_C_ License Applicability. Except to the extent portions of this file are
_C_ made subject to an alternative license as permitted in the SGI Free
_C_ Software License B, Version 1.1 (the "License"), the contents of this
_C_ file are subject only to the provisions of the License. You may not use
_C_ this file except in compliance with the License. You may obtain a copy
_C_ of the License at Silicon Graphics, Inc., attn: Legal Services, 1600
_C_ Amphitheatre Parkway, Mountain View, CA 94043-1351, or at:
_C_ 
_C_ http://oss.sgi.com/projects/FreeB
_C_ 
_C_ Note that, as provided in the License, the Software is distributed on an
_C_ "AS IS" basis, with ALL EXPRESS AND IMPLIED WARRANTIES AND CONDITIONS
_C_ DISCLAIMED, INCLUDING, WITHOUT LIMITATION, ANY IMPLIED WARRANTIES AND
_C_ CONDITIONS OF MERCHANTABILITY, SATISFACTORY QUALITY, FITNESS FOR A
_C_ PARTICULAR PURPOSE, AND NON-INFRINGEMENT.
_C_ 
_C_ Original Code. The Original Code is: OpenGL Sample Implementation,
_C_ Version 1.2.1, released January 26, 2000, developed by Silicon Graphics,
_C_ Inc. The Original Code is Copyright (c) 1991-2000 Silicon Graphics, Inc.
_C_ Copyright in any portions created by third parties is as indicated
_C_ elsewhere herein. All Rights Reserved.
_C_ 
_C_ Additional Notice Provisions: The application programming interfaces
_C_ established by SGI in conjunction with the Original Code are The
_C_ OpenGL(R) Graphics System: A Specification (Version 1.2.1), released
_C_ April 1, 1999; The OpenGL(R) Graphics System Utility Library (Version
_C_ 1.3), released November 4, 1998; and OpenGL(R) Graphics with the X
_C_ Window System(R) (Version 1.3), released October 19, 1998. This software
_C_ was created using the OpenGL(R) version 1.2.1 Sample Implementation
_C_ published by SGI, but has not been independently verified as being
_C_ compliant with the OpenGL(R) version 1.2.1 Specification.
_C_
_C_ The first character in this file must be an '_'!
_C_ Anything on a line after _C_ is ignored
_define(_filters,tbl|eqn)_C_
_C_      eqn is automatically replaced with neqn for nroff
_header(DepthFunc,specify the value used for depth buffer comparisons)
_names(DepthFunc)
.SH PARAMETERS
_phead(_param1)
Specifies the depth comparison function.
Symbolic constants
_const(NEVER),
_const(LESS),
_const(EQUAL),
_const(LEQUAL),
_const(GREATER),
_const(NOTEQUAL),
_const(GEQUAL), and
_const(ALWAYS) are accepted.
The initial value is _const(LESS).
.SH DESCRIPTION
_cmnd specifies the function used to compare each incoming pixel depth value
with the depth value present in the depth buffer.
The comparison is performed only if depth testing is enabled.
(See _cmnd(Enable) and _cmnd(Disable) of _const(DEPTH_TEST).)
.P
_param1 specifies the conditions under which the pixel will be drawn.
The comparison functions are as follows:
.TP 16
_const(NEVER)
Never passes. 
.TP
_const(LESS)
Passes if the incoming depth value is less than the stored depth value.
.TP
_const(EQUAL)
Passes if the incoming depth value is equal to the stored depth value.
.TP
_const(LEQUAL)
Passes if the incoming depth value is less than or equal to
the stored depth value.
.TP
_const(GREATER) 
Passes if the incoming depth value is greater than the stored depth value.
.TP
_const(NOTEQUAL)
Passes if the incoming depth value is not equal to the stored depth value.
.TP
_const(GEQUAL)
Passes if the incoming depth value is greater than or equal to
the stored depth value.
.TP
_const(ALWAYS)
Always passes. 
.P
The initial value of _param1 is _const(LESS).
Initially, depth testing is disabled.
.NOTES
Even if the depth buffer exists and the depth mask is non-zero, the
depth buffer is not updated if the depth test is disabled. 
.SH ERRORS
_const(INVALID_ENUM) is generated if _param1 is not an accepted value.
.P
_const(INVALID_OPERATION) is generated if _cmnd
is executed between the execution of _cmnd(Begin)
and the corresponding execution of _cmnd(End).
.SH ASSOCIATED GETS
_cmnd(Get) with argument _const(DEPTH_FUNC)
.br
_cmnd(IsEnabled) with argument _const(DEPTH_TEST)
.SH SEE ALSO
_cmnd(DepthRange),
_cmnd(Enable),
_cmnd(PolygonOffset)
