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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="glProvokingVertex"> | |
5 | <refmeta> | |
6 | <refmetainfo> | |
7 | <copyright> | |
8 | <year>2010</year> | |
9 | <holder>Khronos Group</holder> | |
10 | </copyright> | |
11 | </refmetainfo> | |
12 | <refentrytitle>glProvokingVertex</refentrytitle> | |
13 | <manvolnum>3G</manvolnum> | |
14 | </refmeta> | |
15 | <refnamediv> | |
16 | <refname>glProvokingVertex</refname> | |
17 | <refpurpose>specifiy the vertex to be used as the source of data for flat shaded varyings</refpurpose> | |
18 | </refnamediv> | |
19 | <refsynopsisdiv><title>C Specification</title> | |
20 | <funcsynopsis> | |
21 | <funcprototype> | |
22 | <funcdef>void <function>glProvokingVertex</function></funcdef> | |
23 | <paramdef>GLenum <parameter>provokeMode</parameter></paramdef> | |
24 | </funcprototype> | |
25 | </funcsynopsis> | |
26 | </refsynopsisdiv> | |
27 | <!-- eqn: ignoring delim $$ --> | |
28 | <refsect1 id="parameters"><title>Parameters</title> | |
29 | <variablelist> | |
30 | <varlistentry> | |
31 | <term><parameter>provokeMode</parameter></term> | |
32 | <listitem> | |
33 | <para> | |
34 | Specifies the vertex to be used as the source of data for flat shaded varyings. | |
35 | </para> | |
36 | </listitem> | |
37 | </varlistentry> | |
38 | </variablelist> | |
39 | </refsect1> | |
40 | <refsect1 id="description"><title>Description</title> | |
41 | <para> | |
42 | <emphasis>Flatshading</emphasis> a vertex shader varying output means to assign all vetices of the primitive the same value | |
43 | for that output. The vertex from which these values is derived is known as the <emphasis>provoking vertex</emphasis> and | |
44 | <function>glProvokingVertex</function> specifies which vertex is to be used as the source of data for flat shaded varyings. | |
45 | </para> | |
46 | <para> | |
47 | <parameter>provokeMode</parameter> must be either <constant>GL_FIRST_VERTEX_CONVENTION</constant> or | |
48 | <constant>GL_LAST_VERTEX_CONVENTION</constant>, and controls the selection of the vertex whose values are assigned to flatshaded | |
49 | varying outputs. The interpretation of these values for the supported primitive types is: | |
50 | <informaltable frame="topbot"> | |
51 | <tgroup cols="3" align="left"> | |
52 | <colspec colwidth="1.1*" /> | |
53 | <colspec colwidth="1*" /> | |
54 | <colspec colwidth="1*" /> | |
55 | <thead> | |
56 | <row> | |
57 | <entry rowsep="1" align="left"><emphasis role="bold"> | |
58 | Primitive Type of Polygon <emphasis>i</emphasis> | |
59 | </emphasis></entry> | |
60 | <entry rowsep="1" align="left"><emphasis role="bold"> | |
61 | First Vertex Convention | |
62 | </emphasis></entry> | |
63 | <entry rowsep="1" align="left"><emphasis role="bold"> | |
64 | Last Vertex Convention | |
65 | </emphasis></entry> | |
66 | </row> | |
67 | <row> | |
68 | <entry> | |
69 | point | |
70 | </entry> | |
71 | <entry> | |
72 | <emphasis>i</emphasis> | |
73 | </entry> | |
74 | <entry> | |
75 | <emphasis>i</emphasis> | |
76 | </entry> | |
77 | </row> | |
78 | <row> | |
79 | <entry> | |
80 | independent line | |
81 | </entry> | |
82 | <entry> | |
83 | 2<emphasis>i</emphasis> - 1 | |
84 | </entry> | |
85 | <entry> | |
86 | 2<emphasis>i</emphasis> | |
87 | </entry> | |
88 | </row> | |
89 | <row> | |
90 | <entry> | |
91 | line loop | |
92 | </entry> | |
93 | <entry> | |
94 | <emphasis>i</emphasis> | |
95 | </entry> | |
96 | <entry> | |
97 | <para> | |
98 | <emphasis>i</emphasis> + 1, if <emphasis>i</emphasis> < <emphasis>n</emphasis> | |
99 | </para> | |
100 | <para> | |
101 | 1, if <emphasis>i</emphasis> = <emphasis>n</emphasis> | |
102 | </para> | |
103 | </entry> | |
104 | </row> | |
105 | <row> | |
106 | <entry> | |
107 | line strip | |
108 | </entry> | |
109 | <entry> | |
110 | <emphasis>i</emphasis> | |
111 | </entry> | |
112 | <entry> | |
113 | <emphasis>i</emphasis> + 1 | |
114 | </entry> | |
115 | </row> | |
116 | <row> | |
117 | <entry> | |
118 | independent triangle | |
119 | </entry> | |
120 | <entry> | |
121 | 3<emphasis>i</emphasis> - 2 | |
122 | </entry> | |
123 | <entry> | |
124 | 3<emphasis>i</emphasis> | |
125 | </entry> | |
126 | </row> | |
127 | <row> | |
128 | <entry> | |
129 | triangle strip | |
130 | </entry> | |
131 | <entry> | |
132 | <emphasis>i</emphasis> | |
133 | </entry> | |
134 | <entry> | |
135 | <emphasis>i</emphasis> + 2 | |
136 | </entry> | |
137 | </row> | |
138 | <row> | |
139 | <entry> | |
140 | triangle fan | |
141 | </entry> | |
142 | <entry> | |
143 | <emphasis>i</emphasis> + 1 | |
144 | </entry> | |
145 | <entry> | |
146 | <emphasis>i</emphasis> + 2 | |
147 | </entry> | |
148 | </row> | |
149 | <row> | |
150 | <entry> | |
151 | line adjacency | |
152 | </entry> | |
153 | <entry> | |
154 | 4<emphasis>i</emphasis> - 2 | |
155 | </entry> | |
156 | <entry> | |
157 | 4<emphasis>i</emphasis> - 1 | |
158 | </entry> | |
159 | </row> | |
160 | <row> | |
161 | <entry> | |
162 | line strip adjacency | |
163 | </entry> | |
164 | <entry> | |
165 | <emphasis>i</emphasis> + 1 | |
166 | </entry> | |
167 | <entry> | |
168 | <emphasis>i</emphasis> + 2 | |
169 | </entry> | |
170 | </row> | |
171 | <row> | |
172 | <entry> | |
173 | triangle adjacency | |
174 | </entry> | |
175 | <entry> | |
176 | 6<emphasis>i</emphasis> - 5 | |
177 | </entry> | |
178 | <entry> | |
179 | 6<emphasis>i</emphasis> - 1 | |
180 | </entry> | |
181 | </row> | |
182 | <row> | |
183 | <entry> | |
184 | triangle strip adjacency | |
185 | </entry> | |
186 | <entry> | |
187 | 2<emphasis>i</emphasis> - 1 | |
188 | </entry> | |
189 | <entry> | |
190 | 2<emphasis>i</emphasis> + 3 | |
191 | </entry> | |
192 | </row> | |
193 | </thead> | |
194 | </tgroup> | |
195 | </informaltable> | |
196 | </para> | |
197 | <para> | |
198 | If a vertex or geometry shader is active, user-defined varying outputs may be flatshaded by using the | |
199 | <code>flat</code> qualifier when declaring the output. | |
200 | </para> | |
201 | </refsect1> | |
202 | <refsect1 id="notes"><title>Notes</title> | |
203 | <para> | |
204 | <function>glProvokingVertex</function> is available only if the GL version is 3.2 or greater. | |
205 | </para> | |
206 | </refsect1> | |
207 | <refsect1 id="errors"><title>Errors</title> | |
208 | <para> | |
209 | <constant>GL_INVALID_ENUM</constant> is generated if <parameter>provokeMode</parameter> is not an accepted value. | |
210 | </para> | |
211 | </refsect1> | |
212 | <refsect1 id="Copyright"><title>Copyright</title> | |
213 | <para> | |
214 | Copyright <trademark class="copyright"></trademark> 2010 Khronos Group. | |
215 | This material may be distributed subject to the terms and conditions set forth in | |
216 | the Open Publication License, v 1.0, 8 June 1999. | |
217 | <ulink url="http://opencontent.org/openpub/">http://opencontent.org/openpub/</ulink>. | |
218 | </para> | |
219 | </refsect1> | |
220 | </refentry> |