_C_ License Applicability. Except to the extent portions of this file are
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_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
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_C_ http://oss.sgi.com/projects/FreeB
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_C_ Note that, as provided in the License, the Software is distributed on an
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_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
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_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,eqn)_C_
_C_      eqn is automatically replaced with neqn for nroff
_header(IndexMask,control the writing of individual bits in the color index buffers)
_names(IndexMask)
.EQ
delim $$
.EN
.SH PARAMETERS
_phead(_param1)
Specifies a bit mask to enable and disable the writing of individual bits
in the color index buffers.
Initially, the mask is all 1's.
.SH DESCRIPTION
_cmnd controls the writing of individual bits in the color index buffers.
The least significant $n$ bits of _param1,
where $n$ is the number of bits in a color index buffer,
specify a mask.
Where a 1 (one) appears in the mask,
it's possible to write to the corresponding bit in the color index
buffer (or buffers). 
Where a 0 (zero) appears,
the corresponding bit is write-protected.
.P
This mask is used only in color index mode,
and it affects only the buffers currently selected for writing
(see _cmnd(DrawBuffer)).
Initially, all bits are enabled for writing.
.SH ERRORS
_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(INDEX_WRITEMASK)
.SH SEE ALSO
_cmnd(ColorMask),
_cmnd(DepthMask),
_cmnd(DrawBuffer),
_cmnd(Index),
_cmnd(IndexPointer),
_cmnd(StencilMask)