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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> |