
<refentry id="glXChooseFBConfig">
    <refmeta>
        <refmetainfo>
            <copyright>
                <year>1991-2006</year>
                <holder>Silicon Graphics, Inc.</holder>
            </copyright>
        </refmetainfo>
        <refentrytitle>glXChooseFBConfig</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glXChooseFBConfig</refname>
        <refpurpose>return a list of GLX frame buffer configurations that match the specified attributes</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>GLXFBConfig * <function>glXChooseFBConfig</function></funcdef>
                <paramdef>Display * <parameter>dpy</parameter></paramdef>
                <paramdef>int <parameter>screen</parameter></paramdef>
                <paramdef>const int * <parameter>attrib_list</parameter></paramdef>
                <paramdef>int * <parameter>nelements</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <!-- eqn: ignoring delim $$ -->
    <refsect1 id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>dpy</parameter></term>
            <listitem>
                <para>
                    Specifies the connection to the X server.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>screen</parameter></term>
            <listitem>
                <para>
                    Specifies the screen number.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>attrib_list</parameter></term>
            <listitem>
                <para>
                    Specifies a list of attribute/value pairs.
                    The last attribute must be <constant>None</constant>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>nelements</parameter></term>
            <listitem>
                <para>
                    Returns the number of elements in the list returned by <function>glXChooseFBConfig</function>.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            <function>glXChooseFBConfig</function> returns GLX frame buffer configurations that match the attributes
            specified in <parameter>attrib_list</parameter>, or <constant>NULL</constant> if no matches are found.
            If <parameter>attrib_list</parameter> is <constant>NULL</constant>, then <function>glXChooseFBConfig</function> returns an array of GLX
            frame buffer configurations that are available on the specified screen.
            If an error occurs, no frame buffer configurations exist on the
            specified screen, or if no frame buffer configurations match the
            specified attributes, then <constant>NULL</constant> is returned.
            Use <function>XFree</function> to free the memory returned by
            <function>glXChooseFBConfig</function>.
        </para>
        <para>
            All attributes in <parameter>attrib_list</parameter>, including boolean attributes, are
            immediately followed by the corresponding desired value. The list is
            terminated with <constant>None</constant>. If an attribute is not specified in <parameter>attrib_list</parameter>,
            then the default value (see below) is used (and the attribute is said to be 
            specified implicitly). For example, if <constant>GLX_STEREO</constant> is not specified, then 
            it is assumed to be <constant>False</constant>. For some attributes, the default is 
            <constant>GLX_DONT_CARE</constant>, meaning that any value is OK for this attribute, so the 
            attribute will not be checked.
        </para>
        <para>
            Attributes are matched in an attribute-specific manner.
            Some of the attributes, such as <constant>GLX_LEVEL</constant>, must match the specified 
            value exactly; others, such as, <constant>GLX_RED_SIZE</constant> must meet or exceed the 
            specified minimum values. If more than one GLX frame buffer configuration is found,
            then a list of configurations, sorted 
            according to the ``best'' match criteria, is returned. The match
            criteria for each attribute and the exact sorting order is
            defined below.  
        </para>
        <para>
            The interpretations of the various GLX visual attributes are as follows:
        </para>
        <variablelist>
            <varlistentry>
                <term><constant>GLX_FBCONFIG_ID</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by a valid XID that indicates the desired GLX frame
                        buffer configuration. When a <constant>GLX_FBCONFIG_ID</constant> is specified, all
                        attributes are ignored. The default value is <constant>GLX_DONT_CARE</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_BUFFER_SIZE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by a nonnegative integer that indicates the desired
                        color index buffer size.
                        The smallest index buffer of at least the specified size is preferred.
                        This attribute is ignored if <constant>GLX_COLOR_INDEX_BIT</constant> is not set in
                        <constant>GLX_RENDER_TYPE</constant>. The default value is 0.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_LEVEL</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by an integer buffer-level specification.
                        This specification is honored exactly.
                        Buffer level 0 corresponds to the default frame buffer of the display.
                        Buffer level 1 is the first overlay frame buffer, level two the second
                        overlay frame buffer, and so on.
                        Negative buffer levels correspond to underlay frame buffers.
                        The default value is 0.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_DOUBLEBUFFER</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by <constant>True</constant> or <constant>False</constant>. If
                        <constant>True</constant> is specified, then
                        only double-buffered frame buffer configurations are considered;
                        if
                        <constant>False</constant> is specified, then
                        only single-buffered frame buffer configurations are considered.
                        The default value is <constant>GLX_DONT_CARE</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_STEREO</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by <constant>True</constant> or <constant>False</constant>. If
                        <constant>True</constant> is specified, then
                        only stereo frame buffer configurations are considered;
                        if
                        <constant>False</constant> is specified, then
                        only monoscopic frame buffer configurations are considered.
                        The default value is <constant>False</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_AUX_BUFFERS</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by a nonnegative integer that indicates the desired
                        number of auxiliary buffers.
                        Configurations with the 
                        smallest number of auxiliary buffers that meet or exceed
                        the specified number are preferred.
                        The default value is 0.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_RED_SIZE</constant>, <constant>GLX_GREEN_SIZE</constant>, <constant>GLX_BLUE_SIZE</constant>, <constant>GLX_ALPHA_SIZE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Each attribute, if present, must be followed by a nonnegative minimum size
                        specification or <constant>GLX_DONT_CARE</constant>.
                        The largest available total RGBA color buffer size (sum of <constant>GLX_RED_SIZE</constant>,
                        <constant>GLX_GREEN_SIZE</constant>, <constant>GLX_BLUE_SIZE</constant>, and <constant>GLX_ALPHA_SIZE</constant>) 
                        of at least the minimum size specified for each color component is preferred.
                        If the requested number of bits for a color component is 0 or 
                        <constant>GLX_DONT_CARE</constant>, it is not considered. The default value for each color 
                        component is 0.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_DEPTH_SIZE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by a nonnegative minimum size specification.
                        If this value is zero,
                        frame buffer configurations with no depth buffer are preferred.
                        Otherwise, the largest available depth buffer of at least the minimum size
                        is preferred.
                        The default value is 0.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_STENCIL_SIZE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by a nonnegative integer that indicates the desired
                        number of stencil bitplanes.
                        The smallest stencil buffer of at least the specified size is preferred.
                        If the desired value is zero,
                        frame buffer configurations with no stencil buffer are preferred.
                        The default value is 0.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_ACCUM_RED_SIZE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by a nonnegative minimum size specification.
                        If this value is zero,
                        frame buffer configurations with no red accumulation buffer are preferred.
                        Otherwise, the largest possible red accumulation buffer
                        of at least the minimum size is preferred.
                        The default value is 0.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_ACCUM_GREEN_SIZE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by a nonnegative minimum size specification.
                        If this value is zero,
                        frame buffer configurations with no green accumulation buffer are preferred.
                        Otherwise, the largest possible green accumulation buffer
                        of at least the minimum size is preferred.
                        The default value is 0.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_ACCUM_BLUE_SIZE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by a nonnegative minimum size specification.
                        If this value is zero,
                        frame buffer configurations with no blue accumulation buffer are preferred.
                        Otherwise, the largest possible blue accumulation buffer
                        of at least the minimum size is preferred.
                        The default value is 0.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_ACCUM_ALPHA_SIZE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by a nonnegative minimum size specification.
                        If this value is zero,
                        frame buffer configurations with no alpha accumulation buffer are preferred.
                        Otherwise, the largest possible alpha accumulation buffer
                        of at least the minimum size is preferred.
                        The default value is 0.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_RENDER_TYPE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by a mask indicating which OpenGL rendering modes
                        the frame buffer configuration must support.
                        Valid bits are <constant>GLX_RGBA_BIT</constant> and 
                        <constant>GLX_COLOR_INDEX_BIT</constant>. If the mask is 
                        set to <constant>GLX_RGBA_BIT</constant> | <constant>GLX_COLOR_INDEX_BIT</constant>,
                        then only frame buffer configurations that can be bound to both
                        RGBA contexts and color index contexts will be considered.
                        The default value is <constant>GLX_RGBA_BIT</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_DRAWABLE_TYPE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by a mask indicating which GLX drawable types
                        the frame buffer configuration must support. Valid bits are 
                        <constant>GLX_WINDOW_BIT</constant>,
                        <constant>GLX_PIXMAP_BIT</constant>, and <constant>GLX_PBUFFER_BIT</constant>.
                        For example, if mask is set to 
                        <constant>GLX_WINDOW_BIT</constant> | <constant>GLX_PIXMAP_BIT</constant>, 
                        only frame buffer configurations that support both windows and GLX pixmaps
                        will be considered.
                        The default value is <constant>GLX_WINDOW_BIT</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_X_RENDERABLE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by <constant>True</constant> or <constant>False</constant>.
                        If <constant>True</constant> is specified, then only frame buffer configurations that
                        have associated X visuals (and can be used to render to Windows and/or
                        GLX pixmaps) will be considered.
                        The default value is <constant>GLX_DONT_CARE</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_X_VISUAL_TYPE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by one of 
                        <constant>GLX_TRUE_COLOR</constant>,
                        <constant>GLX_DIRECT_COLOR</constant>,
                        <constant>GLX_PSEUDO_COLOR</constant>,
                        <constant>GLX_STATIC_COLOR</constant>,
                        <constant>GLX_GRAY_SCALE</constant>, or
                        <constant>GLX_STATIC_GRAY</constant>, indicating the desired X visual type.
                        Not all frame buffer configurations have an associated X visual. If 
                        <constant>GLX_DRAWABLE_TYPE</constant> is specified in <parameter>attrib_list</parameter> and the
                        mask that follows does not have <constant>GLX_WINDOW_BIT</constant> set,
                        then this value is ignored. It is also ignored if 
                        <constant>GLX_X_RENDERABLE</constant> is specified as <constant>False</constant>.
                        RGBA rendering may be supported for visuals of type 
                        <constant>GLX_TRUE_COLOR</constant>,
                        <constant>GLX_DIRECT_COLOR</constant>,
                        <constant>GLX_PSEUDO_COLOR</constant>,
                        or <constant>GLX_STATIC_COLOR</constant>, 
                        but color index rendering is only supported for visuals of type
                        <constant>GLX_PSEUDO_COLOR</constant> or <constant>GLX_STATIC_COLOR</constant>
                        (i.e., single-channel visuals).
                        The tokens <constant>GLX_GRAY_SCALE</constant> and <constant>GLX_STATIC_GRAY</constant> will 
                        not match current OpenGL enabled visuals, but are included for future use.
                        The default value for <constant>GLX_X_VISUAL_TYPE</constant> is <constant>GLX_DONT_CARE</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_CONFIG_CAVEAT</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by one of 
                        <constant>GLX_NONE</constant>,
                        <constant>GLX_SLOW_CONFIG</constant>,
                        <constant>GLX_NON_CONFORMANT_CONFIG</constant>.
                        If <constant>GLX_NONE</constant> is specified, then only frame buffer configurations with
                        no caveats will be considered; if <constant>GLX_SLOW_CONFIG</constant>
                        is specified, then only slow frame buffer configurations will be considered; if
                        <constant>GLX_NON_CONFORMANT_CONFIG</constant> is specified, then only
                        nonconformant frame buffer configurations will be considered.
                        The default value is <constant>GLX_DONT_CARE</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_TRANSPARENT_TYPE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by one of 
                        <constant>GLX_NONE</constant>,
                        <constant>GLX_TRANSPARENT_RGB</constant>,
                        <constant>GLX_TRANSPARENT_INDEX</constant>.
                        If <constant>GLX_NONE</constant> is specified, then only opaque 
                        frame buffer configurations will be considered; if <constant>GLX_TRANSPARENT_RGB</constant>
                        is specified, then only transparent
                        frame buffer configurations that support RGBA rendering will be considered;
                        if <constant>GLX_TRANSPARENT_INDEX</constant> is specified,
                        then only transparent frame buffer configurations that support color 
                        index rendering will be considered.
                        The default value is <constant>GLX_NONE</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_TRANSPARENT_INDEX_VALUE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by an integer value indicating the transparent
                        index value; the value must be between 0 and the maximum
                        frame buffer value for indices.
                        Only frame buffer configurations that use the 
                        specified transparent index value will be considered.
                        The default value is <constant>GLX_DONT_CARE</constant>.
                        This attribute is ignored unless <constant>GLX_TRANSPARENT_TYPE</constant> is 
                        included in <parameter>attrib_list</parameter> and specified as <constant>GLX_TRANSPARENT_INDEX</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_TRANSPARENT_RED_VALUE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by an integer value indicating the transparent
                        red value; the value must be between 0 and the maximum
                        frame buffer value for red.
                        Only frame buffer configurations that use the 
                        specified transparent red value will be considered.
                        The default value is <constant>GLX_DONT_CARE</constant>.
                        This attribute is
                        ignored unless <constant>GLX_TRANSPARENT_TYPE</constant> is included in
                        <parameter>attrib_list</parameter> and specified as <constant>GLX_TRANSPARENT_RGB</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_TRANSPARENT_GREEN_VALUE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by an integer value indicating the transparent
                        green value; the value must be between 0 and the maximum
                        frame buffer value for green.
                        Only frame buffer configurations that use the 
                        specified transparent green value will be considered.
                        The default value is <constant>GLX_DONT_CARE</constant>.
                        This attribute is
                        ignored unless <constant>GLX_TRANSPARENT_TYPE</constant> is included in
                        <parameter>attrib_list</parameter> and specified as <constant>GLX_TRANSPARENT_RGB</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_TRANSPARENT_BLUE_VALUE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by an integer value indicating the transparent
                        blue value; the value must be between 0 and the maximum
                        frame buffer value for blue.
                        Only frame buffer configurations that use the 
                        specified transparent blue value will be considered.
                        The default value is <constant>GLX_DONT_CARE</constant>.
                        This attribute is ignored unless <constant>GLX_TRANSPARENT_TYPE</constant> is included in
                        <parameter>attrib_list</parameter> and specified as <constant>GLX_TRANSPARENT_RGB</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GLX_TRANSPARENT_ALPHA_VALUE</constant></term>
                <listitem>
                    <para>
                    </para>
                    <para>
                        Must be followed by an integer value indicating the transparent
                        alpha value; the value must be between 0 and the maximum
                        frame buffer value for alpha.
                        Only frame buffer configurations that use the 
                        specified transparent alpha value will be considered.
                        The default value is <constant>GLX_DONT_CARE</constant>.
                    </para>
                </listitem>
            </varlistentry>
        </variablelist>
        <para>
            When more than one GLX frame buffer configuration matches the specified attributes,
            a list of matching configurations is returned. The list is sorted 
            according to the following precedence rules, which are applied in ascending 
            order (i.e., configurations
            that are considered equal by a lower numbered rule are sorted by the higher
            numbered rule):
        </para>
        <variablelist>
            <varlistentry>
                <term>1.</term>
                <listitem>
                    <para>
                        By <constant>GLX_CONFIG_CAVEAT</constant> where the precedence is <constant>GLX_NONE</constant>,
                        <constant>GLX_SLOW_CONFIG</constant>, and <constant>GLX_NON_CONFORMANT_CONFIG</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term>2.</term>
                <listitem>
                    <para>
                         Larger total number of RGBA color components
                        (<constant>GLX_RED_SIZE</constant>, <constant>GLX_GREEN_SIZE</constant>, <constant>GLX_BLUE_SIZE</constant>,
                        plus <constant>GLX_ALPHA_SIZE</constant>)
                        that have higher number of bits. If the requested number of bits in
                        <parameter>attrib_list</parameter> is zero or <constant>GLX_DONT_CARE</constant> for a particular color
                        component, then the number of bits for that component is not considered.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term>3.</term>
                <listitem>
                    <para>
                        Smaller <constant>GLX_BUFFER_SIZE</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term>4.</term>
                <listitem>
                    <para>
                        Single buffered configuration (<constant>GLX_DOUBLEBUFFER</constant> being
                        <constant>False</constant> precedes a double buffered one.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term>5.</term>
                <listitem>
                    <para>
                        Smaller <constant>GLX_AUX_BUFFERS</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term>6.</term>
                <listitem>
                    <para>
                        Larger <constant>GLX_DEPTH_SIZE</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term>7.</term>
                <listitem>
                    <para>
                        Smaller <constant>GLX_STENCIL_SIZE</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term>8.</term>
                <listitem>
                    <para>
                        Larger total number of accumulation buffer color components
                        (<constant>GLX_ACCUM_RED_SIZE</constant>, <constant>GLX_ACCUM_GREEN_SIZE</constant>,
                        <constant>GLX_ACCUM_BLUE_SIZE</constant>, plus <constant>GLX_ACCUM_ALPHA_SIZE</constant>) that have
                        higher number of bits. If the requested number of bits in <parameter>attrib_list</parameter> is
                        zero or <constant>GLX_DONT_CARE</constant> for a particular color component, then the
                        number of bits for that component is not considered.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term>9.</term>
                <listitem>
                    <para>
                        By <constant>GLX_X_VISUAL_TYPE</constant> where the precedence order is
                        <constant>GLX_TRUE_COLOR</constant>, <constant>GLX_DIRECT_COLOR</constant>, <constant>GLX_PSEUDO_COLOR</constant>,
                        <constant>GLX_STATIC_COLOR</constant>, <constant>GLX_GRAY_SCALE</constant>, <constant>GLX_STATIC_GRAY</constant>.
                    </para>
                </listitem>
            </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="examples"><title>Examples</title>
        <para>
        </para>
        <variablelist>
            <varlistentry>
                <term><parameter>attrib_list</parameter> =</term>
                <listitem>
                    <para>
                        {<constant>GLX_RENDER_TYPE</constant>, <constant>GLX_RGBA_BIT</constant>,
                        <constant>GLX_RED_SIZE</constant>, 4,
                        <constant>GLX_GREEN_SIZE</constant>, 4,
                        <constant>GLX_BLUE_SIZE</constant>, 4,
                        <constant>None</constant>};
                    </para>
                </listitem>
            </varlistentry>
        </variablelist>
        <para>
            Specifies a frame buffer configuration that supports RGBA rendering
            and exists in the normal frame buffer,
            not an overlay or underlay buffer.
            The returned visual supports at least four bits each of red,
            green, and blue,
            and possibly no bits of alpha.
            It does not support stereo display.
            It may or may not have one or more auxiliary color buffers,
            a back buffer,
            a depth buffer,
            a stencil buffer,
            or an accumulation buffer.
        </para>
    </refsect1>
    <refsect1 id="notes"><title>Notes</title>
        <para>
            <function>glXChooseFBConfig</function> is available only if the GLX version is 1.3 or greater.
        </para>
        <para>
            If the GLX version is 1.1 or 1.0, the GL version must be 1.0.
            If the GLX version is 1.2, then the GL version must be 1.1.
            If the GLX version is 1.3, then the GL version must be 1.2.
        </para>
        <para>
            <citerefentry><refentrytitle>glXGetFBConfigs</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glXGetFBConfigAttrib</refentrytitle></citerefentry> can 
            be used to implement selection algorithms other than the generic 
            one implemented by <function>glXChooseFBConfig</function>. Call <function>glXChooseFBConfig</function> to retrieve all the frame buffer configurations 
            on a particular screen or, alternatively, all the frame buffer configurations with
            a particular set of attributes. Next, call <citerefentry><refentrytitle>glXGetFBConfigAttrib</refentrytitle></citerefentry>
            to retrieve additional attributes for the frame buffer configurations and then
            select between them.
        </para>
        <para>
            GLX implementations are strongly discouraged,
            but not proscribed,
            from changing the selection algorithm used by <function>glXChooseFBConfig</function>.
            Therefore, selections may change from release to release
            of the client-side library.
        </para>
    </refsect1>
    <refsect1 id="errors"><title>Errors</title>
        <para>
            <constant>NULL</constant> is returned if an undefined GLX attribute is
            encountered in <parameter>attrib_list</parameter>, if <parameter>screen</parameter> is invalid, or if <parameter>dpy</parameter> does
            not support the GLX extension.
        </para>
    </refsect1>
    <refsect1 id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glXGetFBConfigAttrib</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glXGetFBConfigs</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glXGetVisualFromFBConfig</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>
