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337 lines
17 KiB
XML
337 lines
17 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="glGetLight">
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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>glGetLight</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glGetLight</refname>
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<refpurpose>return light source parameter values</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>glGetLightfv</function></funcdef>
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<paramdef>GLenum <parameter>light</parameter></paramdef>
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<paramdef>GLenum <parameter>pname</parameter></paramdef>
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<paramdef>GLfloat * <parameter>params</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glGetLightiv</function></funcdef>
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<paramdef>GLenum <parameter>light</parameter></paramdef>
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<paramdef>GLenum <parameter>pname</parameter></paramdef>
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<paramdef>GLint * <parameter>params</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>light</parameter></term>
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<listitem>
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<para>
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Specifies a light source.
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The number of possible lights depends on the implementation,
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but at least eight lights are supported.
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They are identified by symbolic names of the form <constant>GL_LIGHT</constant>
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<inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>
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where
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<inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>
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ranges from 0 to the value of <constant>GL_MAX_LIGHTS</constant> - 1.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>pname</parameter></term>
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<listitem>
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<para>
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Specifies a light source parameter for <parameter>light</parameter>.
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Accepted symbolic names are
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<constant>GL_AMBIENT</constant>,
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<constant>GL_DIFFUSE</constant>,
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<constant>GL_SPECULAR</constant>,
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<constant>GL_POSITION</constant>,
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<constant>GL_SPOT_DIRECTION</constant>,
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<constant>GL_SPOT_EXPONENT</constant>,
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<constant>GL_SPOT_CUTOFF</constant>,
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<constant>GL_CONSTANT_ATTENUATION</constant>,
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<constant>GL_LINEAR_ATTENUATION</constant>, and
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<constant>GL_QUADRATIC_ATTENUATION</constant>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>params</parameter></term>
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<listitem>
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<para>
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Returns the requested data.
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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>glGetLight</function> returns in <parameter>params</parameter> the value or values of a light source parameter.
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<parameter>light</parameter> names the light and is a symbolic name of the form <constant>GL_LIGHT</constant>
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<inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>
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where i ranges from 0 to the value of <constant>GL_MAX_LIGHTS</constant> - 1.
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<constant>GL_MAX_LIGHTS</constant> is an implementation dependent constant that is
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greater than or equal to eight.
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<parameter>pname</parameter> specifies one of ten light source parameters,
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again by symbolic name.
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</para>
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<para>
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The following parameters are defined:
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</para>
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<variablelist>
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<varlistentry>
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<term><constant>GL_AMBIENT</constant></term>
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<listitem>
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<para>
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<parameter>params</parameter> returns four integer or floating-point values representing the
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ambient intensity of the light source.
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Integer values,
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when requested,
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are linearly mapped from the internal floating-point representation
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such that 1.0 maps to the most positive representable integer value,
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and
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<inlineequation><mml:math>
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<!-- eqn: -1.0:-->
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<mml:mn>-1.0</mml:mn>
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</mml:math></inlineequation>
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maps to the most negative representable integer value.
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If the internal value is outside the range
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<inlineequation><mml:math>
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<!-- eqn: [-1,1]:-->
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<mml:mfenced open="[" close="]">
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<mml:mn>-1</mml:mn>
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<mml:mn>1</mml:mn>
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</mml:mfenced>
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</mml:math></inlineequation>,
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the corresponding integer return value is undefined. The initial value is
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(0, 0, 0, 1).
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_DIFFUSE</constant></term>
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<listitem>
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<para>
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<parameter>params</parameter> returns four integer or floating-point values representing the
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diffuse intensity of the light source.
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Integer values,
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when requested,
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are linearly mapped from the internal floating-point representation
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such that 1.0 maps to the most positive representable integer value,
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and
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<inlineequation><mml:math>
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<!-- eqn: -1.0:-->
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<mml:mn>-1.0</mml:mn>
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</mml:math></inlineequation>
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maps to the most negative representable integer value.
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If the internal value is outside the range
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<inlineequation><mml:math>
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<!-- eqn: [-1,1]:-->
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<mml:mfenced open="[" close="]">
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<mml:mn>-1</mml:mn>
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<mml:mn>1</mml:mn>
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</mml:mfenced>
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</mml:math></inlineequation>,
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the corresponding integer return value is undefined. The initial value
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for <constant>GL_LIGHT0</constant> is (1, 1, 1, 1); for other lights, the
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initial value is (0, 0, 0, 0).
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_SPECULAR</constant></term>
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<listitem>
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<para>
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<parameter>params</parameter> returns four integer or floating-point values representing the
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specular intensity of the light source.
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Integer values,
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when requested,
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are linearly mapped from the internal floating-point representation
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such that 1.0 maps to the most positive representable integer value,
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and
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<inlineequation><mml:math>
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<!-- eqn: -1.0:-->
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<mml:mn>-1.0</mml:mn>
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</mml:math></inlineequation>
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maps to the most negative representable integer value.
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If the internal value is outside the range
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<inlineequation><mml:math>
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<!-- eqn: [-1,1]:-->
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<mml:mfenced open="[" close="]">
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<mml:mn>-1</mml:mn>
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<mml:mn>1</mml:mn>
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</mml:mfenced>
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</mml:math></inlineequation>,
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the corresponding integer return value is undefined. The initial value
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for <constant>GL_LIGHT0</constant> is (1, 1, 1, 1); for other lights, the
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initial value is (0, 0, 0, 0).
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_POSITION</constant></term>
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<listitem>
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<para>
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<parameter>params</parameter> returns four integer or floating-point values representing the
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position of the light source.
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Integer values,
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when requested,
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are computed by rounding the internal floating-point values to the
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nearest integer value.
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The returned values are those maintained in eye coordinates.
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They will not be equal to the values specified using <citerefentry><refentrytitle>glLight</refentrytitle></citerefentry>,
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unless the modelview matrix was identity at the time <citerefentry><refentrytitle>glLight</refentrytitle></citerefentry> was
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called. The initial value is (0, 0, 1, 0).
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_SPOT_DIRECTION</constant></term>
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<listitem>
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<para>
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<parameter>params</parameter> returns three integer or floating-point values representing the
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direction of the light source.
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Integer values,
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when requested,
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are computed by rounding the internal floating-point values to the
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nearest integer value.
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The returned values are those maintained in eye coordinates.
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They will not be equal to the values specified using <citerefentry><refentrytitle>glLight</refentrytitle></citerefentry>,
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unless the modelview matrix was identity at the time <citerefentry><refentrytitle>glLight</refentrytitle></citerefentry> was called.
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Although spot direction is normalized before being used in the lighting
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equation,
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the returned values are the transformed versions of the specified values
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prior to normalization. The initial value is
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<inlineequation><mml:math>
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<!-- eqn: (0, 0, -1):-->
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<mml:mfenced open="(" close=")">
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<mml:mn>0</mml:mn>
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<mml:mn>0</mml:mn>
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<mml:mn>-1</mml:mn>
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</mml:mfenced>
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</mml:math></inlineequation>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_SPOT_EXPONENT</constant></term>
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<listitem>
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<para>
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<parameter>params</parameter> returns a single integer or floating-point value representing the
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spot exponent of the light.
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An integer value,
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when requested,
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is computed by rounding the internal floating-point representation to
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the nearest integer. The initial value is 0.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_SPOT_CUTOFF</constant></term>
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<listitem>
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<para>
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<parameter>params</parameter> returns a single integer or floating-point value representing the
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spot cutoff angle of the light.
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An integer value,
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when requested,
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is computed by rounding the internal floating-point representation to
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the nearest integer. The initial value is 180.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_CONSTANT_ATTENUATION</constant></term>
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<listitem>
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<para>
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<parameter>params</parameter> returns a single integer or floating-point value representing the
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constant (not distance-related) attenuation of the light.
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An integer value,
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when requested,
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is computed by rounding the internal floating-point representation to
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the nearest integer. The initial value is 1.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_LINEAR_ATTENUATION</constant></term>
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<listitem>
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<para>
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<parameter>params</parameter> returns a single integer or floating-point value representing the
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linear attenuation of the light.
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An integer value,
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when requested,
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is computed by rounding the internal floating-point representation to
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the nearest integer. The initial value is 0.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>GL_QUADRATIC_ATTENUATION</constant></term>
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<listitem>
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<para>
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<parameter>params</parameter> returns a single integer or floating-point value representing the
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quadratic attenuation of the light.
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An integer value,
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when requested,
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is computed by rounding the internal floating-point representation to
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the nearest integer. The initial value is 0.
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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="notes"><title>Notes</title>
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<para>
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It is always the case that <constant>GL_LIGHT</constant>
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<inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>
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= <constant>GL_LIGHT0</constant> +
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<inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>.
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</para>
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<para>
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If an error is generated,
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no change is made to the contents of <parameter>params</parameter>.
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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_ENUM</constant> is generated if <parameter>light</parameter> or <parameter>pname</parameter> is not an
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accepted value.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <function>glGetLight</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="seealso"><title>See Also</title>
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<para>
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<citerefentry><refentrytitle>glLight</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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