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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="glLineWidth"> | |
5 | <refmeta> | |
6 | <refmetainfo> | |
7 | <copyright> | |
8 | <year>1991-2006</year> | |
9 | <holder>Silicon Graphics, Inc.</holder> | |
10 | </copyright> | |
11 | </refmetainfo> | |
12 | <refentrytitle>glLineWidth</refentrytitle> | |
13 | <manvolnum>3G</manvolnum> | |
14 | </refmeta> | |
15 | <refnamediv> | |
16 | <refname>glLineWidth</refname> | |
17 | <refpurpose>specify the width of rasterized lines</refpurpose> | |
18 | </refnamediv> | |
19 | <refsynopsisdiv><title>C Specification</title> | |
20 | <funcsynopsis> | |
21 | <funcprototype> | |
22 | <funcdef>void <function>glLineWidth</function></funcdef> | |
23 | <paramdef>GLfloat <parameter>width</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>width</parameter></term> | |
32 | <listitem> | |
33 | <para> | |
34 | Specifies the width of rasterized lines. | |
35 | The initial value is 1. | |
36 | </para> | |
37 | </listitem> | |
38 | </varlistentry> | |
39 | </variablelist> | |
40 | </refsect1> | |
41 | <refsect1 id="description"><title>Description</title> | |
42 | <para> | |
43 | <function>glLineWidth</function> specifies the rasterized width of both aliased and antialiased | |
44 | lines. | |
45 | Using a line width other than 1 has different effects, | |
46 | depending on whether line antialiasing is enabled. | |
47 | To enable and disable line antialiasing, call | |
48 | <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> | |
49 | with argument <constant>GL_LINE_SMOOTH</constant>. Line antialiasing is initially | |
50 | disabled. | |
51 | </para> | |
52 | <para> | |
53 | If line antialiasing is disabled, | |
54 | the actual width is determined by rounding the supplied width | |
55 | to the nearest integer. | |
56 | (If the rounding results in the value 0, | |
57 | it is as if the line width were 1.) | |
58 | If | |
59 | <inlineequation><mml:math> | |
60 | <!-- eqn: | DELTA x | >= | DELTA y |:--> | |
61 | <mml:mrow> | |
62 | <mml:mfenced open="∣" close="∣"> | |
63 | <mml:mrow> | |
64 | <mml:mo>Δ</mml:mo> | |
65 | <mml:mi mathvariant="italic">x</mml:mi> | |
66 | </mml:mrow> | |
67 | </mml:mfenced> | |
68 | <mml:mo>>=</mml:mo> | |
69 | <mml:mfenced open="∣" close="∣"> | |
70 | <mml:mrow> | |
71 | <mml:mo>Δ</mml:mo> | |
72 | <mml:mi mathvariant="italic">y</mml:mi> | |
73 | </mml:mrow> | |
74 | </mml:mfenced> | |
75 | </mml:mrow> | |
76 | </mml:math></inlineequation>, | |
77 | <emphasis>i</emphasis> pixels are filled in each column that is rasterized, | |
78 | where <emphasis>i</emphasis> is the rounded value of <parameter>width</parameter>. | |
79 | Otherwise, | |
80 | <emphasis>i</emphasis> pixels are filled in each row that is rasterized. | |
81 | </para> | |
82 | <para> | |
83 | If antialiasing is enabled, | |
84 | line rasterization produces a fragment for each pixel square | |
85 | that intersects the region lying within the rectangle having width | |
86 | equal to the current line width, | |
87 | length equal to the actual length of the line, | |
88 | and centered on the mathematical line segment. | |
89 | The coverage value for each fragment is the window coordinate area | |
90 | of the intersection of the rectangular region with the corresponding | |
91 | pixel square. | |
92 | This value is saved and used in the final rasterization step. | |
93 | </para> | |
94 | <para> | |
95 | Not all widths can be supported when line antialiasing is enabled. If an | |
96 | unsupported width is requested, the nearest supported width is used. | |
97 | Only width 1 is guaranteed to be supported; others depend on the | |
98 | implementation. Likewise, there is a range for aliased line widths as well. | |
99 | To query the range of supported widths and the size | |
100 | difference between supported widths within the range, call <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> | |
101 | with arguments <constant>GL_ALIASED_LINE_WIDTH_RANGE</constant>, | |
102 | <constant>GL_SMOOTH_LINE_WIDTH_RANGE</constant>, and <constant>GL_SMOOTH_LINE_WIDTH_GRANULARITY</constant>. | |
103 | </para> | |
104 | </refsect1> | |
105 | <refsect1 id="notes"><title>Notes</title> | |
106 | <para> | |
107 | The line width specified by <function>glLineWidth</function> is always returned when <constant>GL_LINE_WIDTH</constant> | |
108 | is queried. | |
109 | Clamping and rounding for aliased and antialiased lines have no effect on the specified value. | |
110 | </para> | |
111 | <para> | |
112 | Nonantialiased line width may be clamped to an implementation-dependent maximum. Call <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with <constant>GL_ALIASED_LINE_WIDTH_RANGE</constant> to determine the maximum width. | |
113 | </para> | |
114 | <para> | |
115 | In OpenGL 1.2, the tokens <constant>GL_LINE_WIDTH_RANGE</constant> and <constant>GL_LINE_WIDTH_GRANULARITY</constant> were replaced by <constant>GL_ALIASED_LINE_WIDTH_RANGE</constant>, | |
116 | <constant>GL_SMOOTH_LINE_WIDTH_RANGE</constant>, and <constant>GL_SMOOTH_LINE_WIDTH_GRANULARITY</constant>. The old names are retained for backward compatibility, but should not be used in new code. | |
117 | </para> | |
118 | </refsect1> | |
119 | <refsect1 id="errors"><title>Errors</title> | |
120 | <para> | |
121 | <constant>GL_INVALID_VALUE</constant> is generated if <parameter>width</parameter> is less than or equal to 0. | |
122 | </para> | |
123 | </refsect1> | |
124 | <refsect1 id="associatedgets"><title>Associated Gets</title> | |
125 | <para> | |
126 | <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_LINE_WIDTH</constant> | |
127 | </para> | |
128 | <para> | |
129 | <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_ALIASED_LINE_WIDTH_RANGE</constant> | |
130 | </para> | |
131 | <para> | |
132 | <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_SMOOTH_LINE_WIDTH_RANGE</constant> | |
133 | </para> | |
134 | <para> | |
135 | <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_SMOOTH_LINE_WIDTH_GRANULARITY</constant> | |
136 | </para> | |
137 | <para> | |
138 | <citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_LINE_SMOOTH</constant> | |
139 | </para> | |
140 | </refsect1> | |
141 | <refsect1 id="seealso"><title>See Also</title> | |
142 | <para> | |
143 | <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> | |
144 | </para> | |
145 | </refsect1> | |
146 | <refsect1 id="Copyright"><title>Copyright</title> | |
147 | <para> | |
148 | Copyright <trademark class="copyright"></trademark> 1991-2006 | |
149 | Silicon Graphics, Inc. This document is licensed under the SGI | |
150 | Free Software B License. For details, see | |
151 | <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>. | |
152 | </para> | |
153 | </refsect1> | |
154 | </refentry> |