<!DOCTYPE refentry [ <!ENTITY % mathent SYSTEM "math.ent"> %mathent; ]>

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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glReadPixels">
    <info>
        <copyright>
            <year>1991-2006</year>
            <holder>Silicon Graphics, Inc.</holder>
        </copyright>
        <copyright>
            <year>2010-2014</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <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>
    <refsect1 xml: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_RGBA</constant>, and
                    <constant>GL_RGBA_INTEGER</constant>.
                                        An implementation-chosen format will also be accepted.
                                        This can be queried with <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> and
                                        <constant>GL_IMPLEMENTATION_COLOR_READ_FORMAT</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_UNSIGNED_INT</constant>,
                    <constant>GL_INT</constant>, or
                    <constant>GL_FLOAT</constant>.
                                        An implementation-chosen type will also be accepted.
                                        This can be queried with <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> and
                                        <constant>GL_IMPLEMENTATION_COLOR_READ_TYPE</constant>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>data</parameter></term>
            <listitem>
                <para>
                    Returns the pixel data.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 xml: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>glPixelStorei</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 xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                <!-- 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 xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                <!-- 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 xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                <!-- 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 xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>th
            pixel in the
            <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><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
            <constant>GL_RED</constant>,
            <constant>GL_RED_INTEGER</constant>,
            <constant>GL_RG</constant>,
            <constant>GL_RG_INTEGER</constant>,
            <constant>GL_RGB</constant>,
            <constant>GL_RGB_INTEGER</constant>,
            <constant>GL_RGBA</constant>,
            <constant>GL_RGBA_INTEGER</constant>,
            <constant>GL_LUMINANCE_ALPHA</constant>,
            <constant>GL_LUMINANCE</constant>, and
            <constant>GL_ALPHA</constant>
        </para>
        <para>
            Finally, the indices or components
            are converted to the proper format,
            as specified by <parameter>type</parameter>.
            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_RG</constant>,
            <constant>GL_RGB</constant>, or
            <constant>GL_RGBA</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>
            <tgroup cols="3" align="left">
                <colspec/>
                <colspec align="center"/>
                <colspec align="center"/>
                <thead>
                    <row>
                        <entry>
                            <parameter>type</parameter>
                        </entry>
                        <entry>
                            <emphasis role="bold"> Index Mask </emphasis>
                        </entry>
                        <entry>
                            <emphasis role="bold"> Component Conversion </emphasis>
                        </entry>
                    </row>
                </thead>
                <tbody>
                    <row>
                        <entry>
                        <constant>GL_UNSIGNED_BYTE</constant>
                        </entry>
                        <entry>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                            <!-- 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>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                            <!-- 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>
                        <constant>GL_BYTE</constant>
                        </entry>
                        <entry>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                            <!-- 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>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                            <!-- 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>
                        <constant>GL_HALF_FLOAT</constant>
                        </entry>
                        <entry>
                        none
                        </entry>
                        <entry>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">c</mml:mi></mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry>
                        <constant>GL_FLOAT</constant>
                        </entry>
                        <entry>
                        none
                        </entry>
                        <entry>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">c</mml:mi></mml:math></inlineequation>
                        </entry>
                    </row>
                    <row>
                        <entry>
                        <constant>GL_UNSIGNED_SHORT_5_6_5</constant>
                        </entry>
                        <entry>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                            <!-- 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>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                            <!-- 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>
                        <constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>
                        </entry>
                        <entry>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                            <!-- 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>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                            <!-- 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>
                        <constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>
                        </entry>
                        <entry>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                            <!-- 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>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                            <!-- 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>
                        <constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant>
                        </entry>
                        <entry>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                            <!-- 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>
                        <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                            <!-- 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>
                        <constant>GL_UNSIGNED_INT_10F_11F_11F_REV</constant>
                        </entry>
                        <entry>
                        --
                        </entry>
                        <entry>
                        Special
                        </entry>
                    </row>
                    <row>
                        <entry>
                        <constant>GL_UNSIGNED_INT_5_9_9_9_REV</constant>
                        </entry>
                        <entry>
                        --
                        </entry>
                        <entry>
                        Special
                        </entry>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
        <para>
            Return values are placed in memory as follows.
            If <parameter>format</parameter> is
            <constant>GL_RED</constant>, or
            <constant>GL_RED_INTEGER</constant>,
            a single value is returned and the data for the
            <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>th
            pixel in the
            <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">j</mml:mi></mml:math></inlineequation>th
            row
            is placed in location
            <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                <!-- 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_RG</constant> and <constant>GL_RG_INTEGER</constant> return two values,
            <constant>GL_RGB</constant> and <constant>GL_RGB_INTEGER</constant> return three values,
            <constant>GL_RGBA</constant> and <constant>GL_RGBA_INTEGER</constant> return four values for each pixel,
            with all values corresponding to a single pixel occupying contiguous space
            in <parameter>data</parameter>.
            See <citerefentry><refentrytitle>glPixelStorei</refentrytitle></citerefentry> for a description of parameters which affect
                        the packing of data into memory.
        </para>
    </refsect1>
    <refsect1 xml: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>
        <para>
            Only two <parameter>format</parameter>/<parameter>type</parameter> parameter pairs are
            accepted. For normalized fixed point rendering surfaces,  <constant>GL_RGBA</constant>/<constant>GL_UNSIGNED_BYTE</constant> is
            accepted. For signed integer rendering surfaces, <constant>GL_RGBA_INTEGER</constant>/<constant>GL_INT</constant> is accepted.
                        For unsigned integer rendering surfaces, <constant>GL_RGBA_INTEGER</constant>/<constant>GL_UNSIGNED_INT</constant> is accepted.
                        The other acceptable pair can be discovered by querying
            <constant>GL_IMPLEMENTATION_COLOR_READ_FORMAT</constant> and
            <constant>GL_IMPLEMENTATION_COLOR_READ_TYPE</constant>. The implementation chosen format may also vary depending on the
                        format of the currently bound rendering surface.
        </para>
    </refsect1>
    <refsect1 xml: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 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 <constant>GL_READ_BUFFER</constant> is <constant>GL_NONE</constant> or
                        if <constant>GL_READ_FRAMEBUFFER_BINDING</constant> is non-zero and the read buffer selects an attachment that has no image attached.
        </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>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if the readbuffer of the currently bound framebuffer is
                        a fixed point normalized surface and <parameter>format</parameter>
            and <parameter>type</parameter> are neither <constant>GL_RGBA</constant> and
            <constant>GL_UNSIGNED_BYTE</constant>, respectively, nor the format/type pair
            returned by querying <constant>GL_IMPLEMENTATION_COLOR_READ_FORMAT</constant>
            and <constant>GL_IMPLEMENTATION_COLOR_READ_TYPE</constant>.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if the readbuffer of the currently bound framebuffer is
                        a floating point surface and <parameter>format</parameter>
            and <parameter>type</parameter> are neither <constant>GL_RGBA</constant> and
            <constant>GL_FLOAT</constant>, respectively, nor the format/type pair
            returned by querying <constant>GL_IMPLEMENTATION_COLOR_READ_FORMAT</constant>
            and <constant>GL_IMPLEMENTATION_COLOR_READ_TYPE</constant>.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if the readbuffer of the currently bound framebuffer is
                        a signed integer surface and <parameter>format</parameter>
            and <parameter>type</parameter> are neither <constant>GL_RGBA_INTEGER</constant> and
            <constant>GL_INT</constant>, respectively, nor the format/type pair
            returned by querying <constant>GL_IMPLEMENTATION_COLOR_READ_FORMAT</constant>
            and <constant>GL_IMPLEMENTATION_COLOR_READ_TYPE</constant>.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if the readbuffer of the currently bound framebuffer is
                        an unsigned integer surface and <parameter>format</parameter>
            and <parameter>type</parameter> are neither <constant>GL_RGBA_INTEGER</constant> and
            <constant>GL_UNSIGNED_INT</constant>, respectively, nor the format/type pair
            returned by querying <constant>GL_IMPLEMENTATION_COLOR_READ_FORMAT</constant>
            and <constant>GL_IMPLEMENTATION_COLOR_READ_TYPE</constant>.
        </para>
        <para>
            <constant>GL_INVALID_FRAMEBUFFER_OPERATION</constant> is generated if
            the currently bound framebuffer is not framebuffer complete (i.e. the
            return value from <citerefentry><refentrytitle>glCheckFramebufferStatus</refentrytitle></citerefentry>
            is not <constant>GL_FRAMEBUFFER_COMPLETE</constant>).
        </para>
    </refsect1>
    <refsect1 xml:id="associatedgets"><title>Associated Gets</title>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_PIXEL_PACK_BUFFER_BINDING</constant>
        </para>
    </refsect1>
    <refsect1 xml:id="versions">
        <title>API Version Support</title>
        <informaltable>
            <tgroup cols="3" align="left">
                <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
                <tbody>
                    <row>
                        <entry>glReadPixels</entry>
                        <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='es20']/*)"/>
                    </row>
                </tbody>
            </tgroup>
        </informaltable>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glPixelStorei</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glReadBuffer</refentrytitle></citerefentry>
        </para>
    </refsect1>
    <refsect1 xml:id="Copyright"><title>Copyright</title>
        <para>
            Copyright <trademark class="copyright"/> 1991-2006 Silicon Graphics, Inc.
            Copyright <trademark class="copyright"/> 2010-2014 Khronos Group.
            This document is licensed under the SGI Free Software B License.
            For details, see
            <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</link>.
        </para>
    </refsect1>
</refentry>
