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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
"http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
<refentry id="glPointSize">
<refmeta>
<refmetainfo>
<copyright>
<year>1991-2006</year>
<holder>Silicon Graphics, Inc.</holder>
</copyright>
</refmetainfo>
<refentrytitle>glPointSize</refentrytitle>
<manvolnum>3G</manvolnum>
</refmeta>
<refnamediv>
<refname>glPointSize</refname>
<refpurpose>specify the diameter of rasterized points</refpurpose>
</refnamediv>
<refsynopsisdiv><title>C Specification</title>
<funcsynopsis>
<funcprototype>
<funcdef>void <function>glPointSize</function></funcdef>
<paramdef>GLfloat <parameter>size</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<!-- eqn: ignoring delim $$ -->
<refsect1 id="parameters"><title>Parameters</title>
<variablelist>
<varlistentry>
<term><parameter>size</parameter></term>
<listitem>
<para>
Specifies the diameter of rasterized points.
The initial value is 1.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="description"><title>Description</title>
<para>
<function>glPointSize</function> specifies the rasterized diameter of both aliased and antialiased
points. Using a point size other than 1 has different effects, depending
on whether point antialiasing is enabled. To enable and disable point
antialiasing, call <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> with argument
<constant>GL_POINT_SMOOTH</constant>. Point antialiasing is initially disabled.
</para>
<para>
The specified point size is multiplied with a distance attenuation factor
and clamped to the specified point size range, and further clamped to the
implementation-dependent point size range to produce the derived point size
using
</para>
<para>
<informalequation><mml:math>
<!-- eqn: pointSize = clamp left ( size * sqrt { left ( 1 over {a + b * d + c * {d sup 2}} right ) } right ):-->
<mml:mrow>
<mml:mi mathvariant="italic">pointSize</mml:mi>
<mml:mo>=</mml:mo>
<mml:mrow>
<mml:mi mathvariant="italic">clamp</mml:mi>
<mml:mo>⁢</mml:mo>
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mi mathvariant="italic">size</mml:mi>
<mml:mo>×</mml:mo>
<mml:msqrt>
<mml:mfenced open="" close="">
<mml:mfenced open="(" close=")">
<mml:mfrac>
<mml:mn>1</mml:mn>
<mml:mfenced open="" close="">
<mml:mrow>
<mml:mi mathvariant="italic">a</mml:mi>
<mml:mo>+</mml:mo>
<mml:mrow>
<mml:mi mathvariant="italic">b</mml:mi>
<mml:mo>×</mml:mo>
<mml:mi mathvariant="italic">d</mml:mi>
</mml:mrow>
<mml:mo>+</mml:mo>
<mml:mrow>
<mml:mi mathvariant="italic">c</mml:mi>
<mml:mo>×</mml:mo>
<mml:mfenced open="" close="">
<mml:msup><mml:mi mathvariant="italic">d</mml:mi>
<mml:mn>2</mml:mn>
</mml:msup>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:mfenced>
</mml:mfrac>
</mml:mfenced>
</mml:mfenced>
</mml:msqrt>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math></informalequation>
</para>
<para>
where
<inlineequation><mml:math><mml:mi mathvariant="italic">d</mml:mi></mml:math></inlineequation>
is the eye-coordinate distance from the eye to the vertex, and
<inlineequation><mml:math><mml:mi mathvariant="italic">a</mml:mi></mml:math></inlineequation>,
<inlineequation><mml:math><mml:mi mathvariant="italic">b</mml:mi></mml:math></inlineequation>,
and
<inlineequation><mml:math><mml:mi mathvariant="italic">c</mml:mi></mml:math></inlineequation>
are the distance attenuation coefficients (see
<citerefentry><refentrytitle>glPointParameter</refentrytitle></citerefentry>).
</para>
<para>
If multisampling is disabled, the computed point size is used as the
point's width.
</para>
<para>
If multisampling is enabled, the point may be faded by modifying the point
alpha value (see <citerefentry><refentrytitle>glSampleCoverage</refentrytitle></citerefentry>) instead of allowing the point width
to go below a given threshold (see <citerefentry><refentrytitle>glPointParameter</refentrytitle></citerefentry>). In this case,
the width is further modified in the following manner:
</para>
<para>
<informalequation><mml:math>
<!-- eqn: pointWidth = left { lpile { pointSize above threshold } lpile { pointSize >= threshold above otherwise }:-->
<mml:mrow>
<mml:mi mathvariant="italic">pointWidth</mml:mi>
<mml:mo>=</mml:mo>
<mml:mfenced open="{" close="">
<mml:mrow>
<mml:mtable>
<mml:mtr><mml:mtd>
<mml:mi mathvariant="italic">pointSize</mml:mi>
</mml:mtd></mml:mtr>
<mml:mtr><mml:mtd>
<mml:mi mathvariant="italic">threshold</mml:mi>
</mml:mtd></mml:mtr>
</mml:mtable>
<mml:mo>⁢</mml:mo>
<mml:mtable>
<mml:mtr><mml:mtd>
<mml:mrow>
<mml:mi mathvariant="italic">pointSize</mml:mi>
<mml:mo>>=</mml:mo>
<mml:mi mathvariant="italic">threshold</mml:mi>
</mml:mrow>
</mml:mtd></mml:mtr>
<mml:mtr><mml:mtd>
<mml:mi mathvariant="italic">otherwise</mml:mi>
</mml:mtd></mml:mtr>
</mml:mtable>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math></informalequation>
</para>
<para>
The point alpha value is modified by computing:
</para>
<para>
<informalequation><mml:math>
<!-- eqn: pointAlpha = left { lpile { 1 above left ( pointSize over threshold right ) sup 2 } lpile { pointSize >= threshold above otherwise }:-->
<mml:mrow>
<mml:mi mathvariant="italic">pointAlpha</mml:mi>
<mml:mo>=</mml:mo>
<mml:mfenced open="{" close="">
<mml:mrow>
<mml:mtable>
<mml:mtr><mml:mtd>
<mml:mn>1</mml:mn>
</mml:mtd></mml:mtr>
<mml:mtr><mml:mtd>
<mml:msup><mml:mfenced open="(" close=")">
<mml:mfrac>
<mml:mi mathvariant="italic">pointSize</mml:mi>
<mml:mi mathvariant="italic">threshold</mml:mi>
</mml:mfrac>
</mml:mfenced>
<mml:mn>2</mml:mn>
</mml:msup>
</mml:mtd></mml:mtr>
</mml:mtable>
<mml:mo>⁢</mml:mo>
<mml:mtable>
<mml:mtr><mml:mtd>
<mml:mrow>
<mml:mi mathvariant="italic">pointSize</mml:mi>
<mml:mo>>=</mml:mo>
<mml:mi mathvariant="italic">threshold</mml:mi>
</mml:mrow>
</mml:mtd></mml:mtr>
<mml:mtr><mml:mtd>
<mml:mi mathvariant="italic">otherwise</mml:mi>
</mml:mtd></mml:mtr>
</mml:mtable>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math></informalequation>
</para>
<para>
If point antialiasing is disabled, the actual size is determined by
rounding the supplied size to the nearest integer. (If the rounding
results in the value 0, it is as if the point size were 1.) If the rounded
size is odd, then the center point
(<inlineequation><mml:math>
<!-- eqn: x:-->
<mml:mi mathvariant="italic">x</mml:mi>
</mml:math></inlineequation>,
<inlineequation><mml:math>
<!-- eqn: y:-->
<mml:mi mathvariant="italic">y</mml:mi>
</mml:math></inlineequation>)
of the pixel fragment
that represents the point is computed as
</para>
<para>
<inlineequation><mml:math>
<!-- eqn: ( \(lf x sub w \(rf + .5 , \(lf y sub w \(rf + .5 ):-->
<mml:mfenced open="(" close=")">
<mml:mrow>
<mml:mfenced open="⌊" close="⌋">
<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
<mml:mi mathvariant="italic">w</mml:mi>
</mml:msub>
</mml:mfenced>
<mml:mo>+</mml:mo>
<mml:mn>.5</mml:mn>
</mml:mrow>
<mml:mrow>
<mml:mfenced open="⌊" close="⌋">
<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
<mml:mi mathvariant="italic">w</mml:mi>
</mml:msub>
</mml:mfenced>
<mml:mo>+</mml:mo>
<mml:mn>.5</mml:mn>
</mml:mrow>
</mml:mfenced>
</mml:math></inlineequation>
</para>
<para>
where
<inlineequation><mml:math><mml:mi mathvariant="italic">w</mml:mi></mml:math></inlineequation>
subscripts indicate window coordinates. All pixels that lie
within the square grid of the rounded size centered at
(<inlineequation><mml:math>
<!-- eqn: x:-->
<mml:mi mathvariant="italic">x</mml:mi>
</mml:math></inlineequation>,
<inlineequation><mml:math>
<!-- eqn: y:-->
<mml:mi mathvariant="italic">y</mml:mi>
</mml:math></inlineequation>)
make
up the fragment. If the size is even, the center point is
</para>
<para>
<inlineequation><mml:math>
<!-- eqn: ( \(lf x sub w + .5 \(rf , \(lf y sub w + .5 \(rf ):-->
<mml:mfenced open="(" close=")">
<mml:mfenced open="⌊" close="⌋">
<mml:mrow>
<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
<mml:mi mathvariant="italic">w</mml:mi>
</mml:msub>
<mml:mo>+</mml:mo>
<mml:mn>.5</mml:mn>
</mml:mrow>
</mml:mfenced>
<mml:mfenced open="⌊" close="⌋">
<mml:mrow>
<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
<mml:mi mathvariant="italic">w</mml:mi>
</mml:msub>
<mml:mo>+</mml:mo>
<mml:mn>.5</mml:mn>
</mml:mrow>
</mml:mfenced>
</mml:mfenced>
</mml:math></inlineequation>
</para>
<para>
and the rasterized fragment's centers are the half-integer window
coordinates within the square of the rounded size centered at
<inlineequation><mml:math>
<!-- eqn: (x, y):-->
<mml:mfenced open="(" close=")">
<mml:mi mathvariant="italic">x</mml:mi>
<mml:mi mathvariant="italic">y</mml:mi>
</mml:mfenced>
</mml:math></inlineequation>.
All pixel fragments produced in rasterizing a nonantialiased point are
assigned the same associated data, that of the vertex corresponding to the
point.
</para>
<para>
If antialiasing is enabled, then point rasterization produces a fragment
for each pixel square that intersects the region lying within the circle
having diameter equal to the current point size and centered at the point's
<inlineequation><mml:math>
<!-- eqn: (x sub w, y sub w):-->
<mml:mfenced open="(" close=")">
<mml:msub><mml:mi mathvariant="italic">x</mml:mi>
<mml:mi mathvariant="italic">w</mml:mi>
</mml:msub>
<mml:msub><mml:mi mathvariant="italic">y</mml:mi>
<mml:mi mathvariant="italic">w</mml:mi>
</mml:msub>
</mml:mfenced>
</mml:math></inlineequation>.
The coverage value for each fragment is the
window coordinate area of the intersection of the circular region with the
corresponding pixel square. This value is saved and used in the final
rasterization step. The data associated with each fragment is the data
associated with the point being rasterized.
</para>
<para>
Not all sizes are supported when point antialiasing is enabled. If an
unsupported size is requested, the nearest supported size is used. Only
size 1 is guaranteed to be supported; others depend on the implementation.
To query the range of supported sizes and the size difference between
supported sizes within the range, call <citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with arguments
<constant>GL_SMOOTH_POINT_SIZE_RANGE</constant> and <constant>GL_SMOOTH_POINT_SIZE_GRANULARITY</constant>.
For aliased points, query the supported ranges and granularity with
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with arguments <constant>GL_ALIASED_POINT_SIZE_RANGE</constant>.
</para>
</refsect1>
<refsect1 id="notes"><title>Notes</title>
<para>
The point size specified by <function>glPointSize</function> is always returned when
<constant>GL_POINT_SIZE</constant> is queried. Clamping and rounding for aliased and
antialiased points have no effect on the specified value.
</para>
<para>
A non-antialiased point size may be clamped to an implementation-dependent
maximum. Although this maximum cannot be queried, it must be no less than
the maximum value for antialiased points, rounded to the nearest integer
value.
</para>
<para>
<constant>GL_POINT_SIZE_RANGE</constant> and <constant>GL_POINT_SIZE_GRANULARITY</constant> are
deprecated in GL versions 1.2 and greater. Their functionality has been
replaced by <constant>GL_SMOOTH_POINT_SIZE_RANGE</constant> and
<constant>GL_SMOOTH_POINT_SIZE_GRANULARITY</constant>.
</para>
</refsect1>
<refsect1 id="errors"><title>Errors</title>
<para>
<constant>GL_INVALID_VALUE</constant> is generated if <parameter>size</parameter> is less than or equal to 0.
</para>
<para>
<constant>GL_INVALID_OPERATION</constant> is generated if <function>glPointSize</function>
is executed between the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry>
and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>.
</para>
</refsect1>
<refsect1 id="associatedgets"><title>Associated Gets</title>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_ALIASED_POINT_SIZE_RANGE</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_POINT_SIZE</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_POINT_SIZE_MIN</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_POINT_SIZE_MAX</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_POINT_FADE_THRESHOLD_SIZE</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_POINT_DISTANCE_ATTENUATION</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_SMOOTH_POINT_SIZE_RANGE</constant>
</para>
<para>
<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_SMOOTH_POINT_SIZE_GRANULARITY</constant>
</para>
<para>
<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_POINT_SMOOTH</constant>
</para>
</refsect1>
<refsect1 id="seealso"><title>See Also</title>
<para>
<citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry>,
<citerefentry><refentrytitle>glPointParameter</refentrytitle></citerefentry>
</para>
</refsect1>
<refsect1 id="Copyright"><title>Copyright</title>
<para>
Copyright <trademark class="copyright"></trademark> 1991-2006
Silicon Graphics, Inc. This document is licensed under the SGI
Free Software B License. For details, see
<ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>.
</para>
</refsect1>
</refentry>