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

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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>glDepthFunc - 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="glDepthFunc"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glDepthFunc — specify the value used for depth buffer comparisons</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><p><code class="funcdef">void <b class="fsfunc">glDepthFunc</b>(</code>GLenum <var class="pdparam">func</var><code>)</code>;</p></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>func</code></em></span></dt><dd><p>
   5                     Specifies the depth comparison function.
   6                     Symbolic constants
   7                     <code class="constant">GL_NEVER</code>,
   8                     <code class="constant">GL_LESS</code>,
   9                     <code class="constant">GL_EQUAL</code>,
  10                     <code class="constant">GL_LEQUAL</code>,
  11                     <code class="constant">GL_GREATER</code>,
  12                     <code class="constant">GL_NOTEQUAL</code>,
  13                     <code class="constant">GL_GEQUAL</code>, and
  14                     <code class="constant">GL_ALWAYS</code> are accepted.
  15                     The initial value is <code class="constant">GL_LESS</code>.
  16                 </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
  17             <code class="function">glDepthFunc</code> specifies the function used to compare each incoming pixel depth value
  18             with the depth value present in the depth buffer.
  19             The comparison is performed only if depth testing is enabled.
  20             (See <a href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> and <a href="glDisable.xml"><span class="citerefentry"><span class="refentrytitle">glDisable</span></span></a> of <code class="constant">GL_DEPTH_TEST</code>.)
  21         </p><p>
  22             <em class="parameter"><code>func</code></em> specifies the conditions under which the pixel will be drawn.
  23             The comparison functions are as follows:
  24         </p><div class="variablelist"><dl><dt><span class="term"><code class="constant">GL_NEVER</code></span></dt><dd><p>
  25                         Never passes.
  26                     </p></dd><dt><span class="term"><code class="constant">GL_LESS</code></span></dt><dd><p>
  27                         Passes if the incoming depth value is less than the stored depth value.
  28                     </p></dd><dt><span class="term"><code class="constant">GL_EQUAL</code></span></dt><dd><p>
  29                         Passes if the incoming depth value is equal to the stored depth value.
  30                     </p></dd><dt><span class="term"><code class="constant">GL_LEQUAL</code></span></dt><dd><p>
  31                         Passes if the incoming depth value is less than or equal to
  32                         the stored depth value.
  33                     </p></dd><dt><span class="term"><code class="constant">GL_GREATER</code></span></dt><dd><p>
  34                         Passes if the incoming depth value is greater than the stored depth value.
  35                     </p></dd><dt><span class="term"><code class="constant">GL_NOTEQUAL</code></span></dt><dd><p>
  36                         Passes if the incoming depth value is not equal to the stored depth value.
  37                     </p></dd><dt><span class="term"><code class="constant">GL_GEQUAL</code></span></dt><dd><p>
  38                         Passes if the incoming depth value is greater than or equal to
  39                         the stored depth value.
  40                     </p></dd><dt><span class="term"><code class="constant">GL_ALWAYS</code></span></dt><dd><p>
  41                         Always passes.
  42                     </p></dd></dl></div><p>
  43             The initial value of <em class="parameter"><code>func</code></em> is <code class="constant">GL_LESS</code>.
  44             Initially, depth testing is disabled.  If depth testing is disabled or if no
  45             depth buffer exists, it is as if the depth test always passes.
  46         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>
  47             Even if the depth buffer exists and the depth mask is non-zero, the
  48             depth buffer is not updated if the depth test is disabled. In order to
  49             unconditionally write to the depth buffer, the depth test should be enabled
  50             and set to <code class="constant">GL_ALWAYS</code>.
  51         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p>
  52             <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>func</code></em> is not an accepted value.
  53         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p>
  54             <a href="glGet.xml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_DEPTH_FUNC</code>
  55         </p><p>
  56             <a href="glIsEnabled.xml"><span class="citerefentry"><span class="refentrytitle">glIsEnabled</span></span></a> with argument <code class="constant">GL_DEPTH_TEST</code>
  57         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
  58             <a href="glDepthRange.xml"><span class="citerefentry"><span class="refentrytitle">glDepthRange</span></span></a>,
  59             <a href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>,
  60             <a href="glPolygonOffset.xml"><span class="citerefentry"><span class="refentrytitle">glPolygonOffset</span></span></a>
  61         </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p>
  62             Copyright <span class="trademark"></span>© 1991-2006
  63             Silicon Graphics, Inc. This document is licensed under the SGI
  64             Free Software B License. For details, see
  65             <a href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>.
  66         </p></div></div></body></html>