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1 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd"> |
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3 | <?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" pref:renderer="mathplayer-dl"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>glLight</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><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 border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">glLightf</b>(</code></td><td>GLenum </td><td><var class="pdparam">light</var>, </td></tr><tr><td> </td><td>GLenum </td><td><var class="pdparam">pname</var>, </td></tr><tr><td> </td><td>GLfloat </td><td><var class="pdparam">param</var><code>)</code>;</td></tr></table></div><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">glLighti</b>(</code></td><td>GLenum </td><td><var class="pdparam">light</var>, </td></tr><tr><td> </td><td>GLenum </td><td><var class="pdparam">pname</var>, </td></tr><tr><td> </td><td>GLint </td><td><var class="pdparam">param</var><code>)</code>;</td></tr></table></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> | |
4 | Specifies a light. | |
5 | The number of lights depends on the implementation, | |
6 | but at least eight lights are supported. | |
7 | They are identified by symbolic names of the form <code class="constant">GL_LIGHT</code> | |
8 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">i</mml:mi></mml:math>, | |
9 | where i ranges from 0 to the value of <code class="constant">GL_MAX_LIGHTS</code> - 1. | |
10 | </p></dd><dt><span class="term"><em class="parameter"><code>pname</code></em></span></dt><dd><p> | |
11 | Specifies a single-valued light source parameter for <em class="parameter"><code>light</code></em>. | |
12 | <code class="constant">GL_SPOT_EXPONENT</code>, | |
13 | <code class="constant">GL_SPOT_CUTOFF</code>, | |
14 | <code class="constant">GL_CONSTANT_ATTENUATION</code>, | |
15 | <code class="constant">GL_LINEAR_ATTENUATION</code>, and | |
16 | <code class="constant">GL_QUADRATIC_ATTENUATION</code> are accepted. | |
17 | </p></dd><dt><span class="term"><em class="parameter"><code>param</code></em></span></dt><dd><p> | |
18 | Specifies the value that parameter <em class="parameter"><code>pname</code></em> of light source <em class="parameter"><code>light</code></em> | |
19 | will be set to. | |
20 | </p></dd></dl></div></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">glLightfv</b>(</code></td><td>GLenum </td><td><var class="pdparam">light</var>, </td></tr><tr><td> </td><td>GLenum </td><td><var class="pdparam">pname</var>, </td></tr><tr><td> </td><td>const GLfloat * </td><td><var class="pdparam">params</var><code>)</code>;</td></tr></table></div><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">glLightiv</b>(</code></td><td>GLenum </td><td><var class="pdparam">light</var>, </td></tr><tr><td> </td><td>GLenum </td><td><var class="pdparam">pname</var>, </td></tr><tr><td> </td><td>const GLint * </td><td><var class="pdparam">params</var><code>)</code>;</td></tr></table></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> | |
21 | Specifies a light. | |
22 | The number of lights depends on the implementation, but | |
23 | at least eight lights are supported. | |
24 | They are identified by symbolic names of the form <code class="constant">GL_LIGHT</code> | |
25 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">i</mml:mi></mml:math>, | |
26 | where i ranges from 0 to the value of <code class="constant">GL_MAX_LIGHTS</code> - 1. | |
27 | </p></dd><dt><span class="term"><em class="parameter"><code>pname</code></em></span></dt><dd><p> | |
28 | Specifies a light source parameter for <em class="parameter"><code>light</code></em>. | |
29 | <code class="constant">GL_AMBIENT</code>, | |
30 | <code class="constant">GL_DIFFUSE</code>, | |
31 | <code class="constant">GL_SPECULAR</code>, | |
32 | <code class="constant">GL_POSITION</code>, | |
33 | <code class="constant">GL_SPOT_CUTOFF</code>, | |
34 | <code class="constant">GL_SPOT_DIRECTION</code>, | |
35 | <code class="constant">GL_SPOT_EXPONENT</code>, | |
36 | <code class="constant">GL_CONSTANT_ATTENUATION</code>, | |
37 | <code class="constant">GL_LINEAR_ATTENUATION</code>, and | |
38 | <code class="constant">GL_QUADRATIC_ATTENUATION</code> are accepted. | |
39 | </p></dd><dt><span class="term"><em class="parameter"><code>params</code></em></span></dt><dd><p> | |
40 | Specifies a pointer to the value or values that parameter <em class="parameter"><code>pname</code></em> | |
41 | of light source <em class="parameter"><code>light</code></em> will be set to. | |
42 | </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p> | |
43 | <code class="function">glLight</code> sets the values of individual light source parameters. | |
44 | <em class="parameter"><code>light</code></em> names the light and is a symbolic name of the form <code class="constant">GL_LIGHT</code> | |
45 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">i</mml:mi></mml:math>, | |
46 | where i ranges from 0 to the value of <code class="constant">GL_MAX_LIGHTS</code> - 1. | |
47 | <em class="parameter"><code>pname</code></em> specifies one of ten light source parameters, | |
48 | again by symbolic name. | |
49 | <em class="parameter"><code>params</code></em> is either a single value or a pointer to an array that contains | |
50 | the new values. | |
51 | </p><p> | |
52 | To enable and disable lighting calculation, call <a class="citerefentry" href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> | |
53 | and <a class="citerefentry" href="glDisable.xml"><span class="citerefentry"><span class="refentrytitle">glDisable</span></span></a> with argument <code class="constant">GL_LIGHTING</code>. Lighting is | |
54 | initially disabled. | |
55 | When it is enabled, | |
56 | light sources that are enabled contribute to the lighting calculation. | |
57 | Light source | |
58 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">i</mml:mi></mml:math> | |
59 | is enabled and disabled using <a class="citerefentry" href="glEnable.xml"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> and | |
60 | <a class="citerefentry" href="glDisable.xml"><span class="citerefentry"><span class="refentrytitle">glDisable</span></span></a> with argument <code class="constant">GL_LIGHT</code> | |
61 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">i</mml:mi></mml:math>. | |
62 | </p><p> | |
63 | The ten light parameters are as follows: | |
64 | </p><div class="variablelist"><dl><dt><span class="term"><code class="constant">GL_AMBIENT</code></span></dt><dd><p> | |
65 | <em class="parameter"><code>params</code></em> contains four integer or floating-point values that specify | |
66 | the ambient RGBA intensity of the light. | |
67 | Integer values are mapped linearly such that the most positive representable | |
68 | value maps to 1.0, | |
69 | and the most negative representable value maps to | |
70 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
71 | ||
72 | <mml:mn>-1.0</mml:mn> | |
73 | </mml:math>. | |
74 | Floating-point values are mapped directly. | |
75 | Neither integer nor floating-point values are clamped. | |
76 | The initial ambient light intensity is (0, 0, 0, 1). | |
77 | </p></dd><dt><span class="term"><code class="constant">GL_DIFFUSE</code></span></dt><dd><p> | |
78 | <em class="parameter"><code>params</code></em> contains four integer or floating-point values that specify | |
79 | the diffuse RGBA intensity of the light. | |
80 | Integer values are mapped linearly such that the most positive representable | |
81 | value maps to 1.0, | |
82 | and the most negative representable value maps to | |
83 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
84 | ||
85 | <mml:mn>-1.0</mml:mn> | |
86 | </mml:math>. | |
87 | Floating-point values are mapped directly. | |
88 | Neither integer nor floating-point values are clamped. | |
89 | The initial value | |
90 | for <code class="constant">GL_LIGHT0</code> is (1, 1, 1, 1); for other lights, the | |
91 | initial value is (0, 0, 0, 1). | |
92 | </p></dd><dt><span class="term"><code class="constant">GL_SPECULAR</code></span></dt><dd><p> | |
93 | <em class="parameter"><code>params</code></em> contains four integer or floating-point values that specify | |
94 | the specular RGBA intensity of the light. | |
95 | Integer values are mapped linearly such that the most positive representable | |
96 | value maps to 1.0, | |
97 | and the most negative representable value maps to | |
98 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
99 | ||
100 | <mml:mn>-1.0</mml:mn> | |
101 | </mml:math>. | |
102 | Floating-point values are mapped directly. | |
103 | Neither integer nor floating-point values are clamped. | |
104 | The initial value | |
105 | for <code class="constant">GL_LIGHT0</code> is (1, 1, 1, 1); for other lights, the | |
106 | initial value is (0, 0, 0, 1). | |
107 | </p></dd><dt><span class="term"><code class="constant">GL_POSITION</code></span></dt><dd><p> | |
108 | <em class="parameter"><code>params</code></em> contains four integer or floating-point values that specify | |
109 | the position of the light in homogeneous object coordinates. | |
110 | Both integer and floating-point values are mapped directly. | |
111 | Neither integer nor floating-point values are clamped. | |
112 | </p><p> | |
113 | The position is transformed by the modelview matrix when | |
114 | <code class="function">glLight</code> is called (just as if it were a point), | |
115 | and it is stored in eye coordinates. | |
116 | If the | |
117 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">w</mml:mi></mml:math> | |
118 | component of the position is 0, | |
119 | the light is treated as a directional source. | |
120 | Diffuse and specular lighting calculations take the light's direction, | |
121 | but not its actual position, | |
122 | into account, | |
123 | and attenuation is disabled. | |
124 | Otherwise, | |
125 | diffuse and specular lighting calculations are based on the actual location | |
126 | of the light in eye coordinates, | |
127 | and attenuation is enabled. | |
128 | The initial position is (0, 0, 1, 0); | |
129 | thus, the initial light source is directional, | |
130 | parallel to, and in the direction of the | |
131 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
132 | ||
133 | <mml:mrow> | |
134 | <mml:mo>-</mml:mo> | |
135 | <mml:mi mathvariant="italic">z</mml:mi> | |
136 | </mml:mrow> | |
137 | </mml:math> | |
138 | axis. | |
139 | </p></dd><dt><span class="term"><code class="constant">GL_SPOT_DIRECTION</code></span></dt><dd><p> | |
140 | <em class="parameter"><code>params</code></em> contains three integer or floating-point values that specify | |
141 | the direction of the light in homogeneous object coordinates. | |
142 | Both integer and floating-point values are mapped directly. | |
143 | Neither integer nor floating-point values are clamped. | |
144 | </p><p> | |
145 | The spot direction is transformed by the upper 3x3 of the modelview matrix when | |
146 | <code class="function">glLight</code> is called, | |
147 | and it is stored in eye coordinates. | |
148 | It is significant only when <code class="constant">GL_SPOT_CUTOFF</code> is not 180, | |
149 | which it is initially. | |
150 | The initial direction is | |
151 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
152 | ||
153 | <mml:mfenced open="(" close=")"> | |
154 | <mml:mn>0</mml:mn> | |
155 | <mml:mn>0</mml:mn> | |
156 | <mml:mn>-1</mml:mn> | |
157 | </mml:mfenced> | |
158 | </mml:math>. | |
159 | </p></dd><dt><span class="term"><code class="constant">GL_SPOT_EXPONENT</code></span></dt><dd><p> | |
160 | <em class="parameter"><code>params</code></em> is a single integer or floating-point value that specifies | |
161 | the intensity distribution of the light. | |
162 | Integer and floating-point values are mapped directly. | |
163 | Only values in the range | |
164 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
165 | ||
166 | <mml:mfenced open="[" close="]"> | |
167 | <mml:mn>0</mml:mn> | |
168 | <mml:mn>128</mml:mn> | |
169 | </mml:mfenced> | |
170 | </mml:math> | |
171 | are accepted. | |
172 | </p><p> | |
173 | Effective light intensity is attenuated by the cosine of the angle between | |
174 | the direction of the light and the direction from the light to the vertex | |
175 | being lighted, | |
176 | raised to the power of the spot exponent. | |
177 | Thus, higher spot exponents result in a more focused light source, | |
178 | regardless of the spot cutoff angle (see <code class="constant">GL_SPOT_CUTOFF</code>, next paragraph). | |
179 | The initial spot exponent is 0, | |
180 | resulting in uniform light distribution. | |
181 | </p></dd><dt><span class="term"><code class="constant">GL_SPOT_CUTOFF</code></span></dt><dd><p> | |
182 | <em class="parameter"><code>params</code></em> is a single integer or floating-point value that specifies | |
183 | the maximum spread angle of a light source. | |
184 | Integer and floating-point values are mapped directly. | |
185 | Only values in the range | |
186 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
187 | ||
188 | <mml:mfenced open="[" close="]"> | |
189 | <mml:mn>0</mml:mn> | |
190 | <mml:mn>90</mml:mn> | |
191 | </mml:mfenced> | |
192 | </mml:math> | |
193 | and the special value 180 | |
194 | are accepted. | |
195 | If the angle between the direction of the light and the direction from the | |
196 | light to the vertex being lighted is greater than the spot cutoff angle, | |
197 | the light is completely masked. | |
198 | Otherwise, its intensity is controlled by the spot exponent and the | |
199 | attenuation factors. | |
200 | The initial spot cutoff is 180, | |
201 | resulting in uniform light distribution. | |
202 | </p></dd><dt><span class="term"><code class="constant">GL_CONSTANT_ATTENUATION</code></span></dt><dd></dd><dt><span class="term"><code class="constant">GL_LINEAR_ATTENUATION</code></span></dt><dd></dd><dt><span class="term"><code class="constant">GL_QUADRATIC_ATTENUATION</code></span></dt><dd><p> | |
203 | <em class="parameter"><code>params</code></em> is a single integer or floating-point value that specifies | |
204 | one of the three light attenuation factors. | |
205 | Integer and floating-point values are mapped directly. | |
206 | Only nonnegative values are accepted. | |
207 | If the light is positional, | |
208 | rather than directional, | |
209 | its intensity is attenuated by the reciprocal of the sum of the constant | |
210 | factor, the linear factor times the distance between the light | |
211 | and the vertex being lighted, | |
212 | and the quadratic factor times the square of the same distance. | |
213 | The initial attenuation factors are (1, 0, 0), | |
214 | resulting in no attenuation. | |
215 | </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p> | |
216 | It is always the case that <code class="constant">GL_LIGHT</code> | |
217 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">i</mml:mi></mml:math> | |
218 | = <code class="constant">GL_LIGHT0</code> + | |
219 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="italic">i</mml:mi></mml:math>. | |
220 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p> | |
221 | <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> | |
222 | is not an accepted value. | |
223 | </p><p> | |
224 | <code class="constant">GL_INVALID_VALUE</code> is generated if a spot exponent value is specified | |
225 | outside the range | |
226 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
227 | ||
228 | <mml:mfenced open="[" close="]"> | |
229 | <mml:mn>0</mml:mn> | |
230 | <mml:mn>128</mml:mn> | |
231 | </mml:mfenced> | |
232 | </mml:math>, | |
233 | or if spot cutoff is specified outside the range | |
234 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> | |
235 | ||
236 | <mml:mfenced open="[" close="]"> | |
237 | <mml:mn>0</mml:mn> | |
238 | <mml:mn>90</mml:mn> | |
239 | </mml:mfenced> | |
240 | </mml:math> | |
241 | (except for the | |
242 | special value 180), | |
243 | or if a negative attenuation factor is specified. | |
244 | </p><p> | |
245 | <code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glLight</code> is executed between | |
246 | the execution of | |
247 | <a class="citerefentry" href="glBegin.xml"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a> and the corresponding execution of <a class="citerefentry" href="glEnd.xml"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>. | |
248 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p> | |
249 | <a class="citerefentry" href="glGetLight.xml"><span class="citerefentry"><span class="refentrytitle">glGetLight</span></span></a> | |
250 | </p><p> | |
251 | <a class="citerefentry" href="glIsEnabled.xml"><span class="citerefentry"><span class="refentrytitle">glIsEnabled</span></span></a> with argument <code class="constant">GL_LIGHTING</code> | |
252 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p> | |
253 | <a class="citerefentry" href="glColorMaterial.xml"><span class="citerefentry"><span class="refentrytitle">glColorMaterial</span></span></a>, | |
254 | <a class="citerefentry" href="glLightModel.xml"><span class="citerefentry"><span class="refentrytitle">glLightModel</span></span></a>, | |
255 | <a class="citerefentry" href="glMaterial.xml"><span class="citerefentry"><span class="refentrytitle">glMaterial</span></span></a> | |
256 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p> | |
257 | Copyright <span class="trademark"></span>© 1991-2006 | |
258 | Silicon Graphics, Inc. This document is licensed under the SGI | |
259 | Free Software B License. For details, see | |
260 | <a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>. | |
261 | </p></div></div></body></html> |