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sync code with last improvements from OpenBSD

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purplerain 2023-08-28 05:57:34 +00:00
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'\" e
'\"! eqn | mmdoc
'\"macro stdmacro
.ds Vn Version 1.2
.ds Dt 24 September 1999
.ds Re Release 1.2.1
.ds Dp Jan 14 18:30
.ds Dm 01 frontface
.ds Xs 58804 4 frontface.gl
.TH GLFRONTFACE 3G
.SH NAME
.B "glFrontFace
\- define front- and back-facing polygons
.SH C SPECIFICATION
void \f3glFrontFace\fP(
GLenum \fImode\fP )
.nf
.fi
.EQ
delim $$
.EN
.SH PARAMETERS
.TP \w'\f2mode\fP\ \ 'u
\f2mode\fP
Specifies the orientation of front-facing polygons.
\%\f3GL_CW\fP and \%\f3GL_CCW\fP are accepted.
The initial value is \%\f3GL_CCW\fP.
.SH DESCRIPTION
In a scene composed entirely of opaque closed surfaces,
back-facing polygons are never visible.
Eliminating these invisible polygons has the obvious benefit
of speeding up the rendering of the image.
To enable and disable elimination of back-facing polygons, call \%\f3glEnable\fP
and \%\f3glDisable\fP with argument \%\f3GL_CULL_FACE\fP.
.P
The projection of a polygon to window coordinates is said to have
clockwise winding if an imaginary object following the path
from its first vertex,
its second vertex,
and so on,
to its last vertex,
and finally back to its first vertex,
moves in a clockwise direction about the interior of the polygon.
The polygon's winding is said to be counterclockwise if the imaginary
object following the same path moves in a counterclockwise direction
about the interior of the polygon.
\%\f3glFrontFace\fP specifies whether polygons with clockwise winding in window coordinates,
or counterclockwise winding in window coordinates,
are taken to be front-facing.
Passing \%\f3GL_CCW\fP to \f2mode\fP selects counterclockwise polygons as
front-facing;
\%\f3GL_CW\fP selects clockwise polygons as front-facing.
By default, counterclockwise polygons are taken to be front-facing.
.SH ERRORS
\%\f3GL_INVALID_ENUM\fP is generated if \f2mode\fP is not an accepted value.
.P
\%\f3GL_INVALID_OPERATION\fP is generated if \%\f3glFrontFace\fP
is executed between the execution of \%\f3glBegin\fP
and the corresponding execution of \%\f3glEnd\fP.
.SH ASSOCIATED GETS
\%\f3glGet\fP with argument \%\f3GL_FRONT_FACE\fP
.SH SEE ALSO
\%\f3glCullFace(3G)\fP,
\%\f3glLightModel(3G)\fP