upstream-man-pages/man2/glFeedbackBuffer.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="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>&#x2190;</mml:mn></mml:mrow></mml:math></inlineequation> feedbackItem feedbackList | feedbackItem
 136             </para>
 137             <para>
 138                 feedbackItem <inlineequation><mml:math><mml:mrow><mml:mn>&#x2190;</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>&#x2190;</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>&#x2190;</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>&#x2190;</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>&#x2190;</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>&#x2190;</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>&#x2190;</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>&#x2190;</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>&#x2190;</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>&#x2190;</mml:mn></mml:mrow></mml:math></inlineequation> value value
 166             </para>
 167             <para>
 168                 3d <inlineequation><mml:math><mml:mrow><mml:mn>&#x2190;</mml:mn></mml:mrow></mml:math></inlineequation> value value value
 169             </para>
 170             <para>
 171                 3dColor <inlineequation><mml:math><mml:mrow><mml:mn>&#x2190;</mml:mn></mml:mrow></mml:math></inlineequation> value value value color
 172             </para>
 173             <para>
 174                 3dColorTexture <inlineequation><mml:math><mml:mrow><mml:mn>&#x2190;</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>&#x2190;</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>&#x2190;</mml:mn></mml:mrow></mml:math></inlineequation> rgba | index
 181             </para>
 182             <para>
 183                 rgba <inlineequation><mml:math><mml:mrow><mml:mn>&#x2190;</mml:mn></mml:mrow></mml:math></inlineequation> value value value value
 184             </para>
 185             <para>
 186                 index <inlineequation><mml:math><mml:mrow><mml:mn>&#x2190;</mml:mn></mml:mrow></mml:math></inlineequation> value
 187             </para>
 188             <para>
 189                 tex <inlineequation><mml:math><mml:mrow><mml:mn>&#x2190;</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>