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1 | <?xml version="1.0" encoding="UTF-8"?> |
2 | <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook MathML Module V1.1b1//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd"> | |
4 | <refentry id="glLight"> | |
5 | <refmeta> | |
6 | <refmetainfo> | |
7 | <copyright> | |
8 | <year>1991-2006</year> | |
9 | <holder>Silicon Graphics, Inc.</holder> | |
10 | </copyright> | |
11 | </refmetainfo> | |
12 | <refentrytitle>glLight</refentrytitle> | |
13 | <manvolnum>3G</manvolnum> | |
14 | </refmeta> | |
15 | <refnamediv> | |
16 | <refname>glLight</refname> | |
17 | <refpurpose>set light source parameters</refpurpose> | |
18 | </refnamediv> | |
19 | <refsynopsisdiv><title>C Specification</title> | |
20 | <funcsynopsis> | |
21 | <funcprototype> | |
22 | <funcdef>void <function>glLightf</function></funcdef> | |
23 | <paramdef>GLenum <parameter>light</parameter></paramdef> | |
24 | <paramdef>GLenum <parameter>pname</parameter></paramdef> | |
25 | <paramdef>GLfloat <parameter>param</parameter></paramdef> | |
26 | </funcprototype> | |
27 | </funcsynopsis> | |
28 | <funcsynopsis> | |
29 | <funcprototype> | |
30 | <funcdef>void <function>glLighti</function></funcdef> | |
31 | <paramdef>GLenum <parameter>light</parameter></paramdef> | |
32 | <paramdef>GLenum <parameter>pname</parameter></paramdef> | |
33 | <paramdef>GLint <parameter>param</parameter></paramdef> | |
34 | </funcprototype> | |
35 | </funcsynopsis> | |
36 | </refsynopsisdiv> | |
37 | <!-- eqn: ignoring delim $$ --> | |
38 | <refsect1 id="parameters"><title>Parameters</title> | |
39 | <variablelist> | |
40 | <varlistentry> | |
41 | <term><parameter>light</parameter></term> | |
42 | <listitem> | |
43 | <para> | |
44 | Specifies a light. | |
45 | The number of lights depends on the implementation, | |
46 | but at least eight lights are supported. | |
47 | They are identified by symbolic names of the form <constant>GL_LIGHT</constant> | |
48 | <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>, | |
49 | where i ranges from 0 to the value of <constant>GL_MAX_LIGHTS</constant> - 1. | |
50 | </para> | |
51 | </listitem> | |
52 | </varlistentry> | |
53 | <varlistentry> | |
54 | <term><parameter>pname</parameter></term> | |
55 | <listitem> | |
56 | <para> | |
57 | Specifies a single-valued light source parameter for <parameter>light</parameter>. | |
58 | <constant>GL_SPOT_EXPONENT</constant>, | |
59 | <constant>GL_SPOT_CUTOFF</constant>, | |
60 | <constant>GL_CONSTANT_ATTENUATION</constant>, | |
61 | <constant>GL_LINEAR_ATTENUATION</constant>, and | |
62 | <constant>GL_QUADRATIC_ATTENUATION</constant> are accepted. | |
63 | </para> | |
64 | </listitem> | |
65 | </varlistentry> | |
66 | <varlistentry> | |
67 | <term><parameter>param</parameter></term> | |
68 | <listitem> | |
69 | <para> | |
70 | Specifies the value that parameter <parameter>pname</parameter> of light source <parameter>light</parameter> | |
71 | will be set to. | |
72 | </para> | |
73 | </listitem> | |
74 | </varlistentry> | |
75 | </variablelist> | |
76 | </refsect1> | |
77 | <refsynopsisdiv><title>C Specification</title> | |
78 | <funcsynopsis> | |
79 | <funcprototype> | |
80 | <funcdef>void <function>glLightfv</function></funcdef> | |
81 | <paramdef>GLenum <parameter>light</parameter></paramdef> | |
82 | <paramdef>GLenum <parameter>pname</parameter></paramdef> | |
83 | <paramdef>const GLfloat * <parameter>params</parameter></paramdef> | |
84 | </funcprototype> | |
85 | </funcsynopsis> | |
86 | <funcsynopsis> | |
87 | <funcprototype> | |
88 | <funcdef>void <function>glLightiv</function></funcdef> | |
89 | <paramdef>GLenum <parameter>light</parameter></paramdef> | |
90 | <paramdef>GLenum <parameter>pname</parameter></paramdef> | |
91 | <paramdef>const GLint * <parameter>params</parameter></paramdef> | |
92 | </funcprototype> | |
93 | </funcsynopsis> | |
94 | </refsynopsisdiv> | |
95 | <refsect1 id="parameters2"><title>Parameters</title> | |
96 | <variablelist> | |
97 | <varlistentry> | |
98 | <term><parameter>light</parameter></term> | |
99 | <listitem> | |
100 | <para> | |
101 | Specifies a light. | |
102 | The number of lights depends on the implementation, but | |
103 | at least eight lights are supported. | |
104 | They are identified by symbolic names of the form <constant>GL_LIGHT</constant> | |
105 | <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>, | |
106 | where i ranges from 0 to the value of <constant>GL_MAX_LIGHTS</constant> - 1. | |
107 | </para> | |
108 | </listitem> | |
109 | </varlistentry> | |
110 | <varlistentry> | |
111 | <term><parameter>pname</parameter></term> | |
112 | <listitem> | |
113 | <para> | |
114 | Specifies a light source parameter for <parameter>light</parameter>. | |
115 | <constant>GL_AMBIENT</constant>, | |
116 | <constant>GL_DIFFUSE</constant>, | |
117 | <constant>GL_SPECULAR</constant>, | |
118 | <constant>GL_POSITION</constant>, | |
119 | <constant>GL_SPOT_CUTOFF</constant>, | |
120 | <constant>GL_SPOT_DIRECTION</constant>, | |
121 | <constant>GL_SPOT_EXPONENT</constant>, | |
122 | <constant>GL_CONSTANT_ATTENUATION</constant>, | |
123 | <constant>GL_LINEAR_ATTENUATION</constant>, and | |
124 | <constant>GL_QUADRATIC_ATTENUATION</constant> are accepted. | |
125 | </para> | |
126 | </listitem> | |
127 | </varlistentry> | |
128 | <varlistentry> | |
129 | <term><parameter>params</parameter></term> | |
130 | <listitem> | |
131 | <para> | |
132 | Specifies a pointer to the value or values that parameter <parameter>pname</parameter> | |
133 | of light source <parameter>light</parameter> will be set to. | |
134 | </para> | |
135 | </listitem> | |
136 | </varlistentry> | |
137 | </variablelist> | |
138 | </refsect1> | |
139 | <refsect1 id="description"><title>Description</title> | |
140 | <para> | |
141 | <function>glLight</function> sets the values of individual light source parameters. | |
142 | <parameter>light</parameter> names the light and is a symbolic name of the form <constant>GL_LIGHT</constant> | |
143 | <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>, | |
144 | where i ranges from 0 to the value of <constant>GL_MAX_LIGHTS</constant> - 1. | |
145 | <parameter>pname</parameter> specifies one of ten light source parameters, | |
146 | again by symbolic name. | |
147 | <parameter>params</parameter> is either a single value or a pointer to an array that contains | |
148 | the new values. | |
149 | </para> | |
150 | <para> | |
151 | To enable and disable lighting calculation, call <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> | |
152 | and <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> with argument <constant>GL_LIGHTING</constant>. Lighting is | |
153 | initially disabled. | |
154 | When it is enabled, | |
155 | light sources that are enabled contribute to the lighting calculation. | |
156 | Light source | |
157 | <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation> | |
158 | is enabled and disabled using <citerefentry><refentrytitle>glEnable</refentrytitle></citerefentry> and | |
159 | <citerefentry><refentrytitle>glDisable</refentrytitle></citerefentry> with argument <constant>GL_LIGHT</constant> | |
160 | <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>. | |
161 | </para> | |
162 | <para> | |
163 | The ten light parameters are as follows: | |
164 | </para> | |
165 | <variablelist> | |
166 | <varlistentry> | |
167 | <term><constant>GL_AMBIENT</constant></term> | |
168 | <listitem> | |
169 | <para> | |
170 | <parameter>params</parameter> contains four integer or floating-point values that specify | |
171 | the ambient RGBA intensity of the light. | |
172 | Integer values are mapped linearly such that the most positive representable | |
173 | value maps to 1.0, | |
174 | and the most negative representable value maps to | |
175 | <inlineequation><mml:math> | |
176 | <!-- eqn: -1.0:--> | |
177 | <mml:mn>-1.0</mml:mn> | |
178 | </mml:math></inlineequation>. | |
179 | Floating-point values are mapped directly. | |
180 | Neither integer nor floating-point values are clamped. | |
181 | The initial ambient light intensity is (0, 0, 0, 1). | |
182 | </para> | |
183 | </listitem> | |
184 | </varlistentry> | |
185 | <varlistentry> | |
186 | <term><constant>GL_DIFFUSE</constant></term> | |
187 | <listitem> | |
188 | <para> | |
189 | <parameter>params</parameter> contains four integer or floating-point values that specify | |
190 | the diffuse RGBA intensity of the light. | |
191 | Integer values are mapped linearly such that the most positive representable | |
192 | value maps to 1.0, | |
193 | and the most negative representable value maps to | |
194 | <inlineequation><mml:math> | |
195 | <!-- eqn: -1.0:--> | |
196 | <mml:mn>-1.0</mml:mn> | |
197 | </mml:math></inlineequation>. | |
198 | Floating-point values are mapped directly. | |
199 | Neither integer nor floating-point values are clamped. | |
200 | The initial value | |
201 | for <constant>GL_LIGHT0</constant> is (1, 1, 1, 1); for other lights, the | |
202 | initial value is (0, 0, 0, 1). | |
203 | </para> | |
204 | </listitem> | |
205 | </varlistentry> | |
206 | <varlistentry> | |
207 | <term><constant>GL_SPECULAR</constant></term> | |
208 | <listitem> | |
209 | <para> | |
210 | <parameter>params</parameter> contains four integer or floating-point values that specify | |
211 | the specular RGBA intensity of the light. | |
212 | Integer values are mapped linearly such that the most positive representable | |
213 | value maps to 1.0, | |
214 | and the most negative representable value maps to | |
215 | <inlineequation><mml:math> | |
216 | <!-- eqn: -1.0:--> | |
217 | <mml:mn>-1.0</mml:mn> | |
218 | </mml:math></inlineequation>. | |
219 | Floating-point values are mapped directly. | |
220 | Neither integer nor floating-point values are clamped. | |
221 | The initial value | |
222 | for <constant>GL_LIGHT0</constant> is (1, 1, 1, 1); for other lights, the | |
223 | initial value is (0, 0, 0, 1). | |
224 | </para> | |
225 | </listitem> | |
226 | </varlistentry> | |
227 | <varlistentry> | |
228 | <term><constant>GL_POSITION</constant></term> | |
229 | <listitem> | |
230 | <para> | |
231 | <parameter>params</parameter> contains four integer or floating-point values that specify | |
232 | the position of the light in homogeneous object coordinates. | |
233 | Both integer and floating-point values are mapped directly. | |
234 | Neither integer nor floating-point values are clamped. | |
235 | </para> | |
236 | <para> | |
237 | The position is transformed by the modelview matrix when | |
238 | <function>glLight</function> is called (just as if it were a point), | |
239 | and it is stored in eye coordinates. | |
240 | If the | |
241 | <inlineequation><mml:math><mml:mi mathvariant="italic">w</mml:mi></mml:math></inlineequation> | |
242 | component of the position is 0, | |
243 | the light is treated as a directional source. | |
244 | Diffuse and specular lighting calculations take the light's direction, | |
245 | but not its actual position, | |
246 | into account, | |
247 | and attenuation is disabled. | |
248 | Otherwise, | |
249 | diffuse and specular lighting calculations are based on the actual location | |
250 | of the light in eye coordinates, | |
251 | and attenuation is enabled. | |
252 | The initial position is (0, 0, 1, 0); | |
253 | thus, the initial light source is directional, | |
254 | parallel to, and in the direction of the | |
255 | <inlineequation><mml:math> | |
256 | <!-- eqn: -z:--> | |
257 | <mml:mrow> | |
258 | <mml:mo>-</mml:mo> | |
259 | <mml:mi mathvariant="italic">z</mml:mi> | |
260 | </mml:mrow> | |
261 | </mml:math></inlineequation> | |
262 | axis. | |
263 | </para> | |
264 | </listitem> | |
265 | </varlistentry> | |
266 | <varlistentry> | |
267 | <term><constant>GL_SPOT_DIRECTION</constant></term> | |
268 | <listitem> | |
269 | <para> | |
270 | <parameter>params</parameter> contains three integer or floating-point values that specify | |
271 | the direction of the light in homogeneous object coordinates. | |
272 | Both integer and floating-point values are mapped directly. | |
273 | Neither integer nor floating-point values are clamped. | |
274 | </para> | |
275 | <para> | |
276 | The spot direction is transformed by the upper 3x3 of the modelview matrix when | |
277 | <function>glLight</function> is called, | |
278 | and it is stored in eye coordinates. | |
279 | It is significant only when <constant>GL_SPOT_CUTOFF</constant> is not 180, | |
280 | which it is initially. | |
281 | The initial direction is | |
282 | <inlineequation><mml:math> | |
283 | <!-- eqn: (0, 0, -1):--> | |
284 | <mml:mfenced open="(" close=")"> | |
285 | <mml:mn>0</mml:mn> | |
286 | <mml:mn>0</mml:mn> | |
287 | <mml:mn>-1</mml:mn> | |
288 | </mml:mfenced> | |
289 | </mml:math></inlineequation>. | |
290 | </para> | |
291 | </listitem> | |
292 | </varlistentry> | |
293 | <varlistentry> | |
294 | <term><constant>GL_SPOT_EXPONENT</constant></term> | |
295 | <listitem> | |
296 | <para> | |
297 | <parameter>params</parameter> is a single integer or floating-point value that specifies | |
298 | the intensity distribution of the light. | |
299 | Integer and floating-point values are mapped directly. | |
300 | Only values in the range | |
301 | <inlineequation><mml:math> | |
302 | <!-- eqn: [0,128]:--> | |
303 | <mml:mfenced open="[" close="]"> | |
304 | <mml:mn>0</mml:mn> | |
305 | <mml:mn>128</mml:mn> | |
306 | </mml:mfenced> | |
307 | </mml:math></inlineequation> | |
308 | are accepted. | |
309 | </para> | |
310 | <para> | |
311 | Effective light intensity is attenuated by the cosine of the angle between | |
312 | the direction of the light and the direction from the light to the vertex | |
313 | being lighted, | |
314 | raised to the power of the spot exponent. | |
315 | Thus, higher spot exponents result in a more focused light source, | |
316 | regardless of the spot cutoff angle (see <constant>GL_SPOT_CUTOFF</constant>, next paragraph). | |
317 | The initial spot exponent is 0, | |
318 | resulting in uniform light distribution. | |
319 | </para> | |
320 | </listitem> | |
321 | </varlistentry> | |
322 | <varlistentry> | |
323 | <term><constant>GL_SPOT_CUTOFF</constant></term> | |
324 | <listitem> | |
325 | <para> | |
326 | <parameter>params</parameter> is a single integer or floating-point value that specifies | |
327 | the maximum spread angle of a light source. | |
328 | Integer and floating-point values are mapped directly. | |
329 | Only values in the range | |
330 | <inlineequation><mml:math> | |
331 | <!-- eqn: [0,90]:--> | |
332 | <mml:mfenced open="[" close="]"> | |
333 | <mml:mn>0</mml:mn> | |
334 | <mml:mn>90</mml:mn> | |
335 | </mml:mfenced> | |
336 | </mml:math></inlineequation> | |
337 | and the special value 180 | |
338 | are accepted. | |
339 | If the angle between the direction of the light and the direction from the | |
340 | light to the vertex being lighted is greater than the spot cutoff angle, | |
341 | the light is completely masked. | |
342 | Otherwise, its intensity is controlled by the spot exponent and the | |
343 | attenuation factors. | |
344 | The initial spot cutoff is 180, | |
345 | resulting in uniform light distribution. | |
346 | </para> | |
347 | </listitem> | |
348 | </varlistentry> | |
349 | <varlistentry> | |
350 | <term><constant>GL_CONSTANT_ATTENUATION</constant></term> | |
351 | <listitem> | |
352 | </listitem> | |
353 | </varlistentry> | |
354 | <varlistentry> | |
355 | <term><constant>GL_LINEAR_ATTENUATION</constant></term> | |
356 | <listitem> | |
357 | </listitem> | |
358 | </varlistentry> | |
359 | <varlistentry> | |
360 | <term><constant>GL_QUADRATIC_ATTENUATION</constant></term> | |
361 | <listitem> | |
362 | <para> | |
363 | <parameter>params</parameter> is a single integer or floating-point value that specifies | |
364 | one of the three light attenuation factors. | |
365 | Integer and floating-point values are mapped directly. | |
366 | Only nonnegative values are accepted. | |
367 | If the light is positional, | |
368 | rather than directional, | |
369 | its intensity is attenuated by the reciprocal of the sum of the constant | |
370 | factor, the linear factor times the distance between the light | |
371 | and the vertex being lighted, | |
372 | and the quadratic factor times the square of the same distance. | |
373 | The initial attenuation factors are (1, 0, 0), | |
374 | resulting in no attenuation. | |
375 | </para> | |
376 | </listitem> | |
377 | </varlistentry> | |
378 | </variablelist> | |
379 | </refsect1> | |
380 | <refsect1 id="notes"><title>Notes</title> | |
381 | <para> | |
382 | It is always the case that <constant>GL_LIGHT</constant> | |
383 | <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation> | |
384 | = <constant>GL_LIGHT0</constant> + | |
385 | <inlineequation><mml:math><mml:mi mathvariant="italic">i</mml:mi></mml:math></inlineequation>. | |
386 | </para> | |
387 | </refsect1> | |
388 | <refsect1 id="errors"><title>Errors</title> | |
389 | <para> | |
390 | <constant>GL_INVALID_ENUM</constant> is generated if either <parameter>light</parameter> or <parameter>pname</parameter> | |
391 | is not an accepted value. | |
392 | </para> | |
393 | <para> | |
394 | <constant>GL_INVALID_VALUE</constant> is generated if a spot exponent value is specified | |
395 | outside the range | |
396 | <inlineequation><mml:math> | |
397 | <!-- eqn: [0,128]:--> | |
398 | <mml:mfenced open="[" close="]"> | |
399 | <mml:mn>0</mml:mn> | |
400 | <mml:mn>128</mml:mn> | |
401 | </mml:mfenced> | |
402 | </mml:math></inlineequation>, | |
403 | or if spot cutoff is specified outside the range | |
404 | <inlineequation><mml:math> | |
405 | <!-- eqn: [0,90]:--> | |
406 | <mml:mfenced open="[" close="]"> | |
407 | <mml:mn>0</mml:mn> | |
408 | <mml:mn>90</mml:mn> | |
409 | </mml:mfenced> | |
410 | </mml:math></inlineequation> | |
411 | (except for the | |
412 | special value 180), | |
413 | or if a negative attenuation factor is specified. | |
414 | </para> | |
415 | <para> | |
416 | <constant>GL_INVALID_OPERATION</constant> is generated if <function>glLight</function> is executed between | |
417 | the execution of | |
418 | <citerefentry><refentrytitle>glBegin</refentrytitle></citerefentry> and the corresponding execution of <citerefentry><refentrytitle>glEnd</refentrytitle></citerefentry>. | |
419 | </para> | |
420 | </refsect1> | |
421 | <refsect1 id="associatedgets"><title>Associated Gets</title> | |
422 | <para> | |
423 | <citerefentry><refentrytitle>glGetLight</refentrytitle></citerefentry> | |
424 | </para> | |
425 | <para> | |
426 | <citerefentry><refentrytitle>glIsEnabled</refentrytitle></citerefentry> with argument <constant>GL_LIGHTING</constant> | |
427 | </para> | |
428 | </refsect1> | |
429 | <refsect1 id="seealso"><title>See Also</title> | |
430 | <para> | |
431 | <citerefentry><refentrytitle>glColorMaterial</refentrytitle></citerefentry>, | |
432 | <citerefentry><refentrytitle>glLightModel</refentrytitle></citerefentry>, | |
433 | <citerefentry><refentrytitle>glMaterial</refentrytitle></citerefentry> | |
434 | </para> | |
435 | </refsect1> | |
436 | <refsect1 id="Copyright"><title>Copyright</title> | |
437 | <para> | |
438 | Copyright <trademark class="copyright"></trademark> 1991-2006 | |
439 | Silicon Graphics, Inc. This document is licensed under the SGI | |
440 | Free Software B License. For details, see | |
441 | <ulink url="http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/</ulink>. | |
442 | </para> | |
443 | </refsect1> | |
444 | </refentry> |