Single Scattering Effects for Computer Games

This paper addresses the rendering of single scattering effects such as glows and shafts of light, along with volumetric shadows induced by shadow casters in the participating media in real-time. Our method is easy to integrate in a video game graphics engine using the shadow volume technique since it requires only a little additional texture memory and is implemented with simple shaders. Realistic images can be produced in real-time for usual graphic scenes and at a high level framerate for complex scenes, allowing changes in the properties of participating medium, animations of objects and even light sources movements. Keywords— Single scattering, Real Time, Hardware rendering I. GOALS AND CONTRIBUTIONS In this paper we show how to render a complete single scattering illumination model. The originality of the model is the introduction of the indirect single scattering. Indeed, we will call direct single scattering the effect of the first scattering of light along view rays. The indirect single scattering is the same effect but along illumination rays of any point of scene. Our contributions in this subject are : • Define an analytic and comprehensive formulation of light scattering along view rays and illumination rays. Based on a angular formulation of the radiative transfer equation, we present precomputed 2D tables to compute directly these contributions. • Integration of the volumetric shadows. We build a method based on the shadow volume technique and using spatial coherence strategy, allowing the rendering of volumetric shadows in the scene, especially discernable around light sources. • Hardware implementation. Except for the determination of object’s silhouette, all the work is done with GPU. We store our precomputed 2D tables in textures and use simple shaders to render the illumination of objects and participating media. The rendering of volumetric shadows also involves an intensive use of the stencil buffer. Our method is not restricted to isotropic participating media which can be lit by one or several, static or moving, point light sources since no precomputation are done involving either lights or camera. Our technique produces high resolution images and takes into account volumetric shadows, cast by occluders contained in the media. With very few texture memory cost, but using intensively graphics hardware, our method can render images at a high frame rate and is realtime for classical graphics scene. Our method is also easy S