Volumetric clouds in the VR movie, Allumette

Abstract

Allumette is an immersive, highly emotional, and visually complex virtual reality movie that takes place in a city floating amongst clouds. The story unfolds around you, and as the viewer, you are free to experience the action from a perspective of your choosing. This means you can move around and view the clouds from all angles, while the set and characters interact intimately with the landscape. This type of set is a formidable challenge for traditional animated films where you have huge resources and hours to render each frame, which makes achieving the look and feel of immersive clouds in VR uncharted territory full of difficult challenges. Existing lightweight techniques for real time clouds, such as using geometric shells with translucency shaders, and sprite-based methods, have a combination of poor quality and bad performance in VR, which led us to seek novel methods to tackle the problem. For Allumette, we first modeled clouds in virtual reality by painting cloud shells using a proprietary modeling tool, then used a third party procedural modeling package to create and light the cloud voxel grids. Finally, these grids were exported with a custom file format, and rendered using a ray marcher in our game engine. The resulting clouds take .6ms per eye to render, and immerse the viewer in our cloud city.