A similar method (James 2004) removes the need for depth peeling using accumulated volume thickness. Another real-time method, based on the work of Radomir Mech (2001), uses polygonal volumes (James 2003), in which overlapping volumes are accumulated using frame-buffer blending with depth peeling. While a shadow-map method increases efficiency, here it also has the slice-based detractors and requires further video memory resources and rendering synchronization. However, slice-based volume-rendering methods can exhibit sampling artifacts, demand high fill rate, and require extra scene setup.
2002) and more recently applied using hardware shadow maps (Mitchell 2004). This topic was revisited in real-time rendering, using a slice-based volume-rendering technique (Dobashi et al. Rendering crepuscular rays was first tackled in non-real-time rendering using a modified shadow volume algorithm (Max 1986) and shortly after that, an approach was developed for multiple light sources (Nishita et al. In sunlight, such volumes are effectively parallel but appear to spread out from the sun in perspective. These phenomena are variously known as crepuscular rays, sunbeams, sunbursts, star flare, god rays, or light shafts. Under the right conditions, when a space contains a sufficiently dense mixture of light scattering media such as gas molecules and aerosols, light occluding objects will cast volumes of shadow and appear to create rays of light radiating from the light source. "A Shading Model for Atmospheric Scattering Considering Luminous Intensity Distribution of Light Sources." In Computer Graphics (Proceedings of SIGGRAPH 87) 21(4), pp. "Light Shafts: Rendering Shadows in Participating Media." Presentation at Game Developers Conference 2004. "Hardware-Accelerated Real-Time Rendering of Gaseous Phenomena." Journal of Graphics Tools 6(3), pp. "Atmospheric Illumination and Shadows." In Computer Graphics (Proceedings of SIGGRAPH 86) 20(4), pp. "Efficient Simulation of Light Transport in Scenes with Participating Media Using Photon Maps." In Proceedings of SIGGRAPH 98, pp. "True Volumetric Shadows." In Graphics Programming Methods, edited by Jeff Lander, pp. "Real-Time Light-Atmosphere Interactions for Outdoor Scenes." In Graphics Programming Methods, edited by Jeff Lander, pp. "Methods for Dynamic, Photorealistic Terrain Lighting." In Game Programming Gems 3, edited by D. "Interactive Rendering of Atmospheric Scattering Effects Using Graphics Hardware." Graphics Hardware. In this chapter, we consider the effect of volumetric shadows in the atmosphere on light scattering, and we show how this effect can be computed in real time with a GPU pixel shader post-process applied to one or more image light sources. This is due to the intractable nature of the radiative transport equation (Jensen and Christensen 1998), accounting for emission, absorption, and scattering, in a complex interactive animated environment.
In real-time rendering, the effect of participating media on light transport is often subject to low-complexity homogeneous assumptions. In the real world, we rarely see things in a vacuum, where nothing exists between an object and its observer. Figure 13-1 Volumetric Light Scattering on a Highly Animated Scene in Real Time 13.1 Introduction