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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="glFeedbackBuffer"> | |
5 | <refmeta> | |
6 | <refmetainfo> | |
7 | <copyright> | |
8 | <year>1991-2006</year> | |
9 | <holder>Silicon Graphics, Inc.</holder> | |
10 | </copyright> | |
11 | </refmetainfo> | |
12 | <refentrytitle>glFeedbackBuffer</refentrytitle> | |
13 | <manvolnum>3G</manvolnum> | |
14 | </refmeta> | |
15 | <refnamediv> | |
16 | <refname>glFeedbackBuffer</refname> | |
17 | <refpurpose>controls feedback mode</refpurpose> | |
18 | </refnamediv> | |
19 | <refsynopsisdiv><title>C Specification</title> | |
20 | <funcsynopsis> | |
21 | <funcprototype> | |
22 | <funcdef>void <function>glFeedbackBuffer</function></funcdef> | |
23 | <paramdef>GLsizei <parameter>size</parameter></paramdef> | |
24 | <paramdef>GLenum <parameter>type</parameter></paramdef> | |
25 | <paramdef>GLfloat * <parameter>buffer</parameter></paramdef> | |
26 | </funcprototype> | |
27 | </funcsynopsis> | |
28 | </refsynopsisdiv> | |
29 | <!-- eqn: ignoring delim $$ --> | |
30 | <refsect1 id="parameters"><title>Parameters</title> | |
31 | <variablelist> | |
32 | <varlistentry> | |
33 | <term><parameter>size</parameter></term> | |
34 | <listitem> | |
35 | <para> | |
36 | Specifies the maximum number of values that can be written into <parameter>buffer</parameter>. | |
37 | </para> | |
38 | </listitem> | |
39 | </varlistentry> | |
40 | <varlistentry> | |
41 | <term><parameter>type</parameter></term> | |
42 | <listitem> | |
43 | <para> | |
44 | Specifies a symbolic constant that describes the information | |
45 | that will be returned for each vertex. | |
46 | <constant>GL_2D</constant>, | |
47 | <constant>GL_3D</constant>, | |
48 | <constant>GL_3D_COLOR</constant>, | |
49 | <constant>GL_3D_COLOR_TEXTURE</constant>, and | |
50 | <constant>GL_4D_COLOR_TEXTURE</constant> are accepted. | |
51 | </para> | |
52 | </listitem> | |
53 | </varlistentry> | |
54 | <varlistentry> | |
55 | <term><parameter>buffer</parameter></term> | |
56 | <listitem> | |
57 | <para> | |
58 | Returns the feedback data. | |
59 | </para> | |
60 | </listitem> | |
61 | </varlistentry> | |
62 | </variablelist> | |
63 | </refsect1> | |
64 | <refsect1 id="description"><title>Description</title> | |
65 | <para> | |
66 | The <function>glFeedbackBuffer</function> function controls feedback. | |
67 | Feedback, like selection, is a GL mode. | |
68 | The mode is selected by calling | |
69 | <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry> with <constant>GL_FEEDBACK</constant>. | |
70 | When the GL is in feedback mode, | |
71 | no pixels are produced by rasterization. | |
72 | Instead, information about primitives that would have been | |
73 | rasterized is fed back to the application using the GL. | |
74 | </para> | |
75 | <para> | |
76 | <function>glFeedbackBuffer</function> has three arguments: | |
77 | <parameter>buffer</parameter> is a pointer to an array of floating-point values | |
78 | into which feedback information is placed. | |
79 | <parameter>size</parameter> indicates the size of the array. | |
80 | <parameter>type</parameter> is a symbolic constant describing the information | |
81 | that is fed back for each vertex. | |
82 | <function>glFeedbackBuffer</function> must be issued before feedback mode is enabled | |
83 | (by calling <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry> with argument <constant>GL_FEEDBACK</constant>). | |
84 | Setting <constant>GL_FEEDBACK</constant> without establishing the feedback buffer, | |
85 | or calling <function>glFeedbackBuffer</function> while the GL is in feedback mode, | |
86 | is an error. | |
87 | </para> | |
88 | <para> | |
89 | When <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry> is called while in feedback mode, it returns the number of entries | |
90 | placed in the feedback array and resets the feedback array pointer to the base | |
91 | of the feedback buffer. The returned value never exceeds <parameter>size</parameter>. If the feedback | |
92 | data required more room than was available in <parameter>buffer</parameter>, | |
93 | <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry> returns a negative value. | |
94 | To take the GL out of feedback mode, call | |
95 | <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry> with a parameter value other than <constant>GL_FEEDBACK</constant>. | |
96 | </para> | |
97 | <para> | |
98 | While in feedback mode, | |
99 | each primitive, bitmap, or pixel rectangle that would be rasterized | |
100 | generates a block of values that are copied into the feedback array. | |
101 | If doing so would cause the number of entries to exceed the maximum, | |
102 | the block is partially written so as to fill the array | |
103 | (if there is any room left at all), | |
104 | and an overflow flag is set. | |
105 | Each block begins with a code indicating the primitive type, | |
106 | followed by values that describe the primitive's vertices and | |
107 | associated data. | |
108 | Entries are also written for bitmaps and pixel rectangles. | |
109 | Feedback occurs after polygon culling and <citerefentry><refentrytitle>glPolygonMode</refentrytitle></citerefentry> interpretation | |
110 | of polygons has taken place, | |
111 | so polygons that are culled are not returned in the feedback buffer. | |
112 | It can also occur after polygons with more than three edges are broken up | |
113 | into triangles, | |
114 | if the GL implementation renders polygons by performing this decomposition. | |
115 | </para> | |
116 | <para> | |
117 | The <citerefentry><refentrytitle>glPassThrough</refentrytitle></citerefentry> command can be used to insert a marker | |
118 | into the feedback buffer. | |
119 | See <citerefentry><refentrytitle>glPassThrough</refentrytitle></citerefentry>. | |
120 | </para> | |
121 | <para> | |
122 | Following is the grammar for the blocks of values written | |
123 | into the feedback buffer. | |
124 | Each primitive is indicated with a unique identifying value | |
125 | followed by some number of vertices. | |
126 | Polygon entries include an integer value indicating how many vertices follow. | |
127 | A vertex is fed back as some number of floating-point values, | |
128 | as determined by <parameter>type</parameter>. | |
129 | Colors are fed back as four values in RGBA mode and one value | |
130 | in color index mode. | |
131 | </para> | |
132 | ||
133 | <para> | |
134 | <para> | |
135 | feedbackList <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> feedbackItem feedbackList | feedbackItem | |
136 | </para> | |
137 | <para> | |
138 | feedbackItem <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> point | lineSegment | polygon | bitmap | pixelRectangle | passThru | |
139 | </para> | |
140 | <para> | |
141 | point <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> <constant>GL_POINT_TOKEN</constant> vertex | |
142 | </para> | |
143 | <para> | |
144 | lineSegment <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> <constant>GL_LINE_TOKEN</constant> vertex vertex | <constant>GL_LINE_RESET_TOKEN</constant> vertex vertex | |
145 | </para> | |
146 | <para> | |
147 | polygon <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> <constant>GL_POLYGON_TOKEN</constant> n polySpec | |
148 | </para> | |
149 | <para> | |
150 | polySpec <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> polySpec vertex | vertex vertex vertex | |
151 | </para> | |
152 | <para> | |
153 | bitmap <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> <constant>GL_BITMAP_TOKEN</constant> vertex | |
154 | </para> | |
155 | <para> | |
156 | pixelRectangle <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> <constant>GL_DRAW_PIXEL_TOKEN</constant> vertex | <constant>GL_COPY_PIXEL_TOKEN</constant> vertex | |
157 | </para> | |
158 | <para> | |
159 | passThru <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> <constant>GL_PASS_THROUGH_TOKEN</constant> value | |
160 | </para> | |
161 | <para> | |
162 | vertex <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> 2d | 3d | 3dColor | 3dColorTexture | 4dColorTexture | |
163 | </para> | |
164 | <para> | |
165 | 2d <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> value value | |
166 | </para> | |
167 | <para> | |
168 | 3d <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> value value value | |
169 | </para> | |
170 | <para> | |
171 | 3dColor <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> value value value color | |
172 | </para> | |
173 | <para> | |
174 | 3dColorTexture <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> value value value color tex | |
175 | </para> | |
176 | <para> | |
177 | 4dColorTexture <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> value value value value color tex | |
178 | </para> | |
179 | <para> | |
180 | color <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> rgba | index | |
181 | </para> | |
182 | <para> | |
183 | rgba <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> value value value value | |
184 | </para> | |
185 | <para> | |
186 | index <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> value | |
187 | </para> | |
188 | <para> | |
189 | tex <inlineequation><mml:math><mml:mrow><mml:mn>←</mml:mn></mml:mrow></mml:math></inlineequation> value value value value | |
190 | </para> | |
191 | <para> | |
192 | </para> | |
193 | </para> | |
194 | <para> | |
195 | <emphasis>value</emphasis> | |
196 | is a floating-point number, | |
197 | and | |
198 | <emphasis>n</emphasis> | |
199 | is a floating-point integer giving the number of vertices in the polygon. | |
200 | <constant>GL_POINT_TOKEN</constant>, | |
201 | <constant>GL_LINE_TOKEN</constant>, | |
202 | <constant>GL_LINE_RESET_TOKEN</constant>, | |
203 | <constant>GL_POLYGON_TOKEN</constant>, | |
204 | <constant>GL_BITMAP_TOKEN</constant>, | |
205 | <constant>GL_DRAW_PIXEL_TOKEN</constant>, | |
206 | <constant>GL_COPY_PIXEL_TOKEN</constant> and | |
207 | <constant>GL_PASS_THROUGH_TOKEN</constant> are symbolic floating-point constants. | |
208 | <constant>GL_LINE_RESET_TOKEN</constant> is returned whenever the line stipple pattern | |
209 | is reset. | |
210 | The data returned as a vertex depends on the feedback <parameter>type</parameter>. | |
211 | </para> | |
212 | <para> | |
213 | The following table gives the correspondence between <parameter>type</parameter> | |
214 | and the number of values per vertex. | |
215 | <emphasis>k</emphasis> is 1 in color index mode and 4 in RGBA mode. | |
216 | </para> | |
217 | <para> | |
218 | </para> | |
219 | <informaltable frame="topbot"> | |
220 | <tgroup cols="5" align="left"> | |
221 | <colspec colwidth="2.7*" /> | |
222 | <colspec colwidth="1.5*" /> | |
223 | <colspec colwidth="1*" align="center"/> | |
224 | <colspec colwidth="1*" align="center"/> | |
225 | <colspec colwidth="2.5*" align="center"/> | |
226 | <thead> | |
227 | <row> | |
228 | <entry rowsep="1" align="left"><emphasis role="bold"> | |
229 | Type | |
230 | </emphasis></entry> | |
231 | <entry rowsep="1" align="left"><emphasis role="bold"> | |
232 | Coordinates | |
233 | </emphasis></entry> | |
234 | <entry rowsep="1" align="center"><emphasis role="bold"> | |
235 | Color | |
236 | </emphasis></entry> | |
237 | <entry rowsep="1" align="center"><emphasis role="bold"> | |
238 | Texture | |
239 | </emphasis></entry> | |
240 | <entry rowsep="1" align="center"><emphasis role="bold"> | |
241 | Total Number of Values | |
242 | </emphasis></entry> | |
243 | </row> | |
244 | </thead> | |
245 | <tbody> | |
246 | <row> | |
247 | <entry align="left"> | |
248 | <constant>GL_2D</constant> | |
249 | </entry> | |
250 | <entry align="left"> | |
251 | <emphasis>x</emphasis>, <emphasis>y</emphasis> | |
252 | </entry> | |
253 | <entry align="center"> | |
254 | </entry> | |
255 | <entry align="center"> | |
256 | </entry> | |
257 | <entry align="center"> | |
258 | 2 | |
259 | </entry> | |
260 | </row> | |
261 | <row> | |
262 | <entry align="left"> | |
263 | <constant>GL_3D</constant> | |
264 | </entry> | |
265 | <entry align="left"> | |
266 | <emphasis>x</emphasis>, <emphasis>y</emphasis>, <emphasis>z</emphasis> | |
267 | </entry> | |
268 | <entry align="center"> | |
269 | </entry> | |
270 | <entry align="center"> | |
271 | </entry> | |
272 | <entry align="center"> | |
273 | 3 | |
274 | </entry> | |
275 | </row> | |
276 | <row> | |
277 | <entry align="left"> | |
278 | <constant>GL_3D_COLOR</constant> | |
279 | </entry> | |
280 | <entry align="left"> | |
281 | <emphasis>x</emphasis>, <emphasis>y</emphasis>, <emphasis>z</emphasis> | |
282 | </entry> | |
283 | <entry align="center"> | |
284 | <inlineequation><mml:math><mml:mi mathvariant="italic">k</mml:mi></mml:math></inlineequation> | |
285 | </entry> | |
286 | <entry align="center"> | |
287 | </entry> | |
288 | <entry align="center"> | |
289 | <inlineequation><mml:math> | |
290 | <!-- eqn: 3 + k:--> | |
291 | <mml:mrow> | |
292 | <mml:mn>3</mml:mn> | |
293 | <mml:mo>+</mml:mo> | |
294 | <mml:mi mathvariant="italic">k</mml:mi> | |
295 | </mml:mrow> | |
296 | </mml:math></inlineequation> | |
297 | </entry> | |
298 | </row> | |
299 | <row> | |
300 | <entry align="left"> | |
301 | <constant>GL_3D_COLOR_TEXTURE</constant> | |
302 | </entry> | |
303 | <entry align="left"> | |
304 | <emphasis>x</emphasis>, <emphasis>y</emphasis>, <emphasis>z</emphasis> | |
305 | </entry> | |
306 | <entry align="center"> | |
307 | <inlineequation><mml:math><mml:mi mathvariant="italic">k</mml:mi></mml:math></inlineequation> | |
308 | </entry> | |
309 | <entry align="center"> | |
310 | 4 | |
311 | </entry> | |
312 | <entry align="center"> | |
313 | <inlineequation><mml:math> | |
314 | <!-- eqn: 7 + k:--> | |
315 | <mml:mrow> | |
316 | <mml:mn>7</mml:mn> | |
317 | <mml:mo>+</mml:mo> | |
318 | <mml:mi mathvariant="italic">k</mml:mi> | |
319 | </mml:mrow> | |
320 | </mml:math></inlineequation> | |
321 | </entry> | |
322 | </row> | |
323 | <row> | |
324 | <entry align="left"> | |
325 | <constant>GL_4D_COLOR_TEXTURE</constant> | |
326 | </entry> | |
327 | <entry align="left"> | |
328 | <emphasis>x</emphasis>, <emphasis>y</emphasis>, <emphasis>z</emphasis>, <emphasis>w</emphasis> | |
329 | </entry> | |
330 | <entry align="center"> | |
331 | <inlineequation><mml:math><mml:mi mathvariant="italic">k</mml:mi></mml:math></inlineequation> | |
332 | </entry> | |
333 | <entry align="center"> | |
334 | 4 | |
335 | </entry> | |
336 | <entry align="center"> | |
337 | <inlineequation><mml:math> | |
338 | <!-- eqn: 8 + k:--> | |
339 | <mml:mrow> | |
340 | <mml:mn>8</mml:mn> | |
341 | <mml:mo>+</mml:mo> | |
342 | <mml:mi mathvariant="italic">k</mml:mi> | |
343 | </mml:mrow> | |
344 | </mml:math></inlineequation> | |
345 | </entry> | |
346 | </row> | |
347 | </tbody> | |
348 | </tgroup> | |
349 | </informaltable> | |
350 | <para> | |
351 | Feedback vertex coordinates are in window coordinates, | |
352 | except <emphasis>w</emphasis>, | |
353 | which is in clip coordinates. | |
354 | Feedback colors are lighted, if lighting is enabled. | |
355 | Feedback texture coordinates are generated, | |
356 | if texture coordinate generation is enabled. | |
357 | They are always transformed by the texture matrix. | |
358 | </para> | |
359 | </refsect1> | |
360 | <refsect1 id="notes"><title>Notes</title> | |
361 | <para> | |
362 | <function>glFeedbackBuffer</function>, when used in a display list, is not compiled into the display list | |
363 | but is executed immediately. | |
364 | </para> | |
365 | <para> | |
366 | <function>glFeedbackBuffer</function> returns only the texture coordinate of texture unit <constant>GL_TEXTURE0</constant>. | |
367 | </para> | |
368 | </refsect1> | |
369 | <refsect1 id="errors"><title>Errors</title> | |
370 | <para> | |
371 | <constant>GL_INVALID_ENUM</constant> is generated if <parameter>type</parameter> is not an accepted value. | |
372 | </para> | |
373 | <para> | |
374 | <constant>GL_INVALID_VALUE</constant> is generated if <parameter>size</parameter> is negative. | |
375 | </para> | |
376 | <para> | |
377 | <constant>GL_INVALID_OPERATION</constant> is generated if <function>glFeedbackBuffer</function> is called while the | |
378 | render mode is <constant>GL_FEEDBACK</constant>, | |
379 | or if <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry> is called with argument <constant>GL_FEEDBACK</constant> before | |
380 | <function>glFeedbackBuffer</function> is called at least once. | |
381 | </para> | |
382 | <para> | |
383 | <constant>GL_INVALID_OPERATION</constant> is generated if <function>glFeedbackBuffer</function> | |
384 | is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> | |
385 | and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>. | |
386 | </para> | |
387 | </refsect1> | |
388 | <refsect1 id="associatedgets"><title>Associated Gets</title> | |
389 | <para> | |
390 | <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_RENDER_MODE</constant> | |
391 | </para> | |
392 | <para> | |
393 | <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_FEEDBACK_BUFFER_POINTER</constant> | |
394 | </para> | |
395 | <para> | |
396 | <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_FEEDBACK_BUFFER_SIZE</constant> | |
397 | </para> | |
398 | <para> | |
399 | <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_FEEDBACK_BUFFER_TYPE</constant> | |
400 | </para> | |
401 | </refsect1> | |
402 | <refsect1 id="seealso"><title>See Also</title> | |
403 | <para> | |
404 | <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>, | |
405 | <citerefentry><refentrytitle>glLineStipple</refentrytitle></citerefentry>, | |
406 | <citerefentry><refentrytitle>glPassThrough</refentrytitle></citerefentry>, | |
407 | <citerefentry><refentrytitle>glPolygonMode</refentrytitle></citerefentry>, | |
408 | <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry>, | |
409 | <citerefentry><refentrytitle>glSelectBuffer</refentrytitle></citerefentry> | |
410 | </para> | |
411 | </refsect1> | |
412 | <refsect1 id="Copyright"><title>Copyright</title> | |
413 | <para> | |
414 | Copyright <trademark class="copyright"></trademark> 1991-2006 | |
415 | Silicon Graphics, Inc. This document is licensed under the SGI | |
416 | Free Software B License. For details, see | |
417 | <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>. | |
418 | </para> | |
419 | </refsect1> | |
420 | </refentry> |