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<refentry id="glHint">
    <refmeta>
        <refmetainfo>
            <copyright>
                <year>1991-2006</year>
                <holder>Silicon Graphics, Inc.</holder>
            </copyright>
        </refmetainfo>
        <refentrytitle>glHint</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glHint</refname>
        <refpurpose>specify implementation-specific hints</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glHint</function></funcdef>
                <paramdef>GLenum <parameter>target</parameter></paramdef>
                <paramdef>GLenum <parameter>mode</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>target</parameter></term>
            <listitem>
                <para>
                    Specifies a symbolic constant indicating the behavior to be controlled.
                    <constant>GL_FOG_HINT</constant>,	
                    <constant>GL_GENERATE_MIPMAP_HINT</constant>,
                    <constant>GL_LINE_SMOOTH_HINT</constant>,
                    <constant>GL_PERSPECTIVE_CORRECTION_HINT</constant>,
                    <constant>GL_POINT_SMOOTH_HINT</constant>,
                    <constant>GL_POLYGON_SMOOTH_HINT</constant>,
                    <constant>GL_TEXTURE_COMPRESSION_HINT</constant>, and
                    <constant>GL_FRAGMENT_SHADER_DERIVATIVE_HINT</constant>
                    are accepted.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>mode</parameter></term>
            <listitem>
                <para>
                    Specifies a symbolic constant indicating the desired behavior.
                    <constant>GL_FASTEST</constant>,
                    <constant>GL_NICEST</constant>, and
                    <constant>GL_DONT_CARE</constant> are accepted.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            Certain aspects of GL behavior,
            when there is room for interpretation,
            can be controlled with hints.
            A hint is specified with two arguments.
            <parameter>target</parameter> is a symbolic
            constant indicating the behavior to be controlled,
            and <parameter>mode</parameter> is another symbolic constant indicating the desired
            behavior. The initial value for each <parameter>target</parameter> is <constant>GL_DONT_CARE</constant>.
            <parameter>mode</parameter> can be one of the following:
        </para>
        <variablelist>
            <varlistentry>
                <term><constant>GL_FASTEST</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        The most efficient option should be chosen.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_NICEST</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        The most correct,
                        or highest quality,
                        option should be chosen.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_DONT_CARE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        No preference.
                    </para>
                </listitem>
            </varlistentry>
        </variablelist>
        <para>
            Though the implementation aspects that can be hinted are well defined,
            the interpretation of the hints depends on the implementation.
            The hint aspects that can be specified with <parameter>target</parameter>,
            along with suggested semantics,
            are as follows:
        </para>
        <variablelist>
            <varlistentry>
                <term><constant>GL_FOG_HINT</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Indicates the accuracy of fog calculation.
                        If per-pixel fog calculation is not efficiently supported
                        by the GL implementation,
                        hinting <constant>GL_DONT_CARE</constant> or <constant>GL_FASTEST</constant> can result in per-vertex
                        calculation of fog effects.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_FRAGMENT_SHADER_DERIVATIVE_HINT</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Indicates the accuracy of the derivative calculation for the GL shading language fragment processing built-in functions:
                        <constant>dFdx</constant>, <constant>dFdy</constant>, and <constant>fwidth</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_GENERATE_MIPMAP_HINT</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Indicates the quality of filtering when generating mipmap images.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_LINE_SMOOTH_HINT</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Indicates the sampling quality of antialiased lines.
                        If a larger filter function is applied, hinting <constant>GL_NICEST</constant> can
                        result in more pixel fragments being generated during rasterization.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_PERSPECTIVE_CORRECTION_HINT</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Indicates the quality of color, texture coordinate, and fog coordinate
                        interpolation.  If perspective-corrected parameter interpolation is not
                        efficiently supported by the GL implementation, hinting <constant>GL_DONT_CARE</constant>
                        or <constant>GL_FASTEST</constant> can result in simple linear interpolation of colors
                        and/or texture coordinates.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_POINT_SMOOTH_HINT</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Indicates the sampling quality of antialiased points.
                        If a larger filter function is applied, hinting <constant>GL_NICEST</constant> can
                        result in more pixel fragments being generated during rasterization.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_POLYGON_SMOOTH_HINT</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Indicates the sampling quality of antialiased polygons.
                        Hinting <constant>GL_NICEST</constant> can result in more pixel fragments being generated
                        during rasterization,
                        if a larger filter function is applied.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_TEXTURE_COMPRESSION_HINT</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Indicates the quality and performance of the compressing texture images.
                        Hinting <constant>GL_FASTEST</constant> indicates that texture images should be compressed
                        as quickly as possible, while <constant>GL_NICEST</constant> indicates that texture images
                        should be compressed with as little image quality loss as possible.
                        <constant>GL_NICEST</constant> should be selected if the texture is to be retrieved by
                        <citerefentry><refentrytitle>glGetCompressedTexImage</refentrytitle></citerefentry> for reuse.
                    </para>
                </listitem>
            </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="notes"><title>Notes</title>
        <para>
            The interpretation of hints depends on the implementation.
            Some implementations ignore <function>glHint</function> settings.
        </para>
        <para>
            <constant>GL_TEXTURE_COMPRESSION_HINT</constant> is available only if the GL version is 1.3
            or greater.
        </para>
        <para>
            <constant>GL_GENERATE_MIPMAP_HINT</constant> is available only if the GL version is 1.4
            or greater.
        </para>
        <para>
            <constant>GL_FRAGMENT_SHADER_DERIVATIVE_HINT</constant> is available only if the GL version is 2.0
            or greater.
        </para>
    </refsect1>
    <refsect1 id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if either <parameter>target</parameter> or <parameter>mode</parameter> is not
            an accepted value.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <function>glHint</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="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>
