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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd">
<?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" pref:renderer="mathplayer-dl"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><link rel="stylesheet" type="text/css" href="opengl-man.css" /><title>glDrawElementsInstancedBaseInstance - OpenGL 4 Reference Pages</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1" /></head><body><div class="refentry"><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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void <strong class="fsfunc">glDrawElementsInstancedBaseInstance</strong>(</code></td><td>GLenum <var class="pdparam">mode</var>, </td></tr><tr><td> </td><td>GLsizei <var class="pdparam">count</var>, </td></tr><tr><td> </td><td>GLenum <var class="pdparam">type</var>, </td></tr><tr><td> </td><td>const void * <var class="pdparam">indices</var>, </td></tr><tr><td> </td><td>GLsizei <var class="pdparam">primcount</var>, </td></tr><tr><td> </td><td>GLuitn <var class="pdparam">baseinstance</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>mode</code></em></span></dt><dd><p>
Specifies what kind of primitives to render.
Symbolic constants
<code class="constant">GL_POINTS</code>,
<code class="constant">GL_LINE_STRIP</code>,
<code class="constant">GL_LINE_LOOP</code>,
<code class="constant">GL_LINES</code>,
<code class="constant">GL_LINE_STRIP_ADJACENCY</code>,
<code class="constant">GL_LINES_ADJACENCY</code>,
<code class="constant">GL_TRIANGLE_STRIP</code>,
<code class="constant">GL_TRIANGLE_FAN</code>,
<code class="constant">GL_TRIANGLES</code>,
<code class="constant">GL_TRIANGLE_STRIP_ADJACENCY</code>,
<code class="constant">GL_TRIANGLES_ADJACENCY</code> and <code class="constant">GL_PATCHES</code>
are accepted.
</p></dd><dt><span class="term"><em class="parameter"><code>count</code></em></span></dt><dd><p>
Specifies the number of elements to be rendered.
</p></dd><dt><span class="term"><em class="parameter"><code>type</code></em></span></dt><dd><p>
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>,
<code class="constant">GL_UNSIGNED_SHORT</code>, or <code class="constant">GL_UNSIGNED_INT</code>.
</p></dd><dt><span class="term"><em class="parameter"><code>indices</code></em></span></dt><dd><p>
Specifies a pointer to the location where the indices are stored.
</p></dd><dt><span class="term"><em class="parameter"><code>primcount</code></em></span></dt><dd><p>
Specifies the number of instances of the specified range of indices to be rendered.
</p></dd><dt><span class="term"><em class="parameter"><code>baseinstance</code></em></span></dt><dd><p>
Specifies the base instance for use in fetching instanced vertex attributes.
</p></dd></dl></div></div><div class="refsect1"><a id="description"></a><h2>Description</h2><p>
<code class="function">glDrawElementsInstancedBaseInstance</code> behaves identically to <a class="citerefentry" href="glDrawElements.xml"><span class="citerefentry"><span class="refentrytitle">glDrawElements</span></span></a>
except that <em class="parameter"><code>primcount</code></em> instances of the set of elements are executed and the value of the internal counter
<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
that may be read by a vertex shader as <code class="constant">gl_InstanceID</code>.
</p><p>
<code class="function">glDrawElementsInstancedBaseInstance</code> has the same effect as:
</p><pre class="programlisting"> if (mode, count, or type is invalid )
generate appropriate error
else {
for (int i = 0; i < primcount ; i++) {
instanceID = i;
glDrawElements(mode, count, type, indices);
}
instanceID = 0;
}</pre><p>
</p><p>
Specific vertex attributes may be classified as <span class="emphasis"><em>instanced</em></span> through the use of
<a class="citerefentry" href="glVertexAttribDivisor.xml"><span class="citerefentry"><span class="refentrytitle">glVertexAttribDivisor</span></span></a>. Instanced vertex attributes
supply per-instance vertex data to the vertex shader. The index of the vertex fetched from the enabled instanced vertex
attribute arrays is calculated as
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:mrow>
<mml:mfenced open="⌊" close="⌋">
<mml:mfrac>
<mml:mrow>
<mml:mi>gl</mml:mi>
<mml:mo>_</mml:mo>
<mml:mi>InstanceID</mml:mi>
</mml:mrow>
<mml:mi>divisor</mml:mi>
</mml:mfrac>
</mml:mfenced>
<mml:mo lspace="2px" rspace="2px">+</mml:mo>
<mml:mi>baseInstance</mml:mi>
</mml:mrow>
</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>.
</p></div><div class="refsect1"><a id="notes"></a><h2>Notes</h2><p>
<code class="function">glDrawElementsInstancedBaseInstance</code> is available only if the GL version is 4.2 or greater.
</p><p>
<code class="constant">GL_LINE_STRIP_ADJACENCY</code>,
<code class="constant">GL_LINES_ADJACENCY</code>,
<code class="constant">GL_TRIANGLE_STRIP_ADJACENCY</code> and
<code class="constant">GL_TRIANGLES_ADJACENCY</code>
are available only if the GL version is 3.2 or greater.
</p></div><div class="refsect1"><a id="errors"></a><h2>Errors</h2><p>
<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>,
<code class="constant">GL_LINE_STRIP</code>, <code class="constant">GL_LINE_LOOP</code>, <code class="constant">GL_LINES</code>,
<code class="constant">GL_TRIANGLE_STRIP</code>, <code class="constant">GL_TRIANGLE_FAN</code>, or <code class="constant">GL_TRIANGLES</code>.
</p><p>
<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.
</p><p>
<code class="constant">GL_INVALID_OPERATION</code> is generated if a geometry shader is active and <em class="parameter"><code>mode</code></em>
is incompatible with the input primitive type of the geometry shader in the currently installed program object.
</p><p>
<code class="constant">GL_INVALID_OPERATION</code> is generated if a non-zero buffer object name is bound to an
enabled array and the buffer object's data store is currently mapped.
</p></div><div class="refsect1"><a id="seealso"></a><h2>See Also</h2><p>
<a class="citerefentry" href="glDrawElements.xml"><span class="citerefentry"><span class="refentrytitle">glDrawElements</span></span></a>,
<a class="citerefentry" href="glDrawArraysInstanced.xml"><span class="citerefentry"><span class="refentrytitle">glDrawArraysInstanced</span></span></a>
</p></div><div class="refsect1"><a id="Copyright"></a><h2>Copyright</h2><p>
Copyright <span class="trademark"></span>© 2011-2013 Khronos Group.
This material may be distributed subject to the terms and conditions set forth in
the Open Publication License, v 1.0, 8 June 1999.
<a class="ulink" href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
</p></div></div></body></html>
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