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233 lines
10 KiB
XML
233 lines
10 KiB
XML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
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<refentry id="glShadeModel">
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<refmeta>
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<refmetainfo>
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<copyright>
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<year>1991-2006</year>
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<holder>Silicon Graphics, Inc.</holder>
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</copyright>
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</refmetainfo>
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<refentrytitle>glShadeModel</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glShadeModel</refname>
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<refpurpose>select flat or smooth shading</refpurpose>
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</refnamediv>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glShadeModel</function></funcdef>
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<paramdef>GLenum <parameter>mode</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<!-- eqn: ignoring delim $$ -->
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<refsect1 id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>mode</parameter></term>
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<listitem>
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<para>
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Specifies a symbolic value representing a shading technique.
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Accepted values are <constant>GL_FLAT</constant> and <constant>GL_SMOOTH</constant>.
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The initial value is <constant>GL_SMOOTH</constant>.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="description"><title>Description</title>
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<para>
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GL primitives can have either flat or smooth shading.
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Smooth shading,
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the default,
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causes the computed colors of vertices to be interpolated as the
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primitive is rasterized,
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typically assigning different colors to each resulting pixel fragment.
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Flat shading selects the computed color of just one vertex
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and assigns it to all the pixel fragments
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generated by rasterizing a single primitive.
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In either case, the computed color of a vertex is the result of
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lighting if lighting is enabled,
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or it is the current color at the time the vertex was specified if
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lighting is disabled.
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</para>
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<para>
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Flat and smooth shading are indistinguishable for points.
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Starting when <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> is issued and counting vertices and
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primitives from 1, the GL gives each flat-shaded line segment
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<inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>
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the
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computed color of vertex
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<inlineequation><mml:math>
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<!-- eqn: i + 1:-->
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<mml:mrow>
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<mml:mi mathvariant="italic">i</mml:mi>
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<mml:mo>+</mml:mo>
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<mml:mn>1</mml:mn>
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</mml:mrow>
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</mml:math></inlineequation>,
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its second vertex.
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Counting similarly from 1,
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the GL gives each flat-shaded polygon the computed color of the vertex listed
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in the following table.
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This is the last vertex to specify the polygon in all cases except single
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polygons,
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where the first vertex specifies the flat-shaded color.
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</para>
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<para>
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</para>
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<informaltable frame="topbot">
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<tgroup cols="2" align="left">
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<colspec/>
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<colspec align="center"/>
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<thead>
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<row>
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<entry rowsep="1" align="left"><emphasis role="bold">
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Primitive Type of Polygon
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<inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>
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</emphasis></entry>
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<entry rowsep="1" align="center"><emphasis role="bold">
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Vertex
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</emphasis></entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry align="left">
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Single polygon
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(<inlineequation><mml:math>
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<!-- eqn: i == 1:-->
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<mml:mrow>
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<mml:mi mathvariant="italic">i</mml:mi>
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<mml:mo>==</mml:mo>
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<mml:mn>1</mml:mn>
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</mml:mrow>
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</mml:math></inlineequation>)
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</entry>
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<entry align="center">
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1
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</entry>
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</row>
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<row>
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<entry align="left">
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Triangle strip
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</entry>
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<entry align="center">
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<inlineequation><mml:math>
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<!-- eqn: i + 2:-->
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<mml:mrow>
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<mml:mi mathvariant="italic">i</mml:mi>
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<mml:mo>+</mml:mo>
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<mml:mn>2</mml:mn>
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</mml:mrow>
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</mml:math></inlineequation>
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</entry>
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</row>
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<row>
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<entry align="left">
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Triangle fan
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</entry>
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<entry align="center">
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<inlineequation><mml:math>
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<!-- eqn: i + 2:-->
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<mml:mrow>
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<mml:mi mathvariant="italic">i</mml:mi>
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<mml:mo>+</mml:mo>
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<mml:mn>2</mml:mn>
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</mml:mrow>
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</mml:math></inlineequation>
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</entry>
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</row>
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<row>
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<entry align="left">
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Independent triangle
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</entry>
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<entry align="center">
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<inlineequation><mml:math>
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<!-- eqn: 3 i:-->
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<mml:mrow>
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<mml:mn>3</mml:mn>
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<mml:mo>⁢</mml:mo>
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<mml:mi mathvariant="italic">i</mml:mi>
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</mml:mrow>
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</mml:math></inlineequation>
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</entry>
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</row>
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<row>
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<entry align="left">
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Quad strip
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</entry>
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<entry align="center">
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<inlineequation><mml:math>
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<!-- eqn: 2 i + 2:-->
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<mml:mrow>
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<mml:mn>2</mml:mn>
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<mml:mo>⁢</mml:mo>
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<mml:mi mathvariant="italic">i</mml:mi>
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<mml:mo>+</mml:mo>
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<mml:mn>2</mml:mn>
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</mml:mrow>
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</mml:math></inlineequation>
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</entry>
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</row>
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<row>
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<entry align="left">
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Independent quad
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</entry>
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<entry align="center">
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<inlineequation><mml:math>
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<!-- eqn: 4 i:-->
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<mml:mrow>
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<mml:mn>4</mml:mn>
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<mml:mo>⁢</mml:mo>
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<mml:mi mathvariant="italic">i</mml:mi>
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</mml:mrow>
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</mml:math></inlineequation>
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</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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<para>
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Flat and smooth shading are specified by <function>glShadeModel</function> with <parameter>mode</parameter> set to
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<constant>GL_FLAT</constant> and <constant>GL_SMOOTH</constant>, respectively.
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</para>
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</refsect1>
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<refsect1 id="errors"><title>Errors</title>
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<para>
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<constant>GL_INVALID_ENUM</constant> is generated if <parameter>mode</parameter> is any value other than
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<constant>GL_FLAT</constant> or <constant>GL_SMOOTH</constant>.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <function>glShadeModel</function>
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is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
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and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.
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</para>
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</refsect1>
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<refsect1 id="associatedgets"><title>Associated Gets</title>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_SHADE_MODEL</constant>
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</para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para>
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<citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glColor</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glLight</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glLightModel</refentrytitle></citerefentry>
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</para>
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</refsect1>
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<refsect1 id="Copyright"><title>Copyright</title>
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<para>
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Copyright <trademark class="copyright"></trademark> 1991-2006
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Silicon Graphics, Inc. This document is licensed under the SGI
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Free Software B License. For details, see
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<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
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</para>
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</refsect1>
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</refentry>
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