Z Sorting Function Selectors

QuickDraw 3D RAVE / QuickDraw 3D RAVE Reference

Z Sorting Function Selectors
A drawing engine must support a z sorting function that determines which surfaces are to be removed during hidden surface removal. You specify an engine's z sorting function by assigning a value to its kQATag_ZFunction state variable. The default value of this variable for a drawing engine that is z buffered is kQAZFunction_LT; the default value (and also the only possible value) for a draw context that is not z buffered is kQAZFunction_None.

IMPORTANT
If a drawing engine supports kQAOptional_PerspectiveZ and if the state variable kQATag_PerspectiveZ is set to the value kQAPerspectiveZ_On, then the state variable kQATag_ZFunction should be interpreted so that it yields the same result as when the value of kQATag_PerspectiveZ is kQAPerspectiveZ_Off.
#define kQAZFunction_None              0
#define kQAZFunction_LT                1
#define kQAZFunction_EQ                2
#define kQAZFunction_LE                3
#define kQAZFunction_GT                4
#define kQAZFunction_NE                5
#define kQAZFunction_GE                6
#define kQAZFunction_True              7
Constant descriptions

kQAZFunction_None
The z value is neither tested nor written.
kQAZFunction_LT
A new z value is visible if it is less than the value in the z buffer.
kQAZFunction_EQ
A new z value is visible if it is equal to the value in the z buffer. This selector should be passed only to drawing engines that support the optional OpenGL features.
kQAZFunction_LE
A new z value is visible if it is less than or equal to the value in the z buffer. This selector should be passed only to drawing engines that support the optional OpenGL features.
kQAZFunction_GT
A new z value is visible if it is greater than the value in the z buffer. This selector should be passed only to drawing engines that support the optional OpenGL features.
kQAZFunction_NE
A new z value is visible if it is not equal to the value in the z buffer. This selector should be passed only to drawing engines that support the optional OpenGL features.
kQAZFunction_GE
A new z value is visible if it is greater than or equal to the value in the z buffer. This selector should be passed only to drawing engines that support the optional OpenGL features.
kQAZFunction_True
A new z value is always visible.