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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 polygonof
.ds Xs 10762 4 polygonoffset.gl
.TH GLPOLYGONOFFSET 3G
.SH NAME
.B "glPolygonOffset
\- set the scale and units used to calculate depth values
.SH C SPECIFICATION
void \f3glPolygonOffset\fP(
GLfloat \fIfactor\fP,
.nf
.ta \w'\f3void \fPglPolygonOffset( 'u
GLfloat \fIunits\fP )
.fi
.EQ
delim $$
.EN
.SH PARAMETERS
.TP \w'\f2factor\fP\ \ 'u
\f2factor\fP
Specifies a scale factor that is used to create a variable
depth offset for each polygon. The initial value is 0.
.TP
\f2units\fP
Is multiplied by an implementation-specific value to
create a constant depth offset. The initial value is 0.
.SH DESCRIPTION
When \%\f3GL_POLYGON_OFFSET_FILL\fP, \%\f3GL_POLYGON_OFFSET_LINE\fP, or
\%\f3GL_POLYGON_OFFSET_POINT\fP is enabled, each
fragment's \f2depth\fP value will be offset after it is interpolated
from the \f2depth\fP values of the appropriate vertices.
The value of the offset is $"factor" ~*~ DZ ~~+~~ r ~*~ "units"$,
where $DZ~$ is a measurement of the change in depth relative to the screen
area of the polygon, and $r$ is the smallest value that is guaranteed to
produce a resolvable offset for a given implementation.
The offset is added before the depth test is performed and before
the value is written into the depth buffer.
.P
\%\f3glPolygonOffset\fP is useful for rendering hidden-line images, for applying decals
to surfaces, and for rendering solids with highlighted edges.
.SH NOTES
\%\f3glPolygonOffset\fP is available only if the GL version is 1.1 or greater.
.P
\%\f3glPolygonOffset\fP has no effect on depth coordinates placed in the
feedback buffer.
.P
\%\f3glPolygonOffset\fP has no effect on selection.
.SH ERRORS
\%\f3GL_INVALID_OPERATION\fP is generated if \%\f3glPolygonOffset\fP is executed
between the execution of \%\f3glBegin\fP and the corresponding
execution of \%\f3glEnd\fP.
.bp
.SH ASSOCIATED GETS
\%\f3glIsEnabled\fP with argument
\%\f3GL_POLYGON_OFFSET_FILL\fP,
\%\f3GL_POLYGON_OFFSET_LINE\fP,
or \%\f3GL_POLYGON_OFFSET_POINT\fP.
.P
\%\f3glGet\fP with argument \%\f3GL_POLYGON_OFFSET_FACTOR\fP or
\%\f3GL_POLYGON_OFFSET_UNITS\fP.
.SH SEE ALSO
\%\f3glDepthFunc(3G)\fP,
\%\f3glEnable(3G)\fP,
\%\f3glGet(3G)\fP,
\%\f3glIsEnabled(3G)\fP
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