2008

Ray-tracing: Rays are traced from the camera through a pixel, to the geometry,
then back to their light sources.
The ray-tracing algorithm is very versatile because of the large range of lighting
effects it can model. It can accurately account for the global illumination
characteristics of direct illumination, shadows, specular reflections (for
example, mirrors), and refraction through transparent materials. The main
disadvantage of ray-tracing is that it can be very slow for environments of
even moderate complexity. In 3ds Max, ray-tracing is used selectively on
objects with
ray-trace materials on page 5394 that specify ray-tracing as their
shading option. Ray-tracing can also be specified for light sources as the
method for rendering the shadows they cast.
A significant disadvantage of both ray-tracing and scanline rendering is that
these techniques do not account for one very important characteristic of global
illumination, diffuse inter-reflections. With traditional ray-tracing and scanline
rendering, only the light arriving directly from the light sources themselves
is accurately accounted for. But, as shown in the room example, not only does
light arrive at a surface from the light sources (direct lighting), it also arrives
from other surfaces (indirect lighting). If we were to ray-trace an image of the
kitchen, for example, the areas in shadow would appear black because they
5982 | Chapter 18 Rendering