Procedural Jelly Worms

I apologise if my latest piece invokes feelings of discomfort and unease.

This piece started as a proof-of-concept procedural jellyworms set-up in 2022. Recently, I added an expanding trail of liquid and rendered it. The worms are created, textured and animated procedurally in Houdini. Each worm starts as a point, then it becomes a curve that finally turns into geometry.

There are intersections between worms. I did not account for that in my simulation.

My main focus in this piece is to achieve the squishy feel and the erratic motion of each worm. I think what I had was quite successful in that aspect.

At first, the worms were just a circular extrusion along a spline that taper off at the start and end. Next I added the width variations so we get additional bulging that slide along the worm. These somehow make it look more like the movement of the muscles rippling through the worms that propel them forward.

Next comes the colours stripes and corresponding displacements that give the worms a ribbed appearance. These are tied to the percentage along the curve, like "local space" UVs on the worms.

Then I flattened the bottom of the worms so they looked more grounded to the ground instead of sausages half floating in the air.

At first, the trails that I implemented were just colours that faded over time. This made the trail appear to shrink in on itself over time. But I wanted the worm to emit a trail of liquid that expands instead, to like some kind of slime. What I have here in the end is not slime but more like flowing liquid that expands relatively easily with low viscosity.

In the end, I am still happy that I managed to achieve the expanding behaviour. Water that "bubbles" out and pushes itself outwards is an interesting look that I have not achieved before. It took me a while and quite a bit more tests with values to a believable love.

Once I was able to do the expanding liquid trail with about 4 worms it quickly became apparent that the same settings would overwhelm my processors for about 200 worms in the shot. After multiple crashes when I increased the worms to about 10 worms, I realised I must find a way to achieve a similar look with a much more efficient setting, balancing between detail and being able to simulate.

It was balancing between particle count, at any one time, which has to do with how many points to emit, how long the points should live before deleting them, and how dense the points needed to be to be sufficient for an appropriately detailed mesh.

In the end, I got to learn more about the Pop Fluid node and the Particle Fluid Surface SOP. I managed to achieve a satisfactory look by making efficient use of values like particle count and Pop Fluid parameters like particle separation, tensile strength and tensile radius.

After the simulation, I went and set up lighting and shaders to render this in Houdini Karma. Jelly shaders are a lot of fun!

I hope you like this piece.