TYPE: SOP
TITLE: Rest Position SOP

The Rest operation is used to create an attribute which causes material textures
to stick to surfaces deformed using other operations.

Rest can get the rest position in one of two ways:

1)  By reading a file.~r
2)  By attaching a second input.

The first input is the deforming geometry.
The second input (or file) is the rest position data, which is
typically a static, non-deforming surface.

The topologies of the two geometries should match.

All primitives support the 'rest' attribute, but, in the case of
quadric primitives (circle, tube, sphere and metaball primitives), the
rest position is only translational.  This means that rest normals
will not work correctly for these primitive types either.

The 'rest' attribute is exported to RenderMan as the 'Pr' attribute.
This is output for all surfaces as a 'vertex float attribute'.

Rest normals are required if feathering is used on polygons and meshes
in Mantra.  NURBs/Beziers will use the rest position to compute the
correct resting normals.
