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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glCompressedTexSubImage2D">
    <info>
        <copyright>
            <year>1991-2006</year>
            <holder>Silicon Graphics, Inc.</holder>
        </copyright>
        <copyright>
            <year>2010-2013</year>
            <holder>Khronos Group</holder>
        </copyright>
    </info>
    <refmeta>
        <refentrytitle>glCompressedTexSubImage2D</refentrytitle>
        <manvolnum>3G</manvolnum>
    </refmeta>
    <refnamediv>
        <refname>glCompressedTexSubImage2D</refname>
        <refpurpose>specify a two-dimensional texture subimage in a compressed format</refpurpose>
    </refnamediv>
    <refsynopsisdiv><title>C Specification</title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>void <function>glCompressedTexSubImage2D</function></funcdef>
                <paramdef>GLenum <parameter>target</parameter></paramdef>
                <paramdef>GLint <parameter>level</parameter></paramdef>
                <paramdef>GLint <parameter>xoffset</parameter></paramdef>
                <paramdef>GLint <parameter>yoffset</parameter></paramdef>
                <paramdef>GLsizei <parameter>width</parameter></paramdef>
                <paramdef>GLsizei <parameter>height</parameter></paramdef>
                <paramdef>GLenum <parameter>format</parameter></paramdef>
                <paramdef>GLsizei <parameter>imageSize</parameter></paramdef>
                <paramdef>const GLvoid * <parameter>data</parameter></paramdef>
            </funcprototype>
        </funcsynopsis>
    </refsynopsisdiv>
    <refsect1 xml:id="parameters"><title>Parameters</title>
        <variablelist>
        <varlistentry>
            <term><parameter>target</parameter></term>
            <listitem>
                <para>
                    Specifies the target texture.
                    Must be <constant>GL_TEXTURE_2D</constant>,
                    <constant>GL_TEXTURE_CUBE_MAP_POSITIVE_X</constant>,
                    <constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_X</constant>,
                    <constant>GL_TEXTURE_CUBE_MAP_POSITIVE_Y</constant>,
                    <constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_Y</constant>,
                    <constant>GL_TEXTURE_CUBE_MAP_POSITIVE_Z</constant>, or
                    <constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_Z</constant>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>level</parameter></term>
            <listitem>
                <para>
                    Specifies the level-of-detail number.
                    Level 0 is the base image level.
                    Level <emphasis>n</emphasis> is the <emphasis>n</emphasis>th mipmap reduction image.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>xoffset</parameter></term>
            <listitem>
                <para>
                    Specifies a texel offset in the x direction within the texture array.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>yoffset</parameter></term>
            <listitem>
                <para>
                    Specifies a texel offset in the y direction within the texture array.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>width</parameter></term>
            <listitem>
                <para>
                    Specifies the width of the texture subimage.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>height</parameter></term>
            <listitem>
                <para>
                    Specifies the height of the texture subimage.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>format</parameter></term>
            <listitem>
                <para>
                    Specifies the format of the compressed image data stored at address <parameter>data</parameter>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>imageSize</parameter></term>
            <listitem>
                <para>
                    Specifies the number of unsigned bytes of image data starting at the
                    address specified by <parameter>data</parameter>.
                </para>
            </listitem>
        </varlistentry>
        <varlistentry>
            <term><parameter>data</parameter></term>
            <listitem>
                <para>
                    Specifies a pointer to the compressed image data in memory.
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
    </refsect1>
    <refsect1 xml:id="description"><title>Description</title>
        <para>
            Texturing allows elements of an image array to be read by shaders.
        </para>
        <para>
            <function>glCompressedTexSubImage2D</function> redefines a contiguous subregion of an existing two-dimensional
            texture image.  The texels referenced by <parameter>data</parameter> replace the portion of the
            existing texture array with x indices <parameter>xoffset</parameter> and
            <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                <!-- eqn: xoffset  +  width  -  1: -->
                <mml:mrow>
                    <mml:mi mathvariant="italic">xoffset</mml:mi>
                    <mml:mo>+</mml:mo>
                    <mml:mi mathvariant="italic">width</mml:mi>
                    <mml:mo>-</mml:mo>
                    <mml:mn>1</mml:mn>
                </mml:mrow>
            </mml:math></inlineequation>,
            and the y indices <parameter>yoffset</parameter> and
            <inlineequation><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
                <!-- eqn: yoffset  +  height  -  1: -->
                <mml:mrow>
                    <mml:mi mathvariant="italic">yoffset</mml:mi>
                    <mml:mo>+</mml:mo>
                    <mml:mi mathvariant="italic">height</mml:mi>
                    <mml:mo>-</mml:mo>
                    <mml:mn>1</mml:mn>
                </mml:mrow>
            </mml:math></inlineequation>,
            inclusive.
            This region may not include any texels
            outside the range of the texture array as it was originally specified.  It
            is not an error to specify a subtexture with width of 0, but such a
            specification has no effect.
        </para>
        <para>
            <parameter>internalformat</parameter> must be a known compressed image format (such as <constant>GL_RGTC</constant>)
            or an extension-specified compressed-texture format.
            The <parameter>format</parameter> of the compressed texture
            image is selected by the GL implementation that compressed it (see
            <citerefentry><refentrytitle>glTexImage2D</refentrytitle></citerefentry>) and should be queried at the time the texture was
            compressed with <citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry>.
        </para>
        <para>
            If a non-zero named buffer object is bound to the <constant>GL_PIXEL_UNPACK_BUFFER</constant> target
            (see <citerefentry><refentrytitle>glBindBuffer</refentrytitle></citerefentry>) while a texture image is
            specified, <parameter>data</parameter> is treated as a byte offset into the buffer object's data store.
        </para>
    </refsect1>
    <refsect1 xml:id="errors"><title>Errors</title>
        <para>
          <constant>GL_INVALID_ENUM</constant> is generated if <parameter>internalformat</parameter> is of the generic compressed internal formats:
          <constant>GL_COMPRESSED_RED</constant>,
          <constant>GL_COMPRESSED_RG</constant>,
          <constant>GL_COMPRESSED_RGB</constant>,
          <constant>GL_COMPRESSED_RGBA</constant>.
          <constant>GL_COMPRESSED_SRGB</constant>, or
          <constant>GL_COMPRESSED_SRGB_ALPHA</constant>.
        </para>
        <para>
            <constant>GL_INVALID_VALUE</constant> is generated if <parameter>imageSize</parameter> is not consistent with
            the format, dimensions, and contents of the specified compressed image
            data.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if parameter combinations are not
            supported by the specific compressed internal format as specified in the
            specific texture compression extension.
        </para>
        <para>
            <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
            <constant>GL_PIXEL_UNPACK_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_UNPACK_BUFFER</constant> target and the data would be unpacked from the buffer
            object such that the memory reads required would exceed the data store size.
        </para>
        <para>
            Undefined results, including abnormal program termination, are generated if
            <parameter>data</parameter> is not encoded in a manner consistent with the extension
            specification defining the internal compression format.
        </para>
    </refsect1>
    <refsect1 xml:id="associatedgets"><title>Associated Gets</title>
        <para>
            <citerefentry><refentrytitle>glGetCompressedTexImage</refentrytitle></citerefentry>
        </para>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_TEXTURE_COMPRESSED</constant>
        </para>
        <para>
            <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_PIXEL_UNPACK_BUFFER_BINDING</constant>
        </para>
        <para>
            <citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> with arguments <constant>GL_TEXTURE_INTERNAL_FORMAT</constant>
            and <constant>GL_TEXTURE_COMPRESSED_IMAGE_SIZE</constant>
        </para>
    </refsect1>
    <refsect1 xml:id="seealso"><title>See Also</title>
        <para>
            <citerefentry><refentrytitle>glActiveTexture</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glCompressedTexImage1D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glCompressedTexImage2D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glCompressedTexImage3D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glCompressedTexSubImage1D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glCompressedTexSubImage3D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glCopyTexImage1D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glCopyTexImage2D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glCopyTexSubImage1D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glCopyTexSubImage2D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glCopyTexSubImage3D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glPixelStore</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glTexImage2D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glTexImage3D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glTexSubImage1D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glTexSubImage2D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glTexSubImage3D</refentrytitle></citerefentry>,
            <citerefentry><refentrytitle>glTexParameter</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"/> 2010-2013 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>
