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160 lines
8 KiB
XML
160 lines
8 KiB
XML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
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"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
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<refentry id="glLineWidth">
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<refmeta>
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<refmetainfo>
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<copyright>
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<year>1991-2006</year>
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<holder>Silicon Graphics, Inc.</holder>
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</copyright>
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</refmetainfo>
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<refentrytitle>glLineWidth</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glLineWidth</refname>
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<refpurpose>specify the width of rasterized lines</refpurpose>
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</refnamediv>
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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glLineWidth</function></funcdef>
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<paramdef>GLfloat <parameter>width</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<!-- eqn: ignoring delim $$ -->
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<refsect1 id="parameters"><title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><parameter>width</parameter></term>
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<listitem>
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<para>
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Specifies the width of rasterized lines.
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The initial value is 1.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id="description"><title>Description</title>
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<para>
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<function>glLineWidth</function> specifies the rasterized width of both aliased and antialiased
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lines.
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Using a line width other than 1 has different effects,
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depending on whether line antialiasing is enabled.
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To enable and disable line antialiasing, call
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<citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry>
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with argument <constant>GL_LINE_SMOOTH</constant>. Line antialiasing is initially
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disabled.
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</para>
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<para>
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If line antialiasing is disabled,
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the actual width is determined by rounding the supplied width
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to the nearest integer.
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(If the rounding results in the value 0,
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it is as if the line width were 1.)
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If
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<inlineequation><mml:math>
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<!-- eqn: | DELTA x | >= | DELTA y |:-->
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<mml:mrow>
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<mml:mfenced open="∣" close="∣">
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<mml:mrow>
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<mml:mo>Δ</mml:mo>
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<mml:mi mathvariant="italic">x</mml:mi>
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</mml:mrow>
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</mml:mfenced>
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<mml:mo>>=</mml:mo>
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<mml:mfenced open="∣" close="∣">
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<mml:mrow>
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<mml:mo>Δ</mml:mo>
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<mml:mi mathvariant="italic">y</mml:mi>
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</mml:mrow>
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</mml:mfenced>
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</mml:mrow>
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</mml:math></inlineequation>,
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<emphasis>i</emphasis> pixels are filled in each column that is rasterized,
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where <emphasis>i</emphasis> is the rounded value of <parameter>width</parameter>.
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Otherwise,
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<emphasis>i</emphasis> pixels are filled in each row that is rasterized.
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</para>
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<para>
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If antialiasing is enabled,
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line rasterization produces a fragment for each pixel square
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that intersects the region lying within the rectangle having width
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equal to the current line width,
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length equal to the actual length of the line,
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and centered on the mathematical line segment.
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The coverage value for each fragment is the window coordinate area
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of the intersection of the rectangular region with the corresponding
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pixel square.
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This value is saved and used in the final rasterization step.
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</para>
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<para>
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Not all widths can be supported when line antialiasing is enabled. If an
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unsupported width is requested, the nearest supported width is used.
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Only width 1 is guaranteed to be supported; others depend on the
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implementation. Likewise, there is a range for aliased line widths as well.
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To query the range of supported widths and the size
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difference between supported widths within the range, call <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry>
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with arguments <constant>GL_ALIASED_LINE_WIDTH_RANGE</constant>,
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<constant>GL_SMOOTH_LINE_WIDTH_RANGE</constant>, and <constant>GL_SMOOTH_LINE_WIDTH_GRANULARITY</constant>.
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</para>
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</refsect1>
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<refsect1 id="notes"><title>Notes</title>
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<para>
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The line width specified by <function>glLineWidth</function> is always returned when <constant>GL_LINE_WIDTH</constant>
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is queried.
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Clamping and rounding for aliased and antialiased lines have no effect on the specified value.
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</para>
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<para>
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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.
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</para>
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<para>
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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>,
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<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.
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</para>
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</refsect1>
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<refsect1 id="errors"><title>Errors</title>
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<para>
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<constant>GL_INVALID_VALUE</constant> is generated if <parameter>width</parameter> is less than or equal to 0.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <function>glLineWidth</function>
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is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
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and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.
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</para>
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</refsect1>
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<refsect1 id="associatedgets"><title>Associated Gets</title>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_LINE_WIDTH</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_ALIASED_LINE_WIDTH_RANGE</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_SMOOTH_LINE_WIDTH_RANGE</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_SMOOTH_LINE_WIDTH_GRANULARITY</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_LINE_SMOOTH</constant>
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</para>
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</refsect1>
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<refsect1 id="seealso"><title>See Also</title>
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<para>
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<citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>
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</para>
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</refsect1>
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<refsect1 id="Copyright"><title>Copyright</title>
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<para>
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Copyright <trademark class="copyright"></trademark> 1991-2006
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Silicon Graphics, Inc. This document is licensed under the SGI
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Free Software B License. For details, see
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<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
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</para>
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</refsect1>
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</refentry>
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