HCoop / clinton / guile-figl.git / blame
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1 | <?xml version="1.0" encoding="UTF-8"?> |
| 2 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd"> | |
| 3 | <!-- saved from url=(0013)about:internet --> | |
| 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>gl_ClipDistance - 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_ClipDistance"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>gl_ClipDistance — provides a forward-compatible mechanism for vertex clipping</p></div><div class="refsynopsisdiv"><h2>Declaration</h2><p> | |
| 5 | <code class="function">gl_ClipDistance</code> is a member of the <code class="function">gl_PerVertex</code> | |
| 6 | named block: | |
| 7 | </p><div class="funcsynopsis"><pre class="programlisting"> out gl_PerVertex { | |
| 8 | vec4 gl_Position; | |
| 9 | float gl_PointSize; | |
| 10 | float gl_ClipDistance[]; | |
| 11 | };</pre></div><p> | |
| 12 | In the fragment language, it is intrinsically declared as: | |
| 13 | </p><div class="funcsynopsis"><code class="function">in float gl_ClipDistance[];</code></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p> | |
| 14 | The <code class="function">gl_ClipDistance</code> variable provides a forward compatible | |
| 15 | mechanism for controlling user clipping. The element <code class="function">gl_ClipDistance[<span class="emphasis"><em>i</em></span>]</code> | |
| 16 | specifies a clip distance for each user clip plane <span class="emphasis"><em>i</em></span>. A distance of 0.0 means that | |
| 17 | the vertex is on the plane, a positive distance means that the vertex is insider the clip plane, and a negative | |
| 18 | distance means that the point is outside the clip plane. The clip distances will be linearly interpolated across | |
| 19 | the primitive and the portion of the primitive with interpolated distances less than 0.0 will be clipped. | |
| 20 | </p><p> | |
| 21 | The <code class="function">gl_ClipDistance</code> array is initially predeclared as unsized and must be | |
| 22 | sized by the shader either by redeclaring it with an explicit size, or by indexing it | |
| 23 | with only integral constant expressions. The array must be sized to include all | |
| 24 | clip planes that are enabled via the OpenGL API; if the size does not include all enabled planes, | |
| 25 | results are undefined. The size may be at most <code class="function">gl_MaxClipDistances</code>. The number | |
| 26 | of variing components consumed by <code class="function">gl_ClipDistance</code> will match the size of the | |
| 27 | array, no matter how many planes are enabled. The shader must also set all values in <code class="function">gl_ClipDistance</code> | |
| 28 | that have been enabled via the OpenGL API, or results are undefined. Values written into | |
| 29 | <code class="function">gl_ClipDistance</code> planes that are not enabled have no effect. | |
| 30 | </p><p> | |
| 31 | In the vertex, tessellation evaluation and geoemtry languages, a single | |
| 32 | global instance of the <code class="function">gl_PerVertex</code> named block is available and | |
| 33 | its <code class="function">gl_ClipDistance</code> member is an output that receives the | |
| 34 | clip distances for the current vertex. It may be written at any time during shader execution. | |
| 35 | The value written to <code class="function">gl_ClipDistance</code> will be used by primitive assembly, | |
| 36 | clipping, culling and other fixed functionality operations, if present, that operate on | |
| 37 | primitives after vertex processing has occurred. | |
| 38 | </p><p> | |
| 39 | In the tessellation control language, the <code class="function">gl_PerVertex</code> named block | |
| 40 | is used to construct an array, <code class="function">gl_out[]</code>, whose <code class="function">gl_ClipDistance</code> | |
| 41 | members hold clip distances for each of the control points, which become available as inputs to the subsequent | |
| 42 | tessellation evaluation shader. | |
| 43 | </p><p> | |
| 44 | The value of <code class="function">gl_ClipDistance</code> (or the <code class="function">gl_ClipDistance</code> member of the <code class="function">gl_out[]</code> | |
| 45 | array, in the case of the tessellation control shader) | |
| 46 | is undefined after the vertex, tessellation control, and tessellation evaluation | |
| 47 | shading stages if the corresponding shader executable does | |
| 48 | not write to gl_ClipDistance. It is also undefined after the geometry processing stage if the geometry shader executable calls | |
| 49 | <a href="EmitVertex.xml"><span class="citerefentry"><span class="refentrytitle">EmitVertex</span></span></a> without having | |
| 50 | written <code class="function">gl_ClipDistance</code> since the last call to <a href="EmitVertex.xml"><span class="citerefentry"><span class="refentrytitle">EmitVertex</span></span></a> | |
| 51 | (or hasn't written it at all). | |
| 52 | </p><p> | |
| 53 | In the tessellation control, tessellation evaluation and geoemetry languages, | |
| 54 | the <code class="function">gl_PerVertex</code> named block is used to construct an array, <code class="function">gl_in[]</code> | |
| 55 | of per-vertex or per-control point inputs whose content represents the corresponding | |
| 56 | outputs written by the previous stage. Only elements of the <code class="function">gl_ClipDistance</code> | |
| 57 | array that correspond to enabled clip planes have defined values. | |
| 58 | </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" /><col align="center" /><col align="center" /><col align="center" /><col align="center" /><col align="center" /><col align="center" /><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><th align="left"><span class="bold"><strong>Version 4.20</strong></span></th><th align="center"><span class="bold"><strong>Version 4.30</strong></span></th></tr><tr><th align="left">gl_ClipDistance</th><th align="center"><span class="emphasis"><em>-</em></span></th><th align="center"><span class="emphasis"><em>-</em></span></th><th align="center"><span class="emphasis"><em>Y</em></span></th><th align="center"><span class="emphasis"><em>Y</em></span></th><th align="center"><span class="emphasis"><em>Y</em></span></th><th align="center"><span class="emphasis"><em>Y</em></span></th><th align="center"><span class="emphasis"><em>Y</em></span></th><th align="center"><span class="emphasis"><em>Y</em></span></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 1.30 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> | |
| 59 | <a href="gl_PointSize.xml"><span class="citerefentry"><span class="refentrytitle">gl_PointSize</span></span></a> | |
| 60 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p> | |
| 61 | Copyright <span class="trademark"></span>© 2011 Khronos Group. | |
| 62 | This material may be distributed subject to the terms and conditions set forth in | |
| 63 | the Open Publication License, v 1.0, 8 June 1999. | |
| 64 | <a href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>. | |
| 65 | </p></div></div></body></html> |