Z Perspective Selectors

QuickDraw 3D RAVE / QuickDraw 3D RAVE Reference

Z Perspective Selectors
A drawing engine may support a z perspective control that determines whether the z or the invW field of a vertex (of type TQAVGouraud or TQAVTexture) is to be used for hidden surface removal. You specify an engine's z perspective control by assigning a value to its kQATag_PerspectiveZ state variable. The default value of this variable for a drawing engine that supports z perspective is kQAPerspectiveZ_Off.
#define kQAPerspectiveZ_Off            0
#define kQAPerspectiveZ_On             1
Constant descriptions

kQAPerspectiveZ_Off
The drawing engine performs hidden surface removal using z values, as is standard.
kQAPerspectiveZ_On
The drawing engine performs hidden surface removal using invW values, which results in perspective-correct hidden surface removal.