
<refentry id="glGetConvolutionFilter">
    <refmeta>
        <refmetainfo>
            <copyright>
                <year>1991-2006</year>
                <holder>Silicon Graphics, Inc.</holder>
            </copyright>
        </refmetainfo>
        <refentrytitle>glGetConvolutionFilter</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glGetConvolutionFilter</refname>
        <refpurpose>get current 1D or 2D convolution filter kernel</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glGetConvolutionFilter</function></funcdef>
                <paramdef>GLenum <parameter>target</parameter></paramdef>
                <paramdef>GLenum <parameter>format</parameter></paramdef>
                <paramdef>GLenum <parameter>type</parameter></paramdef>
                <paramdef>GLvoid * <parameter>image</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>target</parameter></term>
            <listitem>
                <para>
                    The filter to be retrieved.
                    Must be one of
                    <constant>GL_CONVOLUTION_1D</constant> or
                    <constant>GL_CONVOLUTION_2D</constant>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>format</parameter></term>
            <listitem>
                <para>
                    Format of the output image.
                    Must be one of
                    <constant>GL_RED</constant>,
                    <constant>GL_GREEN</constant>,
                    <constant>GL_BLUE</constant>,
                    <constant>GL_ALPHA</constant>,
                    <constant>GL_RGB</constant>,
                    <constant>GL_BGR</constant>,
                    <constant>GL_RGBA</constant>,
                    <constant>GL_BGRA</constant>,
                    <constant>GL_LUMINANCE</constant>, or
                    <constant>GL_LUMINANCE_ALPHA</constant>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>type</parameter></term>
            <listitem>
                <para>
                    Data type of components in the output image.
                    Symbolic constants
                    <constant>GL_UNSIGNED_BYTE</constant>,
                    <constant>GL_BYTE</constant>,
                    <constant>GL_BITMAP</constant>,
                    <constant>GL_UNSIGNED_SHORT</constant>,
                    <constant>GL_SHORT</constant>,
                    <constant>GL_UNSIGNED_INT</constant>,
                    <constant>GL_INT</constant>,
                    <constant>GL_FLOAT</constant>,
                    <constant>GL_UNSIGNED_BYTE_3_3_2</constant>,
                    <constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>,
                    <constant>GL_UNSIGNED_SHORT_5_6_5</constant>,
                    <constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant>,
                    <constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>,
                    <constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>,
                    <constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>,
                    <constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>,
                    <constant>GL_UNSIGNED_INT_8_8_8_8</constant>,
                    <constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>,
                    <constant>GL_UNSIGNED_INT_10_10_10_2</constant>, and
                    <constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant>
                    are accepted.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>image</parameter></term>
            <listitem>
                <para>
                    Pointer to storage for the output image.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            <function>glGetConvolutionFilter</function> returns the current 1D or 2D convolution filter kernel as an image.
            The one- or two-dimensional image is placed in <parameter>image</parameter> according to the
            specifications in <parameter>format</parameter> and <parameter>type</parameter>.
            No pixel transfer operations are performed on this image, but the relevant
            pixel storage modes are applied.
        </para>
        <para>
            If a non-zero named buffer object is bound to the <constant>GL_PIXEL_PACK_BUFFER</constant> target 
            (see <citerefentry><refentrytitle>glBindBuffer</refentrytitle></citerefentry>) while a convolution filter is
            requested, <parameter>image</parameter> is treated as a byte offset into the buffer object's data store.
        </para>
        <para>
            Color components that are present in <parameter>format</parameter> but not included in the
            internal format of the filter are returned as zero.
            The assignments of internal color components to the components of <parameter>format</parameter>
            are as follows.
        </para>
        <informaltable frame="topbot">
            <tgroup cols="2" align="left">
                <colspec/>
                <colspec/>
                <thead>
                    <row>
                        <entry rowsep="1" align="left"><emphasis role="bold">
                        Internal Component
                        </emphasis></entry>
                        <entry rowsep="1" align="left"><emphasis role="bold">
                        Resulting Component
                        </emphasis></entry>
                    </row>
                </thead>
                <tbody>
                    <row>
                        <entry align="left">
                        Red
                        </entry>
                        <entry align="left">
                        Red
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        Green
                        </entry>
                        <entry align="left">
                        Green
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        Blue
                        </entry>
                        <entry align="left">
                        Blue
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        Alpha
                        </entry>
                        <entry align="left">
                        Alpha
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        Luminance
                        </entry>
                        <entry align="left">
                        Red
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        Intensity
                        </entry>
                        <entry align="left">
                        Red
                        </entry>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
        <para>
        </para>
    </refsect1>
    <refsect1 id="notes"><title>Notes</title>
        <para>
            <function>glGetConvolutionFilter</function> is present only if <code>ARB_imaging</code> is returned when <citerefentry><refentrytitle>glGetString</refentrytitle></citerefentry>
            is called with an argument of <constant>GL_EXTENSIONS</constant>.
        </para>
        <para>
            The current separable 2D filter must be retrieved with
            <citerefentry><refentrytitle>glGetSeparableFilter</refentrytitle></citerefentry> rather than <function>glGetConvolutionFilter</function>.
        </para>
    </refsect1>
    <refsect1 id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>target</parameter> is not one of the allowable
            values.
        </para>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>format</parameter> is not one of the allowable
            values.
        </para>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>type</parameter> is not one of the allowable
            values.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>type</parameter> is one of
            <constant>GL_UNSIGNED_BYTE_3_3_2</constant>,
            <constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>,
            <constant>GL_UNSIGNED_SHORT_5_6_5</constant>, or
            <constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant>
            and <parameter>format</parameter> is not <constant>GL_RGB</constant>.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>type</parameter> is one of
            <constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>,
            <constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>,
            <constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>,
            <constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>,
            <constant>GL_UNSIGNED_INT_8_8_8_8</constant>,
            <constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>,
            <constant>GL_UNSIGNED_INT_10_10_10_2</constant>, or
            <constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant>
            and <parameter>format</parameter> is neither <constant>GL_RGBA</constant> nor <constant>GL_BGRA</constant>.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
            <constant>GL_PIXEL_PACK_BUFFER</constant> target and the buffer object's data store is currently mapped.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
            <constant>GL_PIXEL_PACK_BUFFER</constant> target and the data would be packed to the buffer 
            object such that the memory writes required would exceed the data store size.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
            <constant>GL_PIXEL_PACK_BUFFER</constant> target and <parameter>image</parameter> is not evenly divisible 
            into the number of bytes needed to store in memory a datum indicated by <parameter>type</parameter>.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <function>glGetConvolutionFilter</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>glGetConvolutionParameter</refentrytitle></citerefentry>
        </para>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_PIXEL_PACK_BUFFER_BINDING</constant>
        </para>
    </refsect1>
    <refsect1 id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glGetSeparableFilter</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glConvolutionParameter</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glConvolutionFilter1D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glConvolutionFilter2D</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>
