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Procedurally generate a sine wave in a chramp?

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toMilkman
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Joined: 9月 2018
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Hi everyone,
I want to use the chramp() function in VEX to drive an attribute, but I'd like the ramp's curve to be a perfect sine wave (similar to the attached image).

Manually clicking and adjusting points in the ramp interface is tedious and imprecise. Is there a way to procedurally or programmatically set the ramp's shape without doing it by hand?

Any tips would be greatly appreciated. Thanks!

Attachments:
ramp sample.jpg (13.6 KB)

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tamte
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If you want to procedurally define key positions and values use spline() [www.sidefx.com] or ramp_lookup() [www.sidefx.com] function

You can likely also just multiply sin() and -exp() functions for similar shape without having to sample any ramp
Edited by tamte - 2026年2月24日 02:50:30
Tomas Slancik
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Framestore, NY
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animatrix_
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Hi,

You can easily do this using Python:

import math

node = hou.pwd()
parm_path = node.evalParm("parm_ref")
parm = hou.parm(parm_path)
if parm is None:
    raise hou.NodeError("Bad parm path in parm_ref: " + parm_path)

N = 32
cycles = 1.0
phase = 0.0
amp = 0.5
offset = 0.5
decay = 0.0

keys = [i / (N - 1) for i in range(N)]
vals = []
for t in keys:
    y = math.sin(2.0 * math.pi * cycles * t + phase)
    y *= math.exp(-decay * t)
    vals.append(offset + amp * y)

basis = [hou.rampBasis.CatmullRom] * (N - 1)

r = hou.Ramp(basis, keys, vals)

parm.set(r)

Attachments:
a.png (625.8 KB)

Senior FX TD @ Industrial Light & Magic
Get to the NEXT level in Houdini & VEX with Pragmatic VEX! [www.pragmatic-vfx.com] https://lnk.bio/animatrix [lnk.bio]
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Konstantin Magnus
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Hi toMilkman,

you could also set one remap node to cyclically roll a wave-shaped ramp and another one to define the amplitude. Combine both with the attribute combine node.
Edited by Konstantin Magnus - 2026年2月24日 09:00:11

Attachments:
wave.hip (101.2 KB)
wave_sshot.jpg (47.6 KB)

https://procegen.konstantinmagnus.de/ [procegen.konstantinmagnus.de]
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toMilkman
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Hi tamte,

Thank you so much! I wasn't aware of those functions, so this is very helpful. I also appreciate you taking the time to provide the links.

I’ll definitely give them a try right away. I'm also interested in the sin() and -exp() approach, so I’ll be testing that out as well.

Thanks again for your help!
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toMilkman
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Hi animatrix_,

That’s exactly what I was looking for! Thank you so much for taking the time to write the Python script for me. It’s incredibly helpful.

I’ll put it to use right away. I really appreciate your help!
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toMilkman
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Hi Konstantin Magnus,

Thank you for the hip file! It's a very interesting approach, and I’ve learned a lot from it.

By the way, I’m a big fan of your YouTube channel. Thank you for uploading so many insightful tutorials; they are always incredibly helpful. I especially learned a lot from your recent tutorial on Smooth Tangential Boolean Unions.

I’m looking forward to your future content. Thanks again!
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