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21 KiB
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404 lines
21 KiB
XML
<?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="glPointSize">
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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>glPointSize</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glPointSize</refname>
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<refpurpose>specify the diameter of rasterized points</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>glPointSize</function></funcdef>
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<paramdef>GLfloat <parameter>size</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>size</parameter></term>
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<listitem>
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<para>
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Specifies the diameter of rasterized points.
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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>glPointSize</function> specifies the rasterized diameter of both aliased and antialiased
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points. Using a point size other than 1 has different effects, depending
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on whether point antialiasing is enabled. To enable and disable point
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antialiasing, call <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> with argument
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<constant>GL_POINT_SMOOTH</constant>. Point antialiasing is initially disabled.
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</para>
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<para>
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The specified point size is multiplied with a distance attenuation factor
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and clamped to the specified point size range, and further clamped to the
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implementation-dependent point size range to produce the derived point size
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using
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</para>
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<para>
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<informalequation><mml:math>
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<!-- eqn: pointSize = clamp left ( size * sqrt { left ( 1 over {a + b * d + c * {d sup 2}} right ) } right ):-->
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<mml:mrow>
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<mml:mi mathvariant="italic">pointSize</mml:mi>
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<mml:mo>=</mml:mo>
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<mml:mrow>
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<mml:mi mathvariant="italic">clamp</mml:mi>
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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:mi mathvariant="italic">size</mml:mi>
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<mml:mo>×</mml:mo>
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<mml:msqrt>
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<mml:mfenced open="" close="">
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<mml:mfenced open="(" close=")">
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<mml:mfrac>
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<mml:mn>1</mml:mn>
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<mml:mfenced open="" close="">
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<mml:mrow>
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<mml:mi mathvariant="italic">a</mml:mi>
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<mml:mo>+</mml:mo>
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<mml:mrow>
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<mml:mi mathvariant="italic">b</mml:mi>
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<mml:mo>×</mml:mo>
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<mml:mi mathvariant="italic">d</mml:mi>
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</mml:mrow>
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<mml:mo>+</mml:mo>
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<mml:mrow>
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<mml:mi mathvariant="italic">c</mml:mi>
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<mml:mo>×</mml:mo>
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<mml:mfenced open="" close="">
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<mml:msup><mml:mi mathvariant="italic">d</mml:mi>
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<mml:mn>2</mml:mn>
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</mml:msup>
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</mml:mfenced>
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</mml:mrow>
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</mml:mrow>
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</mml:mfenced>
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</mml:mfrac>
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</mml:mfenced>
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</mml:mfenced>
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</mml:msqrt>
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</mml:mrow>
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</mml:mfenced>
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</mml:mrow>
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</mml:mrow>
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</mml:math></informalequation>
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</para>
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<para>
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where
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<inlineequation><mml:math><mml:mi mathvariant="italic">d</mml:mi></mml:math></inlineequation>
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is the eye-coordinate distance from the eye to the vertex, and
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<inlineequation><mml:math><mml:mi mathvariant="italic">a</mml:mi></mml:math></inlineequation>,
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<inlineequation><mml:math><mml:mi mathvariant="italic">b</mml:mi></mml:math></inlineequation>,
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and
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<inlineequation><mml:math><mml:mi mathvariant="italic">c</mml:mi></mml:math></inlineequation>
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are the distance attenuation coefficients (see
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<citerefentry><refentrytitle>glPointParameter</refentrytitle></citerefentry>).
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</para>
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<para>
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If multisampling is disabled, the computed point size is used as the
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point's width.
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</para>
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<para>
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If multisampling is enabled, the point may be faded by modifying the point
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alpha value (see <citerefentry><refentrytitle>glSampleCoverage</refentrytitle></citerefentry>) instead of allowing the point width
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to go below a given threshold (see <citerefentry><refentrytitle>glPointParameter</refentrytitle></citerefentry>). In this case,
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the width is further modified in the following manner:
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</para>
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<para>
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<informalequation><mml:math>
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<!-- eqn: pointWidth = left { lpile { pointSize above threshold } lpile { pointSize >= threshold above otherwise }:-->
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<mml:mrow>
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<mml:mi mathvariant="italic">pointWidth</mml:mi>
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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:mtable>
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<mml:mtr><mml:mtd>
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<mml:mi mathvariant="italic">pointSize</mml:mi>
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</mml:mtd></mml:mtr>
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<mml:mtr><mml:mtd>
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<mml:mi mathvariant="italic">threshold</mml:mi>
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</mml:mtd></mml:mtr>
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</mml:mtable>
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<mml:mo>⁢</mml:mo>
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<mml:mtable>
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<mml:mtr><mml:mtd>
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<mml:mrow>
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<mml:mi mathvariant="italic">pointSize</mml:mi>
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<mml:mo>>=</mml:mo>
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<mml:mi mathvariant="italic">threshold</mml:mi>
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</mml:mrow>
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</mml:mtd></mml:mtr>
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<mml:mtr><mml:mtd>
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<mml:mi mathvariant="italic">otherwise</mml:mi>
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</mml:mtd></mml:mtr>
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</mml:mtable>
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</mml:mrow>
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</mml:mfenced>
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</mml:mrow>
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</mml:math></informalequation>
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</para>
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<para>
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The point alpha value is modified by computing:
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</para>
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<para>
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<informalequation><mml:math>
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<!-- eqn: pointAlpha = left { lpile { 1 above left ( pointSize over threshold right ) sup 2 } lpile { pointSize >= threshold above otherwise }:-->
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<mml:mrow>
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<mml:mi mathvariant="italic">pointAlpha</mml:mi>
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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:mtable>
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<mml:mtr><mml:mtd>
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<mml:mn>1</mml:mn>
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</mml:mtd></mml:mtr>
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<mml:mtr><mml:mtd>
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<mml:msup><mml:mfenced open="(" close=")">
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<mml:mfrac>
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<mml:mi mathvariant="italic">pointSize</mml:mi>
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<mml:mi mathvariant="italic">threshold</mml:mi>
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</mml:mfrac>
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</mml:mfenced>
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<mml:mn>2</mml:mn>
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</mml:msup>
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</mml:mtd></mml:mtr>
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</mml:mtable>
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<mml:mo>⁢</mml:mo>
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<mml:mtable>
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<mml:mtr><mml:mtd>
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<mml:mrow>
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<mml:mi mathvariant="italic">pointSize</mml:mi>
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<mml:mo>>=</mml:mo>
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<mml:mi mathvariant="italic">threshold</mml:mi>
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</mml:mrow>
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</mml:mtd></mml:mtr>
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<mml:mtr><mml:mtd>
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<mml:mi mathvariant="italic">otherwise</mml:mi>
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</mml:mtd></mml:mtr>
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</mml:mtable>
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</mml:mrow>
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</mml:mfenced>
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</mml:mrow>
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</mml:math></informalequation>
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</para>
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<para>
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If point antialiasing is disabled, the actual size is determined by
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rounding the supplied size to the nearest integer. (If the rounding
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results in the value 0, it is as if the point size were 1.) If the rounded
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size is odd, then the center point
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(<inlineequation><mml:math>
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<!-- eqn: x:-->
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<mml:mi mathvariant="italic">x</mml:mi>
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</mml:math></inlineequation>,
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<inlineequation><mml:math>
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<!-- eqn: y:-->
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<mml:mi mathvariant="italic">y</mml:mi>
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</mml:math></inlineequation>)
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of the pixel fragment
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that represents the point is computed as
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</para>
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<para>
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<inlineequation><mml:math>
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<!-- eqn: ( \(lf x sub w \(rf + .5 , \(lf y sub w \(rf + .5 ):-->
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<mml:mfenced open="(" close=")">
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<mml:mrow>
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<mml:mfenced open="⌊" close="⌋">
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<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
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<mml:mi mathvariant="italic">w</mml:mi>
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</mml:msub>
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</mml:mfenced>
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<mml:mo>+</mml:mo>
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<mml:mn>.5</mml:mn>
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</mml:mrow>
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<mml:mrow>
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<mml:mfenced open="⌊" close="⌋">
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<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
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<mml:mi mathvariant="italic">w</mml:mi>
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</mml:msub>
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</mml:mfenced>
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<mml:mo>+</mml:mo>
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<mml:mn>.5</mml:mn>
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</mml:mrow>
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</mml:mfenced>
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</mml:math></inlineequation>
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</para>
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<para>
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where
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<inlineequation><mml:math><mml:mi mathvariant="italic">w</mml:mi></mml:math></inlineequation>
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subscripts indicate window coordinates. All pixels that lie
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within the square grid of the rounded size centered at
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(<inlineequation><mml:math>
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<!-- eqn: x:-->
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<mml:mi mathvariant="italic">x</mml:mi>
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</mml:math></inlineequation>,
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<inlineequation><mml:math>
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<!-- eqn: y:-->
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<mml:mi mathvariant="italic">y</mml:mi>
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</mml:math></inlineequation>)
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make
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up the fragment. If the size is even, the center point is
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</para>
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<para>
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<inlineequation><mml:math>
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<!-- eqn: ( \(lf x sub w + .5 \(rf , \(lf y sub w + .5 \(rf ):-->
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<mml:mfenced open="(" close=")">
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<mml:mfenced open="⌊" close="⌋">
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<mml:mrow>
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<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
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<mml:mi mathvariant="italic">w</mml:mi>
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</mml:msub>
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<mml:mo>+</mml:mo>
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<mml:mn>.5</mml:mn>
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</mml:mrow>
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</mml:mfenced>
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<mml:mfenced open="⌊" close="⌋">
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<mml:mrow>
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<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
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<mml:mi mathvariant="italic">w</mml:mi>
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</mml:msub>
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<mml:mo>+</mml:mo>
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<mml:mn>.5</mml:mn>
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</mml:mrow>
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</mml:mfenced>
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</mml:mfenced>
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</mml:math></inlineequation>
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</para>
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<para>
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and the rasterized fragment's centers are the half-integer window
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coordinates within the square of the rounded size centered at
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<inlineequation><mml:math>
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<!-- eqn: (x, y):-->
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<mml:mfenced open="(" close=")">
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<mml:mi mathvariant="italic">x</mml:mi>
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<mml:mi mathvariant="italic">y</mml:mi>
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</mml:mfenced>
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</mml:math></inlineequation>.
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All pixel fragments produced in rasterizing a nonantialiased point are
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assigned the same associated data, that of the vertex corresponding to the
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point.
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</para>
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<para>
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If antialiasing is enabled, then point rasterization produces a fragment
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for each pixel square that intersects the region lying within the circle
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having diameter equal to the current point size and centered at the point's
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<inlineequation><mml:math>
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<!-- eqn: (x sub w, y sub w):-->
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<mml:mfenced open="(" close=")">
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<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
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<mml:mi mathvariant="italic">w</mml:mi>
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</mml:msub>
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<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
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<mml:mi mathvariant="italic">w</mml:mi>
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</mml:msub>
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</mml:mfenced>
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</mml:math></inlineequation>.
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The coverage value for each fragment is the
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window coordinate area of the intersection of the circular region with the
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corresponding pixel square. This value is saved and used in the final
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rasterization step. The data associated with each fragment is the data
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associated with the point being rasterized.
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</para>
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<para>
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Not all sizes are supported when point antialiasing is enabled. If an
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unsupported size is requested, the nearest supported size is used. Only
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size 1 is guaranteed to be supported; others depend on the implementation.
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To query the range of supported sizes and the size difference between
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supported sizes within the range, call <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with arguments
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<constant>GL_SMOOTH_POINT_SIZE_RANGE</constant> and <constant>GL_SMOOTH_POINT_SIZE_GRANULARITY</constant>.
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For aliased points, query the supported ranges and granularity with
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with arguments <constant>GL_ALIASED_POINT_SIZE_RANGE</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 point size specified by <function>glPointSize</function> is always returned when
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<constant>GL_POINT_SIZE</constant> is queried. Clamping and rounding for aliased and
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antialiased points have no effect on the specified value.
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</para>
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<para>
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A non-antialiased point size may be clamped to an implementation-dependent
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maximum. Although this maximum cannot be queried, it must be no less than
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the maximum value for antialiased points, rounded to the nearest integer
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value.
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</para>
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<para>
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<constant>GL_POINT_SIZE_RANGE</constant> and <constant>GL_POINT_SIZE_GRANULARITY</constant> are
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deprecated in GL versions 1.2 and greater. Their functionality has been
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replaced by <constant>GL_SMOOTH_POINT_SIZE_RANGE</constant> and
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<constant>GL_SMOOTH_POINT_SIZE_GRANULARITY</constant>.
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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>size</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>glPointSize</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_ALIASED_POINT_SIZE_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_POINT_SIZE</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_POINT_SIZE_MIN</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_POINT_SIZE_MAX</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_POINT_FADE_THRESHOLD_SIZE</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_POINT_DISTANCE_ATTENUATION</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_POINT_SIZE_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_POINT_SIZE_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_POINT_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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<citerefentry><refentrytitle>glPointParameter</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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