upstream-doc/man2/glGetTexImage.xml

   1 <?xml version="1.0" encoding="UTF-8"?>
   2 <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
   3               "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
   4 <refentry id="glGetTexImage">
   5     <refmeta>
   6         <refmetainfo>
   7             <copyright>
   8                 <year>1991-2006</year>
   9                 <holder>Silicon Graphics, Inc.</holder>
  10             </copyright>
  11         </refmetainfo>
  12         <refentrytitle>glGetTexImage</refentrytitle>
  13         <manvolnum>3G</manvolnum>
  14     </refmeta>
  15     <refnamediv>
  16         <refname>glGetTexImage</refname>
  17         <refpurpose>return a texture image</refpurpose>
  18     </refnamediv>
  19     <refsynopsisdiv><title>C Specification</title>
  20         <funcsynopsis>
  21             <funcprototype>
  22                 <funcdef>void <function>glGetTexImage</function></funcdef>
  23                 <paramdef>GLenum <parameter>target</parameter></paramdef>
  24                 <paramdef>GLint <parameter>level</parameter></paramdef>
  25                 <paramdef>GLenum <parameter>format</parameter></paramdef>
  26                 <paramdef>GLenum <parameter>type</parameter></paramdef>
  27                 <paramdef>GLvoid * <parameter>img</parameter></paramdef>
  28             </funcprototype>
  29         </funcsynopsis>
  30     </refsynopsisdiv>
  31     <!-- eqn: ignoring delim $$ -->
  32     <refsect1 id="parameters"><title>Parameters</title>
  33         <variablelist>
  34         <varlistentry>
  35             <term><parameter>target</parameter></term>
  36             <listitem>
  37                 <para>
  38                     Specifies which texture is to be obtained.
  39                     <constant>GL_TEXTURE_1D</constant>, <constant>GL_TEXTURE_2D</constant>, <constant>GL_TEXTURE_3D</constant>,
  40                     <constant>GL_TEXTURE_CUBE_MAP_POSITIVE_X</constant>,
  41                     <constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_X</constant>,
  42                     <constant>GL_TEXTURE_CUBE_MAP_POSITIVE_Y</constant>,
  43                     <constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_Y</constant>,
  44                     <constant>GL_TEXTURE_CUBE_MAP_POSITIVE_Z</constant>, and
  45                     <constant>GL_TEXTURE_CUBE_MAP_NEGATIVE_Z</constant>
  46                     are accepted.
  47                 </para>
  48             </listitem>
  49         </varlistentry>
  50         <varlistentry>
  51             <term><parameter>level</parameter></term>
  52             <listitem>
  53                 <para>
  54                     Specifies the level-of-detail number of the desired image.
  55                     Level 0 is the base image level.
  56                     Level
  57                     <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>
  58                     is the
  59                     <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation>th
  60                     mipmap reduction image.
  61                 </para>
  62             </listitem>
  63         </varlistentry>
  64         <varlistentry>
  65             <term><parameter>format</parameter></term>
  66             <listitem>
  67                 <para>
  68                     Specifies a pixel format for the returned data.
  69                     The supported formats are
  70                     <constant>GL_RED</constant>,
  71                     <constant>GL_GREEN</constant>,
  72                     <constant>GL_BLUE</constant>,
  73                     <constant>GL_ALPHA</constant>,
  74                     <constant>GL_RGB</constant>,
  75                     <constant>GL_BGR</constant>,
  76                     <constant>GL_RGBA</constant>,
  77                     <constant>GL_BGRA</constant>,
  78                     <constant>GL_LUMINANCE</constant>, and
  79                     <constant>GL_LUMINANCE_ALPHA</constant>.
  80                 </para>
  81             </listitem>
  82         </varlistentry>
  83         <varlistentry>
  84             <term><parameter>type</parameter></term>
  85             <listitem>
  86                 <para>
  87                     Specifies a pixel type for the returned data.
  88                     The supported types are
  89                     <constant>GL_UNSIGNED_BYTE</constant>,
  90                     <constant>GL_BYTE</constant>,
  91                     <constant>GL_UNSIGNED_SHORT</constant>,
  92                     <constant>GL_SHORT</constant>,
  93                     <constant>GL_UNSIGNED_INT</constant>,
  94                     <constant>GL_INT</constant>,
  95                     <constant>GL_FLOAT</constant>,
  96                     <constant>GL_UNSIGNED_BYTE_3_3_2</constant>,
  97                     <constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>,
  98                     <constant>GL_UNSIGNED_SHORT_5_6_5</constant>,
  99                     <constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant>,
 100                     <constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>,
 101                     <constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>,
 102                     <constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>,
 103                     <constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>,
 104                     <constant>GL_UNSIGNED_INT_8_8_8_8</constant>,
 105                     <constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>,
 106                     <constant>GL_UNSIGNED_INT_10_10_10_2</constant>, and
 107                     <constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant>.
 108                 </para>
 109             </listitem>
 110         </varlistentry>
 111         <varlistentry>
 112             <term><parameter>img</parameter></term>
 113             <listitem>
 114                 <para>
 115                     Returns the texture image.
 116                     Should be a pointer to an array of the type specified by <parameter>type</parameter>.
 117                 </para>
 118             </listitem>
 119         </varlistentry>
 120         </variablelist>
 121     </refsect1>
 122     <refsect1 id="description"><title>Description</title>
 123         <para>
 124             <function>glGetTexImage</function> returns a texture image into <parameter>img</parameter>.
 125             <parameter>target</parameter> specifies whether the desired texture image is one specified by
 126             <citerefentry><refentrytitle>glTexImage1D</refentrytitle></citerefentry> (<constant>GL_TEXTURE_1D</constant>),
 127             <citerefentry><refentrytitle>glTexImage2D</refentrytitle></citerefentry> (<constant>GL_TEXTURE_2D</constant> or any of
 128             <constant>GL_TEXTURE_CUBE_MAP_*</constant>),
 129             or
 130             <citerefentry><refentrytitle>glTexImage3D</refentrytitle></citerefentry> (<constant>GL_TEXTURE_3D</constant>).
 131             <parameter>level</parameter> specifies the level-of-detail number of the desired image.
 132             <parameter>format</parameter> and <parameter>type</parameter> specify the format and type of the desired image array.
 133             See the reference pages <citerefentry><refentrytitle>glTexImage1D</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glDrawPixels</refentrytitle></citerefentry>
 134             for a description of the acceptable values for the <parameter>format</parameter> and <parameter>type</parameter>
 135             parameters, respectively.
 136         </para>
 137         <para>
 138             If a non-zero named buffer object is bound to the <constant>GL_PIXEL_PACK_BUFFER</constant> target
 139             (see <citerefentry><refentrytitle>glBindBuffer</refentrytitle></citerefentry>) while a texture image is
 140             requested, <parameter>img</parameter> is treated as a byte offset into the buffer object's data store.
 141         </para>
 142         <para>
 143             To understand the operation of <function>glGetTexImage</function>, consider the selected internal
 144             four-component texture image to be an RGBA color buffer the size of the image.
 145             The semantics of <function>glGetTexImage</function> are then identical to those of <citerefentry><refentrytitle>glReadPixels</refentrytitle></citerefentry>,
 146             with the exception that no pixel transfer operations are performed,
 147             when called with the same <parameter>format</parameter> and <parameter>type</parameter>,
 148             with <emphasis>x</emphasis> and <emphasis>y</emphasis> set to 0,
 149             <emphasis>width</emphasis> set to the width of the texture image
 150             (including border if one was specified),
 151             and <emphasis>height</emphasis> set to 1 for 1D images,
 152             or to the height of the texture image
 153             (including border if one was specified)
 154             for 2D images.
 155             Because the internal texture image is an RGBA image,
 156             pixel formats <constant>GL_COLOR_INDEX</constant>,
 157             <constant>GL_STENCIL_INDEX</constant>,
 158             and <constant>GL_DEPTH_COMPONENT</constant> are not accepted,
 159             and pixel type <constant>GL_BITMAP</constant> is not accepted.
 160         </para>
 161         <para>
 162             If the selected texture image does not contain four components,
 163             the following mappings are applied.
 164             Single-component textures are treated as RGBA buffers with red set
 165             to the single-component value,
 166             green set to 0, blue set to 0, and alpha set to 1.
 167             Two-component textures are treated as RGBA buffers with red set to
 168             the value of component zero,
 169             alpha set to the value of component one,
 170             and green and blue set to 0.
 171             Finally,
 172             three-component textures are treated as RGBA buffers with red set to
 173             component zero,
 174             green set to component one,
 175             blue set to component two,
 176             and alpha set to 1.
 177         </para>
 178         <para>
 179             To determine the required size of <parameter>img</parameter>,
 180             use <citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> to determine the dimensions of the
 181             internal texture image,
 182             then scale the required number of pixels by the storage required for
 183             each pixel,
 184             based on <parameter>format</parameter> and <parameter>type</parameter>.
 185             Be sure to take the pixel storage parameters into account,
 186             especially <constant>GL_PACK_ALIGNMENT</constant>.
 187         </para>
 188     </refsect1>
 189     <refsect1 id="notes"><title>Notes</title>
 190         <para>
 191             If an error is generated,
 192             no change is made to the contents of <parameter>img</parameter>.
 193         </para>
 194         <para>
 195             The types <constant>GL_UNSIGNED_BYTE_3_3_2</constant>,
 196             <constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>,
 197             <constant>GL_UNSIGNED_SHORT_5_6_5</constant>,
 198             <constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant>,
 199             <constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>,
 200             <constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>,
 201             <constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>,
 202             <constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>,
 203             <constant>GL_UNSIGNED_INT_8_8_8_8</constant>,
 204             <constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>,
 205             <constant>GL_UNSIGNED_INT_10_10_10_2</constant>,
 206             <constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant>,
 207             and the formats
 208             <constant>GL_BGR</constant>, and <constant>GL_BGRA</constant> are available only if the GL version is
 209             1.2 or greater.
 210         </para>
 211         <para>
 212             For OpenGL versions 1.3 and greater, or when the <code>ARB_multitexture</code> extension is supported, <function>glGetTexImage</function> returns
 213             the texture image for the active texture unit.
 214         </para>
 215     </refsect1>
 216     <refsect1 id="errors"><title>Errors</title>
 217         <para>
 218             <constant>GL_INVALID_ENUM</constant> is generated if <parameter>target</parameter>, <parameter>format</parameter>, or <parameter>type</parameter> is not
 219             an accepted value.
 220         </para>
 221         <para>
 222             <constant>GL_INVALID_VALUE</constant> is generated if <parameter>level</parameter> is less than 0.
 223         </para>
 224         <para>
 225             <constant>GL_INVALID_VALUE</constant> may be generated if <parameter>level</parameter> is greater
 226             than
 227             <inlineequation><mml:math>
 228                 <!-- eqn: log sub 2 (max):-->
 229                 <mml:mrow>
 230                     <mml:msub><mml:mi mathvariant="italic">log</mml:mi>
 231                     <mml:mn>2</mml:mn>
 232                     </mml:msub>
 233                     <mml:mo>&af;</mml:mo>
 234                     <mml:mfenced open="(" close=")">
 235                         <mml:mi mathvariant="italic">max</mml:mi>
 236                     </mml:mfenced>
 237                 </mml:mrow>
 238             </mml:math></inlineequation>,
 239             where
 240             <inlineequation><mml:math><mml:mi mathvariant="italic">max</mml:mi></mml:math></inlineequation>
 241             is the returned value of <constant>GL_MAX_TEXTURE_SIZE</constant>.
 242         </para>
 243         <para>
 244             <constant>GL_INVALID_OPERATION</constant> is returned if <parameter>type</parameter> is one of
 245             <constant>GL_UNSIGNED_BYTE_3_3_2</constant>,
 246             <constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>,
 247             <constant>GL_UNSIGNED_SHORT_5_6_5</constant>, or
 248             <constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant> and <parameter>format</parameter> is not <constant>GL_RGB</constant>.
 249         </para>
 250         <para>
 251             <constant>GL_INVALID_OPERATION</constant> is returned if <parameter>type</parameter> is one of
 252             <constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>,
 253             <constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>,
 254             <constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>,
 255             <constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>,
 256             <constant>GL_UNSIGNED_INT_8_8_8_8</constant>,
 257             <constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>,
 258             <constant>GL_UNSIGNED_INT_10_10_10_2</constant>, or
 259             <constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant>, and <parameter>format</parameter> is neither <constant>GL_RGBA</constant>
 260             or <constant>GL_BGRA</constant>.
 261         </para>
 262         <para>
 263             <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
 264             <constant>GL_PIXEL_PACK_BUFFER</constant> target and the buffer object's data store is currently mapped.
 265         </para>
 266         <para>
 267             <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
 268             <constant>GL_PIXEL_PACK_BUFFER</constant> target and the data would be packed to the buffer
 269             object such that the memory writes required would exceed the data store size.
 270         </para>
 271         <para>
 272             <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the
 273             <constant>GL_PIXEL_PACK_BUFFER</constant> target and <parameter>img</parameter> is not evenly divisible
 274             into the number of bytes needed to store in memory a datum indicated by <parameter>type</parameter>.
 275         </para>
 276         <para>
 277             <constant>GL_INVALID_OPERATION</constant> is generated if <function>glGetTexImage</function>
 278             is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
 279             and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.
 280         </para>
 281     </refsect1>
 282     <refsect1 id="associatedgets"><title>Associated Gets</title>
 283         <para>
 284             <citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> with argument <constant>GL_TEXTURE_WIDTH</constant>
 285         </para>
 286         <para>
 287             <citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> with argument <constant>GL_TEXTURE_HEIGHT</constant>
 288         </para>
 289         <para>
 290             <citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> with argument <constant>GL_TEXTURE_BORDER</constant>
 291         </para>
 292         <para>
 293             <citerefentry><refentrytitle>glGetTexLevelParameter</refentrytitle></citerefentry> with argument <constant>GL_TEXTURE_INTERNAL_FORMAT</constant>
 294         </para>
 295         <para>
 296             <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with arguments <constant>GL_PACK_ALIGNMENT</constant> and others
 297         </para>
 298         <para>
 299             <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_PIXEL_PACK_BUFFER_BINDING</constant>
 300         </para>
 301     </refsect1>
 302     <refsect1 id="seealso"><title>See Also</title>
 303         <para>
 304             <citerefentry><refentrytitle>glActiveTexture</refentrytitle></citerefentry>,
 305             <citerefentry><refentrytitle>glDrawPixels</refentrytitle></citerefentry>,
 306             <citerefentry><refentrytitle>glReadPixels</refentrytitle></citerefentry>,
 307             <citerefentry><refentrytitle>glTexEnv</refentrytitle></citerefentry>,
 308             <citerefentry><refentrytitle>glTexGen</refentrytitle></citerefentry>,
 309             <citerefentry><refentrytitle>glTexImage1D</refentrytitle></citerefentry>,
 310             <citerefentry><refentrytitle>glTexImage2D</refentrytitle></citerefentry>,
 311             <citerefentry><refentrytitle>glTexImage3D</refentrytitle></citerefentry>,
 312             <citerefentry><refentrytitle>glTexSubImage1D</refentrytitle></citerefentry>,
 313             <citerefentry><refentrytitle>glTexSubImage2D</refentrytitle></citerefentry>,
 314             <citerefentry><refentrytitle>glTexSubImage3D</refentrytitle></citerefentry>,
 315             <citerefentry><refentrytitle>glTexParameter</refentrytitle></citerefentry>
 316         </para>
 317     </refsect1>
 318     <refsect1 id="Copyright"><title>Copyright</title>
 319         <para>
 320             Copyright <trademark class="copyright"></trademark> 1991-2006
 321             Silicon Graphics, Inc. This document is licensed under the SGI
 322             Free Software B License. For details, see
 323             <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
 324         </para>
 325     </refsect1>
 326 </refentry>