Large-scale ray traced water caustics in real-time using cascaded caustic maps

Achieving interactivity for applications with physically-accurate caustics is proven to be a challenging task. We present a hybrid method utilizing ray tracing and rasterization which enables water caustic coverage to vast view distance in real-time. Inspired by photon mapping, we optimize the generation of photons using cascaded caustic maps to avoid tracing the first bounce of a ray from a light, replacing that step with rasterization. We introduce cascades as a set of caustic maps with varying resolution based on the distance from the viewer. In addition, since we adopt a splatting approach where each photon is rasterized into the image based on the extent of its contribution, we trace photon differentials in order to determine the size, shape and intensity of the splats so as to achieve adaptive anisotropic flux density estimation. Finally, to mitigate undersampled regions where lack of photons leads to noise, we propose the use of a cross-bilateral filter with an adaptive kernel radius. The radius is based on the perceived radiant energy of a photon relative to the scene’s luminance, and drastically improves performance. We demonstrate how the use of our method is able to perform interactive rendering of large-scale dynamic water caustics.