<div class="refentry" lang="en" xml:lang="en"><a id="glLight"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glLight — set light source parameters</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">glLightf</b>(</code></td><td>GLenum <var class="pdparam">light</var>, </td></tr><tr><td> </td><td>GLenum <var class="pdparam">pname</var>, </td></tr><tr><td> </td><td>GLfloat <var class="pdparam">param</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">glLightx</b>(</code></td><td>GLenum <var class="pdparam">light</var>, </td></tr><tr><td> </td><td>GLenum <var class="pdparam">pname</var>, </td></tr><tr><td> </td><td>GLfixed <var class="pdparam">param</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term">

<em class="parameter"><code>light</code></em>

</span></dt><dd><p>Specifies a light. The number of lights depends on

the implementation, but at least eight lights are

supported. They are identified by symbolic names of the

form <code class="constant">GL_LIGHT</code><em class="replaceable"><code>i</code></em>

where

<math overflow="scroll">

<mn>0</mn>

<mo>&lt;=</mo>

<mi>i</mi>

<mo>&lt;</mo>

<mi>GL_MAX_LIGHTS</mi>

</math>.

</p></dd><dt><span class="term">

<em class="parameter"><code>pname</code></em>

</span></dt><dd><p>Specifies a single-valued light source parameter for

<em class="parameter"><code>light</code></em>.

<code class="constant">GL_SPOT_EXPONENT</code>,

<code class="constant">GL_SPOT_CUTOFF</code>,

<code class="constant">GL_CONSTANT_ATTENUATION</code>,

<code class="constant">GL_LINEAR_ATTENUATION</code>, and

<code class="constant">GL_QUADRATIC_ATTENUATION</code>

are accepted.</p></dd><dt><span class="term">

<em class="parameter"><code>param</code></em>

</span></dt><dd><p>Specifies the value that parameter <em class="parameter"><code>pname</code></em>

of light source <em class="parameter"><code>light</code></em> will be set to.</p></dd></dl></div></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">glLightfv</b>(</code></td><td>GLenum <var class="pdparam">light</var>, </td></tr><tr><td> </td><td>GLenum <var class="pdparam">pname</var>, </td></tr><tr><td> </td><td>const GLfloat * <var class="pdparam">params</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">glLightxv</b>(</code></td><td>GLenum <var class="pdparam">light</var>, </td></tr><tr><td> </td><td>GLenum <var class="pdparam">pname</var>, </td></tr><tr><td> </td><td>const GLfixed * <var class="pdparam">params</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters2"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term">

<em class="parameter"><code>light</code></em>

</span></dt><dd><p>Specifies a light. The number of lights depends on

the implementation, but at least eight lights are

supported. They are identified by symbolic names of the

form

<code class="constant">GL_LIGHT</code><em class="replaceable"><code>i</code></em>

where

<math overflow="scroll">

<mn>0</mn>

<mo>&lt;=</mo>

<mi>i</mi>

<mo>&lt;</mo>

<mi>GL_MAX_LIGHTS</mi>

</math>.

</p></dd><dt><span class="term">

<em class="parameter"><code>pname</code></em>

</span></dt><dd><p>Specifies a light source parameter for

<em class="parameter"><code>light</code></em>.

<code class="constant">GL_AMBIENT</code>,

<code class="constant">GL_DIFFUSE</code>,

<code class="constant">GL_SPECULAR</code>,

<code class="constant">GL_POSITION</code>,

<code class="constant">GL_SPOT_CUTOFF</code>,

<code class="constant">GL_SPOT_DIRECTION</code>,

<code class="constant">GL_SPOT_EXPONENT</code>,

<code class="constant">GL_CONSTANT_ATTENUATION</code>,

<code class="constant">GL_LINEAR_ATTENUATION</code>, and

<code class="constant">GL_QUADRATIC_ATTENUATION</code> are accepted.</p></dd><dt><span class="term">

<em class="parameter"><code>params</code></em>

</span></dt><dd><p>Specifies a pointer to the value or values that parameter

<em class="parameter"><code>pname</code></em> of light source

<em class="parameter"><code>light</code></em> will be set to.</p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p><code class="function">glLight</code>

sets the values of individual light source parameters.

<em class="parameter"><code>light</code></em>

names the light and is a symbolic name of the form

<code class="constant">GL_LIGHT</code><em class="replaceable"><code>i</code></em>,

where

<math overflow="scroll">

<mn>0</mn>

<mo>&lt;=</mo>

<mi>i</mi>

<mo>&lt;</mo>

<mi>GL_MAX_LIGHTS</mi>

</math>.

<em class="parameter"><code>pname</code></em>

specifies one of ten light source parameters, again by symbolic

name. <em class="parameter"><code>params</code></em>

is either a single value or a pointer to an array that contains

the new values.</p><p>To enable and disable lighting calculation, call

<a class="citerefentry" href="glEnable"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> and

<a class="citerefentry" href="glDisable"><span class="citerefentry"><span class="refentrytitle">glDisable</span></span></a>

with argument <code class="constant">GL_LIGHTING</code>.

Lighting is initially disabled. When it is enabled, light

sources that are enabled contribute to the lighting

calculation. Light source <em class="replaceable"><code>i</code></em>

is enabled and disabled using

<a class="citerefentry" href="glEnable"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> and

<a class="citerefentry" href="glDisable"><span class="citerefentry"><span class="refentrytitle">glDisable</span></span></a>

with argument <code class="constant">GL_LIGHT</code><em class="replaceable"><code>i</code></em>.

</p><p>The ten light parameters are as follows:</p><div class="variablelist"><dl><dt><span class="term">

<code class="constant">GL_AMBIENT</code>

</span></dt><dd><p><em class="parameter"><code>params</code></em>

contains four fixed-point or floating-point values that

specify the ambient RGBA intensity of the light. Both

fixed-point and floating-point values are mapped

directly. Neither fixed-point nor floating-point values

are clamped. The initial ambient light intensity is (0,

0, 0, 1).</p></dd><dt><span class="term">

<code class="constant">GL_DIFFUSE</code>

</span></dt><dd><p><em class="parameter"><code>params</code></em>

contains four fixed-point or floating-point values that

specify the diffuse RGBA intensity of the light. Both

fixed-point and floating-point values are mapped

directly. Neither fixed-point nor floating-point values

are clamped. The initial value for <code class="constant">GL_LIGHT0</code>

is (1, 1, 1, 1). For other lights, the initial value is

(0, 0, 0, 0).</p></dd><dt><span class="term">

<code class="constant">GL_SPECULAR</code>

</span></dt><dd><p><em class="parameter"><code>params</code></em>

contains four fixed-point or floating-point values that

specify the specular RGBA intensity of the light. Both

fixed-point and floating-point values are mapped

directly. Neither fixed-point nor floating-point values

are clamped. The initial value for <code class="constant">GL_LIGHT0</code>

is (1, 1, 1, 1). For other lights, the initial value is

(0, 0, 0, 0).</p></dd><dt><span class="term"><code class="constant">GL_POSITION</code></span></dt><dd><p>

<em class="parameter"><code>params</code></em> contains four fixed-point or floating-point values that specify

the position of the light in homogeneous object coordinates.

Both fixed-point and floating-point values are mapped directly.

Neither fixed-point nor floating-point values are clamped.

</p><p>

The position is transformed by the modelview matrix when

<code class="function">glLight</code> is called (just as if it were a point),

and it is stored in eye coordinates.

If the

<math overflow="scroll"><mi mathvariant="italic">w</mi></math>

component of the position is 0,

the light is treated as a directional source.

Diffuse and specular lighting calculations take the light's direction,

but not its actual position,

into account,

and attenuation is disabled.

Otherwise,

diffuse and specular lighting calculations are based on the actual location

of the light in eye coordinates,

and attenuation is enabled.

The initial position is (0, 0, 1, 0);

thus, the initial light source is directional,

parallel to, and in the direction of the

<math overflow="scroll">

<mrow>

<mo>-</mo>

<mi mathvariant="italic">z</mi>

</mrow>

</math>

axis.

</p></dd><dt><span class="term">

<code class="constant">GL_SPOT_DIRECTION</code>

</span></dt><dd><p><em class="parameter"><code>params</code></em>

contains three fixed-point or floating-point values that

specify the direction of the light in homogeneous object

coordinates. Both fixed-point and floating-point values

are mapped directly. Neither fixed-point nor

floating-point values are clamped.</p><p>The spot direction is transformed by the upper 3x3 of the

modelview matrix when <code class="function">glLight</code>

is called, and it is stored in

eye coordinates. It is significant only when

<code class="constant">GL_SPOT_CUTOFF</code>

is not 180, which it is initially. The initial direction is (0,

0, -1).</p></dd><dt><span class="term">

<code class="constant">GL_SPOT_EXPONENT</code>

</span></dt><dd><p><em class="parameter"><code>params</code></em>

is a single fixed-point or floating-point value that

specifies the intensity distribution of the light.

Fixed-point and floating-point values are mapped

directly. Only values in the range [0, 128] are

accepted.</p><p>Effective light intensity is attenuated by the cosine of

the angle between the direction of the light and the direction

from the light to the vertex being lighted, raised to the power

of the spot exponent. Thus, higher spot exponents result in a

more focused light source, regardless of the spot cutoff angle

(see <code class="constant">GL_SPOT_CUTOFF</code>,

next paragraph). The initial spot exponent is 0, resulting in

uniform light distribution.</p></dd><dt><span class="term">

<code class="constant">GL_SPOT_CUTOFF</code>

</span></dt><dd><p><em class="parameter"><code>params</code></em>

is a single fixed-point or floating-point value that

specifies the maximum spread angle of a light source.

Fixed-point and floating-point values are mapped

directly. Only values in the range [0, 90] and the special

value 180 are accepted. If the angle between the

direction of the light and the direction from the light

to the vertex being lighted is greater than the spot

cutoff angle, the light is completely masked.

Otherwise, its intensity is controlled by the spot

exponent and the attenuation factors. The initial spot

cutoff is 180, resulting in uniform light

distribution.</p></dd><dt><span class="term">

<code class="constant">GL_CONSTANT_ATTENUATION</code>,

<code class="constant">GL_LINEAR_ATTENUATION</code>,

<code class="constant">GL_QUADRATIC_ATTENUATION</code>

</span></dt><dd><p><em class="parameter"><code>params</code></em>

is a single fixed-point or floating-point value that

specifies one of the three light attenuation factors.

Fixed-point and floating-point values are mapped

directly. Only nonnegative values are accepted. If the

light is positional, rather than directional, its

intensity is attenuated by the reciprocal of the sum of

the constant factor, the linear factor times the distance

between the light and the vertex being lighted, and the

quadratic factor times the square of the same distance.

The initial attenuation factors are (1, 0, 0), resulting

in no attenuation.</p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>It is always the case that

<math overflow="scroll">

<mi>GL_LIGHT</mi><mi>i</mi> <mo>=</mo>

<mi>GL_LIGHT0</mi><mo>+</mo><mi>i</mi>

</math>.

</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p><code class="constant">GL_INVALID_ENUM</code> is generated if either

<em class="parameter"><code>light</code></em> or

<em class="parameter"><code>pname</code></em> is not an accepted value.</p><p> <code class="constant">GL_INVALID_VALUE</code>

is generated if a spot exponent value is specified outside the

range [0, 128], or if spot cutoff is specified outside the range

[0, 90] (except for the special value 180), or if a negative

attenuation factor is specified.</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>

<a class="citerefentry" href="glEnable"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a>,

<a class="citerefentry" href="glLightModel"><span class="citerefentry"><span class="refentrytitle">glLightModel</span></span></a>,

<a class="citerefentry" href="glMaterial"><span class="citerefentry"><span class="refentrytitle">glMaterial</span></span></a>

</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="copyright"></a><h2>Copyright</h2><p>

Copyright © 2003-2004

Silicon Graphics, Inc. This document is licensed under the SGI

Free Software B License. For details, see

<a class="ulink" href="https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/" target="_top">https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/</a>.

</p></div></div>