eye view rays light min max min max min max min max min max min max rectified view direction min max light rays rectified light direction Figure 1: To compute single scattering in scenes with occluders (left) we compute a depth image from the camera, and a shadow map from the light. After epipolar rectification, each row of the shadow map is a 1D heightfield. We optimize the computation of the scattering integral by using an efficient data structure (a 1D min-max mipmap, center) over this heightfield. This data structure helps compute the scattering integral for all camera rays in parallel. Our method can render complex high-quality scenes with textured lights (right) in real-time (55 FPS). Light scattering in a participating medium is responsible for several important effects we see in the natural world. In the presence of occluders, computing single scattering requires integrating the illumination scattered towards the eye along the camera ray, modulated by the visibility towards the light at each point. Unfortunately, incorporating volumetric shadows into this integral, while maintaining real-time performance, remains challenging. In this paper we present a new real-time algorithm for computing volumetric shadows in single-scattering media on the GPU. This computation requires evaluating the scattering integral over the intersections of camera rays with the shadow map, expressed as a 2D height field. We observe that by applying epipolar rectification to the shadow map, each camera ray only travels through a single row of the shadow map (an epipolar slice), which allows us to find the visible segments by considering only 1D height fields. At the core of our algorithm is the use of an acceleration structure (a 1D minmax mipmap) which allows us to quickly find the lit segments for all pixels in an epipolar slice in parallel. The simplicity of this data structure and its traversal allows for efficient implementation using only pixel shaders on the GPU.

a b c Figure 1: Natural glowy effects attenuating from the light center and shafts of light and naturally jitted in the shafts of light due to particles. (a) Real Picture. (b) Our Implementation. (c) Our Implementation with Lighting Jittered through Particles. In real life, we often face some lighting situations where glowy effects are produced by light sources where there are many visibly big particles. Using functions in existing shading languages or built-in functions in graphics hardware can generate rather artificial images because it does not consider scattering. Previous works have proposed similar lighting effects, including visualization of shafts of light and atmosphere of the earth. However, although plausible, those lighting effects can look artificial due to the little difference from the those of the real world – particle visualization in the lighting effect. Our method visualizes lighting effects with natural attenuation at the edge in the shafts of light. It also visualizes decently distributed particle effects. Also, our technique can be used in general lighting situation since it is based on comprehensive model on particle distribution. Also, it can easily be extended in such a way that users can manipulate the distribution of particle density. Users can also equalize scattering effect by changing the user input β.

The interaction of light and matter in the world surrounding us is of striking complexity and beauty. Since the very beginning of computer graphics, adequate modeling of these processes and efficient computation is an intensively studied research topic and still not a solved problem. The inherent complexity stems from the underlying physical processes as well as the global nature of the interactions that let light travel within a scene. This article reviews the state of the art in interactive global illumination computation, that is, methods that generate an image of a virtual scene in less than one second with an as exact as possible, or plausible, solution to the light transport. Additionally, the theoretical background and attempts to classify the broad field of methods are described. The strengths and weaknesses of different approaches, when applied to the different visual phenomena, arising from light interaction are compared and discussed. Finally, the article concludes by highlighting design patterns for interactive global illumination and a list of open problems.