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3 <?xml-stylesheet type=
"text/xsl" href=
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pref=
"http://www.w3.org/2002/Math/preference" pref:
renderer=
"mathplayer-dl"><head><meta http-equiv=
"Content-Type" content=
"text/html; charset=UTF-8" /><title>glPolygonOffset
</title><meta name=
"generator" content=
"DocBook XSL Stylesheets V1.73.2" /></head><body><div class=
"refentry" lang=
"en" xml:
lang=
"en"><a id=
"glPolygonOffset"></a><div class=
"titlepage"></div><div class=
"refnamediv"><h2>Name
</h2><p>glPolygonOffset — set the scale and units used to calculate depth values
</p></div><div class=
"refsynopsisdiv"><h2>C Specification
</h2><div class=
"funcsynopsis"><table border=
"0" summary=
"Function synopsis" cellspacing=
"0" cellpadding=
"0"><tr><td><code class=
"funcdef">void
<b class=
"fsfunc">glPolygonOffset
</b>(
</code></td><td>GLfloat
</td><td><var class=
"pdparam">factor
</var>,
</td></tr><tr><td> </td><td>GLfloat
</td><td><var class=
"pdparam">units
</var><code>)
</code>;
</td></tr></table></div></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"parameters"></a><h2>Parameters
</h2><div class=
"variablelist"><dl><dt><span class=
"term"><em class=
"parameter"><code>factor
</code></em></span></dt><dd><p>
4 Specifies a scale factor that is used to create a variable
5 depth offset for each polygon. The initial value is
0.
6 </p></dd><dt><span class=
"term"><em class=
"parameter"><code>units
</code></em></span></dt><dd><p>
7 Is multiplied by an implementation-specific value to
8 create a constant depth offset. The initial value is
0.
9 </p></dd></dl></div></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"description"></a><h2>Description
</h2><p>
10 When
<code class=
"constant">GL_POLYGON_OFFSET_FILL
</code>,
<code class=
"constant">GL_POLYGON_OFFSET_LINE
</code>, or
11 <code class=
"constant">GL_POLYGON_OFFSET_POINT
</code> is enabled, each
12 fragment's
<span class=
"emphasis"><em>depth
</em></span> value will be offset after it is interpolated
13 from the
<span class=
"emphasis"><em>depth
</em></span> values of the appropriate vertices.
14 The value of the offset is
15 <mml:math xmlns:
mml=
"http://www.w3.org/1998/Math/MathML" overflow=
"scroll">
19 <mml:mi mathvariant=
"italic">factor
</mml:mi>
21 <mml:mi mathvariant=
"italic">DZ
</mml:mi>
25 <mml:mi mathvariant=
"italic">r
</mml:mi>
27 <mml:mi mathvariant=
"italic">units
</mml:mi>
32 <mml:math xmlns:
mml=
"http://www.w3.org/1998/Math/MathML" overflow=
"scroll">
34 <mml:mi mathvariant=
"italic">DZ
</mml:mi>
36 is a measurement of the change in depth relative to the screen
37 area of the polygon, and
38 <mml:math xmlns:
mml=
"http://www.w3.org/1998/Math/MathML" overflow=
"scroll"><mml:mi mathvariant=
"italic">r
</mml:mi></mml:math>
39 is the smallest value that is guaranteed to
40 produce a resolvable offset for a given implementation.
41 The offset is added before the depth test is performed and before
42 the value is written into the depth buffer.
44 <code class=
"function">glPolygonOffset
</code> is useful for rendering hidden-line images, for applying decals
45 to surfaces, and for rendering solids with highlighted edges.
46 </p></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"notes"></a><h2>Notes
</h2><p>
47 <code class=
"function">glPolygonOffset
</code> is available only if the GL version is
1.1 or greater.
49 <code class=
"function">glPolygonOffset
</code> has no effect on depth coordinates placed in the
52 <code class=
"function">glPolygonOffset
</code> has no effect on selection.
53 </p></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"errors"></a><h2>Errors
</h2><p>
54 <code class=
"constant">GL_INVALID_OPERATION
</code> is generated if
<code class=
"function">glPolygonOffset
</code> is executed
55 between the execution of
<a class=
"citerefentry" href=
"glBegin.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glBegin
</span></span></a> and the corresponding
56 execution of
<a class=
"citerefentry" href=
"glEnd.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glEnd
</span></span></a>.
57 </p></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"associatedgets"></a><h2>Associated Gets
</h2><p>
58 <a class=
"citerefentry" href=
"glIsEnabled.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glIsEnabled
</span></span></a> with argument
59 <code class=
"constant">GL_POLYGON_OFFSET_FILL
</code>,
60 <code class=
"constant">GL_POLYGON_OFFSET_LINE
</code>,
61 or
<code class=
"constant">GL_POLYGON_OFFSET_POINT
</code>.
63 <a class=
"citerefentry" href=
"glGet.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glGet
</span></span></a> with argument
<code class=
"constant">GL_POLYGON_OFFSET_FACTOR
</code> or
64 <code class=
"constant">GL_POLYGON_OFFSET_UNITS
</code>.
65 </p></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"seealso"></a><h2>See Also
</h2><p>
66 <a class=
"citerefentry" href=
"glDepthFunc.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glDepthFunc
</span></span></a>,
67 <a class=
"citerefentry" href=
"glEnable.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glEnable
</span></span></a>,
68 <a class=
"citerefentry" href=
"glGet.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glGet
</span></span></a>,
69 <a class=
"citerefentry" href=
"glIsEnabled.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glIsEnabled
</span></span></a>
70 </p></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"Copyright"></a><h2>Copyright
</h2><p>
71 Copyright
<span class=
"trademark"></span>©
1991-
2006
72 Silicon Graphics, Inc. This document is licensed under the SGI
73 Free Software B License. For details, see
74 <a class=
"ulink" href=
"http://oss.sgi.com/projects/FreeB/" target=
"_top">http://oss.sgi.com/projects/FreeB/
</a>.
75 </p></div></div></body></html>