upstream-man-pages/man4/xhtml/glDrawElementsInstancedBaseInstance.xml

   1 <?xml version="1.0" encoding="UTF-8"?>
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   4 <?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 V1.69.1" /></head><body><div class="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.
   6                     Symbolic constants
   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>
  18                     are accepted.
  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>.
  35         </p><p>
  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
  39     else {
  40         for (int i = 0; i &lt; primcount ; i++) {
  41             instanceID = i;
  42             glDrawElements(mode, count, type, indices);
  43         }
  44         instanceID = 0;
  45     }</pre><p>
  46         </p><p>
  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">
  52   <mml:mrow>
  53     <mml:mfenced open="&#x230A;" close="&#x230B;">
  54       <mml:mfrac>
  55         <mml:mrow>
  56           <mml:mi>gl</mml:mi>
  57           <mml:mo>_</mml:mo>
  58           <mml:mi>InstanceID</mml:mi>
  59         </mml:mrow>
  60         <mml:mi>divisor</mml:mi>
  61       </mml:mfrac>
  62     </mml:mfenced>
  63     <mml:mo lspace="2px" rspace="2px">+</mml:mo>
  64     <mml:mi>baseInstance</mml:mi>
  65   </mml:mrow>
  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.
  69         </p><p>
  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>.
  79         </p><p>
  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.
  81         </p><p>
  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.
  84         </p><p>
  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>