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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> |