GPBSPR - Set Back Surface Properties

Purpose

Use GPBSPR to insert a Set Back Surface Properties structure element into the open structure following the element pointer, or to replace the element pointed at by the element pointer with a Set Back Surface Properties structure element depending on the current edit mode.

During structure traversal, this structure element specifies the coefficients and exponents used in calculating lighting and transparency effects.

Face distinguish mode (GPFDMO) must be 2=COLOR_SURFACE_PROPERTIES for the graPHIGS API to use these values to calculate the lighting and transparency effects on the back facing portions of a surface. If face distinguish mode is 1=NONE , then the graPHIGS API uses the current surface properties to calculate the effects on the back facing portions of a surface.

The traversal default coefficients and exponent for the back surface properties are as follows:

• amb = 1.0 (back ambient reflection coefficient)
• diff = 1.0 (back diffuse reflection coefficient)
• spec = 1.0 (back specular reflection coefficient)
• exp = 0.0 (back specular reflection exponent) (i.e., no specular effect)
• trans = 0.0 (back transparency coefficient) (i.e., opaque)

To use the specified transparency coefficient, the transparency mode for the view must be a value other than 1=NONE The current back transparency coefficient in the graPHIGS API Traversal State List is also set by the back transparency coefficient of the Set Back Transparency Coefficient (GPBTCO) subroutine.

Parameters