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.\" RCSid "$Id" |
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.\" Print using the -ms macro package |
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.DA 1/20/99 |
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.LP |
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.tl """Copyright \(co 1996 Regents, University of California |
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.sp 2 |
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.TL |
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The |
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.so ../src/rt/VERSION |
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.br |
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Synthetic Imaging System |
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.AU |
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Greg Ward |
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.br |
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Lawrence Berkeley Laboratory |
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.br |
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1 Cyclotron Rd. |
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.br |
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Berkeley, CA 94720 |
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.br |
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(510) 486-4757 |
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.NH 1 |
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Introduction |
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.PP |
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RADIANCE was developed as a research tool |
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for predicting the distribution of visible radiation in |
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illuminated spaces. |
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It takes as input a three-dimensional geometric model of |
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the physical environment, and produces a map of |
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spectral radiance values in a color image. |
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The technique of ray-tracing follows light backwards |
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from the image plane to the source(s). |
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Because it can produce realistic images from a simple description, |
34 |
RADIANCE has a wide range of applications in graphic arts, |
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lighting design, computer-aided engineering and architecture. |
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.KF |
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.sp 25 |
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.ce |
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.B "Figure 1." |
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.sp |
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.KE |
42 |
.PP |
43 |
The diagram in Figure 1 shows the flow between programs (boxes) and |
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data (ovals). |
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The central program is |
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.I rpict, |
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which produces a picture from a scene description. |
48 |
.I Rview |
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is a variation of |
50 |
.I rpict |
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that computes and displays images interactively. |
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.PP |
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A scene description file lists the surfaces and materials |
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that make up a specific environment. |
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The current surface types are spheres, polygons, cones, |
56 |
and cylinders. |
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They can be made from materials such as plastic, metal, |
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and glass. |
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Light sources can be distant disks as well as local spheres, discs and |
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polygons. |
61 |
.PP |
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From a three-dimensional scene description and a specified view, |
63 |
.I rpict |
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produces a two-dimensional image. |
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A picture file is a compressed binary representation of the |
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pixels in the image. |
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This picture can be scaled in size and |
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brightness, anti-aliased, and sent to a graphics output device. |
69 |
.PP |
70 |
A header in each picture file lists the program(s) and |
71 |
parameters that produced it. |
72 |
This is useful for identifying a picture |
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without having to display it. |
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The information can be read by the program |
75 |
.I getinfo. |
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.NH 1 |
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Scene Description |
78 |
.PP |
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A scene description file represents a |
80 |
three-dimensional physical environment |
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in Cartesian (rectilinear) world coordinates. |
82 |
It is stored as ASCII text, with the following basic format: |
83 |
.DS |
84 |
# comment |
85 |
|
86 |
modifier type identifier |
87 |
n S1 S2 S3 .. Sn |
88 |
0 |
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m R1 R2 R3 .. Rm |
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|
91 |
modifier alias identifier reference |
92 |
|
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! command |
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|
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... |
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.DE |
97 |
.PP |
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A comment line begins with a pound sign, `#'. |
99 |
.PP |
100 |
The scene description |
101 |
.I primitives |
102 |
all have the same general format, and can |
103 |
be either surfaces or modifiers. |
104 |
A primitive has a modifier, a type, and an identifier. |
105 |
A modifier is either the identifier of a |
106 |
.I "previously defined" |
107 |
primitive, or "void"\(dg. |
108 |
.FS |
109 |
\(dgThe most recent definition of a modifier is the one used, |
110 |
and later definitions do not cause relinking of loaded |
111 |
primitives. |
112 |
Thus, the same identifier may be used repeatedly, and each new |
113 |
definition will apply to the primitives following it. |
114 |
.FE |
115 |
An identifier can be any string (i.e. sequence of non-blank |
116 |
characters). |
117 |
The |
118 |
.I arguments |
119 |
associated with a primitive can be strings or real numbers. |
120 |
The first integer following the identifier is the number |
121 |
of string arguments, and it is followed by the arguments themselves |
122 |
(separated by white space). |
123 |
The next integer is the number of integer arguments, and is followed |
124 |
by the integer arguments. |
125 |
(There are currently no primitives that use them, however.) |
126 |
The next integer is the real argument count, and it is followed |
127 |
by the real arguments. |
128 |
.PP |
129 |
An alias gets its type and arguments from a previously defined primitive. |
130 |
This is useful when the same material is used with a different |
131 |
modifier, or as a convenient naming mechanism. |
132 |
The reserved modifier name "inherit" may be used to specificy that |
133 |
an alias will inherit its modifier from the original. |
134 |
Surfaces cannot be aliased. |
135 |
.PP |
136 |
A line beginning with an exclamation point, `!', |
137 |
is interpreted as a command. |
138 |
It is executed by the shell, and its output is read as input to |
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the program. |
140 |
The command must not try to read from its standard input, or |
141 |
confusion will result. |
142 |
A command may be continued over multiple lines using a backslash, `\\', |
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to escape the newline. |
144 |
.PP |
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Blank space is generally ignored, except as a separator. |
146 |
The exception is the newline character after a command or comment. |
147 |
Commands, comments and primitives may appear in any combination, so long |
148 |
as they are not intermingled. |
149 |
.NH 2 |
150 |
Primitive Types |
151 |
.PP |
152 |
Primitives can be surfaces, materials, textures or patterns. |
153 |
Modifiers can be materials, textures or patterns. |
154 |
Simple surfaces must have one material in their modifier list. |
155 |
.NH 3 |
156 |
Surfaces |
157 |
.PP |
158 |
A scene description will consist mostly of surfaces. |
159 |
The basic types are given below. |
160 |
.LP |
161 |
.UL Source |
162 |
.PP |
163 |
A source is not really a surface, but a solid angle. |
164 |
It is used for specifying light sources that are very distant. |
165 |
The direction to the center of the source and the number of degrees |
166 |
subtended by its disk are given as follows: |
167 |
.DS |
168 |
mod source id |
169 |
0 |
170 |
0 |
171 |
4 xdir ydir zdir angle |
172 |
.DE |
173 |
.LP |
174 |
.UL Sphere |
175 |
.PP |
176 |
A sphere is given by its center and radius: |
177 |
.DS |
178 |
mod sphere id |
179 |
0 |
180 |
0 |
181 |
4 xcent ycent zcent radius |
182 |
.DE |
183 |
.LP |
184 |
.UL Bubble |
185 |
.PP |
186 |
A bubble is simply a sphere whose surface normal points inward. |
187 |
.LP |
188 |
.UL Polygon |
189 |
.PP |
190 |
A polygon is given by a list of three-dimensional vertices, |
191 |
which are ordered counter-clockwise as viewed from |
192 |
the front side (into the surface normal). |
193 |
The last vertex is automatically connected to the first. |
194 |
Holes are represented in polygons as interior vertices connected to |
195 |
the outer perimeter by coincident edges (seams). |
196 |
.DS |
197 |
mod polygon id |
198 |
0 |
199 |
0 |
200 |
3n |
201 |
x1 y1 z1 |
202 |
x2 y2 z2 |
203 |
... |
204 |
xn yn zn |
205 |
.DE |
206 |
.LP |
207 |
.UL Cone |
208 |
.PP |
209 |
A cone is a megaphone-shaped object. |
210 |
It is truncated by two planes perpendicular to its axis, |
211 |
and one of its ends may come to a point. |
212 |
It is given as two axis endpoints, and the starting |
213 |
and ending radii: |
214 |
.DS |
215 |
mod cone id |
216 |
0 |
217 |
0 |
218 |
8 |
219 |
x0 y0 z0 |
220 |
x1 y1 z1 |
221 |
r0 r1 |
222 |
.DE |
223 |
.LP |
224 |
.UL Cup |
225 |
.PP |
226 |
A cup is an inverted cone (i.e. has an inward surface normal). |
227 |
.LP |
228 |
.UL Cylinder |
229 |
.PP |
230 |
A cylinder is like a cone, but its starting and ending radii are |
231 |
equal. |
232 |
.DS |
233 |
mod cylinder id |
234 |
0 |
235 |
0 |
236 |
7 |
237 |
x0 y0 z0 |
238 |
x1 y1 z1 |
239 |
rad |
240 |
.DE |
241 |
.LP |
242 |
.UL Tube |
243 |
.PP |
244 |
A tube is an inverted cylinder. |
245 |
.LP |
246 |
.UL Ring |
247 |
.PP |
248 |
A ring is a circular disk given by its center, surface |
249 |
normal, and inner and outer radii: |
250 |
.DS |
251 |
mod ring id |
252 |
0 |
253 |
0 |
254 |
8 |
255 |
xcent ycent zcent |
256 |
xdir ydir zdir |
257 |
r0 r1 |
258 |
.DE |
259 |
.LP |
260 |
.UL Mesh |
261 |
.PP |
262 |
A mesh is a compound surface, made up of many triangles and |
263 |
an octree data structure to accelerate ray intersection. |
264 |
It is typically converted from a Wavefront .OBJ file using the |
265 |
obj2mesh program. |
266 |
.DS |
267 |
mod mesh id |
268 |
1+ meshfile transform |
269 |
0 |
270 |
0 |
271 |
.DE |
272 |
If the modifier is "void", then surfaces will use the modifiers given |
273 |
in the original mesh description. |
274 |
Otherwise, the modifier specified is used in their place. |
275 |
The transform moves the mesh to the desired location in the scene. |
276 |
Multiple instances using the same meshfile take little extra memory, |
277 |
and the compiled mesh itself takes much less space than individual |
278 |
polygons would. |
279 |
In the case of an unsmoothed mesh, using the mesh primitive reduces |
280 |
memory requirements by a factor of 30 relative to individual triangles. |
281 |
If a mesh has smoothed surfaces, we save a factor of 50 or more, |
282 |
permitting very detailed geometries that would otherwise exhaust the |
283 |
available memory. |
284 |
In addition, the mesh primitive can have associated (u,v) coordinates |
285 |
for pattern and texture mapping. |
286 |
These are made available to function files via the Lu and Lu variables. |
287 |
.LP |
288 |
.UL Instance |
289 |
.PP |
290 |
An instance is a compound surface, given by the contents of an |
291 |
octree file (created by oconv). |
292 |
.DS |
293 |
mod instance id |
294 |
1+ octree transform |
295 |
0 |
296 |
0 |
297 |
.DE |
298 |
If the modifier is "void", then surfaces will use the modifiers given |
299 |
in the original description. |
300 |
Otherwise, the modifier specified is used in their place. |
301 |
The transform moves the octree to the desired location in the scene. |
302 |
Multiple instances using the same octree take little extra memory, |
303 |
hence very complex descriptions can be rendered using this primitive. |
304 |
.PP |
305 |
There are a number of important limitations to be aware of when using |
306 |
instances. |
307 |
First, the scene description used to generate the octree must stand on |
308 |
its own, without referring to modifiers in the parent description. |
309 |
This is necessary for oconv to create the octree. |
310 |
Second, light sources in the octree will not be incorporated correctly |
311 |
in the calculation, and they are not recommended. |
312 |
Finally, there is no advantage (other than convenience) to |
313 |
using a single instance of an octree, or an octree containing only a |
314 |
few surfaces. |
315 |
An xform command on the subordinate description is prefered in such cases. |
316 |
.NH 3 |
317 |
Materials |
318 |
.PP |
319 |
A material defines the way light interacts with a surface. |
320 |
The basic types are given below. |
321 |
.LP |
322 |
.UL Light |
323 |
.PP |
324 |
Light is the basic material for self-luminous surfaces (i.e. light |
325 |
sources). |
326 |
In addition to the source surface type, spheres, discs (rings with zero |
327 |
inner radius), cylinders (provided they are long enough), and |
328 |
polygons can act as light sources. |
329 |
Polygons work best when they are rectangular. |
330 |
Cones cannot be used at this time. |
331 |
A pattern may be used to specify a light output distribution. |
332 |
Light is defined simply as a RGB radiance value (watts/steradian/m2): |
333 |
.DS |
334 |
mod light id |
335 |
0 |
336 |
0 |
337 |
3 red green blue |
338 |
.DE |
339 |
.LP |
340 |
.UL Illum |
341 |
.PP |
342 |
Illum is used for secondary light sources with broad distributions. |
343 |
A secondary light source is treated like any other |
344 |
light source, except when viewed directly. |
345 |
It then acts like it is made of a different material (indicated by |
346 |
the string argument), or becomes invisible (if no string argument is given, |
347 |
or the argument is "void"). |
348 |
Secondary sources are useful when modeling windows or |
349 |
brightly illuminated surfaces. |
350 |
.DS |
351 |
mod illum id |
352 |
1 material |
353 |
0 |
354 |
3 red green blue |
355 |
.DE |
356 |
.LP |
357 |
.UL Glow |
358 |
.PP |
359 |
Glow is used for surfaces that are self-luminous, but limited |
360 |
in their effect. |
361 |
In addition to the radiance value, a maximum radius for |
362 |
shadow testing is given: |
363 |
.DS |
364 |
mod glow id |
365 |
0 |
366 |
0 |
367 |
4 red green blue maxrad |
368 |
.DE |
369 |
If maxrad is zero, then the surface will never be tested |
370 |
for shadow, although it may participate in an interreflection calculation. |
371 |
If maxrad is negative, then the surface will never contribute to scene |
372 |
illumination. |
373 |
Glow sources will never illuminate objects on the other side of an |
374 |
illum surface. |
375 |
This provides a convenient way to illuminate local light fixture |
376 |
geometry without overlighting nearby objects. |
377 |
.LP |
378 |
.UL Spotlight |
379 |
.PP |
380 |
Spotlight is used for self-luminous surfaces having directed output. |
381 |
As well as radiance, the full cone angle (in degrees) |
382 |
and orientation (output direction) vector are given. |
383 |
The length of the orientation vector is the distance |
384 |
of the effective focus behind the source center (i.e. the focal length). |
385 |
.DS |
386 |
mod spotlight id |
387 |
0 |
388 |
0 |
389 |
7 red green blue angle xdir ydir zdir |
390 |
.DE |
391 |
.LP |
392 |
.UL Mirror |
393 |
.PP |
394 |
Mirror is used for planar surfaces that produce secondary |
395 |
source reflections. |
396 |
This material should be used sparingly, as it may cause the light |
397 |
source calculation to blow up if it is applied to many small surfaces. |
398 |
This material is only supported for flat surfaces such as polygons |
399 |
and rings. |
400 |
The arguments are simply the RGB reflectance values, which should be |
401 |
between 0 and 1. |
402 |
An optional string argument may be used like the illum type to specify a |
403 |
different material to be used for shading non-source rays. |
404 |
If this alternate material is given as "void", then the mirror surface |
405 |
will be invisible. |
406 |
This is only appropriate if the surface hides other (more detailed) |
407 |
geometry with the same overall reflectance. |
408 |
.DS |
409 |
mod mirror id |
410 |
1 material |
411 |
0 |
412 |
3 red green blue |
413 |
.DE |
414 |
.LP |
415 |
.UL Prism1 |
416 |
.PP |
417 |
The prism1 material is for general light redirection from prismatic |
418 |
glazings, generating secondary light sources. |
419 |
It can only be used to modify a planar surface (i.e. a polygon or disk) |
420 |
and should not result in either light concentration or scattering. |
421 |
The new direction of the ray can be on either side of the material, |
422 |
and the definitions must have the correct bidirectional properties |
423 |
to work properly with secondary light sources. |
424 |
The arguments give the coefficient for the redirected light |
425 |
and its direction. |
426 |
.DS |
427 |
mod prism1 id |
428 |
5+ coef dx dy dz funcfile transform |
429 |
0 |
430 |
n A1 A2 .. An |
431 |
.DE |
432 |
The new direction variables |
433 |
.I "dx, dy" |
434 |
and |
435 |
.I dz |
436 |
need not produce a normalized vector. |
437 |
For convenience, the variables |
438 |
.I "DxA, DyA" |
439 |
and |
440 |
.I DzA |
441 |
are defined as the normalized direction to the target light source. |
442 |
See section 2.2.1 on function files for further information. |
443 |
.LP |
444 |
.UL Prism2 |
445 |
.PP |
446 |
The material prism2 is identical to prism1 except that |
447 |
it provides for two ray redirections rather than one. |
448 |
.DS |
449 |
mod prism2 id |
450 |
9+ coef1 dx1 dy1 dz1 coef2 dx2 dy2 dz2 funcfile transform |
451 |
0 |
452 |
n A1 A2 .. An |
453 |
.DE |
454 |
.LP |
455 |
.UL Mist |
456 |
.PP |
457 |
Mist is a virtual material used to delineate a volume |
458 |
of participating atmosphere. |
459 |
A list of important light sources may be given, along with an |
460 |
extinction coefficient, scattering albedo and scattering eccentricity |
461 |
parameter. |
462 |
The light sources named by the string argument list |
463 |
will be tested for scattering within the volume. |
464 |
Sources are identified by name, and virtual light sources may be indicated |
465 |
by giving the relaying object followed by '>' followed by the source, i.e: |
466 |
.DS |
467 |
3 source1 mirror1>source10 mirror2>mirror1>source3 |
468 |
.DE |
469 |
Normally, only one source is given per mist material, and there is an |
470 |
upper limit of 32 to the total number of active scattering sources. |
471 |
The extinction coefficient, if given, is added to the global |
472 |
coefficient set on the command line. |
473 |
Extinction is in units of 1/distance (distance based on the world coordinates), |
474 |
and indicates the proportional loss of radiance over one unit distance. |
475 |
The scattering albedo, if present, will override the global setting within |
476 |
the volume. |
477 |
An albedo of 0\00\00 means a perfectly absorbing medium, and an albedo of |
478 |
1\01\01\0 means |
479 |
a perfectly scattering medium (no absorption). |
480 |
The scattering eccentricity parameter will likewise override the global |
481 |
setting if it is present. |
482 |
Scattering eccentricity indicates how much scattered light favors the |
483 |
forward direction, as fit by the Heyney-Greenstein function: |
484 |
.DS |
485 |
P(theta) = (1 - g*g) / (1 + g*g - 2*g*cos(theta))^1.5 |
486 |
.DE |
487 |
A perfectly isotropic scattering medium has a g parameter of 0, and |
488 |
a highly directional material has a g parameter close to 1. |
489 |
Fits to the g parameter may be found along with typical extinction |
490 |
coefficients and scattering albedos for various atmospheres and |
491 |
cloud types in USGS meteorological tables. |
492 |
(A pattern will be applied to the extinction values.)\0 |
493 |
.DS |
494 |
mod mist id |
495 |
N src1 src2 .. srcN |
496 |
0 |
497 |
0|3|6|7 [ rext gext bext [ ralb galb balb [ g ] ] ] |
498 |
.DE |
499 |
There are two usual uses of the mist type. |
500 |
One is to surround a beam from a spotlight or laser so that it is |
501 |
visible during rendering. |
502 |
For this application, it is important to use a cone (or cylinder) that |
503 |
is long enough and wide enough to contain the important visible portion. |
504 |
Light source photometry and intervening objects will have the desired |
505 |
effect, and crossing beams will result in additive scattering. |
506 |
For this application, it is best to leave off the real arguments, and |
507 |
use the global rendering parameters to control the atmosphere. |
508 |
The second application is to model clouds or other localized media. |
509 |
Complex boundary geometry may be used to give shape to a uniform medium, |
510 |
so long as the boundary encloses a proper volume. |
511 |
Alternatively, a pattern may be used to set the line integral value |
512 |
through the cloud for a ray entering or exiting a point in a given |
513 |
direction. |
514 |
For this application, it is best if cloud volumes do not overlap each other, |
515 |
and opaque objects contained within them may not be illuminated correctly |
516 |
unless the line integrals consider enclosed geometry. |
517 |
.LP |
518 |
.UL Plastic |
519 |
.PP |
520 |
Plastic is a material with uncolored highlights. |
521 |
It is given by its RGB reflectance, its fraction of specularity, |
522 |
and its roughness value. |
523 |
Roughness is specified as the rms slope of surface facets. |
524 |
A value of 0 corresponds to a perfectly smooth surface, and |
525 |
a value of 1 would be a very rough surface. |
526 |
Specularity fractions greater than 0.1 and |
527 |
roughness values greater than 0.2 are not very |
528 |
realistic. |
529 |
(A pattern modifying plastic will affect the material color.) |
530 |
.DS |
531 |
mod plastic id |
532 |
0 |
533 |
0 |
534 |
5 red green blue spec rough |
535 |
.DE |
536 |
.LP |
537 |
.UL Metal |
538 |
.PP |
539 |
Metal is similar to plastic, but specular highlights |
540 |
are modified by the material color. |
541 |
Specularity of metals is usually .9 or greater. |
542 |
As for plastic, roughness values above .2 are uncommon. |
543 |
.LP |
544 |
.UL Trans |
545 |
.PP |
546 |
Trans is a translucent material, similar to plastic. |
547 |
The transmissivity is the fraction of penetrating light that |
548 |
travels all the way through the material. |
549 |
The transmitted specular component is the fraction of transmitted |
550 |
light that is not diffusely scattered. |
551 |
Transmitted and diffusely reflected light is modified by the material color. |
552 |
Translucent objects are infinitely thin. |
553 |
.DS |
554 |
mod trans id |
555 |
0 |
556 |
0 |
557 |
7 red green blue spec rough trans tspec |
558 |
.DE |
559 |
.LP |
560 |
.UL Plastic2 |
561 |
.PP |
562 |
Plastic2 is similar to plastic, but with anisotropic |
563 |
roughness. |
564 |
This means that highlights in the surface will appear elliptical rather |
565 |
than round. |
566 |
The orientation of the anisotropy is determined by the unnormalized |
567 |
direction vector |
568 |
.I "ux uy uz". |
569 |
These three expressions (separated by white space) are evaluated in |
570 |
the context of the function file |
571 |
.I funcfile. |
572 |
If no function file is required (i.e. no special variables or |
573 |
functions are required), a period (`.') may be given in its |
574 |
place. |
575 |
(See the discussion of Function Files in the Auxiliary Files section). |
576 |
The |
577 |
.I urough |
578 |
value defines the roughness along the |
579 |
.B u |
580 |
vector given projected onto the surface. |
581 |
The |
582 |
.I vrough |
583 |
value defines the roughness perpendicular to this vector. |
584 |
Note that the highlight will be narrower in the direction of the |
585 |
smaller roughness value. |
586 |
Roughness values of zero are not allowed for efficiency reasons |
587 |
since the behavior would be the same as regular plastic in that |
588 |
case. |
589 |
.DS |
590 |
mod plastic2 id |
591 |
4+ ux uy uz funcfile transform |
592 |
0 |
593 |
6 red green blue spec urough vrough |
594 |
.DE |
595 |
.LP |
596 |
.UL Metal2 |
597 |
.PP |
598 |
Metal2 is the same as plastic2, except that the highlights are |
599 |
modified by the material color. |
600 |
.LP |
601 |
.UL Trans2 |
602 |
.PP |
603 |
Trans2 is the anisotropic version of trans. |
604 |
The string arguments are the same as for plastic2, and the real |
605 |
arguments are the same as for trans but with an additional roughness |
606 |
value. |
607 |
.DS |
608 |
mod trans2 id |
609 |
4+ ux uy uz funcfile transform |
610 |
0 |
611 |
8 red green blue spec urough vrough trans tspec |
612 |
.DE |
613 |
.LP |
614 |
.UL Dielectric |
615 |
.PP |
616 |
A dielectric material is transparent, and it refracts light |
617 |
as well as reflecting it. |
618 |
Its behavior is determined by the index of refraction and |
619 |
transmission coefficient in each wavelength band per unit length. |
620 |
Common glass has a index of refraction (n) around 1.5, |
621 |
and a transmission coefficient of roughly 0.92 over an inch. |
622 |
An additional number, the Hartmann constant, describes how |
623 |
the index of refraction changes as a function of wavelength. |
624 |
It is usually zero. |
625 |
(A pattern modifies only the refracted value.) |
626 |
.DS |
627 |
mod dielectric id |
628 |
0 |
629 |
0 |
630 |
5 rtn gtn btn n hc |
631 |
.DE |
632 |
.LP |
633 |
.UL Interface |
634 |
.PP |
635 |
An interface is a boundary between two dielectrics. |
636 |
The first transmission coefficient and refractive index are for the inside; |
637 |
the second ones are for the outside. |
638 |
Ordinary dielectrics are surrounded by a vacuum (1 1 1 1). |
639 |
.DS |
640 |
mod interface id |
641 |
0 |
642 |
0 |
643 |
8 rtn1 gtn1 btn1 n1 rtn2 gtn2 btn2 n2 |
644 |
.DE |
645 |
.LP |
646 |
.UL Glass |
647 |
.PP |
648 |
Glass is similar to dielectric, but it is optimized for thin glass |
649 |
surfaces (n = 1.52). |
650 |
One transmitted ray and one reflected ray is produced. |
651 |
By using a single surface is in place of two, internal reflections |
652 |
are avoided. |
653 |
The surface orientation is irrelevant, as it is for plastic, |
654 |
metal, and trans. |
655 |
The only specification required is the transmissivity at normal |
656 |
incidence. |
657 |
(Transmissivity is the amount of light not absorbed in one traversal |
658 |
of the material. |
659 |
Transmittance -- the value usually measured -- is the total light |
660 |
transmitted through the pane including multiple reflections.)\0 |
661 |
To compute transmissivity (tn) from transmittance (Tn) use: |
662 |
.DS |
663 |
tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn |
664 |
.DE |
665 |
Standard 88% transmittance glass has a transmissivity of 0.96. |
666 |
(A pattern modifying glass will affect the transmissivity.) |
667 |
If a fourth real argument is given, it is interpreted as the index of |
668 |
refraction to use instead of 1.52. |
669 |
.DS |
670 |
mod glass id |
671 |
0 |
672 |
0 |
673 |
3 rtn gtn btn |
674 |
.DE |
675 |
.LP |
676 |
.UL Plasfunc |
677 |
.PP |
678 |
Plasfunc in used for the procedural definition of plastic-like |
679 |
materials with arbitrary bidirectional reflectance distribution |
680 |
functions (BRDF's). |
681 |
The arguments to this material include the color and specularity, |
682 |
as well as the function defining the specular distribution and the |
683 |
auxiliary file where it may be found. |
684 |
.DS |
685 |
mod plasfunc id |
686 |
2+ refl funcfile transform |
687 |
0 |
688 |
4+ red green blue spec A5 .. |
689 |
.DE |
690 |
The function |
691 |
.I refl |
692 |
takes four arguments, the x, y and z |
693 |
direction towards the incident light, and the solid angle |
694 |
subtended by the source. |
695 |
The solid angle is provided to facilitate averaging, and is usually |
696 |
ignored. |
697 |
The |
698 |
.I refl |
699 |
function should integrate to 1 over |
700 |
the projected hemisphere to maintain energy balance. |
701 |
At least four real arguments must be given, and these are made |
702 |
available along with any additional values to the reflectance |
703 |
function. |
704 |
Currently, only the contribution from direct light sources is |
705 |
considered in the specular calculation. |
706 |
As in most material types, the surface normal is always |
707 |
altered to face the incoming ray. |
708 |
.LP |
709 |
.UL Metfunc |
710 |
.PP |
711 |
Metfunc is identical to plasfunc and takes the same arguments, but |
712 |
the specular component is multiplied also by the material color. |
713 |
.LP |
714 |
.UL Transfunc |
715 |
.PP |
716 |
Transfunc is similar to plasfunc but with an arbitrary bidirectional |
717 |
transmittance distribution as well as a reflectance distribution. |
718 |
Both reflectance and transmittance are specified with the same function. |
719 |
.DS |
720 |
mod transfunc id |
721 |
2+ brtd funcfile transform |
722 |
0 |
723 |
6+ red green blue rspec trans tspec A7 .. |
724 |
.DE |
725 |
Where |
726 |
.I trans |
727 |
is the total light transmitted and |
728 |
.I tspec |
729 |
is the non-Lambertian fraction of transmitted light. |
730 |
The function |
731 |
.I brtd |
732 |
should integrate to 1 over each projected hemisphere. |
733 |
.LP |
734 |
.UL BRTDfunc |
735 |
.PP |
736 |
The material BRTDfunc gives the maximum flexibility over surface |
737 |
reflectance and transmittance, providing for spectrally-dependent |
738 |
specular rays and reflectance and transmittance distribution functions. |
739 |
.DS |
740 |
mod BRTDfunc id |
741 |
10+ rrefl grefl brefl |
742 |
rtrns gtrns btrns |
743 |
rbrtd gbrtd bbrtd |
744 |
funcfile transform |
745 |
0 |
746 |
9+ rfdif gfdif bfdif |
747 |
rbdif gbdif bbdif |
748 |
rtdif gtdif btdif |
749 |
A10 .. |
750 |
.DE |
751 |
The variables |
752 |
.I "rrefl, grefl" |
753 |
and |
754 |
.I brefl |
755 |
specify the color coefficients for |
756 |
the ideal specular (mirror) reflection of the surface. |
757 |
The variables |
758 |
.I "rtrns, gtrns" |
759 |
and |
760 |
.I btrns |
761 |
specify the color coefficients for the ideal specular transmission. |
762 |
The functions |
763 |
.I "rbrtd, gbrtd" |
764 |
and |
765 |
.I bbrtd |
766 |
take the direction to the incident light (and its solid angle) |
767 |
and compute the color coefficients for the directional diffuse part of |
768 |
reflection and transmission. |
769 |
As a special case, three identical values of '0' may be given in place of |
770 |
these function names to indicate no directional diffuse component. |
771 |
.PP |
772 |
Unlike most other material types, the surface normal is not altered to |
773 |
face the incoming ray. |
774 |
Thus, functions and variables must pay attention to the orientation of |
775 |
the surface and make adjustments appropriately. |
776 |
However, the special variables for the perturbed dot product and surface |
777 |
normal, |
778 |
.I "RdotP, NxP, NyP" |
779 |
and |
780 |
.I NzP |
781 |
are reoriented as if the ray hit the front surface for convenience. |
782 |
.PP |
783 |
A diffuse reflection component may be given for the front side with |
784 |
.I "rfdif, gfdif" |
785 |
and |
786 |
.I bfdif |
787 |
for the front side of the surface or |
788 |
.I "rbdif, gbdif" |
789 |
and |
790 |
.I bbdif |
791 |
for the back side. |
792 |
The diffuse transmittance (must be the same for both sides by physical law) |
793 |
is given by |
794 |
.I "rtdif, gtdif" |
795 |
and |
796 |
.I btdif. |
797 |
A pattern will modify these diffuse scattering values, |
798 |
and will be available through the special variables |
799 |
.I "CrP, CgP" |
800 |
and |
801 |
.I CbP. |
802 |
.PP |
803 |
Care must be taken when using this material type to produce a physically |
804 |
valid reflection model. |
805 |
The reflectance functions should be bidirectional, and under no circumstances |
806 |
should the sum of reflected diffuse, transmitted diffuse, reflected specular, |
807 |
transmitted specular and the integrated directional diffuse component be |
808 |
greater than one. |
809 |
.LP |
810 |
.UL Plasdata |
811 |
.PP |
812 |
Plasdata is used for arbitrary BRDF's that are most conveniently |
813 |
given as interpolated data. |
814 |
The arguments to this material are the data file and coordinate index |
815 |
functions, as well as a function to optionally modify the data |
816 |
values. |
817 |
.DS |
818 |
mod plasdata id |
819 |
3+n+ |
820 |
func datafile |
821 |
funcfile x1 x2 .. xn transform |
822 |
0 |
823 |
4+ red green blue spec A5 .. |
824 |
.DE |
825 |
The coordinate indices |
826 |
.I "(x1, x2," |
827 |
etc.) are themselves functions of |
828 |
the x, y and z direction to the incident light, plus the solid angle |
829 |
subtended by the light source (usually ignored). |
830 |
The data function |
831 |
.I (func) |
832 |
takes five variables, the |
833 |
interpolated value from the n-dimensional data file, followed by the |
834 |
x, y and z direction to the incident light and the solid angle of the source. |
835 |
The light source direction and size may of course be ignored by the function. |
836 |
.LP |
837 |
.UL Metdata |
838 |
.PP |
839 |
As metfunc is to plasfunc, metdata is to plasdata. |
840 |
Metdata takes the same arguments as plasdata, but the specular |
841 |
component is modified by the given material color. |
842 |
.LP |
843 |
.UL Transdata |
844 |
.PP |
845 |
Transdata is like plasdata but the specification includes transmittance |
846 |
as well as reflectance. |
847 |
The parameters are as follows. |
848 |
.DS |
849 |
mod transdata id |
850 |
3+n+ |
851 |
func datafile |
852 |
funcfile x1 x2 .. xn transform |
853 |
0 |
854 |
6+ red green blue rspec trans tspec A7 .. |
855 |
.DE |
856 |
.LP |
857 |
.UL Antimatter |
858 |
.PP |
859 |
Antimatter is a material that can "subtract" volumes from other volumes. |
860 |
A ray passing into an antimatter object becomes blind to all the specified |
861 |
modifiers: |
862 |
.DS |
863 |
mod antimatter id |
864 |
N mod1 mod2 .. modN |
865 |
0 |
866 |
0 |
867 |
.DE |
868 |
The first modifier will also be used to shade the area leaving the |
869 |
antimatter volume and entering the regular volume. |
870 |
If mod1 is void, the antimatter volume is completely invisible. |
871 |
Antimatter does not work properly with the material type "trans", |
872 |
and multiple antimatter surfaces should be disjoint. |
873 |
The viewpoint must be outside all volumes concerned for a correct |
874 |
rendering. |
875 |
.NH 3 |
876 |
Textures |
877 |
.PP |
878 |
A texture is a perturbation of the surface normal, and |
879 |
is given by either a function or data. |
880 |
.LP |
881 |
.UL Texfunc |
882 |
.PP |
883 |
A texfunc uses an auxiliary function file |
884 |
to specify a procedural texture: |
885 |
.DS |
886 |
mod texfunc id |
887 |
4+ xpert ypert zpert funcfile transform |
888 |
0 |
889 |
n A1 A2 .. An |
890 |
.DE |
891 |
.LP |
892 |
.UL Texdata |
893 |
.PP |
894 |
A texdata texture uses three data files to get the surface |
895 |
normal perturbations. |
896 |
The variables |
897 |
.I xfunc, |
898 |
.I yfunc |
899 |
and |
900 |
.I zfunc |
901 |
take three arguments |
902 |
each from the interpolated values in |
903 |
.I xdfname, |
904 |
.I ydfname |
905 |
and |
906 |
.I zdfname. |
907 |
.DS |
908 |
mod texdata id |
909 |
8+ xfunc yfunc zfunc xdfname ydfname zdfname vfname x0 x1 .. xf |
910 |
0 |
911 |
n A1 A2 .. An |
912 |
.DE |
913 |
.NH 3 |
914 |
Patterns |
915 |
.PP |
916 |
Patterns are used to modify the reflectance of materials. |
917 |
The basic types are given below. |
918 |
.LP |
919 |
.UL Colorfunc |
920 |
.PP |
921 |
A colorfunc is a procedurally defined color pattern. |
922 |
It is specified as follows: |
923 |
.DS |
924 |
mod colorfunc id |
925 |
4+ red green blue funcfile transform |
926 |
0 |
927 |
n A1 A2 .. An |
928 |
.DE |
929 |
.LP |
930 |
.UL Brightfunc |
931 |
.PP |
932 |
A brightfunc is the same as a colorfunc, except it is monochromatic. |
933 |
.DS |
934 |
mod brightfunc id |
935 |
2+ refl funcfile transform |
936 |
0 |
937 |
n A1 A2 .. An |
938 |
.DE |
939 |
.LP |
940 |
.UL Colordata |
941 |
.PP |
942 |
Colordata uses an interpolated data map to modify a material's color. |
943 |
The map is n-dimensional, and is stored in three |
944 |
auxiliary files, one for each color. |
945 |
The coordinates used to look up and interpolate the data are |
946 |
defined in another auxiliary file. |
947 |
The interpolated data values are modified by functions of |
948 |
one or three variables. |
949 |
If the functions are of one variable, then they are passed the |
950 |
corresponding color component (red or green or blue). |
951 |
If the functions are of three variables, then they are passed the |
952 |
original red, green, and blue values as parameters. |
953 |
.DS |
954 |
mod colordata id |
955 |
7+n+ |
956 |
rfunc gfunc bfunc rdatafile gdatafile bdatafile |
957 |
funcfile x1 x2 .. xn transform |
958 |
0 |
959 |
m A1 A2 .. Am |
960 |
.DE |
961 |
.LP |
962 |
.UL Brightdata |
963 |
.PP |
964 |
Brightdata is like colordata, except monochromatic. |
965 |
.DS |
966 |
mod brightdata id |
967 |
3+n+ |
968 |
func datafile |
969 |
funcfile x1 x2 .. xn transform |
970 |
0 |
971 |
m A1 A2 .. Am |
972 |
.DE |
973 |
.LP |
974 |
.UL Colorpict |
975 |
.PP |
976 |
Colorpict is a special case of colordata, where the pattern is |
977 |
a two-dimensional image stored in the RADIANCE picture format. |
978 |
The dimensions of the image data are determined by the picture |
979 |
such that the smaller dimension is always 1, and the other |
980 |
is the ratio between the larger and the smaller. |
981 |
For example, a 500x338 picture would have coordinates (u,v) |
982 |
in the rectangle between (0,0) and (1.48,1). |
983 |
.DS |
984 |
mod colorpict id |
985 |
7+ |
986 |
rfunc gfunc bfunc pictfile |
987 |
funcfile u v transform |
988 |
0 |
989 |
m A1 A2 .. Am |
990 |
.DE |
991 |
.LP |
992 |
.UL Colortext |
993 |
.PP |
994 |
Colortext is dichromatic writing in a polygonal font. |
995 |
The font is defined in an auxiliary file, such as |
996 |
.I helvet.fnt. |
997 |
The text itself is also specified in a separate file, or |
998 |
can be part of the material arguments. |
999 |
The character size, orientation, aspect ratio and slant is |
1000 |
determined by right and down motion vectors. |
1001 |
The upper left origin for the text block as well as |
1002 |
the foreground and background colors |
1003 |
must also be given. |
1004 |
.DS |
1005 |
mod colortext id |
1006 |
2 fontfile textfile |
1007 |
0 |
1008 |
15+ |
1009 |
Ox Oy Oz |
1010 |
Rx Ry Rz |
1011 |
Dx Dy Dz |
1012 |
rfore gfore bfore |
1013 |
rback gback bback |
1014 |
[spacing] |
1015 |
.DE |
1016 |
or: |
1017 |
.DS |
1018 |
mod colortext id |
1019 |
2+N fontfile . This is a line with N words ... |
1020 |
0 |
1021 |
15+ |
1022 |
Ox Oy Oz |
1023 |
Rx Ry Rz |
1024 |
Dx Dy Dz |
1025 |
rfore gfore bfore |
1026 |
rback gback bback |
1027 |
[spacing] |
1028 |
.DE |
1029 |
.LP |
1030 |
.UL Brighttext |
1031 |
.PP |
1032 |
Brighttext is like colortext, but the writing is monochromatic. |
1033 |
.DS |
1034 |
mod brighttext id |
1035 |
2 fontfile textfile |
1036 |
0 |
1037 |
11+ |
1038 |
Ox Oy Oz |
1039 |
Rx Ry Rz |
1040 |
Dx Dy Dz |
1041 |
foreground background |
1042 |
[spacing] |
1043 |
.DE |
1044 |
or: |
1045 |
.DS |
1046 |
mod brighttext id |
1047 |
2+N fontfile . This is a line with N words ... |
1048 |
0 |
1049 |
11+ |
1050 |
Ox Oy Oz |
1051 |
Rx Ry Rz |
1052 |
Dx Dy Dz |
1053 |
foreground background |
1054 |
[spacing] |
1055 |
.DE |
1056 |
.LP |
1057 |
By default, a uniform spacing algorithm is used that guarantees |
1058 |
every character will appear in a precisely determined position. |
1059 |
Unfortunately, such a scheme results in rather unattractive and difficult to |
1060 |
read text with most fonts. |
1061 |
The optional |
1062 |
.I spacing |
1063 |
value defines the distance between characters for proportional spacing. |
1064 |
A positive value selects a spacing algorithm that preserves right margins and |
1065 |
indentation, but does not provide the ultimate in proportionally spaced text. |
1066 |
A negative value insures that characters are properly spaced, but the |
1067 |
placement of words then varies unpredictably. |
1068 |
The choice depends on the relative importance of spacing versus formatting. |
1069 |
When presenting a section of formatted text, a positive spacing value is |
1070 |
usually preferred. |
1071 |
A single line of text will often be accompanied by a negative spacing value. |
1072 |
A section of text meant to depict a picture, perhaps using a special purpose |
1073 |
font such as hexbit4x1.fnt, calls for uniform spacing. |
1074 |
Reasonable magnitudes for proportional spacing are |
1075 |
between 0.1 (for tightly spaced characters) and 0.3 (for wide spacing). |
1076 |
.NH 3 |
1077 |
Mixtures |
1078 |
.PP |
1079 |
A mixture is a blend of one or more materials or textures and patterns. |
1080 |
The basic types are given below. |
1081 |
.LP |
1082 |
.UL Mixfunc |
1083 |
.PP |
1084 |
A mixfunc mixes two modifiers procedurally. |
1085 |
It is specified as follows: |
1086 |
.DS |
1087 |
mod mixfunc id |
1088 |
4+ foreground background vname funcfile transform |
1089 |
0 |
1090 |
n A1 A2 .. An |
1091 |
.DE |
1092 |
Foreground and background are modifier names that must be |
1093 |
defined earlier in the scene description. |
1094 |
If one of these is a material, then |
1095 |
the modifier of the mixfunc must be "void". |
1096 |
(Either the foreground or background modifier may be "void", |
1097 |
which serves as a form of opacity control when used with a material.)\0 |
1098 |
Vname is the coefficient defined in funcfile that determines the influence |
1099 |
of foreground. |
1100 |
The background coefficient is always (1-vname). |
1101 |
Since the references are not resolved until runtime, the last |
1102 |
definitions of the modifier id's will be used. |
1103 |
This can result in modifier loops, which are detected by the |
1104 |
renderer. |
1105 |
.LP |
1106 |
.UL Mixdata |
1107 |
.PP |
1108 |
Mixdata combines two modifiers using an auxiliary data file: |
1109 |
.DS |
1110 |
mod mixdata id |
1111 |
5+n+ |
1112 |
foreground background func datafile |
1113 |
funcfile x1 x2 .. xn transform |
1114 |
0 |
1115 |
m A1 A2 .. Am |
1116 |
.DE |
1117 |
.LP |
1118 |
.UL Mixpict |
1119 |
.PP |
1120 |
Mixpict combines two modifiers based on a picture: |
1121 |
.DS |
1122 |
mod mixpict id |
1123 |
7+ |
1124 |
foreground background func pictfile |
1125 |
funcfile u v transform |
1126 |
0 |
1127 |
m A1 A2 .. Am |
1128 |
.DE |
1129 |
The mixing coefficient function "func" takes three |
1130 |
arguments, the red, green and blue values |
1131 |
corresponding to the pixel at (u,v). |
1132 |
.LP |
1133 |
.UL Mixtext |
1134 |
.PP |
1135 |
Mixtext uses one modifier for the text foreground, and one for the |
1136 |
background: |
1137 |
.DS |
1138 |
mod mixtext id |
1139 |
4 foreground background fontfile textfile |
1140 |
0 |
1141 |
9+ |
1142 |
Ox Oy Oz |
1143 |
Rx Ry Rz |
1144 |
Dx Dy Dz |
1145 |
[spacing] |
1146 |
.DE |
1147 |
or: |
1148 |
.DS |
1149 |
mod mixtext id |
1150 |
4+N |
1151 |
foreground background fontfile . |
1152 |
This is a line with N words ... |
1153 |
0 |
1154 |
9+ |
1155 |
Ox Oy Oz |
1156 |
Rx Ry Rz |
1157 |
Dx Dy Dz |
1158 |
[spacing] |
1159 |
.DE |
1160 |
.NH 2 |
1161 |
Auxiliary Files |
1162 |
.PP |
1163 |
Auxiliary files used in textures and patterns |
1164 |
are accessed by the programs during image generation. |
1165 |
These files may be located in the working directory, or in |
1166 |
a library directory. |
1167 |
The environment variable |
1168 |
.I RAYPATH |
1169 |
can be assigned an alternate set of search directories. |
1170 |
Following is a brief description of some common file types. |
1171 |
.NH 3 |
1172 |
Function Files |
1173 |
.PP |
1174 |
A function file contains the definitions of variables, functions |
1175 |
and constants used by a primitive. |
1176 |
The transformation that accompanies the file name contains the necessary |
1177 |
rotations, translations and scalings to bring the coordinates of |
1178 |
the function file into agreement with the world coordinates. |
1179 |
The transformation specification is the same as for the |
1180 |
.I xform |
1181 |
command. |
1182 |
An example function file is given below: |
1183 |
.DS |
1184 |
{ |
1185 |
This is a comment, enclosed in curly braces. |
1186 |
{Comments can be nested.} |
1187 |
} |
1188 |
{ standard expressions use +,-,*,/,^,(,) } |
1189 |
vname = Ny * func(A1) ; |
1190 |
{ constants are defined with a colon } |
1191 |
const : sqrt(PI/2) ; |
1192 |
{ user-defined functions add to library } |
1193 |
func(x) = 5 + A1*sin(x/3) ; |
1194 |
{ functions may be passed and recursive } |
1195 |
rfunc(f,x) = if(x,f(x),f(-x)*rfunc(f,x+1)) ; |
1196 |
{ constant functions may also be defined } |
1197 |
cfunc(x) : 10*x / sqrt(x) ; |
1198 |
.DE |
1199 |
Many variables and functions are already defined by the program, |
1200 |
and they are listed in the file |
1201 |
.I rayinit.cal. |
1202 |
The following variables are particularly important: |
1203 |
.DS |
1204 |
Dx, Dy, Dz - incident ray direction |
1205 |
Px, Py, Pz - intersection point |
1206 |
Nx, Ny, Nz - surface normal at intersection point |
1207 |
Rdot - cosine between ray and normal |
1208 |
arg(0) - number of real arguments |
1209 |
arg(i) - i'th real argument |
1210 |
.DE |
1211 |
For BRDF types, the following variables are defined as well: |
1212 |
.DS |
1213 |
NxP, NyP, NzP - perturbed surface normal |
1214 |
RdotP - perturbed dot product |
1215 |
CrP, CgP, CbP - perturbed material color |
1216 |
.DE |
1217 |
A unique context is set up for each file so that the same variable |
1218 |
may appear in different function files without conflict. |
1219 |
The variables listed above and any others defined in |
1220 |
rayinit.cal are available globally. |
1221 |
If no file is needed by a given primitive because all the required |
1222 |
variables are global, a period (`.') can be given in |
1223 |
place of the file name. |
1224 |
It is also possible to give an expression instead of a straight |
1225 |
variable name in a scene file, although such expressions should |
1226 |
be kept simple as they cannot contain any white space. |
1227 |
Also, functions (requiring parameters) |
1228 |
must be given as names and not as expressions. |
1229 |
.PP |
1230 |
Constant expressions are used as an optimization in function |
1231 |
files. |
1232 |
They are replaced wherever they occur in an expression by their |
1233 |
value. |
1234 |
Constant expressions are evaluated only once, so they must not |
1235 |
contain any variables or values that can change, such as the ray |
1236 |
variables Px and Ny or the primitive argument function arg(). |
1237 |
All the math library functions such as sqrt() and cos() have the |
1238 |
constant attribute, so they will be replaced by immediate values |
1239 |
whenever they are given constant arguments. |
1240 |
Thus, the subexpression cos(PI*sqrt(2)) is immediately replaced |
1241 |
by its value, -.266255342, and does not cause any additional overhead |
1242 |
in the calculation. |
1243 |
.PP |
1244 |
It is generally a good idea to define constants and variables before |
1245 |
they are referred to in a function file. |
1246 |
Although evaluation does not take place until later, the interpreter |
1247 |
does variable scoping and constant subexpression evaluation based on |
1248 |
what it has compiled already. |
1249 |
For example, a variable that is defined globally in rayinit.cal then |
1250 |
referenced in the local context of a function file cannot |
1251 |
subsequently be redefined in the same file because the compiler |
1252 |
has already determined the scope of the referenced variable as global. |
1253 |
To avoid such conflicts, one can state the scope of a variable explicitly |
1254 |
by preceding the variable name with a context mark (a back-quote) for |
1255 |
a local variable, or following the name with a context mark for a global |
1256 |
variable. |
1257 |
.NH 3 |
1258 |
Data Files |
1259 |
.PP |
1260 |
Data files contain n-dimensional arrays of real numbers used |
1261 |
for interpolation. |
1262 |
Typically, definitions in a function file determine how |
1263 |
to index and use interpolated data values. |
1264 |
The basic data file format is as follows: |
1265 |
.DS |
1266 |
N |
1267 |
beg1 end1 m1 |
1268 |
0 0 m2 x2.1 x2.2 x2.3 x2.4 .. x2.m2 |
1269 |
... |
1270 |
begN endN mN |
1271 |
DATA, later dimensions changing faster. |
1272 |
.DE |
1273 |
N is the number of dimensions. |
1274 |
For each dimension, the beginning and ending coordinate |
1275 |
values and the dimension size is given. |
1276 |
Alternatively, individual coordinate values can be given when |
1277 |
the points are not evenly spaced. |
1278 |
These values must either be increasing or decreasing monotonically. |
1279 |
The data is m1*m2*...*mN real numbers in ASCII form. |
1280 |
Comments may appear anywhere in the file, beginning with a pound |
1281 |
sign ('#') and continuing to the end of line. |
1282 |
.NH 3 |
1283 |
Font Files |
1284 |
.PP |
1285 |
A font file lists the polygons which make up a character set. |
1286 |
Comments may appear anywhere in the file, beginning with a pound |
1287 |
sign ('#') and continuing to the end of line. |
1288 |
All numbers are decimal integers: |
1289 |
.DS |
1290 |
code n |
1291 |
x0 y0 |
1292 |
x1 y1 |
1293 |
... |
1294 |
xn yn |
1295 |
... |
1296 |
.DE |
1297 |
The ASCII codes can appear in any order. |
1298 |
N is the number of vertices, and the last is automatically |
1299 |
connected to the first. |
1300 |
Separate polygonal sections are joined by coincident sides. |
1301 |
The character coordinate system is a square with lower left corner at |
1302 |
(0,0), lower right at (255,0) and upper right at (255,255). |
1303 |
.NH 2 |
1304 |
Generators |
1305 |
.PP |
1306 |
A generator is any program that produces a scene description |
1307 |
as its output. |
1308 |
They usually appear as commands in a scene description file. |
1309 |
An example of a simple generator is |
1310 |
.I genbox. |
1311 |
.I Genbox |
1312 |
takes the arguments of width, height and depth to produce |
1313 |
a parallelepiped description. |
1314 |
.I Genprism |
1315 |
takes a list of 2-dimensional coordinates and extrudes them along a vector to |
1316 |
produce a 3-dimensional prism. |
1317 |
.I Genrev |
1318 |
is a more sophisticated generator |
1319 |
that produces an object of rotation from parametric functions |
1320 |
for radius and axis position. |
1321 |
.I Gensurf |
1322 |
tessellates a surface defined by the |
1323 |
parametric functions x(s,t), y(s,t), and z(s,t). |
1324 |
.I Genworm |
1325 |
links cylinders and spheres along a curve. |
1326 |
.I Gensky |
1327 |
produces a sun and sky distribution corresponding |
1328 |
to a given time and date. |
1329 |
.PP |
1330 |
.I Xform |
1331 |
is a program that transforms a scene description from one |
1332 |
coordinate space to another. |
1333 |
.I Xform |
1334 |
does rotation, translation, scaling, and mirroring. |
1335 |
.NH 1 |
1336 |
Image Generation |
1337 |
.PP |
1338 |
Once the scene has been described in three-dimensions, it |
1339 |
is possible to generate a two-dimensional image from a |
1340 |
given perspective. |
1341 |
.PP |
1342 |
The image generating programs use an |
1343 |
.I octree |
1344 |
to efficiently trace rays through the scene. |
1345 |
An octree subdivides space into nested octants which |
1346 |
contain sets of surfaces. |
1347 |
In RADIANCE, an octree is created from a scene description by |
1348 |
.I oconv. |
1349 |
The details of this process are not important, |
1350 |
but the octree will serve as input to the ray-tracing |
1351 |
programs and directs the use of a scene description. |
1352 |
.PP |
1353 |
.I Rview |
1354 |
is ray-tracing program for viewing a scene interactively. |
1355 |
When the user specifies a new perspective, |
1356 |
.I rview |
1357 |
quickly displays a rough |
1358 |
image on the terminal, then progressively |
1359 |
increases the resolution as the user looks on. |
1360 |
He can select a particular section of the image to improve, |
1361 |
or move to a different view and start over. |
1362 |
This mode of interaction is useful for debugging scenes |
1363 |
as well as determining the best view for a final image. |
1364 |
.PP |
1365 |
.I Rpict |
1366 |
produces a high-resolution picture of a scene from |
1367 |
a particular perspective. |
1368 |
This program features adaptive sampling, crash |
1369 |
recovery and progress reporting, all of which are important |
1370 |
for time-consuming images. |
1371 |
.PP |
1372 |
A number of filters are available for manipulating picture files. |
1373 |
.I Pfilt |
1374 |
sets the exposure and performs anti-aliasing. |
1375 |
.I Pcompos |
1376 |
composites (cuts and pastes) pictures. |
1377 |
.I Pcond |
1378 |
conditions a picture for a specific display device. |
1379 |
.I Pcomb |
1380 |
performs arbitrary math on one or more pictures. |
1381 |
.I Protate |
1382 |
rotates a picture 90 degrees clockwise. |
1383 |
.I Pflip |
1384 |
flips a picture horizontally, vertically, or both (180 degree rotation). |
1385 |
.I Pvalue |
1386 |
converts a picture to and from simpler formats. |
1387 |
.PP |
1388 |
Pictures may be displayed directly under X11 using the program |
1389 |
.I ximage, |
1390 |
or converted a standard image format. |
1391 |
.I Ra_avs |
1392 |
converts to and from AVS image format. |
1393 |
.I Ra_pict |
1394 |
converts to Macintosh 32-bit PICT2 format. |
1395 |
.I Ra_ppm |
1396 |
converts to and from Poskanzer Portable Pixmap formats. |
1397 |
.I Ra_pr |
1398 |
converts to and from Sun 8-bit rasterfile format. |
1399 |
.I Ra_pr24 |
1400 |
converts to and from Sun 24-bit rasterfile format. |
1401 |
.I Ra_ps |
1402 |
converts to PostScript color and greyscale formats. |
1403 |
.I Ra_rgbe |
1404 |
converts to and from Radiance uncompressed picture format. |
1405 |
.I Ra_t16 |
1406 |
converts to and from Targa 16 and 24-bit image formats. |
1407 |
.I Ra_t8 |
1408 |
converts to and from Targa 8-bit image format. |
1409 |
.I Ra_tiff |
1410 |
converts to and from TIFF. |
1411 |
.I Ra_xyze |
1412 |
converts to and from Radiance CIE picture format. |
1413 |
.NH 1 |
1414 |
License |
1415 |
.PP |
1416 |
Radiance is a registered copyright of The Regents of the University of |
1417 |
California ("The Regents"). The Regents grant to you a nonexclusive, |
1418 |
nontransferable license ("License") to use Radiance source code without fee. |
1419 |
You may not sell or distribute Radiance to others without the prior express |
1420 |
written permission of The Regents. |
1421 |
You may compile and use this software on any machines to which you have |
1422 |
personal access, and may share its use with others who have access to the |
1423 |
same machines. |
1424 |
.PP |
1425 |
NEITHER THE UNITED STATES NOR THE UNITED STATES DEPARTMENT OF ENERGY, NOR ANY |
1426 |
OF THEIR EMPLOYEES, MAKES ANY WARRANTY, EXPRESS OR IMPLIED, OR ASSUMES ANY |
1427 |
LEGAL LIABILITY OR RESPONSIBILITY FOR THE ACCURACY, COMPLETENESS, OR |
1428 |
USEFULNESS OF ANY INFORMATION, APPARATUS, PRODUCT, OR PROCESS DISCLOSED, OR |
1429 |
REPRESENTS THAT ITS USE WOULD NOT INFRINGE PRIVATELY OWNED RIGHTS. |
1430 |
By downloading, using or copying this software, you agree to abide by the |
1431 |
intellectual property laws and all other applicable laws of the United |
1432 |
States, and by the terms of this License Agreement. Ownership of the software |
1433 |
shall remain solely in The Regents. |
1434 |
The Regents shall have the right to terminate this License immediately by |
1435 |
written notice upon your breach of, or noncompliance with, any of its terms. |
1436 |
You shall be liable for any infringement or damages resulting from your |
1437 |
failure to abide by the terms of this License Agreement. |
1438 |
.PP |
1439 |
NOTICE: The Government is granted for itself and others acting on its behalf |
1440 |
a paid-up, nonexclusive irrevocable worldwide license in this data to |
1441 |
reproduce, prepare derivative works, and perform publicly and display |
1442 |
publicly. Beginning five (5) years after permission to assert copyright is |
1443 |
granted, subject to two possible five year renewals, the Government is |
1444 |
granted for itself and others acting on its behalf a paid-up, non-exclusive, |
1445 |
irrevocable worldwide license in this data to reproduce, prepare derivative |
1446 |
works, distribute copies to the public, perform publicly and display |
1447 |
publicly, and to permit others to do so. |
1448 |
.NH 1 |
1449 |
Acknowledgements |
1450 |
.PP |
1451 |
This work was supported by the Assistant Secretary of Conservation |
1452 |
and Renewable Energy, Office of Building Energy Research and |
1453 |
Development, Buildings Equipment Division of the U.S. Department of |
1454 |
Energy under Contract No. DE-AC03-76SF00098. |
1455 |
.PP |
1456 |
Additional work was sponsored by the Swiss federal government |
1457 |
under the Swiss LUMEN Project and was |
1458 |
carried out in the Laboratoire d'Energie Solaire (LESO Group) at |
1459 |
the Ecole Polytechnique Federale de Lausanne (EPFL University) |
1460 |
in Lausanne, Switzerland. |
1461 |
.NH 1 |
1462 |
References |
1463 |
.LP |
1464 |
Ward, G., |
1465 |
``The Radiance Lighting Simulation and Rendering System,'' |
1466 |
.I "Computer Graphics", |
1467 |
Orlando, July 1994. |
1468 |
.LP |
1469 |
Rushmeier, H., G. Ward, |
1470 |
``Energy-Preserving Non-Linear Filters,'' |
1471 |
.I "Computer Graphics", |
1472 |
Orlando, July 1994. |
1473 |
.LP |
1474 |
Ward, G., |
1475 |
``A Contrast-Based Scalefactor for Luminance Display,'' |
1476 |
.I "Graphics Gems IV", |
1477 |
Edited by Paul Heckbert, |
1478 |
Academic Press 1994. |
1479 |
.LP |
1480 |
Ward, G., |
1481 |
``Measuring and Modeling Anisotropic Reflection,'' |
1482 |
.I "Computer Graphics", |
1483 |
Chicago, July 1992. |
1484 |
.LP |
1485 |
Ward, G., P. Heckbert, |
1486 |
``Irradiance Gradients,'' |
1487 |
.I "Third Annual Eurographics Workshop on Rendering", |
1488 |
to be published by Springer-Verlag, held in Bristol, UK, May 1992. |
1489 |
.LP |
1490 |
Ward, G., |
1491 |
``Adaptive Shadow Testing for Ray Tracing,'' |
1492 |
.I "Second Annual Eurographics Workshop on Rendering", |
1493 |
to be published by Springer-Verlag, held in Barcelona, SPAIN, May 1991. |
1494 |
.LP |
1495 |
Ward, G., |
1496 |
``Visualization,'' |
1497 |
.I "Lighting Design and Application", |
1498 |
Vol. 20, No. 6, June 1990. |
1499 |
.LP |
1500 |
Ward, G., F. Rubinstein, R. Clear, |
1501 |
``A Ray Tracing Solution for Diffuse Interreflection,'' |
1502 |
.I "Computer Graphics", |
1503 |
Vol. 22, No. 4, August 1988. |
1504 |
.LP |
1505 |
Ward, G., F. Rubinstein, |
1506 |
``A New Technique for Computer Simulation of Illuminated Spaces,'' |
1507 |
.I "Journal of the Illuminating Engineering Society", |
1508 |
Vol. 17, No. 1, Winter 1988. |