3D Graphics Programming with QuickDraw 3D 1.5.4

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 .

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.