2008

at the Maximum Trace Depth spinners. If you haven’t changed the parameters,
then you should see Max. Reflections and Max. Refractions set to the default
of 6, and Max. Depth set to 6.
There’s the problem: you actually have six surfaces that need to be traced by
the light rays for both reflections and refractions. The way to always calculate
the number of rays needed for a scene is to take the ray-traced objects in your
scene and draw an imaginary line through them, originating at the point of
view. Then, count the number of surfaces the line intersects.
For the wineglass and wine, you need at least six reflections and refractions
that correspond to the following surfaces:
■ Near outer glass surface (“near” relative to your Camera viewpoint)
■ Near inner glass surface
■ Near wine surface
■ Far wine surface
■ Far inner glass surface
■ Far outer glass surface
Therefore, increase the value of Max. Depth to 12.
Caustics and Global Illumination
Before rendering with caustics, there are several things you need to set up in
your scene:
■ For caustics to work properly, the generating object must use a material
that contains some degree of shininess, reflectivity, or refraction. Assign
a Raytrace or other map as either a Reflection map or Refraction map before
you render caustics.
■ Most often, you’ll be using very shiny, highly reflective materials (such as
chrome and other metals), or transparent or translucent materials (such
as glass goblets or water), to generate caustics in your scene. If you’re using
a glassy material, make sure it’s double-sided to create the proper results.
■ Make sure you have
object properties on page 262 set to Receive Caustics
or Generate Caustics (or both). To set up these properties, right-click an
object and choose Properties. For example, if you’re rendering a wineglass
on a tabletop, you probably want the wineglass both to generate and receive
6046 | Chapter 18 Rendering