upstream-man-pages/man4/glMultiDrawElementsIndirect.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="glMultiDrawElementsIndirect">
   5     <refmeta>
   6         <refmetainfo>
   7             <copyright>
   8                 <year>2012</year>
   9                 <holder>Khronos Group.</holder>
  10             </copyright>
  11         </refmetainfo>
  12         <refentrytitle>glMultiDrawElementsIndirect</refentrytitle>
  13         <manvolnum>3G</manvolnum>
  14     </refmeta>
  15     <refnamediv>
  16         <refname>glMultiDrawElementsIndirect</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>glMultiDrawElementsIndirect</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                 <paramdef>GLsizei <parameter>drawcount</parameter></paramdef>
  27                 <paramdef>GLsizei <parameter>stride</parameter></paramdef>
  28             </funcprototype>
  29         </funcsynopsis>
  30     </refsynopsisdiv>
  31     <!-- eqn: ignoring delim $$ -->
  32     <refsect1 id="parameters"><title>Parameters</title>
  33         <variablelist>
  34         <varlistentry>
  35             <term><parameter>mode</parameter></term>
  36             <listitem>
  37                 <para>
  38                     Specifies what kind of primitives to render.
  39                     Symbolic constants
  40                     <constant>GL_POINTS</constant>,
  41                     <constant>GL_LINE_STRIP</constant>,
  42                     <constant>GL_LINE_LOOP</constant>,
  43                     <constant>GL_LINES</constant>,
  44                     <constant>GL_LINE_STRIP_ADJACENCY</constant>,
  45                     <constant>GL_LINES_ADJACENCY</constant>,
  46                     <constant>GL_TRIANGLE_STRIP</constant>,
  47                     <constant>GL_TRIANGLE_FAN</constant>,
  48                     <constant>GL_TRIANGLES</constant>,
  49                     <constant>GL_TRIANGLE_STRIP_ADJACENCY</constant>,
  50                     <constant>GL_TRIANGLES_ADJACENCY</constant>, and
  51                     <constant>GL_PATCHES</constant>
  52                     are accepted.
  53                 </para>
  54             </listitem>
  55         </varlistentry>
  56         <varlistentry>
  57             <term><parameter>type</parameter></term>
  58             <listitem>
  59                 <para>
  60                     Specifies the type of data in the buffer bound to the <constant>GL_ELEMENT_ARRAY_BUFFER</constant> binding.
  61                 </para>
  62             </listitem>
  63         </varlistentry>
  64         <varlistentry>
  65             <term><parameter>indirect</parameter></term>
  66             <listitem>
  67                 <para>
  68                     Specifies the address of a structure containing an array of draw parameters.
  69                 </para>
  70             </listitem>
  71         </varlistentry>
  72         <varlistentry>
  73             <term><parameter>drawcount</parameter></term>
  74             <listitem>
  75                 <para>
  76                     Specifies the number of elements in the array addressed by <parameter>indirect</parameter>.
  77                 </para>
  78             </listitem>
  79         </varlistentry>
  80         <varlistentry>
  81             <term><parameter>stride</parameter></term>
  82             <listitem>
  83                 <para>
  84                     Specifies the distance in basic machine units between elements of the draw parameter array.
  85                 </para>
  86             </listitem>
  87         </varlistentry>
  88         </variablelist>
  89     </refsect1>
  90     <refsect1 id="description"><title>Description</title>
  91         <para>
  92             <function>glMultiDrawElementsIndirect</function> specifies multiple indexed geometric primitives
  93             with very few subroutine calls. <function>glMultiDrawElementsIndirect</function> behaves
  94             similarly to a multitude of calls to <citerefentry><refentrytitle>glDrawElementsInstancedBaseVertexBaseInstance</refentrytitle></citerefentry>,
  95             execpt that the parameters to <citerefentry><refentrytitle>glDrawElementsInstancedBaseVertexBaseInstance</refentrytitle></citerefentry>
  96             are stored in an array in memory at the address given by <parameter>indirect</parameter>, separated
  97             by the stride, in basic machine units, specified by <parameter>stride</parameter>. If <parameter>stride</parameter>
  98             is zero, then the array is assumed to be tightly packed in memory.
  99         </para>
 100         <para>
 101             The parameters addressed by <parameter>indirect</parameter> are packed into a structure
 102             that takes the form (in C):
 103             <programlisting><![CDATA[    typedef  struct {
 104         uint  count;
 105         uint  primCount;
 106         uint  firstIndex;
 107         uint  baseVertex;
 108         uint  baseInstance;
 109     } DrawElementsIndirectCommand;]]></programlisting>
 110         </para>
 111         <para>
 112             A single call to <function>glMultiDrawElementsIndirect</function> is equivalent, assuming no errors
 113             are generated to:
 114             <programlisting><![CDATA[    GLsizei n;
 115     for (n = 0; n < drawcount; n++)
 116     {
 117         const DrawElementsIndirectCommand  *cmd;
 118         if (stride != 0)
 119         {
 120             cmd = (const DrawElementsIndirectCommand  *)((uintptr)indirect + n * stride);
 121         }
 122         else
 123         {
 124             cmd = (const DrawElementsIndirectCommand  *)indirect + n;
 125         }
 126
 127         glDrawElementsInstancedBaseVertexBaseInstance(mode,
 128                                                       cmd->count,
 129                                                       type,
 130                                                       cmd->firstIndex + size-of-type,
 131                                                       cmd->primCount,
 132                                                       cmd->baseVertex,
 133                                                       cmd->baseInstance);
 134     }]]></programlisting>
 135         </para>
 136         <para>
 137             If a buffer is bound to the <constant>GL_DRAW_INDIRECT_BUFFER</constant> binding at the time
 138             of a call to <function>glDrawElementsIndirect</function>, <parameter>indirect</parameter>
 139             is interpreted as an offset, in basic machine units, into that buffer and the parameter
 140             data is read from the buffer rather than from client memory.
 141         </para>
 142         <para>
 143             Note that indices stored in client memory are not supported. If no buffer is bound to the
 144             <constant>GL_ELEMENT_ARRAY_BUFFER</constant> binding, an error will be generated.
 145         </para>
 146         <para>
 147             The results of the operation are undefined if the <code>reservedMustBeZero</code> member
 148             of the parameter structure is non-zero. However, no error is generated in this case.
 149         </para>
 150         <para>
 151             Vertex attributes that are modified by <function>glDrawElementsIndirect</function> have an
 152             unspecified value after <function>glDrawElementsIndirect</function> returns. Attributes that aren't
 153             modified remain well defined.
 154         </para>
 155     </refsect1>
 156     <refsect1 id="notes"><title>Notes</title>
 157         <para>
 158             The <parameter>baseInstance</parameter> member of the <parameter>DrawElementsIndirectCommand</parameter>
 159             structure is defined only if the GL version is 4.2 or greater. For versions of the GL less than 4.2,
 160             this parameter is present but is reserved and should be set to zero. On earlier versions of the GL,
 161             behavior is undefined if it is non-zero.
 162         </para>
 163     </refsect1>
 164     <refsect1 id="errors"><title>Errors</title>
 165         <para>
 166             <constant>GL_INVALID_ENUM</constant> is generated if <parameter>mode</parameter> is not an accepted value.
 167         </para>
 168         <para>
 169             <constant>GL_INVALID_VALUE</constant> is generated if <parameter>stride</parameter> is not a multiple
 170             of four.
 171         </para>
 172         <para>
 173             <constant>GL_INVALID_VALUE</constant> is generated if <parameter>drawcount</parameter> is negative.
 174         </para>
 175         <para>
 176             <constant>GL_INVALID_OPERATION</constant> is generated if no buffer is bound to the <constant>GL_ELEMENT_ARRAY_BUFFER</constant>
 177             binding, or if such a buffer's data store is currently mapped.
 178         </para>
 179         <para>
 180             <constant>GL_INVALID_OPERATION</constant> is generated if a non-zero buffer object name is bound to an
 181             enabled array or to the <constant>GL_DRAW_INDIRECT_BUFFER</constant> binding and the buffer object's data store is currently mapped.
 182         </para>
 183         <para>
 184             <constant>GL_INVALID_OPERATION</constant> is generated if a geometry shader is active and <parameter>mode</parameter>
 185             is incompatible with the input primitive type of the geometry shader in the currently installed program object.
 186         </para>
 187         <para>
 188             <constant>GL_INVALID_OPERATION</constant> is generated if <parameter>mode</parameter> is <constant>GL_PATCHES</constant>
 189             and no tessellation control shader is active.
 190         </para>
 191     </refsect1>
 192     <refsect1 id="seealso"><title>See Also</title>
 193         <para>
 194             <citerefentry><refentrytitle>glDrawArrays</refentrytitle></citerefentry>,
 195             <citerefentry><refentrytitle>glDrawArraysInstanced</refentrytitle></citerefentry>,
 196             <citerefentry><refentrytitle>glDrawArraysIndirect</refentrytitle></citerefentry>,
 197             <citerefentry><refentrytitle>glDrawElements</refentrytitle></citerefentry>,
 198             <citerefentry><refentrytitle>glDrawRangeElements</refentrytitle></citerefentry>,
 199             <citerefentry><refentrytitle>glDrawElementsIndirect</refentrytitle></citerefentry>,
 200             <citerefentry><refentrytitle>glMultiDrawArraysIndirect</refentrytitle></citerefentry>
 201         </para>
 202     </refsect1>
 203     <refsect1 id="Copyright"><title>Copyright</title>
 204         <para>
 205             Copyright <trademark class="copyright"></trademark> 2010-2012 Khronos Group.
 206             This material may be distributed subject to the terms and conditions set forth in
 207             the Open Publication License, v 1.0, 8 June 1999.
 208             <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>.
 209         </para>
 210     </refsect1>
 211 </refentry>