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OpenGL ES 1.0 and EGL 1.0 reference manual and man pages (written by
Claude Knaus, based on OpenGL SI man pages).

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook V4.2//EN" "DTD/docbook/docbookx.dtd">

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<refentry id="glShadeModel">
  <refmeta>
    <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>

  <refsect1>
    <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>
    <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 at the beginning of the vertex array  and counting
    vertices and primitives from 1, the GL gives each flat-shaded
    line segment <replaceable>i</replaceable>
    the computed color of vertex 
    <inlineequation><math>
      <mi>i</mi>
      <mo>+</mo>
      <mn>1</mn>
    </math></inlineequation>,
    its second vertex. Counting similarly from 1, the GL gives
    each flat-shaded polygon the computed color of vertex
    <inlineequation><math>
      <mi>i</mi>
      <mo>+</mo>
      <mn>2</mn>
    </math></inlineequation>,
    which is the last vertex to specify the polygon.</para>

    <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>
    <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>
  </refsect1>

  <refsect1>
    <title>See Also</title>

    <para>
    <citerefentry><refentrytitle>glColor</refentrytitle></citerefentry>, 
    <citerefentry><refentrytitle>glColorPointer</refentrytitle></citerefentry>, 
    <citerefentry><refentrytitle>glLight</refentrytitle></citerefentry>, 
    <citerefentry><refentrytitle>glLightModel</refentrytitle></citerefentry>,
    <citerefentry><refentrytitle>glMaterial</refentrytitle></citerefentry>
    </para>
  </refsect1>
</refentry>