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<!DOCTYPE refentry [ <!ENTITY % mathent SYSTEM "math.ent"> %mathent; ]>
<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="glGetCompressedTextureSubImage">
<info>
<copyright>
<year>2014</year>
<holder>Khronos Group</holder>
</copyright>
</info>
<refmeta>
<refentrytitle>glGetCompressedTextureSubImage</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glGetCompressedTextureSubImage</refname>
<refpurpose>retrieve a sub-region of a compressed texture image from a
compressed texture object</refpurpose>
</refnamediv>
<refsynopsisdiv>
<title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glGetCompressedTextureSubImage</function></funcdef>
<paramdef>GLuint <parameter>texture</parameter></paramdef>
<paramdef>GLint <parameter>level</parameter></paramdef>
<paramdef>GLint <parameter>xoffset</parameter></paramdef>
<paramdef>GLint <parameter>yoffset</parameter></paramdef>
<paramdef>GLint <parameter>zoffset</parameter></paramdef>
<paramdef>GLsizei <parameter>width</parameter></paramdef>
<paramdef>GLsizei <parameter>height</parameter></paramdef>
<paramdef>GLsizei <parameter>depth</parameter></paramdef>
<paramdef>GLsizei <parameter>bufSize</parameter></paramdef>
<paramdef>void *<parameter>pixels</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 xml:id="parameters">
<title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>texture</parameter></term>
<listitem>
<para>Specifies the name of the source texture object. Must be
<constant>GL_TEXTURE_1D</constant>,
<constant>GL_TEXTURE_1D_ARRAY</constant>,
<constant>GL_TEXTURE_2D</constant>,
<constant>GL_TEXTURE_2D_ARRAY</constant>,
<constant>GL_TEXTURE_3D</constant>,
<constant>GL_TEXTURE_CUBE_MAP</constant>,
<constant>GL_TEXTURE_CUBE_MAP_ARRAY</constant> or
<constant>GL_TEXTURE_RECTANGLE</constant>. In specific, buffer and
multisample textures are not permitted.</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 $n$ is the $n$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>zoffset</parameter></term>
<listitem>
<para>Specifies a texel offset in the z direction within the texture
array.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>width</parameter></term>
<listitem>
<para>Specifies the width of the texture subimage. Must be a
multiple of the compressed block's width, unless the
<parameter>offset</parameter> is zero and the size equals the texture
image size.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>height</parameter></term>
<listitem>
<para>Specifies the height of the texture subimage. Must be a
multiple of the compressed block's height, unless the
<parameter>offset</parameter> is zero and the size equals the texture
image size.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>depth</parameter></term>
<listitem>
<para>Specifies the depth of the texture subimage. Must be a
multiple of the compressed block's depth, unless the
<parameter>offset</parameter> is zero and the size equals the texture
image size.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>bufSize</parameter></term>
<listitem>
<para>Specifies the size of the buffer to receive the retrieved
pixel data.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>pixels</parameter></term>
<listitem>
<para>Returns the texture subimage. Should be a pointer to an array
of the type specified by type.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 xml:id="description">
<title>Description</title>
<para><function>glGetCompressedTextureSubImage</function> can be used to
obtain a sub-region of a compressed texture image instead of the whole
image, as long as the compressed data are arranged into fixed-size blocks
of texels. <parameter>texture</parameter> is the name of the texture
object, and must not be a buffer or multisample texture. The effective
<parameter>target</parameter> is the value of
<constant>GL_TEXTURE_TARGET</constant> for texture.
<parameter>level</parameter> and <parameter>pixels</parameter> have the
same meaning as the corresponding arguments of
<function>glCompressedTexSubImage3D</function>.
<parameter>bufSize</parameter> indicates the size of the buffer to receive
the retrieved pixel data.</para>
<para>For cube map textures, the behavior is as though
<function>glGetCompressedTexImage</function> were called once for each
requested face (selected by <parameter>zoffset</parameter> and
<parameter>depth</parameter>, as described below) with target
corresponding to the requested texture cube map face as indicated by the
table presented below. <parameter>pixels</parameter> is offset
appropriately for each successive image.</para>
<informaltable>
<tgroup cols="2">
<tbody>
<row>
<entry>Layer number</entry>
<entry>Cube Map Face</entry>
</row>
<row>
<entry>0</entry>
<entry><constant>GL_TEXTURE_CUBE_MAP_POSITIVE_X</constant></entry>
</row>
<row>
<entry>1</entry>
<entry><constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_X</constant></entry>
</row>
<row>
<entry>2</entry>
<entry><constant>GL_TEXTURE_CUBE_MAP_POSITIVE_Y</constant></entry>
</row>
<row>
<entry>3</entry>
<entry><constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_Y</constant></entry>
</row>
<row>
<entry>4</entry>
<entry><constant>GL_TEXTURE_CUBE_MAP_POSITIVE_Z</constant></entry>
</row>
<row>
<entry>5</entry>
<entry><constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_Z</constant></entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para><parameter>xoffset</parameter>, <parameter>yoffset</parameter> and
<parameter>zoffset</parameter> indicate the position of the subregion to
return. <parameter>width</parameter>, <parameter>height</parameter> and
<parameter>depth</parameter> indicate the size of the region to return.
These arguments have the same meaning as for
<function>glCompressedTexSubImage3D</function>, though there are extra
restrictions, described in the errors section below.</para>
<para>The mapping between the <parameter>xoffset</parameter>,
<parameter>yoffset</parameter>, <parameter>zoffset</parameter>,
<parameter>width</parameter>, <parameter>height</parameter> and
<parameter>depth</parameter> parameters and the faces, layers, and
layer-faces for cube map, array, and cube map array textures is the same
as for glGetTextureSubImage.</para>
<para>The <parameter>xoffset</parameter>, <parameter>yoffset</parameter>,
<parameter>zoffset</parameter> offsets and <parameter>width</parameter>,
<parameter>height</parameter> and <parameter>depth</parameter> sizes must
be multiples of the values of
<constant>GL_PACK_COMPRESSED_BLOCK_WIDTH</constant>,
<constant>GL_PACK_COMPRESSED_BLOCK_HEIGHT</constant>, and
<constant>GL_PACK_COMPRESSED_BLOCK_DEPTH</constant> respectively, unless
<parameter>offset</parameter> is zero and the corresponding
<parameter>size</parameter> is the same as the texture size in that
dimension.</para>
<para>Pixel storage modes are treated as for
<function>glGetCompressedTexSubImage</function>. The texel at
(<parameter>xoffset</parameter>, <parameter>yoffset</parameter>,
<parameter>zoffset</parameter>) will be stored at the location indicated
by <parameter>pixels</parameter> and the current pixel packing parameters.</para>
</refsect1>
<refsect1 xml:id="errors">
<title>Errors</title>
<para><constant>GL_INVALID_OPERATION</constant> error is generated if
<parameter>texture</parameter> is the name of a buffer or multisample
texture.</para>
<para><constant>GL_INVALID_OPERATION</constant> error is generated if the
buffer size required to store the requested data is greater than
<parameter>bufSize</parameter>.</para>
<para><constant>GL_INVALID_OPERATION</constant> error is generated if the
texture compression format is not based on fixed-size blocks.</para>
<para><constant>GL_INVALID_VALUE</constant> error is generated if
<parameter>texture</parameter> is not the name of an existing texture
object.</para>
<para><constant>GL_INVALID_VALUE</constant> is generated if
<parameter>xoffset</parameter>, <parameter>yoffset</parameter> or
<parameter>zoffset</parameter> are negative.</para>
<para><constant>GL_INVALID_VALUE</constant> is generated if
<parameter>xoffset</parameter> + <parameter>width</parameter> is greater
than the texture's width, <parameter>yoffset</parameter> +
<parameter>height</parameter> is greater than the texture's height, or
<parameter>zoffset</parameter> + <parameter>depth</parameter> is greater
than the texture's depth.</para>
<para><constant>GL_INVALID_VALUE</constant> error is generated if the
effective target is <constant>GL_TEXTURE_1D</constant> and either
<parameter>yoffset</parameter> is not zero, or
<parameter>height</parameter> is not one.</para>
<para><constant>GL_INVALID_VALUE</constant> error is generated if the
effective target is <constant>GL_TEXTURE_1D</constant>,
<constant>GL_TEXTURE_1D_ARRAY</constant>,
<constant>GL_TEXTURE_2D</constant> or
<constant>GL_TEXTURE_RECTANGLE</constant> and either
<parameter>zoffset</parameter> is not zero, or
<parameter>depth</parameter> is not one.</para>
<para><constant>GL_INVALID_VALUE</constant> error is generated if
<parameter>xoffset</parameter>, <parameter>yoffset</parameter> or
<parameter>zoffset</parameter> is not a multiple of the compressed block
width, height or depth respectively.</para>
<para><constant>GL_INVALID_VALUE</constant> error is generated if
<parameter>width</parameter>, <parameter>height</parameter> or
<parameter>depth</parameter> is not a multiple of the compressed block
width, height or depth respectively, unless the
<parameter>offset</parameter> is zero and the <parameter>size</parameter>
equals the texture image size.</para>
</refsect1>
<refsect1 xml:id="versions"><title>Version Support</title>
<informaltable>
<tgroup cols="13" align="left">
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apifunchead.xml" xpointer="xpointer(/*/*)"/>
<tbody>
<row>
<entry><function>glGetCompressedTextureSubImage</function></entry>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="apiversion.xml" xpointer="xpointer(/*/*[@role='45']/*)"/>
</row>
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 xml:id="seealso">
<title>See Also</title>
<para>
<citerefentry><refentrytitle>glCompressedTexImage1D</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glCompressedTexImage2D</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glCompressedTexImage3D</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glCompressedTexSubImage1D</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glCompressedTexSubImage2D</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glCompressedTexSubImage3D</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glGetCompressedTexImage</refentrytitle></citerefentry>,
<!-- FIX: link to glGetCompressedTexImage --> <function>glGetCompressedTextureImage</function>,
<citerefentry><refentrytitle>glReadPixels</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 xml:id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"/> 2014 Khronos Group.
This material may be distributed subject to the terms and conditions set forth in
the Open Publication License, v 1.0, 8 June 1999.
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://opencontent.org/openpub/">http://opencontent.org/openpub/</link>.
</para>
</refsect1>
</refentry>
|
