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<?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>gl_Position - OpenGL Shading Language (GLSL)</title><meta name="generator" content="DocBook XSL Stylesheets V1.69.1" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="gl_Position"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>gl_Position — contains the position of the current vertex</p></div><div class="refsynopsisdiv"><h2>Declaration</h2><p>
            <code class="function">gl_Position</code> is a member of the <code class="function">gl_PerVertex</code>
            named block:
        </p><div class="funcsynopsis"><pre class="programlisting">    out gl_PerVertex {
        vec4 gl_Position;
        float gl_PointSize;
        float gl_ClipDistance[];
    };</pre></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
            In the vertex, tessellation evaluation and geoemtry languages, a single
            global instance of the <code class="function">gl_PerVertex</code> named block is available and
            its <code class="function">gl_Position</code> member is an output that receives the
            homogeneous vertex position. It may be written at any time during shader execution.
            The value written to <code class="function">gl_Position</code> will be used by primitive assembly,
            clipping, culling and other fixed functionality operations, if present, that operate on
            primitives after vertex processing has occurred.
        </p><p>
            In the tessellation control language, the <code class="function">gl_PerVertex</code> named block
            is used to construct an array, <code class="function">gl_out[]</code>, whose <code class="function">gl_Position</code>
            members hold the homogeneous control point position, which become available as inputs to the subsequent
            tessellation evaluation shader.
        </p><p>
            The value of <code class="function">gl_Position</code> (or the <code class="function">gl_Position</code> member of the <code class="function">gl_out[]</code>
            array, in the case of the tessellation control shader)
            is undefined after the vertex, tessellation control, and tessellation evaluation
            shading stages if the corresponding shader executable does
            not write to gl_Position. It is also undefined after the geometry processing stage if the geometry shader executable calls
            <a href="EmitVertex.xml"><span class="citerefentry"><span class="refentrytitle">EmitVertex</span></span></a> without having
            written <code class="function">gl_Position</code> since the last call to <a href="EmitVertex.xml"><span class="citerefentry"><span class="refentrytitle">EmitVertex</span></span></a>
            (or hasn't written it at all).
        </p><p>
            In the tessellation control, tessellation evaluation and geoemetry languages,
            the <code class="function">gl_PerVertex</code> named block is used to construct an array, <code class="function">gl_in[]</code>
            of per-vertex or per-control point inputs whose content represents the corresponding
            outputs written by the previous stage.
         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="versions"></a><h2>Version Support</h2><div class="informaltable"><table border="1"><colgroup><col align="left" /><col align="center" /><col align="center" /></colgroup><thead><tr><th align="left"><span class="bold"><strong>
                        Variable
                        </strong></span></th><th align="left"><span class="bold"><strong>
                        Version 1.10
                        </strong></span></th><th align="left"><span class="bold"><strong>
                        Version 1.20
                        </strong></span></th><th align="left"><span class="bold"><strong>
                        Version 1.30
                        </strong></span></th><th align="left"><span class="bold"><strong>
                        Version 1.40
                        </strong></span></th><th align="left"><span class="bold"><strong>
                        Version 1.50
                        </strong></span></th><th align="left"><span class="bold"><strong>
                        Version 3.30
                        </strong></span></th><th align="left"><span class="bold"><strong>
                        Version 4.00
                        </strong></span></th><th align="left"><span class="bold"><strong>
                        Version 4.10
                        </strong></span></th></tr><tr><th align="left">
                            gl_Position
                        </th><th align="center">
                            <span class="emphasis"><em>Y</em></span><sup>1</sup>  
                        </th><th align="center">
                            <span class="emphasis"><em>Y</em></span><sup>1</sup>  
                        </th><th align="center">
                            <span class="emphasis"><em>Y</em></span><sup>1</sup>  
                        </th><th align="center">
                            <span class="emphasis"><em>Y</em></span><sup>1</sup>  
                        </th><th align="center">
                            <span class="emphasis"><em>Y</em></span><sup>2</sup>  
                        </th><th align="center">
                            <span class="emphasis"><em>Y</em></span><sup>2</sup>  
                        </th><th align="center">
                            <span class="emphasis"><em>Y</em></span>  
                        </th><th align="center">
                            <span class="emphasis"><em>Y</em></span>  
                        </th></tr></thead></table></div><p>Versions 1.10 to 1.40 - vertex shader only.</p><p>Versions 1.50 to 3.30 - vertex and geometry shaders only.</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
            <a href="gl_PointSize.xml"><span class="citerefentry"><span class="refentrytitle">gl_PointSize</span></span></a>, <a href="gl_ClipDistance.xml"><span class="citerefentry"><span class="refentrytitle">gl_ClipDistance</span></span></a>
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
            Copyright <span class="trademark"></span>© 2011 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 href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
        </p></div></div></body></html>
