow donw, but it works quite fast on 500 objects with this setup.

[Adam Ferestad]

That iis ally good to know. I need to meds with ramps, haven't even touched them yet.

[anim]

indeed I need it in vex. but I found a work around. I created a expression ( chramp() )on a second parameter that evaluates the ramp in a certain range and query this second parmater with the ch() vex command. I first thought this would slow donw, but it works quite fast on 500 objects with this setup.

I thought that you want to evaluate different ramp per point, what I cannot imagine right now

but if that's not the case you can probably create new ramp parameter in vex and make relative reference to the one you need to sample, then you can sample the ramp at different positions for each point inside the VOP/VEX, but it may not matter if you already have solution for your problem

[Macha]

<rant>

Uuuh, Sanostol! You almost solved one of my Houdini-bugbears there! I want a propper ramp too, with arbritrary curves (not the tiny little 0-1 ramp we get). The reason why this doesn't work in vex I think is because the float time has to remain constant. The whole thing is strangely scaled anyway and does't work in shop context in any case.

There are some workarounds for this in vopsop but I have never been able to find something that works in shop context.

A beer for anybody who can solve this and an extra present, with admiration, for anybody who can give us a ramp that can use arbritrary curves and log-scale.

</rant>

edit: with a little trickery I can get a ramp working in vopsop by extracting values from a parameter and setting them with vex ch() in a cspline(), but ch() isn't available in shops.

edit2: I wonder if this could be a case for cvex. Anybody know if we can run cvex from within a shader?

Edited August 27, 2011 by Macha

[sanostol]

@anim: every primitiv gets its own ramp from a differenent control object.

Edited August 27, 2011 by sanostol

[anim]

@anim: every primitiv gets its own ramp from a differenent control object.

ah, ok

are you using ch("parameterpath", t) with different t per point?

I've never used it like that since there is a warning in the docs, does it work without problems for you?

[sanostol]

ah, ok

are you using ch("parameterpath", t) with different t per point?

I've never used it like that since there is a warning in the docs, does it work without problems for you?

and different parameterpath per point, until now it works, but thanks for the hint to the warning, I will have a eye on it