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1 | <?xml version="1.0" encoding="UTF-8"?> |
2 | <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd"> | |
4 | <refentry id="glDepthFunc"> | |
5 | <refmeta> | |
6 | <refmetainfo> | |
7 | <copyright> | |
8 | <year>1991-2006</year> | |
9 | <holder>Silicon Graphics, Inc.</holder> | |
10 | </copyright> | |
11 | </refmetainfo> | |
12 | <refentrytitle>glDepthFunc</refentrytitle> | |
13 | <manvolnum>3G</manvolnum> | |
14 | </refmeta> | |
15 | <refnamediv> | |
16 | <refname>glDepthFunc</refname> | |
17 | <refpurpose>specify the value used for depth buffer comparisons</refpurpose> | |
18 | </refnamediv> | |
19 | <refsynopsisdiv><title>C Specification</title> | |
20 | <funcsynopsis> | |
21 | <funcprototype> | |
22 | <funcdef>void <function>glDepthFunc</function></funcdef> | |
23 | <paramdef>GLenum <parameter>func</parameter></paramdef> | |
24 | </funcprototype> | |
25 | </funcsynopsis> | |
26 | </refsynopsisdiv> | |
27 | <refsect1 id="parameters"><title>Parameters</title> | |
28 | <variablelist> | |
29 | <varlistentry> | |
30 | <term><parameter>func</parameter></term> | |
31 | <listitem> | |
32 | <para> | |
33 | Specifies the depth comparison function. | |
34 | Symbolic constants | |
35 | <constant>GL_NEVER</constant>, | |
36 | <constant>GL_LESS</constant>, | |
37 | <constant>GL_EQUAL</constant>, | |
38 | <constant>GL_LEQUAL</constant>, | |
39 | <constant>GL_GREATER</constant>, | |
40 | <constant>GL_NOTEQUAL</constant>, | |
41 | <constant>GL_GEQUAL</constant>, and | |
42 | <constant>GL_ALWAYS</constant> are accepted. | |
43 | The initial value is <constant>GL_LESS</constant>. | |
44 | </para> | |
45 | </listitem> | |
46 | </varlistentry> | |
47 | </variablelist> | |
48 | </refsect1> | |
49 | <refsect1 id="description"><title>Description</title> | |
50 | <para> | |
51 | <function>glDepthFunc</function> specifies the function used to compare each incoming pixel depth value | |
52 | with the depth value present in the depth buffer. | |
53 | The comparison is performed only if depth testing is enabled. | |
54 | (See <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> of <constant>GL_DEPTH_TEST</constant>.) | |
55 | </para> | |
56 | <para> | |
57 | <parameter>func</parameter> specifies the conditions under which the pixel will be drawn. | |
58 | The comparison functions are as follows: | |
59 | </para> | |
60 | <variablelist> | |
61 | <varlistentry> | |
62 | <term><constant>GL_NEVER</constant></term> | |
63 | <listitem> | |
64 | <para> | |
65 | Never passes. | |
66 | </para> | |
67 | </listitem> | |
68 | </varlistentry> | |
69 | <varlistentry> | |
70 | <term><constant>GL_LESS</constant></term> | |
71 | <listitem> | |
72 | <para> | |
73 | Passes if the incoming depth value is less than the stored depth value. | |
74 | </para> | |
75 | </listitem> | |
76 | </varlistentry> | |
77 | <varlistentry> | |
78 | <term><constant>GL_EQUAL</constant></term> | |
79 | <listitem> | |
80 | <para> | |
81 | Passes if the incoming depth value is equal to the stored depth value. | |
82 | </para> | |
83 | </listitem> | |
84 | </varlistentry> | |
85 | <varlistentry> | |
86 | <term><constant>GL_LEQUAL</constant></term> | |
87 | <listitem> | |
88 | <para> | |
89 | Passes if the incoming depth value is less than or equal to | |
90 | the stored depth value. | |
91 | </para> | |
92 | </listitem> | |
93 | </varlistentry> | |
94 | <varlistentry> | |
95 | <term><constant>GL_GREATER</constant></term> | |
96 | <listitem> | |
97 | <para> | |
98 | Passes if the incoming depth value is greater than the stored depth value. | |
99 | </para> | |
100 | </listitem> | |
101 | </varlistentry> | |
102 | <varlistentry> | |
103 | <term><constant>GL_NOTEQUAL</constant></term> | |
104 | <listitem> | |
105 | <para> | |
106 | Passes if the incoming depth value is not equal to the stored depth value. | |
107 | </para> | |
108 | </listitem> | |
109 | </varlistentry> | |
110 | <varlistentry> | |
111 | <term><constant>GL_GEQUAL</constant></term> | |
112 | <listitem> | |
113 | <para> | |
114 | Passes if the incoming depth value is greater than or equal to | |
115 | the stored depth value. | |
116 | </para> | |
117 | </listitem> | |
118 | </varlistentry> | |
119 | <varlistentry> | |
120 | <term><constant>GL_ALWAYS</constant></term> | |
121 | <listitem> | |
122 | <para> | |
123 | Always passes. | |
124 | </para> | |
125 | </listitem> | |
126 | </varlistentry> | |
127 | </variablelist> | |
128 | <para> | |
129 | The initial value of <parameter>func</parameter> is <constant>GL_LESS</constant>. | |
130 | Initially, depth testing is disabled. If depth testing is disabled or if no | |
131 | depth buffer exists, it is as if the depth test always passes. | |
132 | </para> | |
133 | </refsect1> | |
134 | <refsect1 id="notes"><title>Notes</title> | |
135 | <para> | |
136 | Even if the depth buffer exists and the depth mask is non-zero, the | |
137 | depth buffer is not updated if the depth test is disabled. | |
138 | </para> | |
139 | </refsect1> | |
140 | <refsect1 id="errors"><title>Errors</title> | |
141 | <para> | |
142 | <constant>GL_INVALID_ENUM</constant> is generated if <parameter>func</parameter> is not an accepted value. | |
143 | </para> | |
144 | <para> | |
145 | <constant>GL_INVALID_OPERATION</constant> is generated if <function>glDepthFunc</function> | |
146 | is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> | |
147 | and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>. | |
148 | </para> | |
149 | </refsect1> | |
150 | <refsect1 id="associatedgets"><title>Associated Gets</title> | |
151 | <para> | |
152 | <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_DEPTH_FUNC</constant> | |
153 | </para> | |
154 | <para> | |
155 | <citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_DEPTH_TEST</constant> | |
156 | </para> | |
157 | </refsect1> | |
158 | <refsect1 id="seealso"><title>See Also</title> | |
159 | <para> | |
160 | <citerefentry><refentrytitle>glDepthRange</refentrytitle></citerefentry>, | |
161 | <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>, | |
162 | <citerefentry><refentrytitle>glPolygonOffset</refentrytitle></citerefentry> | |
163 | </para> | |
164 | </refsect1> | |
165 | <refsect1 id="Copyright"><title>Copyright</title> | |
166 | <para> | |
167 | Copyright <trademark class="copyright"></trademark> 1991-2006 | |
168 | Silicon Graphics, Inc. This document is licensed under the SGI | |
169 | Free Software B License. For details, see | |
170 | <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>. | |
171 | </para> | |
172 | </refsect1> | |
173 | </refentry> |