Volume Rendering

Abstract

The material shaders introduced on page 45 determine the color of the surface of a geometric object. The mental ray rendering software can also take into account the space between objects, with procedural volume shaders that control what happens when looking through it. In the simplest case, this can be a uniform fog that fades distant objects towards white. Volume shading is also the method of choice for

• anisotropic fog, non-uniform fog banks

• smoke, clouds

• fire

• visible light beams

• fur and feathers

and all other effects that either have no solid substance or are otherwise difficult to model geometrically. In principle, volume shaders can be used for any interaction with rays, including geometric models. It is possible to write volume shaders that act as sub-renderers in their domain of space, performing object and volume intersection tests like mental ray does. However, in practice volume shaders are used for effects like those in the above list; mental ray can handle solid object intersections much more efficiently.