
<refentry id="glCopyConvolutionFilter2D">
    <refmeta>
        <refmetainfo>
            <copyright>
                <year>1991-2006</year>
                <holder>Silicon Graphics, Inc.</holder>
            </copyright>
        </refmetainfo>
        <refentrytitle>glCopyConvolutionFilter2D</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glCopyConvolutionFilter2D</refname>
        <refpurpose>copy pixels into a two-dimensional convolution filter</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glCopyConvolutionFilter2D</function></funcdef>
                <paramdef>GLenum <parameter>target</parameter></paramdef>
                <paramdef>GLenum <parameter>internalformat</parameter></paramdef>
                <paramdef>GLint <parameter>x</parameter></paramdef>
                <paramdef>GLint <parameter>y</parameter></paramdef>
                <paramdef>GLsizei <parameter>width</parameter></paramdef>
                <paramdef>GLsizei <parameter>height</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>target</parameter></term>
            <listitem>
                <para>
                    Must be <constant>GL_CONVOLUTION_2D</constant>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>internalformat</parameter></term>
            <listitem>
                <para>
                    The internal format of the convolution filter kernel.
                    The allowable values are
                    <constant>GL_ALPHA</constant>,
                    <constant>GL_ALPHA4</constant>,
                    <constant>GL_ALPHA8</constant>,
                    <constant>GL_ALPHA12</constant>,
                    <constant>GL_ALPHA16</constant>,
                    <constant>GL_LUMINANCE</constant>,
                    <constant>GL_LUMINANCE4</constant>,
                    <constant>GL_LUMINANCE8</constant>,
                    <constant>GL_LUMINANCE12</constant>,
                    <constant>GL_LUMINANCE16</constant>,
                    <constant>GL_LUMINANCE_ALPHA</constant>,
                    <constant>GL_LUMINANCE4_ALPHA4</constant>,
                    <constant>GL_LUMINANCE6_ALPHA2</constant>,
                    <constant>GL_LUMINANCE8_ALPHA8</constant>,
                    <constant>GL_LUMINANCE12_ALPHA4</constant>,
                    <constant>GL_LUMINANCE12_ALPHA12</constant>,
                    <constant>GL_LUMINANCE16_ALPHA16</constant>,
                    <constant>GL_INTENSITY</constant>,
                    <constant>GL_INTENSITY4</constant>,
                    <constant>GL_INTENSITY8</constant>,
                    <constant>GL_INTENSITY12</constant>,
                    <constant>GL_INTENSITY16</constant>,
                    <constant>GL_R3_G3_B2</constant>,
                    <constant>GL_RGB</constant>,
                    <constant>GL_RGB4</constant>,
                    <constant>GL_RGB5</constant>,
                    <constant>GL_RGB8</constant>,
                    <constant>GL_RGB10</constant>,
                    <constant>GL_RGB12</constant>,
                    <constant>GL_RGB16</constant>,
                    <constant>GL_RGBA</constant>,
                    <constant>GL_RGBA2</constant>,
                    <constant>GL_RGBA4</constant>,
                    <constant>GL_RGB5_A1</constant>,
                    <constant>GL_RGBA8</constant>,
                    <constant>GL_RGB10_A2</constant>,
                    <constant>GL_RGBA12</constant>, or
                    <constant>GL_RGBA16</constant>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>x</parameter></term>
            <term><parameter>y</parameter></term>
            <listitem>
                <para>
                    The window space coordinates of the lower-left coordinate of the
                    pixel array to copy.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>width</parameter></term>
            <listitem>
                <para>
                    The width of the pixel array to copy.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>height</parameter></term>
            <listitem>
                <para>
                    The height of the pixel array to copy.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            <function>glCopyConvolutionFilter2D</function> defines a two-dimensional convolution filter kernel with pixels
            from the current <constant>GL_READ_BUFFER</constant> (rather than from main memory,
            as is the case for <citerefentry><refentrytitle>glConvolutionFilter2D</refentrytitle></citerefentry>).
        </para>
        <para>
            The screen-aligned pixel rectangle with lower-left corner at (<parameter>x</parameter>,\ <parameter>y</parameter>),
            width <parameter>width</parameter> and height <parameter>height</parameter>
            is used to define the convolution filter. If any pixels within this
            region are
            outside the window that is associated with the GL context, the
            values obtained for those pixels are undefined.
        </para>
        <para>
            The pixels in the rectangle are processed
            exactly as if <citerefentry><refentrytitle>glReadPixels</refentrytitle></citerefentry> had been called with <emphasis>format</emphasis>
            set to RGBA, but the process stops just before final conversion.
            The R, G, B, and A components of each pixel are next scaled by the four
            2D <constant>GL_CONVOLUTION_FILTER_SCALE</constant> parameters and biased by the
            four 2D <constant>GL_CONVOLUTION_FILTER_BIAS</constant> parameters.
            (The scale and bias parameters are set by <citerefentry><refentrytitle>glConvolutionParameter</refentrytitle></citerefentry>
            using the <constant>GL_CONVOLUTION_2D</constant> target and the names
            <constant>GL_CONVOLUTION_FILTER_SCALE</constant> and <constant>GL_CONVOLUTION_FILTER_BIAS</constant>.
            The parameters themselves are vectors of four values that are applied to red,
            green, blue, and alpha, in that order.)
            The R, G, B, and A values are not clamped to [0,1] at any time during this
            process.
        </para>
        <para>
            Each pixel is then converted to the internal format specified by
            <parameter>internalformat</parameter>.
            This conversion simply maps the component values of the pixel (R, G, B,
            and A) to the values included in the internal format (red, green, blue,
            alpha, luminance, and intensity).  The mapping is as follows:
        </para>
        <para>
        </para>
        <informaltable frame="topbot">
            <tgroup cols="7" align="left">
                <colspec colwidth="3*"/>
                <colspec colwidth="1*" align="center"/>
                <colspec colwidth="1*" align="center"/>
                <colspec colwidth="1*" align="center"/>
                <colspec colwidth="1*" align="center"/>
                <colspec colwidth="1.7*" align="center"/>
                <colspec colwidth="1.7*" align="center"/>
                <thead>
                    <row>
                        <entry rowsep="1" align="left"><emphasis role="bold">
                        Internal Format
                        </emphasis></entry>
                        <entry rowsep="1" align="center"><emphasis role="bold">
                        Red
                        </emphasis></entry>
                        <entry rowsep="1" align="center"><emphasis role="bold">
                        Green
                        </emphasis></entry>
                        <entry rowsep="1" align="center"><emphasis role="bold">
                        Blue
                        </emphasis></entry>
                        <entry rowsep="1" align="center"><emphasis role="bold">
                        Alpha
                        </emphasis></entry>
                        <entry rowsep="1" align="center"><emphasis role="bold">
                        Luminance
                        </emphasis></entry>
                        <entry rowsep="1" align="center"><emphasis role="bold">
                        Intensity
                        </emphasis></entry>
                    </row>
                </thead>
                <tbody>
                    <row>
                        <entry align="left">
                        <constant>GL_ALPHA</constant>
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        A
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                         
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_LUMINANCE</constant>
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        R
                        </entry>
                        <entry align="center">
                         
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_LUMINANCE_ALPHA</constant>
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        A
                        </entry>
                        <entry align="center">
                        R
                        </entry>
                        <entry align="center">
                         
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_INTENSITY</constant>
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        R
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_RGB</constant>
                        </entry>
                        <entry align="center">
                        R
                        </entry>
                        <entry align="center">
                        G
                        </entry>
                        <entry align="center">
                        B
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                         
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_RGBA</constant>
                        </entry>
                        <entry align="center">
                        R
                        </entry>
                        <entry align="center">
                        G
                        </entry>
                        <entry align="center">
                        B
                        </entry>
                        <entry align="center">
                        A
                        </entry>
                        <entry align="center">
                        </entry>
                        <entry align="center">
                         
                        </entry>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
        <para>
            The red, green, blue, alpha, luminance, and/or intensity components of
            the resulting pixels are stored in floating-point rather than integer
            format.
        </para>
        <para>
            Pixel ordering is such that lower x screen coordinates correspond to
            lower <emphasis>i</emphasis> filter image coordinates, and lower y screen coordinates
            correspond to lower <emphasis>j</emphasis> filter image coordinates.
        </para>
        <para>
            Note that after a convolution is performed, the resulting color
            components are also scaled by their corresponding
            <constant>GL_POST_CONVOLUTION_c_SCALE</constant> parameters and biased by their
            corresponding <constant>GL_POST_CONVOLUTION_c_BIAS</constant> parameters (where
            <emphasis>c</emphasis> takes on the values <emphasis role="bold">RED</emphasis>, <emphasis role="bold">GREEN</emphasis>, <emphasis role="bold">BLUE</emphasis>, and
            <emphasis role="bold">ALPHA</emphasis>).
            These parameters are set by <citerefentry><refentrytitle>glPixelTransfer</refentrytitle></citerefentry>.
        </para>
    </refsect1>
    <refsect1 id="notes"><title>Notes</title>
        <para>
            <function>glCopyConvolutionFilter2D</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>
    </refsect1>
    <refsect1 id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>target</parameter> is not
            <constant>GL_CONVOLUTION_2D</constant>.
        </para>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>internalformat</parameter> is not one of the
            allowable values.
        </para>
        <para>
            <constant>GL_INVALID_VALUE</constant> is generated if <parameter>width</parameter> is less than zero or greater
            than the maximum supported value.
            This value may be queried with <citerefentry><refentrytitle>glGetConvolutionParameter</refentrytitle></citerefentry>
            using target <constant>GL_CONVOLUTION_2D</constant> and name
            <constant>GL_MAX_CONVOLUTION_WIDTH</constant>.
        </para>
        <para>
            <constant>GL_INVALID_VALUE</constant> is generated if <parameter>height</parameter> is less than zero or greater
            than the maximum supported value.
            This value may be queried with <citerefentry><refentrytitle>glGetConvolutionParameter</refentrytitle></citerefentry>
            using target <constant>GL_CONVOLUTION_2D</constant> and name
            <constant>GL_MAX_CONVOLUTION_HEIGHT</constant>.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <function>glCopyConvolutionFilter2D</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>, <citerefentry><refentrytitle>glGetConvolutionFilter</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect1 id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glConvolutionFilter2D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glConvolutionParameter</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glPixelTransfer</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>
