Accelerating physical rainbow model with CUDA

Currently Lorenz-Mie theory is the most accurate technique to simulate rainbows. However, it is still very attractive to use a model based on geometric optics to simulate rainbows, even methods based on geometric optics are not accurate enough. Since the droplets in the nature are non-spherical due to gravity and surface tension, Lorenz-Mie theory has difficult in handling non-spherical droplets, but they are easy for ray tracers. Sadeghi et al. develop a model based on geometric optics and do some extra work to match the prediction of Lorenz-Mie theory. However, the model takes much time on calculating to get sufficiently accurate phase function of droplets. In this paper, we firstly implement the model on PBRT, and then accelerate it with CUDA. The experiment results demonstrate that our acceleration algorithm greatly improves the speed of the model.