Physically Based Rendering, 3rd Edition

11: Volume Scattering

So far, we have assumed that scenes are made up of collections of surfaces in a vacuum, which means that radiance is constant along rays between surfaces. However, there are many real-world situations where this assumption is inaccurate: fog and smoke attenuate and scatter light, and scattering from particles in the atmosphere makes the sky blue and sunsets red. This chapter introduces the mathematics to describe how light is affected as it passes through participating media—large numbers of very small particles distributed throughout a region of 3D space. Volume scattering models are based on the assumption that there are so many particles that scattering is best modeled as a probabilistic process, rather than directly ...