Omar Briceno Studio

Though only a few seconds long, this VFX shot was the work I was most proud of in my time collaborating with the 2023 Brigham Young University(BYU) Student Film Project named The Witch's Cat. While I also polished some shaders and pyro effects, this particular Yarn Transformation VFX was something I took complete ownership of. Within the context of the film, this is the part where the Cat grabs ahold of the Witch's wand and starts causing chaos; and so to convey the magical disarray, the vis-dev team asked me to create a VFX that converted household objects into yarn. Initially they asked me to just do a Pyro poof and swap the asset with a "yarn-ified" version, but I was a little more ambitious ... I wanted this to be a showcase of my prowess as a VFX artist, so I got to work.

The first step of this effect was to figure out how to make the yarn materialize and take the shape of the object its transforming. Above is one of my first explorations of how to make the yarn appear out of thin air. I procedurally generated the Houdini edges (lines) to represent the yarn thread. Then I looked into Pixar's RenderMan Lama Shader (used mainly to render hair) to make the edges look like yarn, I also took advantage of the offset (displacement) and visibility channels to create that visual "crumple into existence" effect. Lastly, to control the shader variables to give that spread effect, I used a Houdini SOP Solver to paint and gradually expand an attribute that will directly control the yarn shader. And voilà! The first layer of my effect is complete!

Now I needed to figure out how to: 1. Create a "yarn-ified" asset duplicate, and 2. Combine the effect on the yarn duplicate. Immediately I knew to just create an HDA that allowed me to input the model it wants to duplicate, and a few geometric controls to direct the flow of the yarn through the model. Then I needed to run the solver to create the "turn-into-yarn" animation. My first unfortunate subject was the sewing machine illustrated above. As you can see, it looks a little rough, stiff, like it was made out of those metal wires covered in plastic; and the appearing animation isn't looking much better, awkwardly phasing everything into existence instead of looking like the fibers are coiling and materializing. 'Tis the nature of VFX; It wouldn't be until many, many iterations later where I got the effect close to something I wanted.

Afterwards, I needed to layer the yarn with other auxiliary effects like: a bit of pyro, some sparks, maybe a bit of animation to really sell the impact of the magic. Fortunately there are many available references and resources, so I didn't have to do extensive research on how to create these effects. Of course, that didn't save me from iterating on each layer of the effect until I got something I liked. Eventually I was able to streamline the process enough to create a series of HDAs that took any asset, and magically converted it into yarn. There was still a bit of tweaking I needed to do that varied from asset to asset, but I was happy with how fast I was able to replicate the effect in other objects.

Working on this film was such a fun experience, and it was also a great opportunity for me to show-off what I can do. I am so grateful to have worked with such a solid team. I especially want to thank the pipeline crew for getting the Houdini Solaris USD-centric project set up. (and also teaching me how to assemble a USD stage, and how to use Payloads properly haha)

The student film has been uploaded on YouTube, here is the link if you'd like to watch it. (please watch it, it's great!)