upstream-man-pages/man4/glDrawElementsIndirect.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="glDrawElementsIndirect">
   5     <refmeta>
   6         <refmetainfo>
   7             <copyright>
   8                 <year>2010</year>
   9                 <holder>Khronos Group.</holder>
  10             </copyright>
  11         </refmetainfo>
  12         <refentrytitle>glDrawElementsIndirect</refentrytitle>
  13         <manvolnum>3G</manvolnum>
  14     </refmeta>
  15     <refnamediv>
  16         <refname>glDrawElementsIndirect</refname>
  17         <refpurpose>render indexed primitives from array data, taking parameters from memory</refpurpose>
  18     </refnamediv>
  19     <refsynopsisdiv><title>C Specification</title>
  20         <funcsynopsis>
  21             <funcprototype>
  22                 <funcdef>void <function>glDrawElementsIndirect</function></funcdef>
  23                 <paramdef>GLenum <parameter>mode</parameter></paramdef>
  24                 <paramdef>GLenum <parameter>type</parameter></paramdef>
  25                 <paramdef>const void *<parameter>indirect</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>mode</parameter></term>
  34             <listitem>
  35                 <para>
  36                     Specifies what kind of primitives to render.
  37                     Symbolic constants
  38                     <constant>GL_POINTS</constant>,
  39                     <constant>GL_LINE_STRIP</constant>,
  40                     <constant>GL_LINE_LOOP</constant>,
  41                     <constant>GL_LINES</constant>,
  42                     <constant>GL_LINE_STRIP_ADJACENCY</constant>,
  43                     <constant>GL_LINES_ADJACENCY</constant>,
  44                     <constant>GL_TRIANGLE_STRIP</constant>,
  45                     <constant>GL_TRIANGLE_FAN</constant>,
  46                     <constant>GL_TRIANGLES</constant>,
  47                     <constant>GL_TRIANGLE_STRIP_ADJACENCY</constant>,
  48                     <constant>GL_TRIANGLES_ADJACENCY</constant>, and
  49                     <constant>GL_PATCHES</constant>
  50                     are accepted.
  51                 </para>
  52             </listitem>
  53         </varlistentry>
  54         <varlistentry>
  55             <term><parameter>type</parameter></term>
  56             <listitem>
  57                 <para>
  58                     Specifies the type of data in the buffer bound to the <constant>GL_ELEMENT_ARRAY_BUFFER</constant> binding.
  59                 </para>
  60             </listitem>
  61         </varlistentry>
  62         <varlistentry>
  63             <term><parameter>indirect</parameter></term>
  64             <listitem>
  65                 <para>
  66                     Specifies the address of a structure containing the draw parameters.
  67                 </para>
  68             </listitem>
  69         </varlistentry>
  70         </variablelist>
  71     </refsect1>
  72     <refsect1 id="description"><title>Description</title>
  73         <para>
  74             <function>glDrawElementsIndirect</function> specifies multiple indexed geometric primitives
  75             with very few subroutine calls. <function>glDrawElementsIndirect</function> behaves
  76             similarly to <citerefentry><refentrytitle>glDrawElementsInstancedBaseVertexBaseInstance</refentrytitle></citerefentry>,
  77             execpt that the parameters to <citerefentry><refentrytitle>glDrawElementsInstancedBaseVertexBaseInstance</refentrytitle></citerefentry>
  78             are stored in memory at the address given by <parameter>indirect</parameter>.
  79         </para>
  80         <para>
  81             The parameters addressed by <parameter>indirect</parameter> are packed into a structure
  82             that takes the form (in C):
  83             <programlisting><![CDATA[    typedef  struct {
  84         uint  count;
  85         uint  primCount;
  86         uint  firstIndex;
  87         uint  baseVertex;
  88         uint  baseInstance;
  89     } DrawElementsIndirectCommand;]]></programlisting>
  90         <para>
  91             <function>glDrawElementsIndirect</function> is equivalent to:
  92         </para>
  93 <programlisting><![CDATA[    void glDrawElementsIndirect(GLenum mode, GLenum type, const void * indirect)
  94     {
  95         const DrawElementsIndirectCommand *cmd  = (const DrawElementsIndirectCommand *)indirect;
  96         glDrawElementsInstancedBaseVertexBaseInstance(mode,
  97                                                       cmd->count,
  98                                                       type,
  99                                                       cmd->firstIndex + size-of-type,
 100                                                       cmd->primCount,
 101                                                       cmd->baseVertex,
 102                                                       cmd->baseInstance);
 103     }]]></programlisting>
 104         </para>
 105         <para>
 106             If a buffer is bound to the <constant>GL_DRAW_INDIRECT_BUFFER</constant> binding at the time
 107             of a call to <function>glDrawElementsIndirect</function>, <parameter>indirect</parameter>
 108             is interpreted as an offset, in basic machine units, into that buffer and the parameter
 109             data is read from the buffer rather than from client memory.
 110         </para>
 111         <para>
 112             Note that indices stored in client memory are not supported. If no buffer is bound to the
 113             <constant>GL_ELEMENT_ARRAY_BUFFER</constant> binding, an error will be generated.
 114         </para>
 115         <para>
 116             The results of the operation are undefined if the <code>reservedMustBeZero</code> member
 117             of the parameter structure is non-zero. However, no error is generated in this case.
 118         </para>
 119         <para>
 120             Vertex attributes that are modified by <function>glDrawElementsIndirect</function> have an
 121             unspecified value after <function>glDrawElementsIndirect</function> returns. Attributes that aren't
 122             modified remain well defined.
 123         </para>
 124     </refsect1>
 125     <refsect1 id="notes"><title>Notes</title>
 126         <para>
 127             The <parameter>baseInstance</parameter> member of the <parameter>DrawElementsIndirectCommand</parameter>
 128             structure is defined only if the GL version is 4.2 or greater. For versions of the GL less than 4.2,
 129             this parameter is present but is reserved and should be set to zero. On earlier versions of the GL,
 130             behavior is undefined if it is non-zero.
 131         </para>
 132     </refsect1>
 133     <refsect1 id="errors"><title>Errors</title>
 134         <para>
 135             <constant>GL_INVALID_ENUM</constant> is generated if <parameter>mode</parameter> is not an accepted value.
 136         </para>
 137         <para>
 138             <constant>GL_INVALID_OPERATION</constant> is generated if no buffer is bound to the <constant>GL_ELEMENT_ARRAY_BUFFER</constant>
 139             binding, or if such a buffer's data store is currently mapped.
 140         </para>
 141         <para>
 142             <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to an
 143             enabled array or to the <constant>GL_DRAW_INDIRECT_BUFFER</constant> binding and the buffer object's data store is currently mapped.
 144         </para>
 145         <para>
 146             <constant>GL_INVALID_OPERATION</constant> is generated if a geometry shader is active and <parameter>mode</parameter>
 147             is incompatible with the input primitive type of the geometry shader in the currently installed program object.
 148         </para>
 149         <para>
 150             <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>mode</parameter> is <constant>GL_PATCHES</constant>
 151             and no tessellation control shader is active.
 152         </para>
 153     </refsect1>
 154     <refsect1 id="seealso"><title>See Also</title>
 155         <para>
 156             <citerefentry><refentrytitle>glDrawArrays</refentrytitle></citerefentry>,
 157             <citerefentry><refentrytitle>glDrawArraysInstanced</refentrytitle></citerefentry>,
 158             <citerefentry><refentrytitle>glDrawArraysIndirect</refentrytitle></citerefentry>,
 159             <citerefentry><refentrytitle>glDrawElements</refentrytitle></citerefentry>,
 160             <citerefentry><refentrytitle>glDrawRangeElements</refentrytitle></citerefentry>,
 161         </para>
 162     </refsect1>
 163     <refsect1 id="Copyright"><title>Copyright</title>
 164         <para>
 165             Copyright <trademark class="copyright"></trademark> 2010 Khronos Group.
 166             This material may be distributed subject to the terms and conditions set forth in
 167             the Open Publication License, v 1.0, 8 June 1999.
 168             <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
 169         </para>
 170     </refsect1>
 171 </refentry>