Interactive calculation of light refraction and caustics using a graphics processor

While modern rendering systems are effective at modeling complex light paths in complex environments, rendering refractive caustics still takes a long time. Caustics are light patterns that occur when light is refracted and reflected from a surface. Due to the sharp density distribution of these mirror events, rendering algorithms mainly rely on direct sampling of the bidirectional scattering distribution function on these surfaces to plot trajectories. This requires many calculations. Photonic maps are also used. However, there are problems limiting the applicability of caustic maps. Since each photon in the photon buffer must be processed, therefore, one has to choose between a strongly underestimated caustic sampling and a large decrease in speed in order to use a sufficient number of photons for caustics in order to obtain high-quality images. Complex mirror interactions cause oversampling in bright focal areas, while other areas of the caustic map remain under-selected and noisy. At the same time, speed takes precedence over realism in most interactive applications. However, the desire to improve the quality of graphics prompted the development of various fast approximations for realistic lighting.

This paper presents a combined method for visualizing refraction of light and caustics using reverse integration for illumination and direct integration for viewing rays. An approach is used for simultaneous propagation of light and for tracking rays in volume and, therefore, it does not require storing data of an intermediate volume of illumination. In the implementation of the method, the distance between the light planes is set to one voxel, which provides at least one sample per voxel for all orientations. The method does not use preliminary calculations; all rendering parameters can be changed interactively.

As a result, using the proposed method, it is possible to create plausible approximations of complex phenomena such as refractions and caustics. The effect of refraction on the shadow is shown. Complex light patterns are demonstrated due to the curved geometry of the objects. The visualization results show the importance of refraction for the appearance of transparent objects. For example, distortions caused by refraction and refraction at the interface between media. The difference in refractive indices between individual media causes a complex interaction between light and shadow areas. It is shown how refraction and caustics improve the visualization of functionally defined objects by providing additional information about shape and location.