Computing light reflection from rough surfaces is an important topic in computer graphics. Reflection models developed based on geometric optics fail to capture wave effects such as diffraction and interference, while existing models based on physical optics approximations give erroneous predictions under many circumstances (e.g. when multiple scattering from the surface cannot be ignored).We present a scalable 3D full-wave simulator for computing reference solutions to surface scattering problems, which can be used to evaluate and guide the development of approximate models for rendering. We investigate the range of validity for some existing wave optics based reflection models; our results confirm these models for low-roughness surfaces but also show that prior rendering methods do not accurately predict the scattering behavior of some types of surfaces.

Our simulator is based on the boundary element method (BEM) and accelerated using the adaptive integral method (AIM), and is implemented to execute on modern GPUs. We demonstrate the simulator on domains up to 60 × 60 × 10 wavelengths, involving surface samples with significant height variations. Furthermore, we propose a system for efficiently computing BRDF values for large numbers of incident and outgoing directions, by combining small simulations to characterize larger areas. Our simulator will be released as an open-source toolkit for computing surface scattering.

We would like to thank Dr. Anil Damle for his helpful suggestions on iterative solvers. We also want to thank Nathaniel Sturniolo and Dr. Lauren Zarzar for providing us with their experimental data on grooved surfaces and for many fruitful discussions on structural color formation and modeling. Lastly, we would like to thank Xi Deng for her help with illustrating some of the figures in this paper. This work is supported by the National Science Foundation under grant IIS-1909467.