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<refentry id="glReadPixels">
    <refmeta>
        <refmetainfo>
            <copyright>
                <year>1991-2006</year>
                <holder>Silicon Graphics, Inc.</holder>
            </copyright>
        </refmetainfo>
        <refentrytitle>glReadPixels</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glReadPixels</refname>
        <refpurpose>read a block of pixels from the frame buffer</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glReadPixels</function></funcdef>
                <paramdef>GLint <parameter>x</parameter></paramdef>
                <paramdef>GLint <parameter>y</parameter></paramdef>
                <paramdef>GLsizei <parameter>width</parameter></paramdef>
                <paramdef>GLsizei <parameter>height</parameter></paramdef>
                <paramdef>GLenum <parameter>format</parameter></paramdef>
                <paramdef>GLenum <parameter>type</parameter></paramdef>
                <paramdef>GLvoid * <parameter>data</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <!-- eqn: ignoring delim $$ -->
    <refsect1 id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>x</parameter></term>
            <term><parameter>y</parameter></term>
            <listitem>
                <para>
                    Specify the window coordinates of the first pixel
                    that is read from the frame buffer.
                    This location is the lower left corner of a rectangular block of pixels.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>width</parameter></term>
            <term><parameter>height</parameter></term>
            <listitem>
                <para>
                    Specify the dimensions of the pixel rectangle.
                    <parameter>width</parameter> and <parameter>height</parameter> of one correspond to a single pixel.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>format</parameter></term>
            <listitem>
                <para>
                    Specifies the format of the pixel data.
                    The following symbolic values are accepted:
                    <constant>GL_STENCIL_INDEX</constant>,
                    <constant>GL_DEPTH_COMPONENT</constant>,
                    <constant>GL_DEPTH_STENCIL</constant>,
                    <constant>GL_RED</constant>,
                    <constant>GL_GREEN</constant>,
                    <constant>GL_BLUE</constant>,
                    <constant>GL_RGB</constant>,
                    <constant>GL_BGR</constant>,
                    <constant>GL_RGBA</constant>, and
                    <constant>GL_BGRA</constant>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>type</parameter></term>
            <listitem>
                <para>
                    Specifies the data type of the pixel data.
                    Must be one of
                    <constant>GL_UNSIGNED_BYTE</constant>,
                    <constant>GL_BYTE</constant>,
                    <constant>GL_UNSIGNED_SHORT</constant>,
                    <constant>GL_SHORT</constant>,
                    <constant>GL_UNSIGNED_INT</constant>,
                    <constant>GL_INT</constant>,
                    <constant>GL_HALF_FLOAT</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>,
                    <constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant>,
                    <constant>GL_UNSIGNED_INT_24_8</constant>,
                    <constant>GL_UNSIGNED_INT_10F_11F_11F_REV</constant>,
                    <constant>GL_UNSIGNED_INT_5_9_9_9_REV</constant>, or
                    <constant>GL_FLOAT_32_UNSIGNED_INT_24_8_REV</constant>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>data</parameter></term>
            <listitem>
                <para>
                    Returns the pixel data.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 id="description"><title>Description</title>
        <para>
            <function>glReadPixels</function> returns pixel data from the frame buffer,
            starting with the pixel whose lower left corner
            is at location (<parameter>x</parameter>, <parameter>y</parameter>),
            into client memory starting at location <parameter>data</parameter>.
            Several parameters control the processing of the pixel data before
            it is placed into client memory.
            These parameters are set with <citerefentry><refentrytitle>glPixelStore</refentrytitle></citerefentry>.
            This reference page describes the effects on <function>glReadPixels</function> of most,
            but not all of the parameters specified by these three commands.
        </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 block of pixels is
            requested, <parameter>data</parameter> is treated as a byte offset into the buffer object's data store
            rather than a pointer to client memory.
        </para>
        <para>
            <function>glReadPixels</function> returns values from each pixel with lower left corner at
            <inlineequation><mml:math>
                <!-- eqn: (x + i, y + j): -->
                <mml:mfenced open="(" close=")">
                    <mml:mrow>
                        <mml:mi mathvariant="italic">x</mml:mi>
                        <mml:mo>+</mml:mo>
                        <mml:mi mathvariant="italic">i</mml:mi>
                    </mml:mrow>
                    <mml:mrow>
                        <mml:mi mathvariant="italic">y</mml:mi>
                        <mml:mo>+</mml:mo>
                        <mml:mi mathvariant="italic">j</mml:mi>
                    </mml:mrow>
                </mml:mfenced>
            </mml:math></inlineequation>
            for 
            <inlineequation><mml:math>
                <!-- eqn: 0 <= i < width: -->
                <mml:mrow>
                    <mml:mn>0</mml:mn>
                    <mml:mo>&lt;=</mml:mo>
                    <mml:mi mathvariant="italic">i</mml:mi>
                    <mml:mo>&lt;</mml:mo>
                    <mml:mi mathvariant="italic">width</mml:mi>
                </mml:mrow>
            </mml:math></inlineequation>
            and
            <inlineequation><mml:math>
                <!-- eqn: 0 <= j < height: -->
                <mml:mrow>
                    <mml:mn>0</mml:mn>
                    <mml:mo>&lt;=</mml:mo>
                    <mml:mi mathvariant="italic">j</mml:mi>
                    <mml:mo>&lt;</mml:mo>
                    <mml:mi mathvariant="italic">height</mml:mi>
                </mml:mrow>
            </mml:math></inlineequation>.
            This pixel is said to be the 
            <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>th
            pixel in the 
            <inlineequation><mml:math><mml:mi mathvariant="italic">j</mml:mi></mml:math></inlineequation>th
            row.
            Pixels are returned in row order from the lowest to the highest row,
            left to right in each row.
        </para>
        <para>
            <parameter>format</parameter> specifies the format for the returned pixel values;
            accepted values are:
        </para>
        <variablelist>
            <varlistentry>
                <term><constant>GL_STENCIL_INDEX</constant></term>
                <listitem>
                    <para>
                        Stencil values are read from the stencil buffer.
                        Each index is converted to fixed point,
                        shifted left or right depending on the value and sign of <constant>GL_INDEX_SHIFT</constant>,
                        and added to <constant>GL_INDEX_OFFSET</constant>.
                        If <constant>GL_MAP_STENCIL</constant> is <constant>GL_TRUE</constant>,
                        indices are replaced by their mappings in the table <constant>GL_PIXEL_MAP_S_TO_S</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_DEPTH_COMPONENT</constant></term>
                <listitem>
                    <para>
                        Depth values are read from the depth buffer.
                        Each component is converted to floating point such that the minimum depth
                        value maps to 0 and the maximum value maps to 1.
                        Each component is then multiplied by <constant>GL_DEPTH_SCALE</constant>,
                        added to <constant>GL_DEPTH_BIAS</constant>,
                        and finally clamped to the range 
                        <inlineequation><mml:math>
                            <!-- eqn: [0,1]: -->
                            <mml:mfenced open="[" close="]">
                                <mml:mn>0</mml:mn>
                                <mml:mn>1</mml:mn>
                            </mml:mfenced>
                        </mml:math></inlineequation>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_DEPTH_STENCIL</constant></term>
                <listitem>
                    <para>
                        Values are taken from both the depth and stencil buffers. The <parameter>type</parameter> parameter
                        must be <constant>GL_UNSIGNED_INT_24_8</constant> or <constant>GL_FLOAT_32_UNSIGNED_INT_24_8_REV</constant>.
                    </para>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_RED</constant></term>
                <listitem>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_GREEN</constant></term>
                <listitem>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_BLUE</constant></term>
                <listitem>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_RGB</constant></term>
                <listitem>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_BGR</constant></term>
                <listitem>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_RGBA</constant></term>
                <listitem>
                </listitem>
            </varlistentry>
            <varlistentry>
                <term><constant>GL_BGRA</constant></term>
                <listitem>
                </listitem>
            </varlistentry>
        </variablelist>
        <para>
            Finally, the indices or components
            are converted to the proper format,
            as specified by <parameter>type</parameter>.
            If <parameter>format</parameter> is <constant>GL_STENCIL_INDEX</constant>
            and <parameter>type</parameter> is not <constant>GL_FLOAT</constant>,
            each index is masked with the mask value given in the following table.
            If <parameter>type</parameter> is <constant>GL_FLOAT</constant>, then each integer index is converted to
            single-precision floating-point format.
        </para>
        <para>
            If <parameter>format</parameter> is
            <constant>GL_RED</constant>,
            <constant>GL_GREEN</constant>,
            <constant>GL_BLUE</constant>,
            <constant>GL_RGB</constant>,
            <constant>GL_BGR</constant>,
            <constant>GL_RGBA</constant>, or
            <constant>GL_BGRA</constant> and <parameter>type</parameter> is not <constant>GL_FLOAT</constant>,
            each component is multiplied by the multiplier shown in the following table.
            If type is <constant>GL_FLOAT</constant>, then each component is passed as is
            (or converted to the client's single-precision floating-point format if
            it is different from the one used by the GL).
        </para>
        <para>
        </para>
        <informaltable frame="topbot">
            <tgroup cols="3" align="left">
                <colspec/>
                <colspec align="center"/>
                <colspec align="center"/>
                <thead>
                    <row>
                        <entry rowsep="1" align="left">
                        <parameter>type</parameter>
                        </entry>
                        <entry rowsep="1" align="center"><emphasis role="bold">
                        Index Mask
                        </emphasis></entry>
                        <entry rowsep="1" align="center"><emphasis role="bold">
                        Component Conversion
                        </emphasis></entry>
                    </row>
                </thead>
                <tbody>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_BYTE</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup 8 - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>8</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup 8 - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>8</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_BYTE</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup 7 - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>7</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: {(2 sup 8 - 1) c - 1} / 2: -->
                            <mml:mfrac>
                                <mml:mfenced open="" close="">
                                    <mml:mrow>
                                        <mml:mfenced open="(" close=")">
                                            <mml:mrow>
                                                <mml:msup><mml:mn>2</mml:mn>
                                                <mml:mn>8</mml:mn>
                                                </mml:msup>
                                                <mml:mo>-</mml:mo>
                                                <mml:mn>1</mml:mn>
                                            </mml:mrow>
                                        </mml:mfenced>
                                        <mml:mo>&it;</mml:mo>
                                        <mml:mi mathvariant="italic">c</mml:mi>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mn>2</mml:mn>
                            </mml:mfrac>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_SHORT</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup 16 - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>16</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup 16 - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>16</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_SHORT</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup 15 - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>15</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: {(2 sup 16 - 1) c - 1} / 2: -->
                            <mml:mfrac>
                                <mml:mfenced open="" close="">
                                    <mml:mrow>
                                        <mml:mfenced open="(" close=")">
                                            <mml:mrow>
                                                <mml:msup><mml:mn>2</mml:mn>
                                                <mml:mn>16</mml:mn>
                                                </mml:msup>
                                                <mml:mo>-</mml:mo>
                                                <mml:mn>1</mml:mn>
                                            </mml:mrow>
                                        </mml:mfenced>
                                        <mml:mo>&it;</mml:mo>
                                        <mml:mi mathvariant="italic">c</mml:mi>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mn>2</mml:mn>
                            </mml:mfrac>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_INT</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup 32 - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>32</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup 32 - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>32</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_INT</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup 31 - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>31</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: {(2 sup 32 - 1) c - 1} / 2: -->
                            <mml:mfrac>
                                <mml:mfenced open="" close="">
                                    <mml:mrow>
                                        <mml:mfenced open="(" close=")">
                                            <mml:mrow>
                                                <mml:msup><mml:mn>2</mml:mn>
                                                <mml:mn>32</mml:mn>
                                                </mml:msup>
                                                <mml:mo>-</mml:mo>
                                                <mml:mn>1</mml:mn>
                                            </mml:mrow>
                                        </mml:mfenced>
                                        <mml:mo>&it;</mml:mo>
                                        <mml:mi mathvariant="italic">c</mml:mi>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mn>2</mml:mn>
                            </mml:mfrac>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_HALF_FLOAT</constant>
                        </entry>
                        <entry align="center">
                        none
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math><mml:mi mathvariant="italic">c</mml:mi></mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_FLOAT</constant>
                        </entry>
                        <entry align="center">
                        none
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math><mml:mi mathvariant="italic">c</mml:mi></mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_BYTE_3_3_2</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup N - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>N</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup N - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>N</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup N - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>N</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup N - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>N</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_SHORT_5_6_5</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup N - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>N</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup N - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>N</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup N - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>N</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup N - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>N</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup N - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>N</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup N - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>N</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup N - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>N</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup N - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>N</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup N - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>N</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup N - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>N</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup N - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>N</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup N - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>N</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_INT_8_8_8_8</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup N - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>N</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup N - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>N</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup N - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>N</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup N - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>N</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_INT_10_10_10_2</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup N - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>N</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup N - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>N</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup N - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>N</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup N - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>N</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_INT_24_8</constant>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: 2 sup N - 1: -->
                            <mml:mrow>
                                <mml:msup><mml:mn>2</mml:mn>
                                <mml:mn>N</mml:mn>
                                </mml:msup>
                                <mml:mo>-</mml:mo>
                                <mml:mn>1</mml:mn>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math>
                            <!-- eqn: (2 sup N - 1) c: -->
                            <mml:mrow>
                                <mml:mfenced open="(" close=")">
                                    <mml:mrow>
                                        <mml:msup><mml:mn>2</mml:mn>
                                        <mml:mn>N</mml:mn>
                                        </mml:msup>
                                        <mml:mo>-</mml:mo>
                                        <mml:mn>1</mml:mn>
                                    </mml:mrow>
                                </mml:mfenced>
                                <mml:mo>&it;</mml:mo>
                                <mml:mi mathvariant="italic">c</mml:mi>
                            </mml:mrow>
                        </mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_INT_10F_11F_11F_REV</constant>
                        </entry>
                        <entry align="center">
                        --
                        </entry>
                        <entry align="left">
                        Special
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_UNSIGNED_INT_5_9_9_9_REV</constant>
                        </entry>
                        <entry align="center">
                        --
                        </entry>
                        <entry align="left">
                        Special
                        </entry>
                    </row>
                    <row>
                        <entry align="left">
                        <constant>GL_FLOAT_32_UNSIGNED_INT_24_8_REV</constant>
                        </entry>
                        <entry align="center">
                        none
                        </entry>
                        <entry align="center">
                        <inlineequation><mml:math><mml:mi mathvariant="italic">c</mml:mi></mml:math></inlineequation> (Depth Only)
                        </entry>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
        <para>
            Return values are placed in memory as follows.
            If <parameter>format</parameter> is
            <constant>GL_STENCIL_INDEX</constant>,
            <constant>GL_DEPTH_COMPONENT</constant>,
            <constant>GL_RED</constant>,
            <constant>GL_GREEN</constant>, or
            <constant>GL_BLUE</constant>,
            a single value is returned and the data for the 
            <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>th
            pixel in the 
            <inlineequation><mml:math><mml:mi mathvariant="italic">j</mml:mi></mml:math></inlineequation>th
            row
            is placed in location 
            <inlineequation><mml:math>
                <!-- eqn: (j) width + i: -->
                <mml:mrow>
                    <mml:mfenced open="(" close=")">
                        <mml:mi mathvariant="italic">j</mml:mi>
                    </mml:mfenced>
                    <mml:mo>&it;</mml:mo>
                    <mml:mi mathvariant="italic">width</mml:mi>
                    <mml:mo>+</mml:mo>
                    <mml:mi mathvariant="italic">i</mml:mi>
                </mml:mrow>
            </mml:math></inlineequation>.
            <constant>GL_RGB</constant> and <constant>GL_BGR</constant> return three values,
            <constant>GL_RGBA</constant> and <constant>GL_BGRA</constant> return four values for each pixel,
            with all values corresponding to a single pixel occupying contiguous space
            in <parameter>data</parameter>.
            Storage parameters set by <citerefentry><refentrytitle>glPixelStore</refentrytitle></citerefentry>,
            such as <constant>GL_PACK_LSB_FIRST</constant> and <constant>GL_PACK_SWAP_BYTES</constant>,
            affect the way that data is written into memory.
            See <citerefentry><refentrytitle>glPixelStore</refentrytitle></citerefentry> for a description.
        </para>
    </refsect1>
    <refsect1 id="notes"><title>Notes</title>
        <para>
            Values for pixels that lie outside the window
            connected to the current GL context are undefined.
        </para>
        <para>
            If an error is generated,
            no change is made to the contents of <parameter>data</parameter>.
        </para>
    </refsect1>
    <refsect1 id="errors"><title>Errors</title>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>format</parameter> or <parameter>type</parameter> is not an
            accepted value.
        </para>
        <para>
            <constant>GL_INVALID_VALUE</constant> is generated if either <parameter>width</parameter> or <parameter>height</parameter> is negative.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>format</parameter> is <constant>GL_STENCIL_INDEX</constant>
            and there is no stencil buffer.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>format</parameter> is <constant>GL_DEPTH_COMPONENT</constant>
            and there is no depth buffer.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>format</parameter> is <constant>GL_DEPTH_STENCIL</constant>
            and there is no depth buffer or if there is no stencil buffer.
        </para>
        <para>
            <constant>GL_INVALID_ENUM</constant> is generated if <parameter>format</parameter> is <constant>GL_DEPTH_STENCIL</constant>
            and <parameter>type</parameter> is not <constant>GL_UNSIGNED_INT_24_8</constant> or <constant>GL_FLOAT_32_UNSIGNED_INT_24_8_REV</constant>.
        </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>data</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 <constant>GL_READ_FRAMEBUFFER_BINDING</constant>
            is non-zero, the read framebuffer is complete, and the value of <constant>GL_SAMPLE_BUFFERS</constant>
            for the read framebuffer is greater than zero.
        </para>
    </refsect1>
    <refsect1 id="associatedgets"><title>Associated Gets</title>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_INDEX_MODE</constant>
        </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>glPixelStore</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glReadBuffer</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>
