upstream-doc/man4/glDrawArraysInstancedBaseInstance.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="glDrawArraysInstancedBaseInstance">
   5     <refmeta>
   6         <refmetainfo>
   7             <copyright>
   8                 <year>2010</year>
   9                 <holder>Khronos Group</holder>
  10             </copyright>
  11         </refmetainfo>
  12         <refentrytitle>glDrawArraysInstancedBaseInstance</refentrytitle>
  13         <manvolnum>3G</manvolnum>
  14     </refmeta>
  15     <refnamediv>
  16         <refname>glDrawArraysInstancedBaseInstance</refname>
  17         <refpurpose>draw multiple instances of a range of elements with offset applied to instanced attributes</refpurpose>
  18     </refnamediv>
  19     <refsynopsisdiv><title>C Specification</title>
  20         <funcsynopsis>
  21             <funcprototype>
  22                 <funcdef>void <function>glDrawArraysInstancedBaseInstance</function></funcdef>
  23                 <paramdef>GLenum <parameter>mode</parameter></paramdef>
  24                 <paramdef>GLint <parameter>first</parameter></paramdef>
  25                 <paramdef>GLsizei <parameter>count</parameter></paramdef>
  26                 <paramdef>GLsizei <parameter>primcount</parameter></paramdef>
  27                 <paramdef>GLuint <parameter>baseinstance</parameter></paramdef>
  28             </funcprototype>
  29         </funcsynopsis>
  30     </refsynopsisdiv>
  31     <refsect1 id="parameters"><title>Parameters</title>
  32         <variablelist>
  33         <varlistentry>
  34             <term><parameter>mode</parameter></term>
  35             <listitem>
  36                 <para>
  37                     Specifies what kind of primitives to render. Symbolic constants <constant>GL_POINTS</constant>,
  38                     <constant>GL_LINE_STRIP</constant>, <constant>GL_LINE_LOOP</constant>, <constant>GL_LINES</constant>,
  39                     <constant>GL_TRIANGLE_STRIP</constant>, <constant>GL_TRIANGLE_FAN</constant>, <constant>GL_TRIANGLES</constant>
  40                     <constant>GL_LINES_ADJACENCY</constant>, <constant>GL_LINE_STRIP_ADJACENCY</constant>,
  41                     <constant>GL_TRIANGLES_ADJACENCY</constant>, <constant>GL_TRIANGLE_STRIP_ADJACENCY</constant> and <constant>GL_PATCHES</constant>
  42                     are accepted.
  43                 </para>
  44             </listitem>
  45         </varlistentry>
  46         <varlistentry>
  47             <term><parameter>first</parameter></term>
  48             <listitem>
  49                 <para>
  50                     Specifies the starting index in the enabled arrays.
  51                 </para>
  52             </listitem>
  53         </varlistentry>
  54         <varlistentry>
  55             <term><parameter>count</parameter></term>
  56             <listitem>
  57                 <para>
  58                     Specifies the number of indices to be rendered.
  59                 </para>
  60             </listitem>
  61         </varlistentry>
  62         <varlistentry>
  63             <term><parameter>primcount</parameter></term>
  64             <listitem>
  65                 <para>
  66                     Specifies the number of instances of the specified range of indices to be rendered.
  67                 </para>
  68             </listitem>
  69         </varlistentry>
  70         <varlistentry>
  71             <term><parameter>baseinstance</parameter></term>
  72             <listitem>
  73                 <para>
  74                     Specifies the base instance for use in fetching instanced vertex attributes.
  75                 </para>
  76             </listitem>
  77         </varlistentry>
  78         </variablelist>
  79     </refsect1>
  80     <refsect1 id="description"><title>Description</title>
  81         <para>
  82             <function>glDrawArraysInstancedBaseInstance</function> behaves identically to <citerefentry><refentrytitle>glDrawArrays</refentrytitle></citerefentry>
  83             except that <parameter>primcount</parameter> instances of the range of elements are executed and the value of the internal counter
  84             <parameter>instanceID</parameter> advances for each iteration. <parameter>instanceID</parameter> is an internal 32-bit integer counter
  85             that may be read by a vertex shader as <constant>gl_InstanceID</constant>.
  86         </para>
  87         <para>
  88             <function>glDrawArraysInstancedBaseInstance</function> has the same effect as:
  89             <programlisting><![CDATA[    if ( mode or count is invalid )
  90         generate appropriate error
  91     else {
  92         for (int i = 0; i < primcount ; i++) {
  93             instanceID = i;
  94             glDrawArrays(mode, first, count);
  95         }
  96         instanceID = 0;
  97     }]]></programlisting>
  98         </para>
  99         <para>
 100             Specific vertex attributes may be classified as <emphasis>instanced</emphasis> through the use of
 101             <citerefentry><refentrytitle>glVertexAttribDivisor</refentrytitle></citerefentry>. Instanced vertex attributes
 102             supply per-instance vertex data to the vertex shader. The index of the vertex fetched from the enabled instanced vertex
 103             attribute arrays is calculated as:
 104 <mml:math>
 105   <mml:mrow>
 106     <mml:mfenced open = '&lfloor;' close = '&rfloor;'>
 107       <mml:mfrac>
 108         <mml:mrow>
 109           <mml:mi>gl</mml:mi>
 110           <mml:mo>_</mml:mo>
 111           <mml:mi>InstanceID</mml:mi>
 112         </mml:mrow>
 113         <mml:mi>divisor</mml:mi>
 114       </mml:mfrac>
 115     </mml:mfenced>
 116     <mml:mo lspace='2px' rspace='2px'>&plus;</mml:mo>
 117     <mml:mi>baseInstance</mml:mi>
 118   </mml:mrow>
 119 </mml:math>. Note that <parameter>baseinstance</parameter> does not affect the shader-visible value of <constant>gl_InstanceID</constant>.
 120         </para>
 121     </refsect1>
 122     <refsect1 id="errors"><title>Errors</title>
 123         <para>
 124             <constant>GL_INVALID_ENUM</constant> is generated if <parameter>mode</parameter> is not one of
 125             the accepted values.
 126         </para>
 127         <para>
 128             <constant>GL_INVALID_OPERATION</constant> is generated if a geometry shader is active and <parameter>mode</parameter>
 129             is incompatible with the input primitive type of the geometry shader in the currently installed program object.
 130         </para>
 131         <para>
 132             <constant>GL_INVALID_VALUE</constant> is generated if <parameter>count</parameter> or <parameter>primcount</parameter> are negative.
 133         </para>
 134         <para>
 135             <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to an
 136             enabled array and the buffer object's data store is currently mapped.
 137         </para>
 138     </refsect1>
 139     <refsect1 id="seealso"><title>See Also</title>
 140         <para>
 141             <citerefentry><refentrytitle>glDrawArrays</refentrytitle></citerefentry>,
 142             <citerefentry><refentrytitle>glDrawElementsInstanced</refentrytitle></citerefentry>
 143         </para>
 144     </refsect1>
 145     <refsect1 id="Copyright"><title>Copyright</title>
 146         <para>
 147             Copyright <trademark class="copyright"></trademark> 2011 Khronos Group.
 148             This material may be distributed subject to the terms and conditions set forth in
 149             the Open Publication License, v 1.0, 8 June 1999.
 150             <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
 151         </para>
 152     </refsect1>
 153 </refentry>