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327 lines
17 KiB
XML
327 lines
17 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
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<refentry id="glGetTexImage">
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<refentryinfo>
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<copyright>
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<year>1991-2006</year>
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<holder>Silicon Graphics, Inc.</holder>
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</copyright>
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<copyright>
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<year>2010-2013</year>
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<holder>Khronos Group</holder>
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</copyright>
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</refentryinfo>
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<refmeta>
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<refentrytitle>glGetTexImage</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glGetTexImage</refname>
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<refpurpose>return a texture image</refpurpose>
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</refnamediv>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glGetTexImage</function></funcdef>
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<paramdef>GLenum <parameter>target</parameter></paramdef>
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<paramdef>GLint <parameter>level</parameter></paramdef>
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<paramdef>GLenum <parameter>format</parameter></paramdef>
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<paramdef>GLenum <parameter>type</parameter></paramdef>
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<paramdef>GLvoid * <parameter>img</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1 id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>target</parameter></term>
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<listitem>
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<para>
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Specifies which texture is to be obtained.
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<constant>GL_TEXTURE_1D</constant>,
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<constant>GL_TEXTURE_2D</constant>,
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<constant>GL_TEXTURE_3D</constant>,
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<constant>GL_TEXTURE_1D_ARRAY</constant>,
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<constant>GL_TEXTURE_2D_ARRAY</constant>,
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<constant>GL_TEXTURE_RECTANGLE</constant>,
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<constant>GL_TEXTURE_CUBE_MAP_POSITIVE_X</constant>,
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<constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_X</constant>,
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<constant>GL_TEXTURE_CUBE_MAP_POSITIVE_Y</constant>,
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<constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_Y</constant>,
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<constant>GL_TEXTURE_CUBE_MAP_POSITIVE_Z</constant>, and
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<constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_Z</constant>
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are accepted.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>level</parameter></term>
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<listitem>
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<para>
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Specifies the level-of-detail number of the desired image.
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Level 0 is the base image level.
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Level
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<inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
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is the
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<inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>th
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mipmap reduction image.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>format</parameter></term>
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<listitem>
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<para>
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Specifies a pixel format for the returned data.
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The supported formats are
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<constant>GL_STENCIL_INDEX</constant>,
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<constant>GL_DEPTH_COMPONENT</constant>,
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<constant>GL_DEPTH_STENCIL</constant>,
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<constant>GL_RED</constant>,
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<constant>GL_GREEN</constant>,
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<constant>GL_BLUE</constant>,
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<constant>GL_RG</constant>,
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<constant>GL_RGB</constant>,
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<constant>GL_RGBA</constant>,
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<constant>GL_BGR</constant>,
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<constant>GL_BGRA</constant>,
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<constant>GL_RED_INTEGER</constant>,
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<constant>GL_GREEN_INTEGER</constant>,
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<constant>GL_BLUE_INTEGER</constant>,
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<constant>GL_RG_INTEGER</constant>,
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<constant>GL_RGB_INTEGER</constant>,
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<constant>GL_RGBA_INTEGER</constant>,
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<constant>GL_BGR_INTEGER</constant>,
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<constant>GL_BGRA_INTEGER</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>type</parameter></term>
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<listitem>
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<para>
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Specifies a pixel type for the returned data.
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The supported types are
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<constant>GL_UNSIGNED_BYTE</constant>,
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<constant>GL_BYTE</constant>,
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<constant>GL_UNSIGNED_SHORT</constant>,
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<constant>GL_SHORT</constant>,
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<constant>GL_UNSIGNED_INT</constant>,
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<constant>GL_INT</constant>,
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<constant>GL_HALF_FLOAT</constant>,
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<constant>GL_FLOAT</constant>,
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<constant>GL_UNSIGNED_BYTE_3_3_2</constant>,
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<constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>,
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<constant>GL_UNSIGNED_SHORT_5_6_5</constant>,
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<constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant>,
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<constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>,
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<constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>,
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<constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>,
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<constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>,
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<constant>GL_UNSIGNED_INT_8_8_8_8</constant>,
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<constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>,
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<constant>GL_UNSIGNED_INT_10_10_10_2</constant>,
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<constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant>,
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<constant>GL_UNSIGNED_INT_24_8</constant>,
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<constant>GL_UNSIGNED_INT_10F_11F_11F_REV</constant>,
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<constant>GL_UNSIGNED_INT_5_9_9_9_REV</constant>, and
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<constant>GL_FLOAT_32_UNSIGNED_INT_24_8_REV</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>img</parameter></term>
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<listitem>
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<para>
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Returns the texture image.
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Should be a pointer to an array of the type specified by <parameter>type</parameter>.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="description"><title>Description</title>
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<para>
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<function>glGetTexImage</function> returns a texture image into <parameter>img</parameter>.
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<parameter>target</parameter> specifies whether the desired texture image is one specified by
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<citerefentry><refentrytitle>glTexImage1D</refentrytitle></citerefentry> (<constant>GL_TEXTURE_1D</constant>),
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<citerefentry><refentrytitle>glTexImage2D</refentrytitle></citerefentry> (<constant>GL_TEXTURE_1D_ARRAY</constant>, <constant>GL_TEXTURE_RECTANGLE</constant>,
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<constant>GL_TEXTURE_2D</constant> or any of
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<constant>GL_TEXTURE_CUBE_MAP_*</constant>),
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or
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<citerefentry><refentrytitle>glTexImage3D</refentrytitle></citerefentry> (<constant>GL_TEXTURE_2D_ARRAY</constant>,
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<constant>GL_TEXTURE_3D</constant>).
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<parameter>level</parameter> specifies the level-of-detail number of the desired image.
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<parameter>format</parameter> and <parameter>type</parameter> specify the format and type of the desired image array.
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See the reference page for <citerefentry><refentrytitle>glTexImage1D</refentrytitle></citerefentry>
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for a description of the acceptable values for the <parameter>format</parameter> and <parameter>type</parameter>
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parameters, respectively.
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</para>
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<para>
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If a non-zero named buffer object is bound to the <constant>GL_PIXEL_PACK_BUFFER</constant> target
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(see <citerefentry><refentrytitle>glBindBuffer</refentrytitle></citerefentry>) while a texture image is
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requested, <parameter>img</parameter> is treated as a byte offset into the buffer object's data store.
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</para>
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<para>
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To understand the operation of <function>glGetTexImage</function>, consider the selected internal
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four-component texture image to be an RGBA color buffer the size of the image.
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The semantics of <function>glGetTexImage</function> are then identical to those of <citerefentry><refentrytitle>glReadPixels</refentrytitle></citerefentry>,
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with the exception that no pixel transfer operations are performed,
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when called with the same <parameter>format</parameter> and <parameter>type</parameter>,
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with <emphasis>x</emphasis> and <emphasis>y</emphasis> set to 0,
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<emphasis>width</emphasis> set to the width of the texture image
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and <emphasis>height</emphasis> set to 1 for 1D images,
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or to the height of the texture image
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for 2D images.
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</para>
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<para>
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If the selected texture image does not contain four components,
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the following mappings are applied.
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Single-component textures are treated as RGBA buffers with red set
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to the single-component value,
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green set to 0, blue set to 0, and alpha set to 1.
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Two-component textures are treated as RGBA buffers with red set to
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the value of component zero,
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alpha set to the value of component one,
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and green and blue set to 0.
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Finally,
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three-component textures are treated as RGBA buffers with red set to
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component zero,
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green set to component one,
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blue set to component two,
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and alpha set to 1.
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</para>
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<para>
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To determine the required size of <parameter>img</parameter>,
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use <citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> to determine the dimensions of the
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internal texture image,
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then scale the required number of pixels by the storage required for
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each pixel,
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based on <parameter>format</parameter> and <parameter>type</parameter>.
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Be sure to take the pixel storage parameters into account,
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especially <constant>GL_PACK_ALIGNMENT</constant>.
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</para>
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</refsect1>
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<refsect1 id="notes"><title>Notes</title>
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<para>
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If an error is generated,
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no change is made to the contents of <parameter>img</parameter>.
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</para>
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<para>
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<function>glGetTexImage</function> returns the texture image for the active texture unit.
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</para>
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<para>
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<constant>GL_STENCIL_INDEX</constant> is accepted for <parameter>format</parameter> only if the GL
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version is 4.4 or greater.
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</para>
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</refsect1>
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<refsect1 id="errors"><title>Errors</title>
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<para>
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<constant>GL_INVALID_ENUM</constant> is generated if <parameter>target</parameter>, <parameter>format</parameter>, or <parameter>type</parameter> is not
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an accepted value.
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</para>
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<para>
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<constant>GL_INVALID_VALUE</constant> is generated if <parameter>level</parameter> is less than 0.
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</para>
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<para>
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<constant>GL_INVALID_VALUE</constant> may be generated if <parameter>level</parameter> is greater
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than
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<inlineequation><mml:math>
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<!-- eqn: log sub 2 (max): -->
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<mml:mrow>
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<mml:msub><mml:mi mathvariant="italic">log</mml:mi>
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<mml:mn>2</mml:mn>
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</mml:msub>
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<mml:mo>⁡</mml:mo>
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<mml:mfenced open="(" close=")">
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<mml:mi mathvariant="italic">max</mml:mi>
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</mml:mfenced>
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</mml:mrow>
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</mml:math></inlineequation>,
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where
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<inlineequation><mml:math><mml:mi mathvariant="italic">max</mml:mi></mml:math></inlineequation>
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is the returned value of <constant>GL_MAX_TEXTURE_SIZE</constant>.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <parameter>type</parameter> is one of
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<constant>GL_UNSIGNED_BYTE_3_3_2</constant>,
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<constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>,
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<constant>GL_UNSIGNED_SHORT_5_6_5</constant>,
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<constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant>, or
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<constant>GL_UNSIGNED_INT_10F_11F_11F_REV</constant> and <parameter>format</parameter> is not <constant>GL_RGB</constant>.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <parameter>type</parameter> is one of
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<constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>,
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<constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>,
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<constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>,
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<constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>,
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<constant>GL_UNSIGNED_INT_8_8_8_8</constant>,
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<constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>,
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<constant>GL_UNSIGNED_INT_10_10_10_2</constant>,
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<constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant>, or
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<constant>GL_UNSIGNED_INT_5_9_9_9_REV</constant> and <parameter>format</parameter> is neither <constant>GL_RGBA</constant>
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or <constant>GL_BGRA</constant>.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <parameter>format</parameter> is
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<constant>GL_STENCIL_INDEX</constant> and the base internal format is not <constant>GL_STENCIL_INDEX</constant>
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or <constant>GL_DEPTH_STENCIL</constant>.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
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<constant>GL_PIXEL_PACK_BUFFER</constant> target and the buffer object's data store is currently mapped.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
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<constant>GL_PIXEL_PACK_BUFFER</constant> target and the data would be packed to the buffer
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object such that the memory writes required would exceed the data store size.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
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<constant>GL_PIXEL_PACK_BUFFER</constant> target and <parameter>img</parameter> is not evenly divisible
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into the number of bytes needed to store in memory a datum indicated by <parameter>type</parameter>.
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</para>
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</refsect1>
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<refsect1 id="associatedgets"><title>Associated Gets</title>
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<para>
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<citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> with argument <constant>GL_TEXTURE_WIDTH</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> with argument <constant>GL_TEXTURE_HEIGHT</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> with argument <constant>GL_TEXTURE_INTERNAL_FORMAT</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with arguments <constant>GL_PACK_ALIGNMENT</constant> and others
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_PIXEL_PACK_BUFFER_BINDING</constant>
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</para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para>
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<citerefentry><refentrytitle>glActiveTexture</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glReadPixels</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexImage1D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexImage2D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexImage3D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexSubImage1D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexSubImage2D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexSubImage3D</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glTexParameter</refentrytitle></citerefentry>
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</para>
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</refsect1>
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<refsect1 id="Copyright"><title>Copyright</title>
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<para>
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Copyright <trademark class="copyright"></trademark> 1991-2006 Silicon Graphics, Inc.
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Copyright <trademark class="copyright"></trademark> 2010-2013 Khronos Group.
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This document is licensed under the SGI
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Free Software B License. For details, see
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<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
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</para>
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</refsect1>
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</refentry>
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