
<refentry id="glLightModel">
    <refmeta>
        <refmetainfo>
            <copyright>
                <year>1991-2006</year>
                <holder>Silicon Graphics, Inc.</holder>
            </copyright>
        </refmetainfo>
        <refentrytitle>glLightModel</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glLightModel</refname>
        <refpurpose>set the lighting model parameters</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glLightModelf</function></funcdef>
                <paramdef>GLenum <parameter>pname</parameter></paramdef>
                <paramdef>GLfloat <parameter>param</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glLightModeli</function></funcdef>
                <paramdef>GLenum <parameter>pname</parameter></paramdef>
                <paramdef>GLint <parameter>param</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <!-- eqn: ignoring delim $$ -->
    <refsect1 id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>pname</parameter></term>
            <listitem>
                <para>
                    Specifies a single-valued lighting model parameter.
                    <constant>GL_LIGHT_MODEL_LOCAL_VIEWER</constant>,
                    <constant>GL_LIGHT_MODEL_COLOR_CONTROL</constant>, and
                    <constant>GL_LIGHT_MODEL_TWO_SIDE</constant> are accepted.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>param</parameter></term>
            <listitem>
                <para>
                    Specifies the value that <parameter>param</parameter> will be set to.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glLightModelfv</function></funcdef>
                <paramdef>GLenum <parameter>pname</parameter></paramdef>
                <paramdef>const GLfloat * <parameter>params</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glLightModeliv</function></funcdef>
                <paramdef>GLenum <parameter>pname</parameter></paramdef>
                <paramdef>const GLint * <parameter>params</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 id="parameters2"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>pname</parameter></term>
            <listitem>
                <para>
                    Specifies a lighting model parameter.
                    <constant>GL_LIGHT_MODEL_AMBIENT</constant>,
                    <constant>GL_LIGHT_MODEL_COLOR_CONTROL</constant>,
                    <constant>GL_LIGHT_MODEL_LOCAL_VIEWER</constant>, and
                    <constant>GL_LIGHT_MODEL_TWO_SIDE</constant> are accepted.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>params</parameter></term>
            <listitem>
                <para>
                    Specifies a pointer to the value or values that <parameter>params</parameter> will be set to.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            <function>glLightModel</function> sets the lighting model parameter.
            <parameter>pname</parameter> names a parameter and <parameter>params</parameter> gives the new value.
            There are three lighting model parameters:
        </para>
        <variablelist>
            <varlistentry>
                <term><constant>GL_LIGHT_MODEL_AMBIENT</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        <parameter>params</parameter> contains four integer or floating-point values that specify
                        the ambient RGBA intensity of the entire scene.
                        Integer values are mapped linearly such that the most positive representable
                        value maps to 1.0,
                        and the most negative representable value maps to 
                        <inlineequation><mml:math>
                            <!-- eqn: -1.0:-->
                            <mml:mn>-1.0</mml:mn>
                        </mml:math></inlineequation>.
                        Floating-point values are mapped directly.
                        Neither integer nor floating-point values are clamped.
                        The initial ambient scene intensity is (0.2, 0.2, 0.2, 1.0).
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_LIGHT_MODEL_COLOR_CONTROL</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        <parameter>params</parameter> must be either <constant>GL_SEPARATE_SPECULAR_COLOR</constant> or
                        <constant>GL_SINGLE_COLOR</constant>.
                        <constant>GL_SINGLE_COLOR</constant> specifies that a single color is generated from the
                        lighting computation for a vertex.  <constant>GL_SEPARATE_SPECULAR_COLOR</constant>
                        specifies that the specular color computation of lighting be stored
                        separately from the remainder of the lighting computation.  The specular
                        color is summed into the generated fragment's color after the application
                        of texture mapping (if enabled).  The initial value is <constant>GL_SINGLE_COLOR</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_LIGHT_MODEL_LOCAL_VIEWER</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        <parameter>params</parameter> is a single integer or floating-point value that specifies
                        how specular reflection angles are computed.
                        If <parameter>params</parameter> is 0 (or 0.0), specular reflection angles take the
                        view direction to be parallel to and in the direction of the -<emphasis>z</emphasis> axis,
                        regardless of the location of the vertex in eye coordinates.
                        Otherwise, specular reflections are computed from the origin
                        of the eye coordinate system.
                        The initial value is 0.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_LIGHT_MODEL_TWO_SIDE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        <parameter>params</parameter> is a single integer or floating-point value that specifies
                        whether one- or two-sided lighting calculations are done for polygons.
                        It has no effect on the lighting calculations for points,
                        lines,
                        or bitmaps.
                        If <parameter>params</parameter> is 0 (or 0.0), one-sided lighting is specified,
                        and only the <emphasis>front</emphasis> material parameters are used in the
                        lighting equation.
                        Otherwise, two-sided lighting is specified.
                        In this case, vertices of back-facing polygons are lighted using the
                        <emphasis>back</emphasis> material parameters
                        and have their normals reversed before the lighting equation is evaluated.
                        Vertices of front-facing polygons are always lighted using the
                        <emphasis>front</emphasis> material parameters,
                        with no change to their normals. The initial value is 0.
                    </para>
                </listitem>
            </varlistentry>
        </variablelist>
        <para>
            In RGBA mode, the lighted color of a vertex is the sum of
            the material emission intensity,
            the product of the material ambient reflectance and the lighting model full-scene
            ambient intensity,
            and the contribution of each enabled light source.
            Each light source contributes the sum of three terms:
            ambient, diffuse, and specular.
            The ambient light source contribution is the product of the material ambient
            reflectance and the light's ambient intensity.
            The diffuse light source contribution is the product of the material diffuse
            reflectance,
            the light's diffuse intensity,
            and the dot product of the vertex's normal with the normalized vector from
            the vertex to the light source.
            The specular light source contribution is the product of the material specular
            reflectance,
            the light's specular intensity,
            and the dot product of the normalized vertex-to-eye and vertex-to-light
            vectors,
            raised to the power of the shininess of the material.
            All three light source contributions are attenuated equally based on
            the distance from the vertex to the light source and on light source
            direction, spread exponent, and spread cutoff angle.
            All dot products are replaced with 0 if they evaluate to a negative value.
        </para>
        <para>
            The alpha component of the resulting lighted color is set to the alpha value
            of the material diffuse reflectance.
        </para>
        <para>
            In color index mode,
            the value of the lighted index of a vertex ranges from the ambient
            to the specular values passed to <citerefentry><refentrytitle>glMaterial</refentrytitle></citerefentry> using <constant>GL_COLOR_INDEXES</constant>.
            Diffuse and specular coefficients,
            computed with a (.30, .59, .11) weighting of the lights' colors,
            the shininess of the material,
            and the same reflection and attenuation equations as in the RGBA case,
            determine how much above ambient the resulting index is.
        </para>
    </refsect1>
    <refsect1 id="notes"><title>Notes</title>
        <para>
            <constant>GL_LIGHT_MODEL_COLOR_CONTROL</constant> is available only if the GL version is
            1.2 or greater.
        </para>
    </refsect1>
    <refsect1 id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>pname</parameter> is not an accepted value.
        </para>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>pname</parameter> is
            <constant>GL_LIGHT_MODEL_COLOR_CONTROL</constant> and <parameter>params</parameter> is not one of
            <constant>GL_SINGLE_COLOR</constant> or <constant>GL_SEPARATE_SPECULAR_COLOR</constant>.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <function>glLightModel</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_LIGHT_MODEL_AMBIENT</constant>
        </para>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_LIGHT_MODEL_COLOR_CONTROL</constant>
        </para>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_LIGHT_MODEL_LOCAL_VIEWER</constant>
        </para>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_LIGHT_MODEL_TWO_SIDE</constant>
        </para>
        <para>
            <citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_LIGHTING</constant>
        </para>
    </refsect1>
    <refsect1 id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glLight</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glMaterial</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>
