Chopped Squabs – Pt 3


Last post, I talked about the tubers, their animation and creation of the pulse attributes.
This post will be about the bulbs on the end of the tubers, the pyro and particles setup.

Great balls of pyro

Since you don’t really get a close look at the tuber bulbs, considering the lighting and pyro cover them quite a bit, all of the bulbs have the same geometry.

Here is what the network looks like:

Bulb geometry network

This is a rather silly thing to do procedurally, I should have just sculpted something for it. Because problem solving in Houdini is fun, I tend to do everything in my home projects procedurally, but there are definitely times where that is a) overkill and b) ends up with a worse result.

Anyway, I’m starting out with a sphere:

  • Jittering the points a bit
  • Extruding the faces (to inset them)
  • Shrinking the extruded faces using the Primitive SOP on the group created by the extrude
  • Extruding again
  • Subdividing

That gives me this:

Animation of bulb geometry from primitives

I’m then boolean-ing a torus on one side, which will be where the tuber connects to the bulb.
I didn’t really need to Boolean that, since just merging the two objects and then converting to VDB and back gives me pretty much the same result, which is this:

Bulb vdb geo

Then I remesh it, and apply some noise in an Attribute VOP using the Displace Along Normal.

Before the Attribute VOP, I’ve set up a “pores” attribute, which is set to 1 on the extruded inside faces, and 0 everywhere else.
The VOP adds some breakup to the pores attribute, which is eventually used for emissive glow:

Attribute VOP for displacement and emissive

There was a very scientific process here of “add noise nodes until you get sick of looking at it”.

Here is the result:

Bulb with displacement

Looks ok if you don’t put much light on it, and you cover it with smoke 🙂

Spores / smoke

I wanted the smoke to look like a cloud of spores, sort of like a fungus sort of thing, with some larger spores created as particles that glow a bit.

The source of the smoke is geometry that has a non zero “pulse” attribute (that I set up in earlier posts), but I also just add a little bit of density from the pores on the tuber bulbs all the time.

So on any given frame I’m converting the following geometry to a smoke source:

Pores and tuber geo for smoke source

The resulting smoke source looks like this:

Smoke source animation

I also copy some metaballs onto points scattered on this geometry, which I’m using in a to push the smoke around:

Magnet force metaballs

I’m feeding that metaball geometry into the magnet force in a SOP Geometry node:

DOP network for particles and pyro

I’m not going to break down the dynamics network much, it is mostly setup with shelf tools and minimal changes.

With the forces and collisions with tuber geometry, the smoke simulation looks like this:

Smoke viewport flipbook


The geometry for the tubers and bulbs is also used to create spawn points for emissive particles:

Particle spawn network

Kind of messy, but on the right I’m capping the tuber sections that I showed before, remeshing them by converting to vdb, smoothing then converting back to polygons, scattering some points, adding velocity and some identifying attributes.

On the left side, I’m scattering points on the bulbs when the density (pulse value) is high.

In both cases, I’m setting particle velocity to a constant value * @N, so they move away from the surface, and faster from the bulbs than the tubers.

There are quite a lot of them, but in the final render the emissive falls off pretty quickly, so you don’t see them all that much:

Animation of generated particles

That’s it for this post!

Still to come: Breaking down creating audio in CHOPs.



2 thoughts on “Chopped Squabs – Pt 3

  1. Hello

    This is great. I have some trouble replicate it, do you mind to shere your houdini sample scene by chance please?
    Im talking about the great balls of pyro setup…

    Vincent Thomas   (VFX and Art since 1998)
    Senior Env artist & Lighting & MattePainter & Creative Concepts

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