Houdini to Unity Bendable Fractures

Houdini to Unity Bendable Fractured Rig from Jason Harmon on Vimeo.

On a recent project I found myself needing to develop a way to get bendable fractured pieces of geometry out of Houdini into Unity. The fracture set up is simple, just a standard voronoi fracture constrained with cone constraints with a max break angle. I wanted the large chunks that remained constrained to bend and flex with no gaps. I set up a for each subnetwork that, for each connected chunk, would delete the inside faces, fuse the remaining points together and then use a point deform with the original fractured pieces driving the deformation of the new single chunk. The for each network also transferred existing UVs as well as mapped the inner edges. After all the new chunks were cached I then used the Game Development tools from sidefx’s github to create joints for each vertex, then merged all the chunks and exported as an FBX. On the Unity side I just imported the FBX and set the animation type to legacy and turned off all keyframe reduction.
If I were doing it over again, I think I’d explore how to use info coming out of DOPS about unbroken constraints to aid in creating the chunks that get worked on in the for each loop. Also the game development tools are pretty good, but have some issues. I had to convert each chunk individually because adjacent chunks got errors due to overlapping verticies (that’s my best guess).

Here’s a link to the Game Development tools from Side FX


Cloth Sim

I had a client request for a spot consisting almost entirely of slow motion silk fabric. Thought it’d be a good excuse to explore Houdini’s cloth solver. I got the slow mo effect working a couple of different ways. First I used the standard scale time function in the DOP settings.


Where that fell short was the fact that my cloth was being constrained to SOP geo outisde the DOP network. The fix was the timewarp SOP… pretty awesome to have straightforward time remapping as a node.


New Start

So I’ve just updated this site with the hopes of using the blog to track my progress learning Houdini. I’ve been interested in the software for years now and have tried to learn it a couple times in the past. This go around it’s actually making sense and I’m starting to get to use it on some client work. I’m excited to post progress as I get going with this amazing software.

Small beginnings.