Prior to Cutter version 5.2.9 rib files generated by Rman Tools were structured
loosely on a simplified version of a typical rib file generated by mtor. Mtor
was a Pixar plugin that enabled Maya to use the facilities of RenderMan. The plugin was
part of a suite of applications collectively known as RenderMan Artist Tools (RAT).
The problem relating to the shading of quadric surfaces outlined on this page
was caused by mtor's use of the rib statement
The rib files produced by mtor and Rfm Pro use a single
ConcatTransform [ 0.707 -0.331 -0.625 0.0 0.0 0.884 -0.469 0.0 -0.707 -0.331 -0.625 0.0 0.0 0.0 44.822 1.0 ]
Cutter uses a sequence of transformation commands because they are easier to understand.
The World According to Mtor
Although the world block is right-handed, surfaces such as polygons have their
vertices ordered to conform to RenderMan's native coordinate orientation ie.
The shader shown in lising 2 assigns red to the (outside) front facing surfaces of an
object and green to (inside) rear-facing surfaces. Figure 1 shows an image of a
sphere that was rendered without taking
Figure 1 - incorrect
AttributeBegin Surface "outside_red" Sphere 1 -1 0 360 AttributeEnd
Figure 2 - correct
AttributeBegin Surface "outside_red" ReverseOrientation Sphere 1 -1 0 360 AttributeEnd
Prior to Rfm Pro it was essential to "sandwich" a quadric and an additional
The situation is made more confusing when reflections are taken into account.
Figure 3 shows what happens to the reflected image of a quadric cylinder that
has not received an additional (compensating)
© 2002- Malcolm Kesson. All rights reserved.