| 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="glReadPixels"> |
| 5 | <refmeta> |
| 6 | <refmetainfo> |
| 7 | <copyright> |
| 8 | <year>1991-2006</year> |
| 9 | <holder>Silicon Graphics, Inc.</holder> |
| 10 | </copyright> |
| 11 | </refmetainfo> |
| 12 | <refentrytitle>glReadPixels</refentrytitle> |
| 13 | <manvolnum>3G</manvolnum> |
| 14 | </refmeta> |
| 15 | <refnamediv> |
| 16 | <refname>glReadPixels</refname> |
| 17 | <refpurpose>read a block of pixels from the frame buffer</refpurpose> |
| 18 | </refnamediv> |
| 19 | <refsynopsisdiv><title>C Specification</title> |
| 20 | <funcsynopsis> |
| 21 | <funcprototype> |
| 22 | <funcdef>void <function>glReadPixels</function></funcdef> |
| 23 | <paramdef>GLint <parameter>x</parameter></paramdef> |
| 24 | <paramdef>GLint <parameter>y</parameter></paramdef> |
| 25 | <paramdef>GLsizei <parameter>width</parameter></paramdef> |
| 26 | <paramdef>GLsizei <parameter>height</parameter></paramdef> |
| 27 | <paramdef>GLenum <parameter>format</parameter></paramdef> |
| 28 | <paramdef>GLenum <parameter>type</parameter></paramdef> |
| 29 | <paramdef>GLvoid * <parameter>data</parameter></paramdef> |
| 30 | </funcprototype> |
| 31 | </funcsynopsis> |
| 32 | </refsynopsisdiv> |
| 33 | <!-- eqn: ignoring delim $$ --> |
| 34 | <refsect1 id="parameters"><title>Parameters</title> |
| 35 | <variablelist> |
| 36 | <varlistentry> |
| 37 | <term><parameter>x</parameter></term> |
| 38 | <term><parameter>y</parameter></term> |
| 39 | <listitem> |
| 40 | <para> |
| 41 | Specify the window coordinates of the first pixel |
| 42 | that is read from the frame buffer. |
| 43 | This location is the lower left corner of a rectangular block of pixels. |
| 44 | </para> |
| 45 | </listitem> |
| 46 | </varlistentry> |
| 47 | <varlistentry> |
| 48 | <term><parameter>width</parameter></term> |
| 49 | <term><parameter>height</parameter></term> |
| 50 | <listitem> |
| 51 | <para> |
| 52 | Specify the dimensions of the pixel rectangle. |
| 53 | <parameter>width</parameter> and <parameter>height</parameter> of one correspond to a single pixel. |
| 54 | </para> |
| 55 | </listitem> |
| 56 | </varlistentry> |
| 57 | <varlistentry> |
| 58 | <term><parameter>format</parameter></term> |
| 59 | <listitem> |
| 60 | <para> |
| 61 | Specifies the format of the pixel data. |
| 62 | The following symbolic values are accepted: |
| 63 | <constant>GL_COLOR_INDEX</constant>, |
| 64 | <constant>GL_STENCIL_INDEX</constant>, |
| 65 | <constant>GL_DEPTH_COMPONENT</constant>, |
| 66 | <constant>GL_RED</constant>, |
| 67 | <constant>GL_GREEN</constant>, |
| 68 | <constant>GL_BLUE</constant>, |
| 69 | <constant>GL_ALPHA</constant>, |
| 70 | <constant>GL_RGB</constant>, |
| 71 | <constant>GL_BGR</constant>, |
| 72 | <constant>GL_RGBA</constant>, |
| 73 | <constant>GL_BGRA</constant>, |
| 74 | <constant>GL_LUMINANCE</constant>, and |
| 75 | <constant>GL_LUMINANCE_ALPHA</constant>. |
| 76 | </para> |
| 77 | </listitem> |
| 78 | </varlistentry> |
| 79 | <varlistentry> |
| 80 | <term><parameter>type</parameter></term> |
| 81 | <listitem> |
| 82 | <para> |
| 83 | Specifies the data type of the pixel data. |
| 84 | Must be one of |
| 85 | <constant>GL_UNSIGNED_BYTE</constant>, |
| 86 | <constant>GL_BYTE</constant>, |
| 87 | <constant>GL_BITMAP</constant>, |
| 88 | <constant>GL_UNSIGNED_SHORT</constant>, |
| 89 | <constant>GL_SHORT</constant>, |
| 90 | <constant>GL_UNSIGNED_INT</constant>, |
| 91 | <constant>GL_INT</constant>, |
| 92 | <constant>GL_FLOAT</constant>, |
| 93 | <constant>GL_UNSIGNED_BYTE_3_3_2</constant>, |
| 94 | <constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>, |
| 95 | <constant>GL_UNSIGNED_SHORT_5_6_5</constant>, |
| 96 | <constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant>, |
| 97 | <constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>, |
| 98 | <constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>, |
| 99 | <constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>, |
| 100 | <constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>, |
| 101 | <constant>GL_UNSIGNED_INT_8_8_8_8</constant>, |
| 102 | <constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>, |
| 103 | <constant>GL_UNSIGNED_INT_10_10_10_2</constant>, or |
| 104 | <constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant>. |
| 105 | </para> |
| 106 | </listitem> |
| 107 | </varlistentry> |
| 108 | <varlistentry> |
| 109 | <term><parameter>data</parameter></term> |
| 110 | <listitem> |
| 111 | <para> |
| 112 | Returns the pixel data. |
| 113 | </para> |
| 114 | </listitem> |
| 115 | </varlistentry> |
| 116 | </variablelist> |
| 117 | </refsect1> |
| 118 | <refsect1 id="description"><title>Description</title> |
| 119 | <para> |
| 120 | <function>glReadPixels</function> returns pixel data from the frame buffer, |
| 121 | starting with the pixel whose lower left corner |
| 122 | is at location (<parameter>x</parameter>, <parameter>y</parameter>), |
| 123 | into client memory starting at location <parameter>data</parameter>. |
| 124 | Several parameters control the processing of the pixel data before |
| 125 | it is placed into client memory. |
| 126 | These parameters are set with three commands: |
| 127 | <citerefentry><refentrytitle>glPixelStore</refentrytitle></citerefentry>, |
| 128 | <citerefentry><refentrytitle>glPixelTransfer</refentrytitle></citerefentry>, and |
| 129 | <citerefentry><refentrytitle>glPixelMap</refentrytitle></citerefentry>. |
| 130 | This reference page describes the effects on <function>glReadPixels</function> of most, |
| 131 | but not all of the parameters specified by these three commands. |
| 132 | </para> |
| 133 | <para> |
| 134 | If a non-zero named buffer object is bound to the <constant>GL_PIXEL_PACK_BUFFER</constant> target |
| 135 | (see <citerefentry><refentrytitle>glBindBuffer</refentrytitle></citerefentry>) while a block of pixels is |
| 136 | requested, <parameter>data</parameter> is treated as a byte offset into the buffer object's data store |
| 137 | rather than a pointer to client memory. |
| 138 | </para> |
| 139 | <para> |
| 140 | When the <code>ARB_imaging</code> extension is supported, the pixel data may |
| 141 | be processed by additional operations including color table lookup, |
| 142 | color matrix transformations, convolutions, histograms, and minimum and |
| 143 | maximum pixel value computations. |
| 144 | </para> |
| 145 | <para> |
| 146 | <function>glReadPixels</function> returns values from each pixel with lower left corner at |
| 147 | <inlineequation><mml:math> |
| 148 | <!-- eqn: (x + i, y + j):--> |
| 149 | <mml:mfenced open="(" close=")"> |
| 150 | <mml:mrow> |
| 151 | <mml:mi mathvariant="italic">x</mml:mi> |
| 152 | <mml:mo>+</mml:mo> |
| 153 | <mml:mi mathvariant="italic">i</mml:mi> |
| 154 | </mml:mrow> |
| 155 | <mml:mrow> |
| 156 | <mml:mi mathvariant="italic">y</mml:mi> |
| 157 | <mml:mo>+</mml:mo> |
| 158 | <mml:mi mathvariant="italic">j</mml:mi> |
| 159 | </mml:mrow> |
| 160 | </mml:mfenced> |
| 161 | </mml:math></inlineequation> |
| 162 | for |
| 163 | <inlineequation><mml:math> |
| 164 | <!-- eqn: 0 <= i < width:--> |
| 165 | <mml:mrow> |
| 166 | <mml:mn>0</mml:mn> |
| 167 | <mml:mo><=</mml:mo> |
| 168 | <mml:mi mathvariant="italic">i</mml:mi> |
| 169 | <mml:mo><</mml:mo> |
| 170 | <mml:mi mathvariant="italic">width</mml:mi> |
| 171 | </mml:mrow> |
| 172 | </mml:math></inlineequation> |
| 173 | and |
| 174 | <inlineequation><mml:math> |
| 175 | <!-- eqn: 0 <= j < height:--> |
| 176 | <mml:mrow> |
| 177 | <mml:mn>0</mml:mn> |
| 178 | <mml:mo><=</mml:mo> |
| 179 | <mml:mi mathvariant="italic">j</mml:mi> |
| 180 | <mml:mo><</mml:mo> |
| 181 | <mml:mi mathvariant="italic">height</mml:mi> |
| 182 | </mml:mrow> |
| 183 | </mml:math></inlineequation>. |
| 184 | This pixel is said to be the |
| 185 | <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>th |
| 186 | pixel in the |
| 187 | <inlineequation><mml:math><mml:mi mathvariant="italic">j</mml:mi></mml:math></inlineequation>th |
| 188 | row. |
| 189 | Pixels are returned in row order from the lowest to the highest row, |
| 190 | left to right in each row. |
| 191 | </para> |
| 192 | <para> |
| 193 | <parameter>format</parameter> specifies the format for the returned pixel values; |
| 194 | accepted values are: |
| 195 | </para> |
| 196 | <variablelist> |
| 197 | <varlistentry> |
| 198 | <term><constant>GL_COLOR_INDEX</constant></term> |
| 199 | <listitem> |
| 200 | <para> |
| 201 | Color indices are read from the color buffer |
| 202 | selected by <citerefentry><refentrytitle>glReadBuffer</refentrytitle></citerefentry>. |
| 203 | Each index is converted to fixed point, |
| 204 | shifted left or right depending on the value and sign of <constant>GL_INDEX_SHIFT</constant>, |
| 205 | and added to <constant>GL_INDEX_OFFSET</constant>. |
| 206 | If <constant>GL_MAP_COLOR</constant> is <constant>GL_TRUE</constant>, |
| 207 | indices are replaced by their mappings in the table <constant>GL_PIXEL_MAP_I_TO_I</constant>. |
| 208 | </para> |
| 209 | </listitem> |
| 210 | </varlistentry> |
| 211 | <varlistentry> |
| 212 | <term><constant>GL_STENCIL_INDEX</constant></term> |
| 213 | <listitem> |
| 214 | <para> |
| 215 | Stencil values are read from the stencil buffer. |
| 216 | Each index is converted to fixed point, |
| 217 | shifted left or right depending on the value and sign of <constant>GL_INDEX_SHIFT</constant>, |
| 218 | and added to <constant>GL_INDEX_OFFSET</constant>. |
| 219 | If <constant>GL_MAP_STENCIL</constant> is <constant>GL_TRUE</constant>, |
| 220 | indices are replaced by their mappings in the table <constant>GL_PIXEL_MAP_S_TO_S</constant>. |
| 221 | </para> |
| 222 | </listitem> |
| 223 | </varlistentry> |
| 224 | <varlistentry> |
| 225 | <term><constant>GL_DEPTH_COMPONENT</constant></term> |
| 226 | <listitem> |
| 227 | <para> |
| 228 | Depth values are read from the depth buffer. |
| 229 | Each component is converted to floating point such that the minimum depth |
| 230 | value maps to 0 and the maximum value maps to 1. |
| 231 | Each component is then multiplied by <constant>GL_DEPTH_SCALE</constant>, |
| 232 | added to <constant>GL_DEPTH_BIAS</constant>, |
| 233 | and finally clamped to the range |
| 234 | <inlineequation><mml:math> |
| 235 | <!-- eqn: [0,1]:--> |
| 236 | <mml:mfenced open="[" close="]"> |
| 237 | <mml:mn>0</mml:mn> |
| 238 | <mml:mn>1</mml:mn> |
| 239 | </mml:mfenced> |
| 240 | </mml:math></inlineequation>. |
| 241 | </para> |
| 242 | </listitem> |
| 243 | </varlistentry> |
| 244 | <varlistentry> |
| 245 | <term><constant>GL_RED</constant></term> |
| 246 | <listitem> |
| 247 | </listitem> |
| 248 | </varlistentry> |
| 249 | <varlistentry> |
| 250 | <term><constant>GL_GREEN</constant></term> |
| 251 | <listitem> |
| 252 | </listitem> |
| 253 | </varlistentry> |
| 254 | <varlistentry> |
| 255 | <term><constant>GL_BLUE</constant></term> |
| 256 | <listitem> |
| 257 | </listitem> |
| 258 | </varlistentry> |
| 259 | <varlistentry> |
| 260 | <term><constant>GL_ALPHA</constant></term> |
| 261 | <listitem> |
| 262 | </listitem> |
| 263 | </varlistentry> |
| 264 | <varlistentry> |
| 265 | <term><constant>GL_RGB</constant></term> |
| 266 | <listitem> |
| 267 | </listitem> |
| 268 | </varlistentry> |
| 269 | <varlistentry> |
| 270 | <term><constant>GL_BGR</constant></term> |
| 271 | <listitem> |
| 272 | </listitem> |
| 273 | </varlistentry> |
| 274 | <varlistentry> |
| 275 | <term><constant>GL_RGBA</constant></term> |
| 276 | <listitem> |
| 277 | </listitem> |
| 278 | </varlistentry> |
| 279 | <varlistentry> |
| 280 | <term><constant>GL_BGRA</constant></term> |
| 281 | <listitem> |
| 282 | </listitem> |
| 283 | </varlistentry> |
| 284 | <varlistentry> |
| 285 | <term><constant>GL_LUMINANCE</constant></term> |
| 286 | <listitem> |
| 287 | </listitem> |
| 288 | </varlistentry> |
| 289 | <varlistentry> |
| 290 | <term><constant>GL_LUMINANCE_ALPHA</constant></term> |
| 291 | <listitem> |
| 292 | <para> |
| 293 | Processing differs depending on whether color buffers store color indices |
| 294 | or RGBA color components. |
| 295 | If color indices are stored, |
| 296 | they are read from the color buffer selected by <citerefentry><refentrytitle>glReadBuffer</refentrytitle></citerefentry>. |
| 297 | Each index is converted to fixed point, |
| 298 | shifted left or right depending on the value and sign of <constant>GL_INDEX_SHIFT</constant>, |
| 299 | and added to <constant>GL_INDEX_OFFSET</constant>. |
| 300 | Indices are then replaced by the red, |
| 301 | green, |
| 302 | blue, |
| 303 | and alpha values obtained by indexing the tables |
| 304 | <constant>GL_PIXEL_MAP_I_TO_R</constant>, |
| 305 | <constant>GL_PIXEL_MAP_I_TO_G</constant>, |
| 306 | <constant>GL_PIXEL_MAP_I_TO_B</constant>, and |
| 307 | <constant>GL_PIXEL_MAP_I_TO_A</constant>. |
| 308 | Each table must be of size |
| 309 | <inlineequation><mml:math> |
| 310 | <!-- eqn: 2 sup n:--> |
| 311 | <mml:msup><mml:mn>2</mml:mn> |
| 312 | <mml:mi mathvariant="italic">n</mml:mi> |
| 313 | </mml:msup> |
| 314 | </mml:math></inlineequation>, |
| 315 | but |
| 316 | <inlineequation><mml:math><mml:mi mathvariant="italic">n</mml:mi></mml:math></inlineequation> |
| 317 | may be different for |
| 318 | different tables. |
| 319 | Before an index is used to look up a value in a table of |
| 320 | size |
| 321 | <inlineequation><mml:math> |
| 322 | <!-- eqn: 2 sup n:--> |
| 323 | <mml:msup><mml:mn>2</mml:mn> |
| 324 | <mml:mi mathvariant="italic">n</mml:mi> |
| 325 | </mml:msup> |
| 326 | </mml:math></inlineequation>, |
| 327 | it must be masked against |
| 328 | <inlineequation><mml:math> |
| 329 | <!-- eqn: 2 sup n - 1:--> |
| 330 | <mml:mrow> |
| 331 | <mml:msup><mml:mn>2</mml:mn> |
| 332 | <mml:mi mathvariant="italic">n</mml:mi> |
| 333 | </mml:msup> |
| 334 | <mml:mo>-</mml:mo> |
| 335 | <mml:mn>1</mml:mn> |
| 336 | </mml:mrow> |
| 337 | </mml:math></inlineequation>. |
| 338 | </para> |
| 339 | <para> |
| 340 | If RGBA color components are stored in the color buffers, |
| 341 | they are read from the color buffer selected by <citerefentry><refentrytitle>glReadBuffer</refentrytitle></citerefentry>. |
| 342 | Each color component is converted to floating point such that zero intensity |
| 343 | maps to 0.0 and full intensity maps to 1.0. |
| 344 | Each component is then multiplied by <constant>GL_c_SCALE</constant> and |
| 345 | added to <constant>GL_c_BIAS</constant>, |
| 346 | where <emphasis>c</emphasis> is RED, GREEN, BLUE, or ALPHA. |
| 347 | Finally, |
| 348 | if <constant>GL_MAP_COLOR</constant> is <constant>GL_TRUE</constant>, |
| 349 | each component is clamped to the range |
| 350 | <inlineequation><mml:math> |
| 351 | <!-- eqn: [0,1]:--> |
| 352 | <mml:mfenced open="[" close="]"> |
| 353 | <mml:mn>0</mml:mn> |
| 354 | <mml:mn>1</mml:mn> |
| 355 | </mml:mfenced> |
| 356 | </mml:math></inlineequation>, |
| 357 | scaled to the size of its corresponding table, and is then |
| 358 | replaced by its mapping in the table |
| 359 | <constant>GL_PIXEL_MAP_c_TO_c</constant>, |
| 360 | where <emphasis>c</emphasis> is R, G, B, or A. |
| 361 | </para> |
| 362 | <para> |
| 363 | Unneeded data is then discarded. |
| 364 | For example, |
| 365 | <constant>GL_RED</constant> discards the green, blue, and alpha components, |
| 366 | while <constant>GL_RGB</constant> discards only the alpha component. |
| 367 | <constant>GL_LUMINANCE</constant> computes a single-component value as the sum of |
| 368 | the red, |
| 369 | green, |
| 370 | and blue components, |
| 371 | and <constant>GL_LUMINANCE_ALPHA</constant> does the same, |
| 372 | while keeping alpha as a second value. |
| 373 | The final values are clamped to the range |
| 374 | <inlineequation><mml:math> |
| 375 | <!-- eqn: [0,1]:--> |
| 376 | <mml:mfenced open="[" close="]"> |
| 377 | <mml:mn>0</mml:mn> |
| 378 | <mml:mn>1</mml:mn> |
| 379 | </mml:mfenced> |
| 380 | </mml:math></inlineequation>. |
| 381 | </para> |
| 382 | </listitem> |
| 383 | </varlistentry> |
| 384 | </variablelist> |
| 385 | <para> |
| 386 | The shift, |
| 387 | scale, |
| 388 | bias, |
| 389 | and lookup factors just described are all specified by |
| 390 | <citerefentry><refentrytitle>glPixelTransfer</refentrytitle></citerefentry>. |
| 391 | The lookup table contents themselves are specified by <citerefentry><refentrytitle>glPixelMap</refentrytitle></citerefentry>. |
| 392 | </para> |
| 393 | <para> |
| 394 | Finally, the indices or components |
| 395 | are converted to the proper format, |
| 396 | as specified by <parameter>type</parameter>. |
| 397 | If <parameter>format</parameter> is <constant>GL_COLOR_INDEX</constant> or <constant>GL_STENCIL_INDEX</constant> |
| 398 | and <parameter>type</parameter> is not <constant>GL_FLOAT</constant>, |
| 399 | each index is masked with the mask value given in the following table. |
| 400 | If <parameter>type</parameter> is <constant>GL_FLOAT</constant>, then each integer index is converted to |
| 401 | single-precision floating-point format. |
| 402 | </para> |
| 403 | <para> |
| 404 | If <parameter>format</parameter> is |
| 405 | <constant>GL_RED</constant>, |
| 406 | <constant>GL_GREEN</constant>, |
| 407 | <constant>GL_BLUE</constant>, |
| 408 | <constant>GL_ALPHA</constant>, |
| 409 | <constant>GL_RGB</constant>, |
| 410 | <constant>GL_BGR</constant>, |
| 411 | <constant>GL_RGBA</constant>, |
| 412 | <constant>GL_BGRA</constant>, |
| 413 | <constant>GL_LUMINANCE</constant>, or |
| 414 | <constant>GL_LUMINANCE_ALPHA</constant> and <parameter>type</parameter> is not <constant>GL_FLOAT</constant>, |
| 415 | each component is multiplied by the multiplier shown in the following table. |
| 416 | If type is <constant>GL_FLOAT</constant>, then each component is passed as is |
| 417 | (or converted to the client's single-precision floating-point format if |
| 418 | it is different from the one used by the GL). |
| 419 | </para> |
| 420 | <para> |
| 421 | </para> |
| 422 | <informaltable frame="topbot"> |
| 423 | <tgroup cols="3" align="left"> |
| 424 | <colspec/> |
| 425 | <colspec align="center"/> |
| 426 | <colspec align="center"/> |
| 427 | <thead> |
| 428 | <row> |
| 429 | <entry rowsep="1" align="left"> |
| 430 | <parameter>type</parameter> |
| 431 | </entry> |
| 432 | <entry rowsep="1" align="center"><emphasis role="bold"> |
| 433 | Index Mask |
| 434 | </emphasis></entry> |
| 435 | <entry rowsep="1" align="center"><emphasis role="bold"> |
| 436 | Component Conversion |
| 437 | </emphasis></entry> |
| 438 | </row> |
| 439 | </thead> |
| 440 | <tbody> |
| 441 | <row> |
| 442 | <entry align="left"> |
| 443 | <constant>GL_UNSIGNED_BYTE</constant> |
| 444 | </entry> |
| 445 | <entry align="center"> |
| 446 | <inlineequation><mml:math> |
| 447 | <!-- eqn: 2 sup 8 - 1:--> |
| 448 | <mml:mrow> |
| 449 | <mml:msup><mml:mn>2</mml:mn> |
| 450 | <mml:mn>8</mml:mn> |
| 451 | </mml:msup> |
| 452 | <mml:mo>-</mml:mo> |
| 453 | <mml:mn>1</mml:mn> |
| 454 | </mml:mrow> |
| 455 | </mml:math></inlineequation> |
| 456 | </entry> |
| 457 | <entry align="center"> |
| 458 | <inlineequation><mml:math> |
| 459 | <!-- eqn: (2 sup 8 - 1) c:--> |
| 460 | <mml:mrow> |
| 461 | <mml:mfenced open="(" close=")"> |
| 462 | <mml:mrow> |
| 463 | <mml:msup><mml:mn>2</mml:mn> |
| 464 | <mml:mn>8</mml:mn> |
| 465 | </mml:msup> |
| 466 | <mml:mo>-</mml:mo> |
| 467 | <mml:mn>1</mml:mn> |
| 468 | </mml:mrow> |
| 469 | </mml:mfenced> |
| 470 | <mml:mo>⁢</mml:mo> |
| 471 | <mml:mi mathvariant="italic">c</mml:mi> |
| 472 | </mml:mrow> |
| 473 | </mml:math></inlineequation> |
| 474 | </entry> |
| 475 | </row> |
| 476 | <row> |
| 477 | <entry align="left"> |
| 478 | <constant>GL_BYTE</constant> |
| 479 | </entry> |
| 480 | <entry align="center"> |
| 481 | <inlineequation><mml:math> |
| 482 | <!-- eqn: 2 sup 7 - 1:--> |
| 483 | <mml:mrow> |
| 484 | <mml:msup><mml:mn>2</mml:mn> |
| 485 | <mml:mn>7</mml:mn> |
| 486 | </mml:msup> |
| 487 | <mml:mo>-</mml:mo> |
| 488 | <mml:mn>1</mml:mn> |
| 489 | </mml:mrow> |
| 490 | </mml:math></inlineequation> |
| 491 | </entry> |
| 492 | <entry align="center"> |
| 493 | <inlineequation><mml:math> |
| 494 | <!-- eqn: {(2 sup 8 - 1) c - 1} / 2:--> |
| 495 | <mml:mfrac> |
| 496 | <mml:mfenced open="" close=""> |
| 497 | <mml:mrow> |
| 498 | <mml:mfenced open="(" close=")"> |
| 499 | <mml:mrow> |
| 500 | <mml:msup><mml:mn>2</mml:mn> |
| 501 | <mml:mn>8</mml:mn> |
| 502 | </mml:msup> |
| 503 | <mml:mo>-</mml:mo> |
| 504 | <mml:mn>1</mml:mn> |
| 505 | </mml:mrow> |
| 506 | </mml:mfenced> |
| 507 | <mml:mo>⁢</mml:mo> |
| 508 | <mml:mi mathvariant="italic">c</mml:mi> |
| 509 | <mml:mo>-</mml:mo> |
| 510 | <mml:mn>1</mml:mn> |
| 511 | </mml:mrow> |
| 512 | </mml:mfenced> |
| 513 | <mml:mn>2</mml:mn> |
| 514 | </mml:mfrac> |
| 515 | </mml:math></inlineequation> |
| 516 | </entry> |
| 517 | </row> |
| 518 | <row> |
| 519 | <entry align="left"> |
| 520 | <constant>GL_BITMAP</constant> |
| 521 | </entry> |
| 522 | <entry align="center"> |
| 523 | <inlineequation><mml:math> |
| 524 | <!-- eqn: 1:--> |
| 525 | <mml:mn>1</mml:mn> |
| 526 | </mml:math></inlineequation> |
| 527 | </entry> |
| 528 | <entry align="center"> |
| 529 | <inlineequation><mml:math> |
| 530 | <!-- eqn: 1:--> |
| 531 | <mml:mn>1</mml:mn> |
| 532 | </mml:math></inlineequation> |
| 533 | </entry> |
| 534 | </row> |
| 535 | <row> |
| 536 | <entry align="left"> |
| 537 | <constant>GL_UNSIGNED_SHORT</constant> |
| 538 | </entry> |
| 539 | <entry align="center"> |
| 540 | <inlineequation><mml:math> |
| 541 | <!-- eqn: 2 sup 16 - 1:--> |
| 542 | <mml:mrow> |
| 543 | <mml:msup><mml:mn>2</mml:mn> |
| 544 | <mml:mn>16</mml:mn> |
| 545 | </mml:msup> |
| 546 | <mml:mo>-</mml:mo> |
| 547 | <mml:mn>1</mml:mn> |
| 548 | </mml:mrow> |
| 549 | </mml:math></inlineequation> |
| 550 | </entry> |
| 551 | <entry align="center"> |
| 552 | <inlineequation><mml:math> |
| 553 | <!-- eqn: (2 sup 16 - 1) c:--> |
| 554 | <mml:mrow> |
| 555 | <mml:mfenced open="(" close=")"> |
| 556 | <mml:mrow> |
| 557 | <mml:msup><mml:mn>2</mml:mn> |
| 558 | <mml:mn>16</mml:mn> |
| 559 | </mml:msup> |
| 560 | <mml:mo>-</mml:mo> |
| 561 | <mml:mn>1</mml:mn> |
| 562 | </mml:mrow> |
| 563 | </mml:mfenced> |
| 564 | <mml:mo>⁢</mml:mo> |
| 565 | <mml:mi mathvariant="italic">c</mml:mi> |
| 566 | </mml:mrow> |
| 567 | </mml:math></inlineequation> |
| 568 | </entry> |
| 569 | </row> |
| 570 | <row> |
| 571 | <entry align="left"> |
| 572 | <constant>GL_SHORT</constant> |
| 573 | </entry> |
| 574 | <entry align="center"> |
| 575 | <inlineequation><mml:math> |
| 576 | <!-- eqn: 2 sup 15 - 1:--> |
| 577 | <mml:mrow> |
| 578 | <mml:msup><mml:mn>2</mml:mn> |
| 579 | <mml:mn>15</mml:mn> |
| 580 | </mml:msup> |
| 581 | <mml:mo>-</mml:mo> |
| 582 | <mml:mn>1</mml:mn> |
| 583 | </mml:mrow> |
| 584 | </mml:math></inlineequation> |
| 585 | </entry> |
| 586 | <entry align="center"> |
| 587 | <inlineequation><mml:math> |
| 588 | <!-- eqn: {(2 sup 16 - 1) c - 1} / 2:--> |
| 589 | <mml:mfrac> |
| 590 | <mml:mfenced open="" close=""> |
| 591 | <mml:mrow> |
| 592 | <mml:mfenced open="(" close=")"> |
| 593 | <mml:mrow> |
| 594 | <mml:msup><mml:mn>2</mml:mn> |
| 595 | <mml:mn>16</mml:mn> |
| 596 | </mml:msup> |
| 597 | <mml:mo>-</mml:mo> |
| 598 | <mml:mn>1</mml:mn> |
| 599 | </mml:mrow> |
| 600 | </mml:mfenced> |
| 601 | <mml:mo>⁢</mml:mo> |
| 602 | <mml:mi mathvariant="italic">c</mml:mi> |
| 603 | <mml:mo>-</mml:mo> |
| 604 | <mml:mn>1</mml:mn> |
| 605 | </mml:mrow> |
| 606 | </mml:mfenced> |
| 607 | <mml:mn>2</mml:mn> |
| 608 | </mml:mfrac> |
| 609 | </mml:math></inlineequation> |
| 610 | </entry> |
| 611 | </row> |
| 612 | <row> |
| 613 | <entry align="left"> |
| 614 | <constant>GL_UNSIGNED_INT</constant> |
| 615 | </entry> |
| 616 | <entry align="center"> |
| 617 | <inlineequation><mml:math> |
| 618 | <!-- eqn: 2 sup 32 - 1:--> |
| 619 | <mml:mrow> |
| 620 | <mml:msup><mml:mn>2</mml:mn> |
| 621 | <mml:mn>32</mml:mn> |
| 622 | </mml:msup> |
| 623 | <mml:mo>-</mml:mo> |
| 624 | <mml:mn>1</mml:mn> |
| 625 | </mml:mrow> |
| 626 | </mml:math></inlineequation> |
| 627 | </entry> |
| 628 | <entry align="center"> |
| 629 | <inlineequation><mml:math> |
| 630 | <!-- eqn: (2 sup 32 - 1) c:--> |
| 631 | <mml:mrow> |
| 632 | <mml:mfenced open="(" close=")"> |
| 633 | <mml:mrow> |
| 634 | <mml:msup><mml:mn>2</mml:mn> |
| 635 | <mml:mn>32</mml:mn> |
| 636 | </mml:msup> |
| 637 | <mml:mo>-</mml:mo> |
| 638 | <mml:mn>1</mml:mn> |
| 639 | </mml:mrow> |
| 640 | </mml:mfenced> |
| 641 | <mml:mo>⁢</mml:mo> |
| 642 | <mml:mi mathvariant="italic">c</mml:mi> |
| 643 | </mml:mrow> |
| 644 | </mml:math></inlineequation> |
| 645 | </entry> |
| 646 | </row> |
| 647 | <row> |
| 648 | <entry align="left"> |
| 649 | <constant>GL_INT</constant> |
| 650 | </entry> |
| 651 | <entry align="center"> |
| 652 | <inlineequation><mml:math> |
| 653 | <!-- eqn: 2 sup 31 - 1:--> |
| 654 | <mml:mrow> |
| 655 | <mml:msup><mml:mn>2</mml:mn> |
| 656 | <mml:mn>31</mml:mn> |
| 657 | </mml:msup> |
| 658 | <mml:mo>-</mml:mo> |
| 659 | <mml:mn>1</mml:mn> |
| 660 | </mml:mrow> |
| 661 | </mml:math></inlineequation> |
| 662 | </entry> |
| 663 | <entry align="center"> |
| 664 | <inlineequation><mml:math> |
| 665 | <!-- eqn: {(2 sup 32 - 1) c - 1} / 2:--> |
| 666 | <mml:mfrac> |
| 667 | <mml:mfenced open="" close=""> |
| 668 | <mml:mrow> |
| 669 | <mml:mfenced open="(" close=")"> |
| 670 | <mml:mrow> |
| 671 | <mml:msup><mml:mn>2</mml:mn> |
| 672 | <mml:mn>32</mml:mn> |
| 673 | </mml:msup> |
| 674 | <mml:mo>-</mml:mo> |
| 675 | <mml:mn>1</mml:mn> |
| 676 | </mml:mrow> |
| 677 | </mml:mfenced> |
| 678 | <mml:mo>⁢</mml:mo> |
| 679 | <mml:mi mathvariant="italic">c</mml:mi> |
| 680 | <mml:mo>-</mml:mo> |
| 681 | <mml:mn>1</mml:mn> |
| 682 | </mml:mrow> |
| 683 | </mml:mfenced> |
| 684 | <mml:mn>2</mml:mn> |
| 685 | </mml:mfrac> |
| 686 | </mml:math></inlineequation> |
| 687 | </entry> |
| 688 | </row> |
| 689 | <row> |
| 690 | <entry align="left"> |
| 691 | <constant>GL_FLOAT</constant> |
| 692 | </entry> |
| 693 | <entry align="center"> |
| 694 | none |
| 695 | </entry> |
| 696 | <entry align="center"> |
| 697 | <inlineequation><mml:math><mml:mi mathvariant="italic">c</mml:mi></mml:math></inlineequation> |
| 698 | </entry> |
| 699 | </row> |
| 700 | </tbody> |
| 701 | </tgroup> |
| 702 | </informaltable> |
| 703 | <para> |
| 704 | Return values are placed in memory as follows. |
| 705 | If <parameter>format</parameter> is |
| 706 | <constant>GL_COLOR_INDEX</constant>, |
| 707 | <constant>GL_STENCIL_INDEX</constant>, |
| 708 | <constant>GL_DEPTH_COMPONENT</constant>, |
| 709 | <constant>GL_RED</constant>, |
| 710 | <constant>GL_GREEN</constant>, |
| 711 | <constant>GL_BLUE</constant>, |
| 712 | <constant>GL_ALPHA</constant>, or |
| 713 | <constant>GL_LUMINANCE</constant>, |
| 714 | a single value is returned and the data for the |
| 715 | <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>th |
| 716 | pixel in the |
| 717 | <inlineequation><mml:math><mml:mi mathvariant="italic">j</mml:mi></mml:math></inlineequation>th |
| 718 | row |
| 719 | is placed in location |
| 720 | <inlineequation><mml:math> |
| 721 | <!-- eqn: (j) width + i:--> |
| 722 | <mml:mrow> |
| 723 | <mml:mfenced open="(" close=")"> |
| 724 | <mml:mi mathvariant="italic">j</mml:mi> |
| 725 | </mml:mfenced> |
| 726 | <mml:mo>⁢</mml:mo> |
| 727 | <mml:mi mathvariant="italic">width</mml:mi> |
| 728 | <mml:mo>+</mml:mo> |
| 729 | <mml:mi mathvariant="italic">i</mml:mi> |
| 730 | </mml:mrow> |
| 731 | </mml:math></inlineequation>. |
| 732 | <constant>GL_RGB</constant> and <constant>GL_BGR</constant> return three values, |
| 733 | <constant>GL_RGBA</constant> and <constant>GL_BGRA</constant> return four values, |
| 734 | and <constant>GL_LUMINANCE_ALPHA</constant> returns two values for each pixel, |
| 735 | with all values corresponding to a single pixel occupying contiguous space |
| 736 | in <parameter>data</parameter>. |
| 737 | Storage parameters set by <citerefentry><refentrytitle>glPixelStore</refentrytitle></citerefentry>, |
| 738 | such as <constant>GL_PACK_LSB_FIRST</constant> and <constant>GL_PACK_SWAP_BYTES</constant>, |
| 739 | affect the way that data is written into memory. |
| 740 | See <citerefentry><refentrytitle>glPixelStore</refentrytitle></citerefentry> for a description. |
| 741 | </para> |
| 742 | </refsect1> |
| 743 | <refsect1 id="notes"><title>Notes</title> |
| 744 | <para> |
| 745 | Values for pixels that lie outside the window |
| 746 | connected to the current GL context are undefined. |
| 747 | </para> |
| 748 | <para> |
| 749 | If an error is generated, |
| 750 | no change is made to the contents of <parameter>data</parameter>. |
| 751 | </para> |
| 752 | </refsect1> |
| 753 | <refsect1 id="errors"><title>Errors</title> |
| 754 | <para> |
| 755 | <constant>GL_INVALID_ENUM</constant> is generated if <parameter>format</parameter> or <parameter>type</parameter> is not an |
| 756 | accepted value. |
| 757 | </para> |
| 758 | <para> |
| 759 | <constant>GL_INVALID_ENUM</constant> is generated if <parameter>type</parameter> is <constant>GL_BITMAP</constant> and <parameter>format</parameter> is |
| 760 | not <constant>GL_COLOR_INDEX</constant> or <constant>GL_STENCIL_INDEX</constant>. |
| 761 | </para> |
| 762 | <para> |
| 763 | <constant>GL_INVALID_VALUE</constant> is generated if either <parameter>width</parameter> or <parameter>height</parameter> is negative. |
| 764 | </para> |
| 765 | <para> |
| 766 | <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>format</parameter> is <constant>GL_COLOR_INDEX</constant> |
| 767 | and the color buffers store RGBA color components. |
| 768 | </para> |
| 769 | <para> |
| 770 | <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>format</parameter> is <constant>GL_STENCIL_INDEX</constant> |
| 771 | and there is no stencil buffer. |
| 772 | </para> |
| 773 | <para> |
| 774 | <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>format</parameter> is <constant>GL_DEPTH_COMPONENT</constant> |
| 775 | and there is no depth buffer. |
| 776 | </para> |
| 777 | <para> |
| 778 | <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>type</parameter> is one of |
| 779 | <constant>GL_UNSIGNED_BYTE_3_3_2</constant>, |
| 780 | <constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>, |
| 781 | <constant>GL_UNSIGNED_SHORT_5_6_5</constant>, or |
| 782 | <constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant> |
| 783 | and <parameter>format</parameter> is not <constant>GL_RGB</constant>. |
| 784 | </para> |
| 785 | <para> |
| 786 | <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>type</parameter> is one of |
| 787 | <constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>, |
| 788 | <constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>, |
| 789 | <constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>, |
| 790 | <constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>, |
| 791 | <constant>GL_UNSIGNED_INT_8_8_8_8</constant>, |
| 792 | <constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>, |
| 793 | <constant>GL_UNSIGNED_INT_10_10_10_2</constant>, or |
| 794 | <constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant> |
| 795 | and <parameter>format</parameter> is neither <constant>GL_RGBA</constant> nor <constant>GL_BGRA</constant>. |
| 796 | </para> |
| 797 | <para> |
| 798 | The formats <constant>GL_BGR</constant>, and <constant>GL_BGRA</constant> and types |
| 799 | <constant>GL_UNSIGNED_BYTE_3_3_2</constant>, |
| 800 | <constant>GL_UNSIGNED_BYTE_2_3_3_REV</constant>, |
| 801 | <constant>GL_UNSIGNED_SHORT_5_6_5</constant>, |
| 802 | <constant>GL_UNSIGNED_SHORT_5_6_5_REV</constant>, |
| 803 | <constant>GL_UNSIGNED_SHORT_4_4_4_4</constant>, |
| 804 | <constant>GL_UNSIGNED_SHORT_4_4_4_4_REV</constant>, |
| 805 | <constant>GL_UNSIGNED_SHORT_5_5_5_1</constant>, |
| 806 | <constant>GL_UNSIGNED_SHORT_1_5_5_5_REV</constant>, |
| 807 | <constant>GL_UNSIGNED_INT_8_8_8_8</constant>, |
| 808 | <constant>GL_UNSIGNED_INT_8_8_8_8_REV</constant>, |
| 809 | <constant>GL_UNSIGNED_INT_10_10_10_2</constant>, and |
| 810 | <constant>GL_UNSIGNED_INT_2_10_10_10_REV</constant> are available only if the GL version |
| 811 | is 1.2 or greater. |
| 812 | </para> |
| 813 | <para> |
| 814 | <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the |
| 815 | <constant>GL_PIXEL_PACK_BUFFER</constant> target and the buffer object's data store is currently mapped. |
| 816 | </para> |
| 817 | <para> |
| 818 | <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the |
| 819 | <constant>GL_PIXEL_PACK_BUFFER</constant> target and the data would be packed to the buffer |
| 820 | object such that the memory writes required would exceed the data store size. |
| 821 | </para> |
| 822 | <para> |
| 823 | <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to the |
| 824 | <constant>GL_PIXEL_PACK_BUFFER</constant> target and <parameter>data</parameter> is not evenly divisible |
| 825 | into the number of bytes needed to store in memory a datum indicated by <parameter>type</parameter>. |
| 826 | </para> |
| 827 | <para> |
| 828 | <constant>GL_INVALID_OPERATION</constant> is generated if <function>glReadPixels</function> |
| 829 | is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> |
| 830 | and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>. |
| 831 | </para> |
| 832 | </refsect1> |
| 833 | <refsect1 id="associatedgets"><title>Associated Gets</title> |
| 834 | <para> |
| 835 | <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_INDEX_MODE</constant> |
| 836 | </para> |
| 837 | <para> |
| 838 | <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_PIXEL_PACK_BUFFER_BINDING</constant> |
| 839 | </para> |
| 840 | </refsect1> |
| 841 | <refsect1 id="seealso"><title>See Also</title> |
| 842 | <para> |
| 843 | <citerefentry><refentrytitle>glCopyPixels</refentrytitle></citerefentry>, |
| 844 | <citerefentry><refentrytitle>glDrawPixels</refentrytitle></citerefentry>, |
| 845 | <citerefentry><refentrytitle>glPixelMap</refentrytitle></citerefentry>, |
| 846 | <citerefentry><refentrytitle>glPixelStore</refentrytitle></citerefentry>, |
| 847 | <citerefentry><refentrytitle>glPixelTransfer</refentrytitle></citerefentry>, |
| 848 | <citerefentry><refentrytitle>glReadBuffer</refentrytitle></citerefentry> |
| 849 | </para> |
| 850 | </refsect1> |
| 851 | <refsect1 id="Copyright"><title>Copyright</title> |
| 852 | <para> |
| 853 | Copyright <trademark class="copyright"></trademark> 1991-2006 |
| 854 | Silicon Graphics, Inc. This document is licensed under the SGI |
| 855 | Free Software B License. For details, see |
| 856 | <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>. |
| 857 | </para> |
| 858 | </refsect1> |
| 859 | </refentry> |