Real-Time Neural Appearance Models
Authors: name: Tizian Zeltner, name: Fabrice Rousselle, name: Andrea Weidlich, name: Petrik Clarberg, name: Jan Novák, name: Benedikt Bitterli, name: Alex Evans, name: Tomáš Davidovič, name: Simon Kallweit, name: Aaron Lefohn

We present a complete system for real-time rendering of scenes with complex
appearance previously reserved for offline use. This is achieved with a
combination of algorithmic and system level innovations.
  Our appearance model utilizes learned hierarchical textures that are
interpreted using neural decoders, which produce reflectance values and
importance-sampled directions. To best utilize the modeling capacity of the
decoders, we equip the decoders with two graphics priors. The first prior --
transformation of directions into learned shading frames -- facilitates
accurate reconstruction of mesoscale effects. The second prior -- a microfacet
sampling distribution -- allows the neural decoder to perform importance
sampling efficiently. The resulting appearance model supports anisotropic
sampling and level-of-detail rendering, and allows baking deeply layered
material graphs into a compact unified neural representation.
  By exposing hardware accelerated tensor operations to ray tracing shaders, we
show that it is possible to inline and execute the neural decoders efficiently
inside a real-time path tracer. We analyze scalability with increasing number
of neural materials and propose to improve performance using code optimized for
coherent and divergent execution. Our neural material shaders can be over an
order of magnitude faster than non-neural layered materials. This opens up the
door for using film-quality visuals in real-time applications such as games and
live previews.