GPPHEC - Set Polyhedron Edge Culling

Purpose

Use GPPHEC to insert a Set Polyhedron Edge Culling structure element into the open structure following the element pointer or to replace the element pointed at by the element pointer with a Set Polyhedron Edge Culling structure element depending on the current edit mode.

During structure traversal, this structure element sets the current polyhedron edge culling mode entry in the graPHIGS API traversal state list to the value specified by the parameter. The graPHIGS API uses this value to create subsequent polyhedron edge output primitives. This value supplies polyhedron edge culling information to the workstation. This structure element specifies a mode which defines which orientation of the adjacent area geometries causes the line segments to not be visualized.

A polyhedron edge is a line segment which is the shared edge of two area geometries. A polyhedron edge has two normals representing the geometric normals of the two adjacent areas. Based on the direction of each normal relative to the viewer, the graPHIGS API defines each area geometry as front facing or back facing. A culling mode set to 1=NONE produces no culling (i.e., area geometries are always visualized) A culling mode of 4=BOTH_BACK_OR_BOTH_FRONT causes the line segment to not be visualized if both adjacent area geometries are either back facing or front facing.

The traversal default for polyhedron edge culling is 1=NONE

If the workstation does not support the specified polyhedron edge, then the polyhedron edge mode defaults to 1=NONE

Parameters