Toon / Stylized Animation using Houdini

Houdini’s Pyro SIM rendered with Blender’s ToonKit Materials

As of late, I’ve been really into Toon and stylized animation, but I’m not very good at hand drawing pictures. That’s when I stumbled upon zBrush’s NPR filter! And this inspired me to explore more ways to create Toon and Stylized animation.

Rendered with zBrush’s NPR Filters

Houdini COPS (Composition)

I then tried to explore some in Houdini’s COP (Composition) Node editor and see if I could recreate the zBrush NPR filters inside Houdini. I managed to create a Toon-ish image, but it doesn’t look as awesome as the zBrush filter. zBrush Matcaps, Materials, and Lightcap settings make it very easy to create NPR filters that look awesome, but I haven’t figured out how to do the same in Houdini yet.

Experimenting with Houdini’s COPs to create Toon Filters

This is what I came up with so far. (screenshot on the right)

It took awhile to get the Outlines for the cartoon-ish look and it’s still not clean lines. I might be able to improve the quality with more time.

Blender 2.83

Coffee Cup Pyro Simulation Rendered with Houdini’s Mantra

I then dug up an old plugin I bought for Blender a couple years ago that is a Toon material shader and started working on getting geometry exported from Houdini into Blender so I could render out the animation using the Toon shader. Sadly even in Blender 2.83 the Alembic import feature still isn’t complete yet and only the “Cd” attribute from Houdini is being fully imported into Blender. BUT there is a silver lining! Blender 2.83 was just released with a new feature for importing VDB volumes!

Houdini to Blender Workflow

This is perfect for Houdini users! Blender’s Cycle rendering engine is extremely fast and free! This was a huge bonus discovery however I was looking for ways to create Toon animation. This discovery was more of a side track on my real mission.

Houdini Pyro Simulation converted to Geometry

I then tried a few ways of exporting the geometry from Houdini, but I still was only able to export the “Cd” attribute along with the geometry. So I looked into a bit of Blender scripting to see if I could fill in the missing attribute data. And to my surprise, I came up with a few lines of test commands that seems like it might do the trick in theory. I haven’t had the time to create a full script in Blender to finish this task off, but things look promising! This will be a project still in the works.

Houdini Pyro Simulation converted to Geometry

I then ended up converting pyro simulation in Houdini into geometry using the VDB Convert node and exporting it out as an Alembic. Then import it into Blender and render it out using the Toon materials from my plugin.