Hosuk Chang
Dust and Cobwebs
I built procedural systems to create dust and cobwebs for Toy Story 4. There was an antique store in the movie, and the dust and cobwebs needed to be in many spots where toys could interact, like behind furniture or in corners – places humans don't usually go. Because we see the dust and cobwebs from such a close-up perspective (since we're seeing the world from a toy's point of view), they needed to look real in 3D. Simple texture tricks wouldn't be believable enough.
The cobweb algorithm is actually quite simple. Imagine virtual spiders jumping to random spots nearby, leaving a trail of web behind them. To make the web lines look tight and realistic, I used a simple smoothing operation that pulls them together. It's not perfectly realistic like real-world physics, but it was fast and looked pretty convincing. The example structure above is created by 5 invisible virtual spiders.
My original plan was to unleash virtual spiders (red dots in the examples) in the antique store and let them do their thing, finding perfect, out-of-the-way spots for their webs. Turns out, they were too good at hiding. They built webs in places we couldn't even see in the movie, like inside vases, shoes or between walls. So, I had to step in and micromanage their web-building locations.
I used 5-10 spiders at a time, let them build complex webs for a while, and then picked the frame that looked the best.
A more automated approach was implemented for the dust system. The process involved dividing the store set into parts and processing them in parallel on a render farm. This division was essential for keeping the overall dust work manageable.
The resulting point clouds that contain density data were further divided into smaller chunks for dynamic, camera-based loading, which was essential for handling the large volume of data efficiently at render time.
At render time, the point cloud data was transformed into dust fibers by a Houdini Engine RenderMan procedural DSO. This process creates significantly more detailed dust, increasing the number of vertices roughly 10x compared to the original point cloud data stored on disk.
In addition to the ambient dust, custom hero dust and debris enhanced the impactful close-up shots. Achieving this look required utilizing libraries of reusable debris and preset dust bunnies to create a wide range of unique visual elements, and this contributed significantly to the overall atmospheric richness of the film.