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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>glDepthFunc</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>
                    Specifies the depth comparison function.
                    Symbolic constants
                    <code class="constant">GL_NEVER</code>,
                    <code class="constant">GL_LESS</code>,
                    <code class="constant">GL_EQUAL</code>,
                    <code class="constant">GL_LEQUAL</code>,
                    <code class="constant">GL_GREATER</code>,
                    <code class="constant">GL_NOTEQUAL</code>,
                    <code class="constant">GL_GEQUAL</code>, and
                    <code class="constant">GL_ALWAYS</code> are accepted.
                    The initial value is <code class="constant">GL_LESS</code>.
                </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
            <code class="function">glDepthFunc</code> specifies the function used to compare each incoming pixel depth value
            with the depth value present in the depth buffer.
            The comparison is performed only if depth testing is enabled.
            (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>.)
        </p><p>
            <em class="parameter"><code>func</code></em> specifies the conditions under which the pixel will be drawn.
            The comparison functions are as follows:
        </p><div class="variablelist"><dl><dt><span class="term"><code class="constant">GL_NEVER</code></span></dt><dd><p>
                        Never passes.
                    </p></dd><dt><span class="term"><code class="constant">GL_LESS</code></span></dt><dd><p>
                        Passes if the incoming depth value is less than the stored depth value.
                    </p></dd><dt><span class="term"><code class="constant">GL_EQUAL</code></span></dt><dd><p>
                        Passes if the incoming depth value is equal to the stored depth value.
                    </p></dd><dt><span class="term"><code class="constant">GL_LEQUAL</code></span></dt><dd><p>
                        Passes if the incoming depth value is less than or equal to
                        the stored depth value.
                    </p></dd><dt><span class="term"><code class="constant">GL_GREATER</code></span></dt><dd><p>
                        Passes if the incoming depth value is greater than the stored depth value.
                    </p></dd><dt><span class="term"><code class="constant">GL_NOTEQUAL</code></span></dt><dd><p>
                        Passes if the incoming depth value is not equal to the stored depth value.
                    </p></dd><dt><span class="term"><code class="constant">GL_GEQUAL</code></span></dt><dd><p>
                        Passes if the incoming depth value is greater than or equal to
                        the stored depth value.
                    </p></dd><dt><span class="term"><code class="constant">GL_ALWAYS</code></span></dt><dd><p>
                        Always passes.
                    </p></dd></dl></div><p>
            The initial value of <em class="parameter"><code>func</code></em> is <code class="constant">GL_LESS</code>.
            Initially, depth testing is disabled.  If depth testing is disabled or if no
            depth buffer exists, it is as if the depth test always passes.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>
            Even if the depth buffer exists and the depth mask is non-zero, the
            depth buffer is not updated if the depth test is disabled. In order to
            unconditionally write to the depth buffer, the depth test should be enabled
            and set to <code class="constant">GL_ALWAYS</code>.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p>
            <code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>func</code></em> is not an accepted value.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p>
            <a href="glGet.xml"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_DEPTH_FUNC</code>
        </p><p>
            <a href="glIsEnabled.xml"><span class="citerefentry"><span class="refentrytitle">glIsEnabled</span></span></a> with argument <code class="constant">GL_DEPTH_TEST</code>
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
            <a href="glDepthRange.xml"><span class="citerefentry"><span class="refentrytitle">glDepthRange</span></span></a>,
            <a href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>,
            <a href="glPolygonOffset.xml"><span class="citerefentry"><span class="refentrytitle">glPolygonOffset</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>© 1991-2006
            Silicon Graphics, Inc. This document is licensed under the SGI
            Free Software B License. For details, see
            <a href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>.
        </p></div></div></body></html>
