Datasheet

Project: Raytracing Reflections  33
A list of the most critical attributes and their functionality follows:
Refractions Activates refractivity for the surface assigned to the material. For the refrac-
tivity to be visible, the material’s Transparency attribute must be set above 0.
Refractive Index Determines the degree of refractivity present. If set to the default 1.0,
no refraction occurs. In the real world, a refractive index is a number that indicates the
change in the speed of light when the light ray crosses the boundary between two materi-
als. For example, water has a refractive index of 1.33, which means light slows by 25 per-
cent. The actual equation is (speed of light in vacuum)/(speed of light in water) or 1.0/0.75,
which equals 1.33. The change in speed affects the perceived angle of the light rays, which
causes refracted surfaces to appear bent. For example, a straw placed in a glass of water
appears bent below the water line. Lists of real-world materials and their refractive indexes
are easily found on the Internet.
Refraction Limit and Reflection Limit Are local material overrides for the Reflections and
Refractions attributes found in the Render Settings window. The lower value between
matching attributes determines the number of reflective or refractive rays that the surface
assigned to the material is permitted to generate. For example, if Reflection Limit is set to
1, the assigned surface is allowed to reflect any ray that hits it so long as that ray has not
been reflected previously. If Reflection Limit is set to 4, an assigned surface is allowed to
reflect any ray that hits it so long as that ray has been reflected previously three times or
less. If refractions and/or reflections are missing from a surface when it renders, yet the
Reflections and Refractions attributes in the Render Settings window have high values,
raise the Refraction Limit and/or Reflection Limit values.
Project: Raytracing Reflections
Thus far, no surface in the headphones scene is creating reflections. To create reflections, you
must select the Raytracing check box in the Maya Software tab of the Render Settings win-
dow. After Raytracing is activated, all surfaces are potentially reflective. To alter this behav-
ior, you must adjust the Reflectivity attribute of each material in the scene. If you prefer that
a surface does not reflect, change the Reflectivity attribute of its assigned material to 0. To
increase the strength of a surface’s reflection, raise the Reflectivity value of its assigned mate-
rial; you can exceed the default limit of 1.0 by entering a higher value into the number cell.
Because reflectivity is also affected by Specular Roll Off and Specular Color, those attributes
may require adjustment. Table 1.2 lists the recommended reflective surfaces and the cor-
responding Specular Color and Reflectivity settings (the Specular Roll Off attributes were
mapped in the section “Creating Custom Bitmaps” earlier in this chapter).
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