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