upstream-man-pages/man4/xhtml/glDrawArraysInstancedBaseInstance.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>glDrawArraysInstancedBaseInstance - 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="glDrawArraysInstancedBaseInstance"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glDrawArraysInstancedBaseInstance — draw multiple instances of a range 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">glDrawArraysInstancedBaseInstance</b>(</code></td><td>GLenum  </td><td><var class="pdparam">mode</var>, </td></tr><tr><td> </td><td>GLint  </td><td><var class="pdparam">first</var>, </td></tr><tr><td> </td><td>GLsizei  </td><td><var class="pdparam">count</var>, </td></tr><tr><td> </td><td>GLsizei  </td><td><var class="pdparam">primcount</var>, </td></tr><tr><td> </td><td>GLuint  </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. Symbolic constants <code class="constant">GL_POINTS</code>,
   6                     <code class="constant">GL_LINE_STRIP</code>, <code class="constant">GL_LINE_LOOP</code>, <code class="constant">GL_LINES</code>,
   7                     <code class="constant">GL_TRIANGLE_STRIP</code>, <code class="constant">GL_TRIANGLE_FAN</code>, <code class="constant">GL_TRIANGLES</code>
   8                     <code class="constant">GL_LINES_ADJACENCY</code>, <code class="constant">GL_LINE_STRIP_ADJACENCY</code>,
   9                     <code class="constant">GL_TRIANGLES_ADJACENCY</code>, <code class="constant">GL_TRIANGLE_STRIP_ADJACENCY</code> and <code class="constant">GL_PATCHES</code>
  10                     are accepted.
  11                 </p></dd><dt><span class="term"><em class="parameter"><code>first</code></em></span></dt><dd><p>
  12                     Specifies the starting index in the enabled arrays.
  13                 </p></dd><dt><span class="term"><em class="parameter"><code>count</code></em></span></dt><dd><p>
  14                     Specifies the number of indices to be rendered.
  15                 </p></dd><dt><span class="term"><em class="parameter"><code>primcount</code></em></span></dt><dd><p>
  16                     Specifies the number of instances of the specified range of indices to be rendered.
  17                 </p></dd><dt><span class="term"><em class="parameter"><code>baseinstance</code></em></span></dt><dd><p>
  18                     Specifies the base instance for use in fetching instanced vertex attributes.
  19                 </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
  20             <code class="function">glDrawArraysInstancedBaseInstance</code> behaves identically to <a href="glDrawArrays.xml"><span class="citerefentry"><span class="refentrytitle">glDrawArrays</span></span></a>
  21             except that <em class="parameter"><code>primcount</code></em> instances of the range of elements are executed and the value of the internal counter
  22             <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
  23             that may be read by a vertex shader as <code class="constant">gl_InstanceID</code>.
  24         </p><p>
  25             <code class="function">glDrawArraysInstancedBaseInstance</code> has the same effect as:
  26             </p><pre class="programlisting">    if ( mode or count is invalid )
  27         generate appropriate error
  28     else {
  29         for (int i = 0; i &lt; primcount ; i++) {
  30             instanceID = i;
  31             glDrawArrays(mode, first, count);
  32         }
  33         instanceID = 0;
  34     }</pre><p>
  35         </p><p>
  36             Specific vertex attributes may be classified as <span class="emphasis"><em>instanced</em></span> through the use of
  37             <a href="glVertexAttribDivisor.xml"><span class="citerefentry"><span class="refentrytitle">glVertexAttribDivisor</span></span></a>. Instanced vertex attributes
  38             supply per-instance vertex data to the vertex shader. The index of the vertex fetched from the enabled instanced vertex
  39             attribute arrays is calculated as:
  40 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
  41   <mml:mrow>
  42     <mml:mfenced open="&#x230A;" close="&#x230B;">
  43       <mml:mfrac>
  44         <mml:mrow>
  45           <mml:mi>gl</mml:mi>
  46           <mml:mo>_</mml:mo>
  47           <mml:mi>InstanceID</mml:mi>
  48         </mml:mrow>
  49         <mml:mi>divisor</mml:mi>
  50       </mml:mfrac>
  51     </mml:mfenced>
  52     <mml:mo lspace="2px" rspace="2px">+</mml:mo>
  53     <mml:mi>baseInstance</mml:mi>
  54   </mml:mrow>
  55 </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>.
  56         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p>
  57             <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>mode</code></em> is not one of
  58             the accepted values.
  59         </p><p>
  60             <code class="constant">GL_INVALID_OPERATION</code> is generated if a geometry shader is active and <em class="parameter"><code>mode</code></em>
  61             is incompatible with the input primitive type of the geometry shader in the currently installed program object.
  62         </p><p>
  63             <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.
  64         </p><p>
  65             <code class="constant">GL_INVALID_OPERATION</code> is generated if a non-zero buffer object name is bound to an
  66             enabled array and the buffer object's data store is currently mapped.
  67         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
  68             <a href="glDrawArrays.xml"><span class="citerefentry"><span class="refentrytitle">glDrawArrays</span></span></a>,
  69             <a href="glDrawElementsInstanced.xml"><span class="citerefentry"><span class="refentrytitle">glDrawElementsInstanced</span></span></a>
  70         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
  71             Copyright <span class="trademark"></span>© 2011 Khronos Group.
  72             This material may be distributed subject to the terms and conditions set forth in
  73             the Open Publication License, v 1.0, 8 June 1999.
  74             <a href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
  75         </p></div></div></body></html>