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4 Reference Pages
</title><meta name=
"generator" content=
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"refentry" lang=
"en" xml:
lang=
"en"><a id=
"glDrawElementsInstancedBaseInstance"></a><div class=
"titlepage"></div><div class=
"refnamediv"><h2>Name
</h2><p>glDrawElementsInstancedBaseInstance — draw multiple instances of a set of elements with offset applied to instanced attributes
</p></div><div class=
"refsynopsisdiv"><h2>C Specification
</h2><div class=
"funcsynopsis"><table border=
"0" summary=
"Function synopsis" cellspacing=
"0" cellpadding=
"0"><tr><td><code class=
"funcdef">void
<b class=
"fsfunc">glDrawElementsInstancedBaseInstance
</b>(
</code></td><td>GLenum
</td><td><var class=
"pdparam">mode
</var>,
</td></tr><tr><td> </td><td>GLsizei
</td><td><var class=
"pdparam">count
</var>,
</td></tr><tr><td> </td><td>GLenum
</td><td><var class=
"pdparam">type
</var>,
</td></tr><tr><td> </td><td>const void *
</td><td><var class=
"pdparam">indices
</var>,
</td></tr><tr><td> </td><td>GLsizei
</td><td><var class=
"pdparam">primcount
</var>,
</td></tr><tr><td> </td><td>GLuitn
</td><td><var class=
"pdparam">baseinstance
</var><code>)
</code>;
</td></tr></table></div></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"parameters"></a><h2>Parameters
</h2><div class=
"variablelist"><dl><dt><span class=
"term"><em class=
"parameter"><code>mode
</code></em></span></dt><dd><p>
5 Specifies what kind of primitives to render.
7 <code class=
"constant">GL_POINTS
</code>,
8 <code class=
"constant">GL_LINE_STRIP
</code>,
9 <code class=
"constant">GL_LINE_LOOP
</code>,
10 <code class=
"constant">GL_LINES
</code>,
11 <code class=
"constant">GL_LINE_STRIP_ADJACENCY
</code>,
12 <code class=
"constant">GL_LINES_ADJACENCY
</code>,
13 <code class=
"constant">GL_TRIANGLE_STRIP
</code>,
14 <code class=
"constant">GL_TRIANGLE_FAN
</code>,
15 <code class=
"constant">GL_TRIANGLES
</code>,
16 <code class=
"constant">GL_TRIANGLE_STRIP_ADJACENCY
</code>,
17 <code class=
"constant">GL_TRIANGLES_ADJACENCY
</code> and
<code class=
"constant">GL_PATCHES
</code>
19 </p></dd><dt><span class=
"term"><em class=
"parameter"><code>count
</code></em></span></dt><dd><p>
20 Specifies the number of elements to be rendered.
21 </p></dd><dt><span class=
"term"><em class=
"parameter"><code>type
</code></em></span></dt><dd><p>
22 Specifies the type of the values in
<em class=
"parameter"><code>indices
</code></em>. Must be one of
<code class=
"constant">GL_UNSIGNED_BYTE
</code>,
23 <code class=
"constant">GL_UNSIGNED_SHORT
</code>, or
<code class=
"constant">GL_UNSIGNED_INT
</code>.
24 </p></dd><dt><span class=
"term"><em class=
"parameter"><code>indices
</code></em></span></dt><dd><p>
25 Specifies a pointer to the location where the indices are stored.
26 </p></dd><dt><span class=
"term"><em class=
"parameter"><code>primcount
</code></em></span></dt><dd><p>
27 Specifies the number of instances of the specified range of indices to be rendered.
28 </p></dd><dt><span class=
"term"><em class=
"parameter"><code>baseinstance
</code></em></span></dt><dd><p>
29 Specifies the base instance for use in fetching instanced vertex attributes.
30 </p></dd></dl></div></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"description"></a><h2>Description
</h2><p>
31 <code class=
"function">glDrawElementsInstancedBaseInstance
</code> behaves identically to
<a href=
"glDrawElements.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glDrawElements
</span></span></a>
32 except that
<em class=
"parameter"><code>primcount
</code></em> instances of the set of elements are executed and the value of the internal counter
33 <em class=
"parameter"><code>instanceID
</code></em> advances for each iteration.
<em class=
"parameter"><code>instanceID
</code></em> is an internal
32-bit integer counter
34 that may be read by a vertex shader as
<code class=
"constant">gl_InstanceID
</code>.
36 <code class=
"function">glDrawElementsInstancedBaseInstance
</code> has the same effect as:
37 </p><pre class=
"programlisting"> if (mode, count, or type is invalid )
38 generate appropriate error
40 for (int i =
0; i
< primcount ; i++) {
42 glDrawElements(mode, count, type, indices);
47 Specific vertex attributes may be classified as
<span class=
"emphasis"><em>instanced
</em></span> through the use of
48 <a href=
"glVertexAttribDivisor.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glVertexAttribDivisor
</span></span></a>. Instanced vertex attributes
49 supply per-instance vertex data to the vertex shader. The index of the vertex fetched from the enabled instanced vertex
50 attribute arrays is calculated as
51 <mml:math xmlns:
mml=
"http://www.w3.org/1998/Math/MathML" overflow=
"scroll">
53 <mml:mfenced open=
"⌊" close=
"⌋">
58 <mml:mi>InstanceID
</mml:mi>
60 <mml:mi>divisor
</mml:mi>
63 <mml:mo lspace=
"2px" rspace=
"2px">+
</mml:mo>
64 <mml:mi>baseInstance
</mml:mi>
66 </mml:math>. Note that
<em class=
"parameter"><code>baseinstance
</code></em> does not affect the shader-visible value of
<code class=
"constant">gl_InstanceID
</code>.
67 </p></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"notes"></a><h2>Notes
</h2><p>
68 <code class=
"function">glDrawElementsInstancedBaseInstance
</code> is available only if the GL version is
4.2 or greater.
70 <code class=
"constant">GL_LINE_STRIP_ADJACENCY
</code>,
71 <code class=
"constant">GL_LINES_ADJACENCY
</code>,
72 <code class=
"constant">GL_TRIANGLE_STRIP_ADJACENCY
</code> and
73 <code class=
"constant">GL_TRIANGLES_ADJACENCY
</code>
74 are available only if the GL version is
3.2 or greater.
75 </p></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"errors"></a><h2>Errors
</h2><p>
76 <code class=
"constant">GL_INVALID_ENUM
</code> is generated if
<em class=
"parameter"><code>mode
</code></em> is not one of
<code class=
"constant">GL_POINTS
</code>,
77 <code class=
"constant">GL_LINE_STRIP
</code>,
<code class=
"constant">GL_LINE_LOOP
</code>,
<code class=
"constant">GL_LINES
</code>,
78 <code class=
"constant">GL_TRIANGLE_STRIP
</code>,
<code class=
"constant">GL_TRIANGLE_FAN
</code>, or
<code class=
"constant">GL_TRIANGLES
</code>.
80 <code class=
"constant">GL_INVALID_VALUE
</code> is generated if
<em class=
"parameter"><code>count
</code></em> or
<em class=
"parameter"><code>primcount
</code></em> are negative.
82 <code class=
"constant">GL_INVALID_OPERATION
</code> is generated if a geometry shader is active and
<em class=
"parameter"><code>mode
</code></em>
83 is incompatible with the input primitive type of the geometry shader in the currently installed program object.
85 <code class=
"constant">GL_INVALID_OPERATION
</code> is generated if a non-zero buffer object name is bound to an
86 enabled array and the buffer object's data store is currently mapped.
87 </p></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"seealso"></a><h2>See Also
</h2><p>
88 <a href=
"glDrawElements.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glDrawElements
</span></span></a>,
89 <a href=
"glDrawArraysInstanced.xml"><span class=
"citerefentry"><span class=
"refentrytitle">glDrawArraysInstanced
</span></span></a>
90 </p></div><div class=
"refsect1" lang=
"en" xml:
lang=
"en"><a id=
"Copyright"></a><h2>Copyright
</h2><p>
91 Copyright
<span class=
"trademark"></span>©
2011 Khronos Group.
92 This material may be distributed subject to the terms and conditions set forth in
93 the Open Publication License, v
1.0,
8 June
1999.
94 <a href=
"http://opencontent.org/openpub/" target=
"_top">http://opencontent.org/openpub/
</a>.
95 </p></div></div></body></html>