Interior Mapping Shader

The BYU Center For Animation 2024 Capstone short film Student Accomplice features a car chase through busy city streets. It was important to make the city feel real and lived in. For this reason, we couldn't settle for featureless windows on our buildings but we also couldn't afford to render room geometry behind the panes. I looked to a technique featured in the recent Spider Man games called Interior Mapping,  which allows a cubemap to be rendered on a flat plane with correct parallax, giving the appearance of a room. Joost van Dongen's paper first described the technique in 2008 and was invaluable for implementation

Because we used RenderMan for the film, I was able to implement the shader using Open Shading Language as a custom node Then, I could use RenderMan's existing tools to randomly vary the cubemap of each window as well as the room's shape and middle ground features like furniture and curtains. Rooms were produced by texturing a box in Substance painter and then rendering it using a custom HDA in Houdini that produced a cubemap. The result was a render efficient and lifelike city.