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279 lines
14 KiB
XML
279 lines
14 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="glLightModel">
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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>glLightModel</refentrytitle>
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<manvolnum>3G</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>glLightModel</refname>
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<refpurpose>set the lighting model parameters</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>glLightModelf</function></funcdef>
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<paramdef>GLenum <parameter>pname</parameter></paramdef>
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<paramdef>GLfloat <parameter>param</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>glLightModeli</function></funcdef>
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<paramdef>GLenum <parameter>pname</parameter></paramdef>
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<paramdef>GLint <parameter>param</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>pname</parameter></term>
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<listitem>
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<para>
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Specifies a single-valued lighting model parameter.
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<constant>GL_LIGHT_MODEL_LOCAL_VIEWER</constant>,
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<constant>GL_LIGHT_MODEL_COLOR_CONTROL</constant>, and
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<constant>GL_LIGHT_MODEL_TWO_SIDE</constant> are accepted.
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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>param</parameter></term>
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<listitem>
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<para>
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Specifies the value that <parameter>param</parameter> will be set to.
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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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<refsynopsisdiv><title>C Specification</title>
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<funcsynopsis>
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<funcprototype>
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<funcdef>void <function>glLightModelfv</function></funcdef>
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<paramdef>GLenum <parameter>pname</parameter></paramdef>
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<paramdef>const 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>glLightModeliv</function></funcdef>
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<paramdef>GLenum <parameter>pname</parameter></paramdef>
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<paramdef>const GLint * <parameter>params</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1 id="parameters2"><title>Parameters</title>
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<variablelist>
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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 lighting model parameter.
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<constant>GL_LIGHT_MODEL_AMBIENT</constant>,
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<constant>GL_LIGHT_MODEL_COLOR_CONTROL</constant>,
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<constant>GL_LIGHT_MODEL_LOCAL_VIEWER</constant>, and
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<constant>GL_LIGHT_MODEL_TWO_SIDE</constant> are accepted.
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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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Specifies a pointer to the value or values that <parameter>params</parameter> will be set to.
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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>glLightModel</function> sets the lighting model parameter.
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<parameter>pname</parameter> names a parameter and <parameter>params</parameter> gives the new value.
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There are three lighting model parameters:
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</para>
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<variablelist>
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<varlistentry>
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<term><constant>GL_LIGHT_MODEL_AMBIENT</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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<parameter>params</parameter> contains four integer or floating-point values that specify
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the ambient RGBA intensity of the entire scene.
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Integer values are mapped linearly such that the most positive representable
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value maps to 1.0,
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and the most negative representable value maps to
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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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Floating-point values are mapped directly.
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Neither integer nor floating-point values are clamped.
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The initial ambient scene intensity is (0.2, 0.2, 0.2, 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_LIGHT_MODEL_COLOR_CONTROL</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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<parameter>params</parameter> must be either <constant>GL_SEPARATE_SPECULAR_COLOR</constant> or
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<constant>GL_SINGLE_COLOR</constant>.
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<constant>GL_SINGLE_COLOR</constant> specifies that a single color is generated from the
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lighting computation for a vertex. <constant>GL_SEPARATE_SPECULAR_COLOR</constant>
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specifies that the specular color computation of lighting be stored
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separately from the remainder of the lighting computation. The specular
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color is summed into the generated fragment's color after the application
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of texture mapping (if enabled). The initial value is <constant>GL_SINGLE_COLOR</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><constant>GL_LIGHT_MODEL_LOCAL_VIEWER</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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<parameter>params</parameter> is a single integer or floating-point value that specifies
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how specular reflection angles are computed.
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If <parameter>params</parameter> is 0 (or 0.0), specular reflection angles take the
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view direction to be parallel to and in the direction of the -<emphasis>z</emphasis> axis,
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regardless of the location of the vertex in eye coordinates.
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Otherwise, specular reflections are computed from the origin
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of the eye coordinate system.
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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_LIGHT_MODEL_TWO_SIDE</constant></term>
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<listitem>
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<para>
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</para>
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<para>
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<parameter>params</parameter> is a single integer or floating-point value that specifies
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whether one- or two-sided lighting calculations are done for polygons.
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It has no effect on the lighting calculations for points,
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lines,
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or bitmaps.
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If <parameter>params</parameter> is 0 (or 0.0), one-sided lighting is specified,
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and only the <emphasis>front</emphasis> material parameters are used in the
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lighting equation.
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Otherwise, two-sided lighting is specified.
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In this case, vertices of back-facing polygons are lighted using the
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<emphasis>back</emphasis> material parameters
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and have their normals reversed before the lighting equation is evaluated.
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Vertices of front-facing polygons are always lighted using the
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<emphasis>front</emphasis> material parameters,
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with no change to their normals. 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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<para>
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In RGBA mode, the lighted color of a vertex is the sum of
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the material emission intensity,
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the product of the material ambient reflectance and the lighting model full-scene
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ambient intensity,
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and the contribution of each enabled light source.
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Each light source contributes the sum of three terms:
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ambient, diffuse, and specular.
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The ambient light source contribution is the product of the material ambient
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reflectance and the light's ambient intensity.
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The diffuse light source contribution is the product of the material diffuse
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reflectance,
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the light's diffuse intensity,
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and the dot product of the vertex's normal with the normalized vector from
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the vertex to the light source.
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The specular light source contribution is the product of the material specular
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reflectance,
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the light's specular intensity,
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and the dot product of the normalized vertex-to-eye and vertex-to-light
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vectors,
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raised to the power of the shininess of the material.
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All three light source contributions are attenuated equally based on
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the distance from the vertex to the light source and on light source
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direction, spread exponent, and spread cutoff angle.
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All dot products are replaced with 0 if they evaluate to a negative value.
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</para>
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<para>
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The alpha component of the resulting lighted color is set to the alpha value
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of the material diffuse reflectance.
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</para>
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<para>
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In color index mode,
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the value of the lighted index of a vertex ranges from the ambient
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to the specular values passed to <citerefentry><refentrytitle>glMaterial</refentrytitle></citerefentry> using <constant>GL_COLOR_INDEXES</constant>.
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Diffuse and specular coefficients,
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computed with a (.30, .59, .11) weighting of the lights' colors,
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the shininess of the material,
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and the same reflection and attenuation equations as in the RGBA case,
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determine how much above ambient the resulting index is.
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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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<constant>GL_LIGHT_MODEL_COLOR_CONTROL</constant> is available only if the GL version is
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1.2 or greater.
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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>pname</parameter> is not an accepted value.
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</para>
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<para>
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<constant>GL_INVALID_ENUM</constant> is generated if <parameter>pname</parameter> is
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<constant>GL_LIGHT_MODEL_COLOR_CONTROL</constant> and <parameter>params</parameter> is not one of
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<constant>GL_SINGLE_COLOR</constant> or <constant>GL_SEPARATE_SPECULAR_COLOR</constant>.
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</para>
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<para>
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<constant>GL_INVALID_OPERATION</constant> is generated if <function>glLightModel</function> is executed between
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the execution of <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> 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_LIGHT_MODEL_AMBIENT</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_LIGHT_MODEL_COLOR_CONTROL</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_LIGHT_MODEL_LOCAL_VIEWER</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glGet</refentrytitle></citerefentry> with argument <constant>GL_LIGHT_MODEL_TWO_SIDE</constant>
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</para>
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<para>
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<citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_LIGHTING</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>glLight</refentrytitle></citerefentry>,
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<citerefentry><refentrytitle>glMaterial</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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