upstream-doc/man2/glSelectBuffer.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="glSelectBuffer">
   5     <refmeta>
   6         <refmetainfo>
   7             <copyright>
   8                 <year>1991-2006</year>
   9                 <holder>Silicon Graphics, Inc.</holder>
  10             </copyright>
  11         </refmetainfo>
  12         <refentrytitle>glSelectBuffer</refentrytitle>
  13         <manvolnum>3G</manvolnum>
  14     </refmeta>
  15     <refnamediv>
  16         <refname>glSelectBuffer</refname>
  17         <refpurpose>establish a buffer for selection mode values</refpurpose>
  18     </refnamediv>
  19     <refsynopsisdiv><title>C Specification</title>
  20         <funcsynopsis>
  21             <funcprototype>
  22                 <funcdef>void <function>glSelectBuffer</function></funcdef>
  23                 <paramdef>GLsizei <parameter>size</parameter></paramdef>
  24                 <paramdef>GLuint * <parameter>buffer</parameter></paramdef>
  25             </funcprototype>
  26         </funcsynopsis>
  27     </refsynopsisdiv>
  28     <!-- eqn: ignoring delim $$ -->
  29     <refsect1 id="parameters"><title>Parameters</title>
  30         <variablelist>
  31         <varlistentry>
  32             <term><parameter>size</parameter></term>
  33             <listitem>
  34                 <para>
  35                     Specifies the size of <parameter>buffer</parameter>.
  36                 </para>
  37             </listitem>
  38         </varlistentry>
  39         <varlistentry>
  40             <term><parameter>buffer</parameter></term>
  41             <listitem>
  42                 <para>
  43                     Returns the selection data.
  44                 </para>
  45             </listitem>
  46         </varlistentry>
  47         </variablelist>
  48     </refsect1>
  49     <refsect1 id="description"><title>Description</title>
  50         <para>
  51             <function>glSelectBuffer</function> has two arguments:
  52             <parameter>buffer</parameter> is a pointer to an array of unsigned integers,
  53             and <parameter>size</parameter> indicates the size of the array.
  54             <parameter>buffer</parameter> returns values from the name stack
  55             (see <citerefentry><refentrytitle>glInitNames</refentrytitle></citerefentry>, <citerefentry><refentrytitle>glLoadName</refentrytitle></citerefentry>, <citerefentry><refentrytitle>glPushName</refentrytitle></citerefentry>)
  56             when the rendering mode is <constant>GL_SELECT</constant> (see <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry>).
  57             <function>glSelectBuffer</function> must be issued before selection mode is enabled,
  58             and it must not be issued while the rendering mode is <constant>GL_SELECT</constant>.
  59         </para>
  60         <para>
  61             A programmer can use selection to determine which primitives
  62             are drawn into some region of a window.
  63             The region is defined by the current modelview and perspective matrices.
  64         </para>
  65         <para>
  66             In selection mode, no pixel fragments are produced from rasterization.
  67             Instead,
  68             if a primitive or a raster position intersects the clipping
  69             volume defined by the viewing frustum
  70             and the user-defined clipping planes,
  71             this primitive causes a selection hit.
  72             (With polygons, no hit occurs if the polygon is culled.)
  73             When a change is made to the name stack,
  74             or when <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry> is called,
  75             a hit record is copied to <parameter>buffer</parameter> if any hits have occurred since the
  76             last such event
  77             (name stack change or
  78             <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry> call).
  79             The hit record consists of the number of names in the name stack at the
  80             time of the event, followed by the minimum and maximum depth values
  81             of all vertices that hit since the previous event,
  82             followed by the name stack contents,
  83             bottom name first.
  84         </para>
  85         <para>
  86             Depth values (which are in the range [0,1]) are multiplied by
  87             <inlineequation><mml:math>
  88                 <!-- eqn: 2 sup 32 - 1:-->
  89                 <mml:mrow>
  90                     <mml:msup><mml:mn>2</mml:mn>
  91                     <mml:mn>32</mml:mn>
  92                     </mml:msup>
  93                     <mml:mo>-</mml:mo>
  94                     <mml:mn>1</mml:mn>
  95                 </mml:mrow>
  96             </mml:math></inlineequation>,
  97             before being placed in the hit record.
  98         </para>
  99         <para>
 100             An internal index into <parameter>buffer</parameter> is reset to 0 whenever selection mode
 101             is entered.
 102             Each time a hit record is copied into <parameter>buffer</parameter>,
 103             the index is incremented to point to the cell just past the end
 104             of the block of names\(emthat is, to the next available cell
 105             If the hit record is larger than the number of remaining locations in <parameter>buffer</parameter>,
 106             as much data as can fit is copied,
 107             and the overflow flag is set.
 108             If the name stack is empty when a hit record is copied,
 109             that record consists of 0 followed by the minimum and maximum depth values.
 110         </para>
 111         <para>
 112             To exit selection mode, call <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry> with an argument
 113             other than <constant>GL_SELECT</constant>.
 114             Whenever <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry> is called while the render mode is <constant>GL_SELECT</constant>,
 115             it returns the number of hit records copied to <parameter>buffer</parameter>,
 116             resets the overflow flag and the selection buffer pointer,
 117             and initializes the name stack to be empty.
 118             If the overflow bit was set when <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry> was called,
 119             a negative hit record count is returned.
 120         </para>
 121     </refsect1>
 122     <refsect1 id="notes"><title>Notes</title>
 123         <para>
 124             The contents of <parameter>buffer</parameter> is undefined until <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry> is called
 125             with an argument other than <constant>GL_SELECT</constant>.
 126         </para>
 127         <para>
 128             <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>/<citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry> primitives and calls to <citerefentry><refentrytitle>glRasterPos</refentrytitle></citerefentry>
 129             can result in hits.  <citerefentry><refentrytitle>glWindowPos</refentrytitle></citerefentry> will always generate a selection hit.
 130         </para>
 131     </refsect1>
 132     <refsect1 id="errors"><title>Errors</title>
 133         <para>
 134             <constant>GL_INVALID_VALUE</constant> is generated if <parameter>size</parameter> is negative.
 135         </para>
 136         <para>
 137             <constant>GL_INVALID_OPERATION</constant> is generated if <function>glSelectBuffer</function> is called while the
 138             render mode is <constant>GL_SELECT</constant>,
 139             or if <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry> is called with argument <constant>GL_SELECT</constant> before
 140             <function>glSelectBuffer</function> is called at least once.
 141         </para>
 142         <para>
 143             <constant>GL_INVALID_OPERATION</constant> is generated if <function>glSelectBuffer</function>
 144             is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
 145             and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.
 146         </para>
 147     </refsect1>
 148     <refsect1 id="associatedgets"><title>Associated Gets</title>
 149         <para>
 150             <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_NAME_STACK_DEPTH</constant>
 151         </para>
 152         <para>
 153             <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_SELECTION_BUFFER_SIZE</constant>
 154         </para>
 155         <para>
 156             <citerefentry><refentrytitle>glGetPointerv</refentrytitle></citerefentry> with argument <constant>GL_SELECTION_BUFFER_POINTER</constant>
 157         </para>
 158     </refsect1>
 159     <refsect1 id="seealso"><title>See Also</title>
 160         <para>
 161             <citerefentry><refentrytitle>glFeedbackBuffer</refentrytitle></citerefentry>,
 162             <citerefentry><refentrytitle>glInitNames</refentrytitle></citerefentry>,
 163             <citerefentry><refentrytitle>glLoadName</refentrytitle></citerefentry>,
 164             <citerefentry><refentrytitle>glPushName</refentrytitle></citerefentry>,
 165             <citerefentry><refentrytitle>glRenderMode</refentrytitle></citerefentry>
 166         </para>
 167     </refsect1>
 168     <refsect1 id="Copyright"><title>Copyright</title>
 169         <para>
 170             Copyright <trademark class="copyright"></trademark> 1991-2006
 171             Silicon Graphics, Inc. This document is licensed under the SGI
 172             Free Software B License. For details, see
 173             <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
 174         </para>
 175     </refsect1>
 176 </refentry>