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Revision: 1.4
Committed: Thu Oct 21 16:16:14 2004 UTC (19 years, 5 months ago) by greg
Content type: text/html
Branch: MAIN
CVS Tags: rad3R6, rad3R6P1
Changes since 1.3: +3 -5 lines
Log Message:
Update for 3.6 official release

File Contents

# User Rev Content
1 greg 1.1 <html>
2     <head>
3     <title>
4 greg 1.4 The RADIANCE 3.6 Synthetic Imaging System
5 greg 1.1 </title>
6     </head>
7     <body>
8    
9     <p>
10    
11     <h1>
12 greg 1.4 The RADIANCE 3.6 Synthetic Imaging System
13 greg 1.1 </h1>
14    
15     <p>
16    
17 greg 1.4 Building Technologies Program<br>
18 greg 1.1 Lawrence Berkeley National Laboratory<br>
19     1 Cyclotron Rd., 90-3111<br>
20     Berkeley, CA 94720<br>
21     <a HREF="http://radsite.lbl.gov/radiance"</a>
22     http://radsite.lbl.gov/radiance<br>
23    
24     <p>
25     <hr>
26    
27     <h2>
28     <a NAME="Overview">Overview</a>
29     </h2>
30     <ol>
31     <li><a HREF="#Intro">Introduction</a><!P>
32     <li><a HREF="#Scene">Scene Description</a><!P>
33     <ol>
34     <li><a HREF="#Primitive"> Primitive Types</a>
35     <ol>
36     <li><a HREF="#Surfaces">Surfaces</a>
37     <li><a HREF="#Materials">Materials</a>
38     <li><a HREF="#Textures">Textures</a>
39     <li><a HREF="#Patterns">Patterns</a>
40     <li><a HREF="#Mixtures">Mixtures</a>
41     </ol><!P>
42     <li><a HREF="#Auxiliary">Auxiliary Files</a>
43     <ol>
44     <li><a HREF="#Function">Function Files</a>
45     <li><a HREF="#Data">Data Files</a>
46     <li><a HREF="#Font">Font Files</a>
47     </ol><!P>
48     <li><a HREF="#Generators">Generators</a>
49     </ol><!P>
50     <li><a HREF="#Image">Image Generation</a><!P>
51     <li><a HREF="#License">License</a><!P>
52     <li><a HREF="#Ack">Acknowledgements</a><!P>
53     <li><a HREF="#Ref">References</a><!P>
54     <li><a HREF="#Index">Types Index</a><!P>
55     </ol>
56    
57     <p>
58     <hr>
59    
60     <h2>
61     <a NAME="Intro">1. Introduction</a>
62     </h2>
63    
64     RADIANCE was developed as a research tool for predicting
65     the distribution of visible radiation in illuminated spaces.
66     It takes as input a three-dimensional geometric model
67     of the physical environment, and produces a map of
68     spectral radiance values in a color image.
69     The technique of ray-tracing follows light backwards
70     from the image plane to the source(s).
71     Because it can produce realistic images from a
72     simple description, RADIANCE has a wide range of applications
73     in graphic arts, lighting design,
74     computer-aided engineering and architecture.
75    
76     <p>
77     <img SRC="diagram1.gif">
78     <p>
79     Figure 1
80     <p>
81     The diagram in Figure 1 shows the flow between programs (boxes) and data
82     (ovals).
83     The central program is <i>rpict</i>, which produces a picture from a scene
84     description.
85     <i>Rview</i> is a variation of rpict that computes and displays images
86     interactively, and rtrace computes single ray values.
87     Other programs (not shown) connect many of these elements together,
88     such as the executive programs
89     <i>rad</i>
90     and
91     <i>ranimate</i>,
92     the interactive rendering program
93     <i>rholo</i>,
94     and the animation program
95     <i>ranimove</i>.
96     The program
97     <i>obj2mesh</i>
98     acts as both a converter and scene compiler, converting a Wavefront .OBJ
99     file into a compiled mesh octree for efficient rendering.
100    
101     <p>
102     A scene description file lists the surfaces and materials
103     that make up a specific environment.
104     The current surface types are spheres, polygons, cones, and cylinders.
105     There is also a composite surface type, called mesh, and a pseudosurface
106     type, called instance, which facilitates very complex geometries.
107     Surfaces can be made from materials such as plastic, metal, and glass.
108     Light sources can be distant disks as well as local spheres, disks
109     and polygons.
110    
111     <p>
112     From a three-dimensional scene description and a specified view,
113     <i>rpict</i> produces a two-dimensional image.
114     A picture file is a compressed binary representation of the
115     pixels in the image.
116     This picture can be scaled in size and brightness,
117     anti-aliased, and sent to a graphics output device.
118    
119     <p>
120     A header in each picture file lists the program(s)
121     and parameters that produced it.
122     This is useful for identifying a picture without having to display it.
123     The information can be read by the program <i>getinfo</i>.
124    
125     <p>
126     <hr>
127    
128     <h2>
129     <a name="Scene">2. Scene Description</a>
130     </h2>
131    
132     A scene description file represents a three-dimensional physical environment in Cartesian (rectilinear) world coordinates.
133     It is stored as ASCII text, with the following basic format:
134    
135     <pre>
136     # comment
137    
138     modifier type identifier
139     n S1 S2 &quot;S 3&quot; .. Sn
140     0
141     m R1 R2 R3 .. Rm
142    
143     modifier alias identifier reference
144    
145     ! command
146    
147     ...
148     </pre>
149    
150     A comment line begins with a pound sign, `#'.
151    
152     <p>
153     The <a NAME="scene_desc">scene description primitives</a>
154     all have the same general format, and can be either surfaces or modifiers.
155     A primitive has a modifier, a type, and an identifier.
156     <p>
157     A <a NAME="modifier"><b>modifier</b></a> is either the
158     identifier of a previously defined primitive, or &quot;void&quot;.
159     <br>
160     [ The most recent definition of a modifier is the
161     one used, and later definitions do not cause relinking
162     of loaded primitives.
163     Thus, the same identifier may be used repeatedly,
164     and each new definition will apply to the primitives following it. ]
165     <p>
166     An <a NAME="identifier"><b>identifier</b></a> can be any string
167     (i.e., any sequence of non-white characters).
168     <p>
169     The arguments associated with a primitive can be strings or real numbers.
170     <ul>
171     <li> The first integer following the identifier is the number of <b>string arguments</b>,
172     and it is followed by the arguments themselves (separated by white space or enclosed in quotes).
173     <li> The next integer is the number of integer arguments, and is followed by the <b>integer arguments</b>.
174     (There are currently no primitives that use them, however.)
175     <li> The next integer is the real argument count, and it is followed by the <b>real arguments</b>.
176     </ul>
177    
178     <p>
179     An <a NAME="alias"><b>alias</b></a> gets its type and arguments from
180     a previously defined primitive.
181     This is useful when the same material is
182     used with a different modifier, or as a convenient naming mechanism.
183     The reserved modifier name &quot;inherit&quot; may be used to specificy that
184     an alias will inherit its modifier from the original.
185     Surfaces cannot be aliased.
186    
187     <p>
188     A line beginning with an exclamation point, `!',
189     is interpreted as a command.
190     It is executed by the shell, and its output is read as input to the program.
191     The command must not try to read from its standard input, or confusion
192     will result.
193     A command may be continued over multiple lines using a
194     backslash, `\', to escape the newline.
195    
196     <p>
197     White space is generally ignored, except as a separator.
198     The exception is the newline character after a command or comment.
199     Commands, comments and primitives may appear in any
200     combination, so long as they are not intermingled.
201    
202     <p>
203     <hr>
204    
205     <h3>
206     <a NAME="Primitive">2.1. Primitive Types</a>
207     </h3>
208    
209     Primitives can be <a HREF="#Surfaces">surfaces</a>,
210     <a HREF="#Materials">materials</a>,
211     <a HREF="#Textures">textures</a> or
212     <a HREF="#Patterns">patterns</a>.
213     Modifiers can be <a HREF="#Materials">materials</a>,
214     <a HREF="#Mixtures">mixtures</a>,
215     <a HREF="#Textures">textures</a> or <a HREF="#Patterns">patterns</a>.
216     Simple surfaces must have one material in their modifier list.
217    
218     <p>
219     <hr>
220    
221     <h4>
222     <a NAME="Surfaces">2.1.1. Surfaces</a>
223     </h4>
224     <dl>
225    
226     A scene description will consist mostly of surfaces.
227     The basic types are given below.
228    
229     <p>
230    
231     <dt>
232     <a NAME="Source">
233     <b>Source </b>
234     </a>
235     <dd>
236     A source is not really a surface, but a solid angle.
237     It is used for specifying light sources that are very distant.
238     The direction to the center of the source and the number of degrees subtended by its disk are given as follows:
239    
240     <pre>
241     mod source id
242     0
243     0
244     4 xdir ydir zdir angle
245     </pre>
246    
247     <p>
248    
249     <dt>
250     <a NAME="Sphere">
251     <b>Sphere</b>
252     </a>
253     <dd>
254     A sphere is given by its center and radius:
255    
256     <pre>
257     mod sphere id
258     0
259     0
260     4 xcent ycent zcent radius
261     </pre>
262    
263     <p>
264    
265     <dt>
266     <a NAME="Bubble">
267     <b>Bubble</b>
268     </a>
269    
270     <dd>
271     A bubble is simply a sphere whose surface normal points inward.
272    
273     <p>
274    
275     <dt>
276     <a NAME="Polygon">
277     <b>Polygon</b>
278     </a>
279     <dd>
280     A polygon is given by a list of three-dimensional vertices,
281     which are ordered counter-clockwise as viewed from the
282     front side (into the surface normal).
283     The last vertex is automatically connected to the first.
284     Holes are represented in polygons as interior vertices
285     connected to the outer perimeter by coincident edges (seams).
286    
287     <pre>
288     mod polygon id
289     0
290     0
291     3n
292     x1 y1 z1
293     x2 y2 z2
294     ...
295     xn yn zn
296     </pre>
297    
298     <p>
299    
300     <dt>
301     <a NAME="Cone">
302     <b>Cone</b>
303     </a>
304     <dd>
305     A cone is a megaphone-shaped object.
306     It is truncated by two planes perpendicular to its axis,
307     and one of its ends may come to a point.
308     It is given as two axis endpoints, and the starting and ending radii:
309    
310     <pre>
311     mod cone id
312     0
313     0
314     8
315     x0 y0 z0
316     x1 y1 z1
317     r0 r1
318     </pre>
319    
320     <p>
321    
322     <dt>
323     <a NAME="Cup">
324     <b>Cup</b>
325     </a>
326     <dd>
327     A cup is an inverted <a HREF="#Cone">cone</a> (i.e., has an
328     inward surface normal).
329    
330     <p>
331    
332     <dt>
333     <a NAME="Cylinder">
334     <b>Cylinder</b>
335     </a>
336     <dd>
337     A cylinder is like a <a HREF="#Cone">cone</a>, but its
338     starting and ending radii are equal.
339    
340     <pre>
341     mod cylinder id
342     0
343     0
344     7
345     x0 y0 z0
346     x1 y1 z1
347     rad
348     </pre>
349    
350     <p>
351    
352     <dt>
353     <a NAME="Tube">
354     <b>Tube</b>
355     </a>
356     <dd>
357     A tube is an inverted <a HREF="#Cylinder">cylinder</a>.
358    
359     <p>
360    
361     <dt>
362     <a NAME="Ring">
363     <b>Ring</b>
364     </a>
365     <dd>
366     A ring is a circular disk given by its center,
367     surface normal, and inner and outer radii:
368    
369     <pre>
370     mod ring id
371     0
372     0
373     8
374     xcent ycent zcent
375     xdir ydir zdir
376     r0 r1
377     </pre>
378    
379     <p>
380    
381     <dt>
382     <a NAME="Instance">
383     <b>Instance</b>
384     </a>
385     <dd>
386     An instance is a compound surface, given
387     by the contents of an octree file (created by oconv).
388    
389     <pre>
390     mod instance id
391     1+ octree transform
392     0
393     0
394     </pre>
395    
396     If the modifier is &quot;void&quot;, then surfaces will
397     use the modifiers given in the original description.
398     Otherwise, the modifier specified is used in their place.
399     The transform moves the octree to the desired location in the scene.
400     Multiple instances using the same octree take
401     little extra memory, hence very complex
402     descriptions can be rendered using this primitive.
403    
404     <p>
405     There are a number of important limitations to be aware of
406     when using instances.
407     First, the scene description used to generate the octree must
408     stand on its own, without referring to modifiers in the
409     parent description.
410     This is necessary for oconv to create the octree.
411     Second, light sources in the octree will not be
412     incorporated correctly in the calculation,
413     and they are not recommended.
414     Finally, there is no advantage (other than
415     convenience) to using a single instance of an octree,
416     or an octree containing only a few surfaces.
417     An <a HREF="../man_html/xform.1.html">xform</a> command
418     on the subordinate description is prefered in such cases.
419     </dl>
420    
421     <p>
422    
423     <dt>
424     <a NAME="Mesh">
425     <b>Mesh</b>
426     </a>
427     <dd>
428     A mesh is a compound surface, made up of many triangles and
429     an octree data structure to accelerate ray intersection.
430     It is typically converted from a Wavefront .OBJ file using the
431     <i>obj2mesh</i> program.
432    
433     <pre>
434     mod mesh id
435     1+ meshfile transform
436     0
437     0
438     </pre>
439    
440     If the modifier is &quot;void&quot;, then surfaces will
441     use the modifiers given in the original mesh description.
442     Otherwise, the modifier specified is used in their place.
443     The transform moves the mesh to the desired location in the scene.
444     Multiple instances using the same meshfile take little extra memory,
445     and the compiled mesh itself takes much less space than individual
446     polygons would.
447     In the case of an unsmoothed mesh, using the mesh primitive reduces
448     memory requirements by a factor of 30 relative to individual triangles.
449     If a mesh has smoothed surfaces, we save a factor of 50 or more,
450     permitting very detailed geometries that would otherwise exhaust the
451     available memory.
452     In addition, the mesh primitive can have associated (u,v) coordinates
453     for pattern and texture mapping.
454     These are made available to function files via the Lu and Lv variables.
455    
456     </dl>
457    
458     <p>
459     <hr>
460    
461     <h4>
462     <a NAME="Materials">2.1.2. Materials</a>
463     </h4>
464    
465     A material defines the way light interacts with a surface. The basic types are given below.
466    
467     <p>
468    
469     <dl>
470    
471     <dt>
472     <a NAME="Light">
473     <b>Light</b>
474     </a>
475     <dd>
476     Light is the basic material for self-luminous surfaces (i.e.,
477     light sources).
478     In addition to the <a HREF="#Source">source</a> surface type,
479     <a HREF="#Sphere">spheres</a>,
480     discs (<a HREF="#Ring">rings</a> with zero inner radius),
481     <a HREF="#Cylinder">cylinders</a> (provided they are long enough), and <a HREF="#Polygon">polygons</a> can act as light sources.
482     Polygons work best when they are rectangular.
483     Cones cannot be used at this time.
484     A pattern may be used to specify a light output distribution.
485     Light is defined simply as a RGB radiance value (watts/steradian/m2):
486    
487     <pre>
488     mod light id
489     0
490     0
491     3 red green blue
492     </pre>
493    
494     <p>
495    
496     <dt>
497     <a NAME="Illum">
498     <b>Illum</b>
499     </a>
500    
501     <dd>
502     Illum is used for secondary light sources with broad distributions.
503     A secondary light source is treated like any other light source, except when viewed directly.
504     It then acts like it is made of a different material (indicated by
505     the string argument), or becomes invisible (if no string argument is given,
506     or the argument is &quot;void&quot;).
507     Secondary sources are useful when modeling windows or brightly illuminated surfaces.
508    
509     <pre>
510     mod illum id
511     1 material
512     0
513     3 red green blue
514     </pre>
515    
516     <p>
517    
518     <dt>
519     <a NAME="Glow">
520     <b>Glow</b>
521     </a>
522    
523     <dd>
524     Glow is used for surfaces that are self-luminous, but limited in their effect.
525     In addition to the radiance value, a maximum radius for shadow testing is given:
526    
527     <pre>
528     mod glow id
529     0
530     0
531     4 red green blue maxrad
532     </pre>
533    
534     If maxrad is zero, then the surface will never be tested for shadow, although it may participate in an interreflection calculation.
535     If maxrad is negative, then the surface will never contribute to scene illumination.
536     Glow sources will never illuminate objects on the other side of an illum surface.
537     This provides a convenient way to illuminate local light fixture geometry without overlighting nearby objects.
538    
539     <p>
540    
541     <dt>
542     <a NAME="Spotlight">
543     <b>Spotlight</b>
544     </a>
545    
546     <dd>
547     Spotlight is used for self-luminous surfaces having directed output.
548     As well as radiance, the full cone angle (in degrees) and orientation (output direction) vector are given.
549     The length of the orientation vector is the distance of the effective
550     focus behind the source center (i.e., the focal length).
551    
552     <pre>
553     mod spotlight id
554     0
555     0
556     7 red green blue angle xdir ydir zdir
557     </pre>
558    
559     <p>
560    
561     <dt>
562     <a NAME="Mirror">
563     <b>Mirror</b>
564     </a>
565    
566     <dd>
567     Mirror is used for planar surfaces that produce secondary source reflections.
568     This material should be used sparingly, as it may cause the light source calculation to blow up if it is applied to many small surfaces.
569     This material is only supported for flat surfaces such as <a HREF="#Polygon">polygons</a> and <a HREF="#Ring">rings</a>.
570     The arguments are simply the RGB reflectance values, which should be between 0 and 1.
571     An optional string argument may be used like the illum type to specify a different material to be used for shading non-source rays.
572     If this alternate material is given as &quot;void&quot;, then the mirror surface will be invisible.
573     This is only appropriate if the surface hides other (more detailed) geometry with the same overall reflectance.
574    
575     <pre>
576     mod mirror id
577     1 material
578     0
579     3 red green blue
580     </pre>
581    
582     <p>
583    
584     <dt>
585     <a NAME="Prism1">
586     <b>Prism1</b>
587     </a>
588    
589     <dd>
590     The prism1 material is for general light redirection from prismatic glazings, generating secondary light sources.
591     It can only be used to modify a planar surface
592     (i.e., a <a HREF="#Polygon">polygon</a> or <a HREF="#Ring">disk</a>)
593     and should not result in either light concentration or scattering.
594     The new direction of the ray can be on either side of the material,
595     and the definitions must have the correct bidirectional properties to work properly with secondary light sources.
596     The arguments give the coefficient for the redirected light and its direction.
597    
598     <pre>
599     mod prism1 id
600     5+ coef dx dy dz funcfile transform
601     0
602     n A1 A2 .. An
603     </pre>
604    
605     The new direction variables dx, dy and dz need not produce a normalized vector.
606     For convenience, the variables DxA, DyA and DzA are defined as the normalized direction to the target light source.
607     See <a HREF="#Function">section 2.2.1</a> on function files for further information.
608    
609     <p>
610    
611     <dt>
612     <a NAME="Prism2">
613     <b>Prism2</b>
614     </a>
615    
616     <dd>
617     The material prism2 is identical to <a HREF="#Prism1">prism1</a> except that it provides for two ray redirections rather than one.
618    
619     <pre>
620     mod prism2 id
621     9+ coef1 dx1 dy1 dz1 coef2 dx2 dy2 dz2 funcfile transform
622     0
623     n A1 A2 .. An
624     </pre>
625    
626     <p>
627    
628     <dt>
629     <a NAME="Mist">
630     <b>Mist</b>
631     </a>
632    
633     <dd>
634     Mist is a virtual material used to delineate a volume
635     of participating atmosphere.
636     A list of important light sources may be given, along with an
637     extinction coefficient, scattering albedo and scattering eccentricity
638     parameter.
639     The light sources named by the string argument list
640     will be tested for scattering within the volume.
641     Sources are identified by name, and virtual light sources may be indicated
642     by giving the relaying object followed by '&gt;' followed by the source, i.e:
643    
644     <pre>
645     3 source1 mirror1&gt;source10 mirror2&gt;mirror1&gt;source3
646     </pre>
647    
648     Normally, only one source is given per mist material, and there is an
649     upper limit of 32 to the total number of active scattering sources.
650     The extinction coefficient, if given, is added the the global
651     coefficient set on the command line.
652     Extinction is in units of 1/distance (distance based on the world coordinates),
653     and indicates the proportional loss of radiance over one unit distance.
654     The scattering albedo, if present, will override the global setting within
655     the volume.
656     An albedo of 0 0 0 means a perfectly absorbing medium, and an albedo of
657     1 1 1 means
658     a perfectly scattering medium (no absorption).
659     The scattering eccentricity parameter will likewise override the global
660     setting if it is present.
661     Scattering eccentricity indicates how much scattered light favors the
662     forward direction, as fit by the Heyney-Greenstein function:
663    
664     <pre>
665     P(theta) = (1 - g*g) / (1 + g*g - 2*g*cos(theta))^1.5
666     </pre>
667    
668     A perfectly isotropic scattering medium has a g parameter of 0, and
669     a highly directional material has a g parameter close to 1.
670     Fits to the g parameter may be found along with typical extinction
671     coefficients and scattering albedos for various atmospheres and
672     cloud types in USGS meteorological tables.
673     (A pattern will be applied to the extinction values.)
674    
675     <pre>
676     mod mist id
677     N src1 src2 .. srcN
678     0
679     0|3|6|7 [ rext gext bext [ ralb galb balb [ g ] ] ]
680     </pre>
681    
682     There are two usual uses of the mist type.
683     One is to surround a beam from a spotlight or laser so that it is
684     visible during rendering.
685     For this application, it is important to use a <a HREF="#Cone">cone</a>
686     (or <a HREF="#Cylinder">cylinder</a>) that
687     is long enough and wide enough to contain the important visible portion.
688     Light source photometry and intervening objects will have the desired
689     effect, and crossing beams will result in additive scattering.
690     For this application, it is best to leave off the real arguments, and
691     use the global rendering parameters to control the atmosphere.
692     The second application is to model clouds or other localized media.
693     Complex boundary geometry may be used to give shape to a uniform medium,
694     so long as the boundary encloses a proper volume.
695     Alternatively, a pattern may be used to set the line integral value
696     through the cloud for a ray entering or exiting a point in a given
697     direction.
698     For this application, it is best if cloud volumes do not overlap each other,
699     and opaque objects contained within them may not be illuminated correctly
700     unless the line integrals consider enclosed geometry.
701    
702     <dt>
703     <a NAME="Plastic">
704     <b>Plastic</b>
705     </a>
706    
707     <dd>
708     Plastic is a material with uncolored highlights.
709     It is given by its RGB reflectance, its fraction of specularity, and its roughness value.
710     Roughness is specified as the rms slope of surface facets.
711     A value of 0 corresponds to a perfectly smooth surface, and a value of 1 would be a very rough surface.
712     Specularity fractions greater than 0.1 and roughness values greater than 0.2 are not very realistic.
713     (A pattern modifying plastic will affect the material color.)
714    
715     <pre>
716     mod plastic id
717     0
718     0
719     5 red green blue spec rough
720     </pre>
721    
722     <p>
723    
724     <dt>
725     <a NAME="Metal">
726     <b>Metal</b>
727     </a>
728    
729     <dd>
730     Metal is similar to <a HREF="#Plastic">plastic</a>, but specular highlights are modified by the material color.
731     Specularity of metals is usually .9 or greater.
732     As for plastic, roughness values above .2 are uncommon.
733    
734     <p>
735    
736     <dt>
737     <a NAME="Trans">
738     <b>Trans</b>
739     </a>
740    
741     <dd>
742     Trans is a translucent material, similar to <a HREF="#Plastic">plastic</a>.
743     The transmissivity is the fraction of penetrating light that travels all the way through the material.
744     The transmitted specular component is the fraction of transmitted light that is not diffusely scattered.
745     Transmitted and diffusely reflected light is modified by the material color.
746     Translucent objects are infinitely thin.
747    
748     <pre>
749     mod trans id
750     0
751     0
752     7 red green blue spec rough trans tspec
753     </pre>
754    
755     <p>
756    
757     <dt>
758     <a NAME="Plastic2">
759     <b>Plastic2</b>
760     </a>
761    
762     <dd>
763     Plastic2 is similar to <a HREF="#Plastic">plastic</a>, but with anisotropic roughness.
764     This means that highlights in the surface will appear elliptical rather than round.
765     The orientation of the anisotropy is determined by the unnormalized direction vector ux uy uz.
766     These three expressions (separated by white space) are evaluated in the context of the function file funcfile.
767     If no function file is required (i.e., no special variables or functions are required), a period (`.') may be given in its place.
768     (See the discussion of <a HREF="#Function">Function Files</a> in the Auxiliary Files section).
769     The urough value defines the roughness along the u vector given projected onto the surface.
770     The vrough value defines the roughness perpendicular to this vector.
771     Note that the highlight will be narrower in the direction of the smaller roughness value.
772     Roughness values of zero are not allowed for efficiency reasons since the behavior would be the same as regular plastic in that case.
773    
774     <pre>
775     mod plastic2 id
776     4+ ux uy uz funcfile transform
777     0
778     6 red green blue spec urough vrough
779     </pre>
780    
781     <p>
782    
783     <dt>
784     <a NAME="Metal2">
785     <b>Metal2</b>
786     </a>
787    
788     <dd>
789     Metal2 is the same as <a HREF="#Plastic2">plastic2</a>, except that the highlights are modified by the material color.
790    
791     <p>
792    
793     <dt>
794     <a NAME="Trans2">
795     <b>Trans2</b>
796     </a>
797    
798     <dd>
799     Trans2 is the anisotropic version of <a HREF="#Trans">trans</a>.
800     The string arguments are the same as for plastic2, and the real arguments are the same as for trans but with an additional roughness value.
801    
802     <pre>
803     mod trans2 id
804     4+ ux uy uz funcfile transform
805     0
806     8 red green blue spec urough vrough trans tspec
807     </pre>
808    
809     <p>
810    
811     <dt>
812     <a NAME="Dielectric">
813     <b>Dielectric</b>
814     </a>
815    
816     <dd>
817     A dielectric material is transparent, and it refracts light as well as reflecting it.
818     Its behavior is determined by the index of refraction and transmission coefficient in each wavelength band per unit length.
819     Common glass has a index of refraction (n) around 1.5, and a transmission coefficient of roughly 0.92 over an inch.
820     An additional number, the Hartmann constant, describes how the index of refraction changes as a function of wavelength.
821     It is usually zero. (A <a HREF="#Patterns">pattern</a> modifies only the refracted value.)
822    
823     <pre>
824     mod dielectric id
825     0
826     0
827     5 rtn gtn btn n hc
828     </pre>
829    
830     <p>
831    
832     <dt>
833     <a NAME="Interface">
834     <b>Interface</b>
835     </a>
836    
837     <dd>
838     An interface is a boundary between two dielectrics.
839     The first transmission coefficient and refractive index are for the inside; the second ones are for the outside.
840     Ordinary dielectrics are surrounded by a vacuum (1 1 1 1).
841    
842     <pre>
843     mod interface id
844     0
845     0
846     8 rtn1 gtn1 btn1 n1 rtn2 gtn2 btn2 n2
847     </pre>
848    
849     <p>
850    
851     <dt>
852     <a NAME="Glass">
853     <b>Glass</b>
854     </a>
855    
856     <dd>
857     Glass is similar to <a HREF="#Dielectric">dielectric</a>, but it is optimized for thin glass surfaces (n = 1.52).
858     One transmitted ray and one reflected ray is produced.
859     By using a single surface is in place of two, internal reflections are avoided.
860     The surface orientation is irrelevant, as it is for <a HREF="#Plastic">plastic</a>, <a HREF="#Metal">metal</a>, and <a HREF="#Trans">trans</a>.
861     The only specification required is the transmissivity at normal incidence.
862     (Transmissivity is the amount of light not absorbed in one traversal
863     of the material.
864     Transmittance -- the value usually measured -- is the total light
865     transmitted through the pane including multiple reflections.)
866     To compute transmissivity (tn) from transmittance (Tn) use:
867    
868     <pre>
869     tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn
870     </pre>
871    
872     Standard 88% transmittance glass has a transmissivity of 0.96.
873     (A <a HREF="#Patterns">pattern</a> modifying glass will affect the transmissivity.)
874     If a fourth real argument is given, it is interpreted as the index of refraction to use instead of 1.52.
875    
876     <pre>
877     mod glass id
878     0
879     0
880     3 rtn gtn btn
881     </pre>
882    
883     <p>
884    
885     <dt>
886     <a NAME="Plasfunc">
887     <b>Plasfunc</b>
888     </a>
889    
890     <dd>
891     Plasfunc in used for the procedural definition of plastic-like materials
892     with arbitrary bidirectional reflectance distribution functions (BRDF's).
893     The arguments to this material include the color and specularity,
894     as well as the function defining the specular distribution and the auxiliary file where it may be found.
895    
896     <pre>
897     mod plasfunc id
898     2+ refl funcfile transform
899     0
900     4+ red green blue spec A5 ..
901     </pre>
902    
903     The function refl takes four arguments, the x, y and z
904     direction towards the incident light, and the solid angle
905     subtended by the source.
906     The solid angle is provided to facilitate averaging, and is usually
907     ignored.
908     The refl function should integrate to 1 over
909     the projected hemisphere to maintain energy balance.
910     At least four real arguments must be given, and these are made available along with any additional values to the reflectance function.
911     Currently, only the contribution from direct light sources is considered in the specular calculation.
912     As in most material types, the surface normal is always altered to face the incoming ray.
913    
914     <p>
915    
916     <dt>
917     <a NAME="Metfunc">
918     <b>Metfunc</b>
919     </a>
920    
921     <dd>
922     Metfunc is identical to <a HREF="#Plasfunc">plasfunc</a> and takes the same arguments,
923     but the specular component is multiplied also by the material color.
924    
925     <p>
926    
927     <dt>
928     <a NAME="Transfunc">
929     <b>Transfunc</b>
930     </a>
931    
932     <dd>
933     Transfunc is similar to <a HREF="#Plasfunc">plasfunc</a> but with an arbitrary bidirectional transmittance distribution
934     as well as a reflectance distribution.
935     Both reflectance and transmittance are specified with the same function.
936    
937     <pre>
938     mod transfunc id
939     2+ brtd funcfile transform
940     0
941     6+ red green blue rspec trans tspec A7 ..
942     </pre>
943    
944     Where trans is the total light transmitted and tspec is the non-Lambertian fraction of transmitted light.
945     The function brtd should integrate to 1 over each projected hemisphere.
946    
947     <p>
948    
949     <dt>
950     <a NAME="BRTDfunc">
951     <b>BRTDfunc</b>
952     </a>
953    
954     <dd>
955     The material BRTDfunc gives the maximum flexibility over surface reflectance and transmittance,
956     providing for spectrally-dependent specular rays and reflectance and transmittance distribution functions.
957    
958     <pre>
959     mod BRTDfunc id
960     10+ rrefl grefl brefl
961     rtrns gtrns btrns
962     rbrtd gbrtd bbrtd
963     funcfile transform
964     0
965     9+ rfdif gfdif bfdif
966     rbdif gbdif bbdif
967     rtdif gtdif btdif
968     A10 ..
969     </pre>
970    
971     The variables rrefl, grefl and brefl specify the color coefficients for the ideal specular (mirror) reflection of the surface.
972     The variables rtrns, gtrns and btrns specify the color coefficients for the ideal specular transmission.
973     The functions rbrtd, gbrtd and bbrtd take the direction to the incident light (and its solid angle) and
974     compute the color coefficients for the directional diffuse part of reflection and transmission.
975     As a special case, three identical values of '0' may be given in place of these function names to indicate no directional diffuse component.
976    
977     <p>
978     Unlike most other material types, the surface normal is not altered to face the incoming ray.
979     Thus, functions and variables must pay attention to the orientation of the surface and make adjustments appropriately.
980     However, the special variables for the perturbed dot product and surface normal, RdotP, NxP, NyP and NzP are reoriented
981     as if the ray hit the front surface for convenience.
982    
983     <p>
984     A diffuse reflection component may be given for the front side with rfdif, gfdif and bfdif for the front side of the surface
985     or rbdif, gbdif and bbdif for the back side.
986     The diffuse transmittance (must be the same for both sides by physical law) is given by rtdif, gtdif and btdif.
987     A pattern will modify these diffuse scattering values, and will be available through the special variables CrP, CgP and CbP.
988    
989     <p>
990     Care must be taken when using this material type to produce a physically valid reflection model.
991     The reflectance functions should be bidirectional, and under no circumstances should the sum of reflected diffuse,
992     transmitted diffuse, reflected specular, transmitted specular and the integrated directional diffuse component be greater than one.
993    
994     <p>
995    
996     <dt>
997     <a NAME="Plasdata">
998     <b>Plasdata</b>
999     </a>
1000    
1001     <dd>
1002     Plasdata is used for arbitrary BRDF's that are most conveniently given as interpolated data.
1003     The arguments to this material are the <a HREF="#Data">data file</a> and coordinate index functions,
1004     as well as a function to optionally modify the data values.
1005    
1006     <pre>
1007     mod plasdata id
1008     3+n+
1009     func datafile
1010     funcfile x1 x2 .. xn transform
1011     0
1012     4+ red green blue spec A5 ..
1013     </pre>
1014    
1015     The coordinate indices (x1, x2, etc.) are themselves functions of the x, y and z direction to the incident light, plus the solid angle
1016     subtended by the light source (usually ignored).
1017     The data function (func) takes five variables, the
1018     interpolated value from the n-dimensional data file, followed by the
1019     x, y and z direction to the incident light and the solid angle of the source.
1020     The light source direction and size may of course be ignored by the function.
1021    
1022     <p>
1023    
1024     <dt>
1025     <a NAME="Metdata">
1026     <b>Metdata</b>
1027     </a>
1028    
1029     <dd>
1030     As metfunc is to plasfunc, metdata is to <a HREF="#Plasdata">plasdata</a>.
1031     Metdata takes the same arguments as plasdata, but the specular component is modified by the given material color.
1032    
1033     <p>
1034    
1035     <dt>
1036     <a NAME="Transdata">
1037     <b>Transdata</b>
1038     </a>
1039    
1040     <dd>
1041     Transdata is like <a HREF="#Plasdata">plasdata</a> but the specification includes transmittance as well as reflectance.
1042     The parameters are as follows.
1043    
1044     <pre>
1045     mod transdata id
1046     3+n+
1047     func datafile
1048     funcfile x1 x2 .. xn transform
1049     0
1050     6+ red green blue rspec trans tspec A7 ..
1051     </pre>
1052    
1053     <p>
1054    
1055     <dt>
1056     <a NAME="Antimatter">
1057     <b>Antimatter</b>
1058     </a>
1059    
1060     <dd>
1061     Antimatter is a material that can &quot;subtract&quot; volumes from other volumes.
1062     A ray passing into an antimatter object becomes blind to all the specified modifiers:
1063    
1064     <pre>
1065     mod antimatter id
1066     N mod1 mod2 .. modN
1067     0
1068     0
1069     </pre>
1070    
1071     The first modifier will also be used to shade the area leaving the antimatter volume and entering the regular volume.
1072     If mod1 is void, the antimatter volume is completely invisible.
1073     Antimatter does not work properly with the material type <a HREF="#Trans">&quot;trans&quot;</a>,
1074     and multiple antimatter surfaces should be disjoint.
1075     The viewpoint must be outside all volumes concerned for a correct rendering.
1076    
1077     </dl>
1078    
1079     <p>
1080     <hr>
1081    
1082     <h4>
1083     <a NAME="Textures">2.1.3. Textures</a>
1084     </h4>
1085    
1086     A texture is a perturbation of the surface normal, and is given by either a function or data.
1087    
1088     <p>
1089    
1090     <dl>
1091    
1092     <dt>
1093     <a NAME="Texfunc">
1094     <b>Texfunc</b>
1095     </a>
1096    
1097     <dd>
1098     A texfunc uses an auxiliary function file to specify a procedural texture:
1099    
1100     <pre>
1101     mod texfunc id
1102     4+ xpert ypert zpert funcfile transform
1103     0
1104     n A1 A2 .. An
1105     </pre>
1106    
1107     <p>
1108    
1109     <dt>
1110     <a NAME="Texdata">
1111     <b>Texdata</b>
1112     </a>
1113    
1114     <dd>
1115     A texdata texture uses three data files to get the surface normal perturbations.
1116     The variables xfunc, yfunc and zfunc take three arguments each from the interpolated values in xdfname, ydfname and zdfname.
1117    
1118     <pre>
1119     mod texdata id
1120     8+ xfunc yfunc zfunc xdfname ydfname zdfname vfname x0 x1 .. xf
1121     0
1122     n A1 A2 .. An
1123     </pre>
1124    
1125     </dl>
1126    
1127     <p>
1128     <hr>
1129    
1130     <h4>
1131     <a NAME="Patterns">2.1.4. Patterns</a>
1132     </h4>
1133    
1134     Patterns are used to modify the reflectance of materials. The basic types are given below.
1135    
1136     <p>
1137    
1138     <dl>
1139    
1140     <dt>
1141     <a NAME="Colorfunc">
1142     <b>Colorfunc</b>
1143     </a>
1144    
1145     <dd>
1146     A colorfunc is a procedurally defined color pattern. It is specified as follows:
1147    
1148     <pre>
1149     mod colorfunc id
1150     4+ red green blue funcfile transform
1151     0
1152     n A1 A2 .. An
1153     </pre>
1154    
1155     <p>
1156    
1157     <dt>
1158     <a NAME="Brightfunc">
1159     <b>Brightfunc</b>
1160     </a>
1161    
1162     <dd>
1163     A brightfunc is the same as a colorfunc, except it is monochromatic.
1164    
1165     <pre>
1166     mod brightfunc id
1167     2+ refl funcfile transform
1168     0
1169     n A1 A2 .. An
1170     </pre>
1171    
1172     <p>
1173    
1174     <dt>
1175     <a NAME="Colordata">
1176     <b>Colordata</b>
1177     </a>
1178    
1179     <dd>
1180     Colordata uses an interpolated data map to modify a material's color.
1181     The map is n-dimensional, and is stored in three auxiliary files, one for each color.
1182     The coordinates used to look up and interpolate the data are defined in another auxiliary file.
1183     The interpolated data values are modified by functions of one or three variables.
1184     If the functions are of one variable, then they are passed the corresponding color component (red or green or blue).
1185     If the functions are of three variables, then they are passed the original red, green, and blue values as parameters.
1186    
1187     <pre>
1188     mod colordata id
1189     7+n+
1190     rfunc gfunc bfunc rdatafile gdatafile bdatafile
1191     funcfile x1 x2 .. xn transform
1192     0
1193     m A1 A2 .. Am
1194     </pre>
1195    
1196     <p>
1197    
1198     <dt>
1199     <a NAME="Brightdata">
1200     <b>Brightdata</b>
1201     </a>
1202    
1203     <dd>
1204     Brightdata is like colordata, except monochromatic.
1205    
1206     <pre>
1207     mod brightdata id
1208     3+n+
1209     func datafile
1210     funcfile x1 x2 .. xn transform
1211     0
1212     m A1 A2 .. Am
1213     </pre>
1214    
1215     <p>
1216    
1217     <dt>
1218     <a NAME="Colorpict">
1219     <b>Colorpict</b>
1220     </a>
1221    
1222     <dd>
1223     Colorpict is a special case of colordata, where the pattern is a two-dimensional image stored in the RADIANCE picture format.
1224     The dimensions of the image data are determined by the picture such that the smaller dimension is always 1,
1225     and the other is the ratio between the larger and the smaller.
1226     For example, a 500x338 picture would have coordinates (u,v) in the rectangle between (0,0) and (1.48,1).
1227    
1228     <pre>
1229     mod colorpict id
1230     7+
1231     rfunc gfunc bfunc pictfile
1232     funcfile u v transform
1233     0
1234     m A1 A2 .. Am
1235     </pre>
1236    
1237     <p>
1238    
1239     <dt>
1240     <a NAME="Colortext">
1241     <b>Colortext</b>
1242     </a>
1243    
1244     <dd>
1245     Colortext is dichromatic writing in a polygonal font.
1246     The font is defined in an auxiliary file, such as helvet.fnt.
1247     The text itself is also specified in a separate file, or can be part of the material arguments.
1248     The character size, orientation, aspect ratio and slant is determined by right and down motion vectors.
1249     The upper left origin for the text block as well as the foreground and background colors must also be given.
1250    
1251     <pre>
1252     mod colortext id
1253     2 fontfile textfile
1254     0
1255     15+
1256     Ox Oy Oz
1257     Rx Ry Rz
1258     Dx Dy Dz
1259     rfore gfore bfore
1260     rback gback bback
1261     [spacing]
1262     </pre>
1263    
1264     or:
1265    
1266     <pre>
1267     mod colortext id
1268     2+N fontfile . This is a line with N words ...
1269     0
1270     15+
1271     Ox Oy Oz
1272     Rx Ry Rz
1273     Dx Dy Dz
1274     rfore gfore bfore
1275     rback gback bback
1276     [spacing]
1277     </pre>
1278    
1279     <p>
1280    
1281     <dt>
1282     <a NAME="Brighttext">
1283     <b>Brighttext</b>
1284     </a>
1285    
1286     <dd>
1287     Brighttext is like colortext, but the writing is monochromatic.
1288    
1289     <pre>
1290     mod brighttext id
1291     2 fontfile textfile
1292     0
1293     11+
1294     Ox Oy Oz
1295     Rx Ry Rz
1296     Dx Dy Dz
1297     foreground background
1298     [spacing]
1299     </pre>
1300    
1301     or:
1302    
1303     <pre>
1304     mod brighttext id
1305     2+N fontfile . This is a line with N words ...
1306     0
1307     11+
1308     Ox Oy Oz
1309     Rx Ry Rz
1310     Dx Dy Dz
1311     foreground background
1312     [spacing]
1313     </pre>
1314    
1315     <p>
1316    
1317     By default, a uniform spacing algorithm is used that guarantees every character will appear in a precisely determined position.
1318     Unfortunately, such a scheme results in rather unattractive and difficult to read text with most fonts.
1319     The optional spacing value defines the distance between characters for proportional spacing.
1320     A positive value selects a spacing algorithm that preserves right margins and indentation,
1321     but does not provide the ultimate in proportionally spaced text.
1322     A negative value insures that characters are properly spaced, but the placement of words then varies unpredictably.
1323     The choice depends on the relative importance of spacing versus formatting.
1324     When presenting a section of formatted text, a positive spacing value is usually preferred.
1325     A single line of text will often be accompanied by a negative spacing value.
1326     A section of text meant to depict a picture, perhaps using a special purpose font such as hexbit4x1.fnt, calls for uniform spacing.
1327     Reasonable magnitudes for proportional spacing are between 0.1 (for tightly spaced characters) and 0.3 (for wide spacing).
1328    
1329     </dl>
1330    
1331     <p>
1332     <hr>
1333    
1334     <h4>
1335     <a NAME="Mixtures">2.1.5. Mixtures</a>
1336     </h4>
1337    
1338     A mixture is a blend of one or more materials or textures and patterns.
1339     The basic types are given below.
1340    
1341     <p>
1342    
1343     <dl>
1344    
1345     <dt>
1346     <a NAME="Mixfunc">
1347     <b>Mixfunc</b>
1348     </a>
1349    
1350     <dd>
1351     A mixfunc mixes two modifiers procedurally. It is specified as follows:
1352    
1353     <pre>
1354     mod mixfunc id
1355     4+ foreground background vname funcfile transform
1356     0
1357     n A1 A2 .. An
1358     </pre>
1359    
1360     Foreground and background are modifier names that must be
1361     defined earlier in the scene description.
1362     If one of these is a material, then
1363     the modifier of the mixfunc must be &quot;void&quot;.
1364     (Either the foreground or background modifier may be &quot;void&quot;,
1365     which serves as a form of opacity control when used with a material.)
1366     Vname is the coefficient defined in funcfile that determines the influence of foreground.
1367     The background coefficient is always (1-vname).
1368     Since the references are not resolved until run-time, the last definitions of the modifier id's will be used.
1369     This can result in modifier loops, which are detected by the renderer.
1370    
1371     <p>
1372    
1373     <dt>
1374     <a NAME="Mixdata">
1375     <b>Mixdata</b>
1376     </a>
1377    
1378     <dd>
1379     Mixdata combines two modifiers using an auxiliary data file:
1380    
1381     <pre>
1382     mod mixdata id
1383     5+n+
1384     foreground background func datafile
1385     funcfile x1 x2 .. xn transform
1386     0
1387     m A1 A2 .. Am
1388     </pre>
1389    
1390     <dt>
1391     <a NAME="Mixpict">
1392     <b>Mixpict</b>
1393     </a>
1394    
1395     <dd>
1396     Mixpict combines two modifiers based on a picture:
1397    
1398     <pre>
1399     mod mixpict id
1400     7+
1401     foreground background func pictfile
1402     funcfile u v transform
1403     0
1404     m A1 A2 .. Am
1405     </pre>
1406    
1407     <p>
1408    
1409     The mixing coefficient function &quot;func&quot; takes three
1410     arguments, the red, green and blue values
1411     corresponding to the pixel at (u,v).
1412    
1413     </dl>
1414     <p>
1415    
1416     <dt>
1417     <a NAME="Mixtext">
1418     <b>Mixtext</b>
1419     </a>
1420    
1421     <dd>
1422     Mixtext uses one modifier for the text foreground, and one for the background:
1423    
1424     <pre>
1425     mod mixtext id
1426     4 foreground background fontfile textfile
1427     0
1428     9+
1429     Ox Oy Oz
1430     Rx Ry Rz
1431     Dx Dy Dz
1432     [spacing]
1433     </pre>
1434    
1435     or:
1436    
1437     <pre>
1438     mod mixtext id
1439     4+N
1440     foreground background fontfile .
1441     This is a line with N words ...
1442     0
1443     9+
1444     Ox Oy Oz
1445     Rx Ry Rz
1446     Dx Dy Dz
1447     [spacing]
1448     </pre>
1449    
1450     </dl>
1451    
1452     <p>
1453     <hr>
1454    
1455     <h3>
1456     <a NAME="Auxiliary">2.2. Auxiliary Files</a>
1457     </h3>
1458    
1459     Auxiliary files used in <a HREF="#Textures">textures</a> and <a HREF="#Patterns">patterns</a>
1460     are accessed by the programs during image generation.
1461     These files may be located in the working directory, or in a library directory.
1462     The environment variable RAYPATH can be assigned an alternate set of search directories.
1463     Following is a brief description of some common file types.
1464    
1465     <p>
1466    
1467     <h4>
1468     <a NAME="Function">12.2.1. Function Files</a>
1469     </h4>
1470    
1471     A function file contains the definitions of variables, functions and constants used by a primitive.
1472     The transformation that accompanies the file name contains the necessary rotations, translations and scalings
1473     to bring the coordinates of the function file into agreement with the world coordinates.
1474     The transformation specification is the same as for the <a HREF="#Generators">xform</a> command.
1475     An example function file is given below:
1476    
1477     <pre>
1478     {
1479     This is a comment, enclosed in curly braces.
1480     {Comments can be nested.}
1481     }
1482     { standard expressions use +,-,*,/,^,(,) }
1483     vname = Ny * func(A1) ;
1484     { constants are defined with a colon }
1485     const : sqrt(PI/2) ;
1486     { user-defined functions add to library }
1487     func(x) = 5 + A1*sin(x/3) ;
1488     { functions may be passed and recursive }
1489     rfunc(f,x) = if(x,f(x),f(-x)*rfunc(f,x+1)) ;
1490     { constant functions may also be defined }
1491     cfunc(x) : 10*x / sqrt(x) ;
1492     </pre>
1493    
1494     Many variables and functions are already defined by the program, and they are listed in the file rayinit.cal.
1495     The following variables are particularly important:
1496    
1497     <pre>
1498     Dx, Dy, Dz - incident ray direction
1499     Nx, Ny, Nz - surface normal at intersection point
1500     Px, Py, Pz - intersection point
1501     T - distance from start
1502     Ts - single ray (shadow) distance
1503     Rdot - cosine between ray and normal
1504     arg(0) - number of real arguments
1505     arg(i) - i'th real argument
1506     </pre>
1507    
1508     For mesh objects, the local surface coordinates are available:
1509    
1510     <pre>
1511     Lu, Lv - local (u,v) coordinates
1512     </pre>
1513    
1514     For BRDF types, the following variables are defined as well:
1515    
1516     <pre>
1517     NxP, NyP, NzP - perturbed surface normal
1518     RdotP - perturbed dot product
1519     CrP, CgP, CbP - perturbed material color
1520     </pre>
1521    
1522     A unique context is set up for each file so
1523     that the same variable may appear in different
1524     function files without conflict.
1525     The variables listed above and any others defined in
1526     rayinit.cal are available globally.
1527     If no file is needed by a given primitive because all
1528     the required variables are global,
1529     a period (`.') can be given in place of the file name.
1530     It is also possible to give an expression instead
1531     of a straight variable name in a scene file,
1532     although such expressions should be kept
1533     simple if possible.
1534     Also, functions (requiring parameters) must be given
1535     as names and not as expressions.
1536    
1537     <p>
1538     Constant expressions are used as an optimization in function files.
1539     They are replaced wherever they occur in an expression by their value.
1540     Constant expressions are evaluated only once, so they must not contain any variables or values that can change,
1541     such as the ray variables Px and Ny or the primitive argument function arg().
1542     All the math library functions such as sqrt() and cos() have the constant attribute,
1543     so they will be replaced by immediate values whenever they are given constant arguments.
1544     Thus, the subexpression cos(PI*sqrt(2)) is immediately replaced by its value, -.266255342,
1545     and does not cause any additional overhead in the calculation.
1546    
1547     <p>
1548     It is generally a good idea to define constants and variables before they are referred to in a function file.
1549     Although evaluation does not take place until later, the interpreter does variable scoping and
1550     constant subexpression evaluation based on what it has compiled already.
1551     For example, a variable that is defined globally in rayinit.cal
1552     then referenced in the local context of a function file
1553     cannot subsequently be redefined in the same file
1554     because the compiler has already determined the scope of the referenced variable as global.
1555     To avoid such conflicts, one can state the scope of a variable explicitly by
1556     preceding the variable name with a context mark (a back-quote) for a local variable,
1557     or following the name with a context mark for a global variable.
1558    
1559     <p>
1560    
1561     <h4>
1562     <a NAME="Data">2.2.2. Data Files</a>
1563     </h4>
1564    
1565     Data files contain n-dimensional arrays of real numbers used for interpolation.
1566     Typically, definitions in a function file determine how to index and use interpolated data values.
1567     The basic data file format is as follows:
1568    
1569     <pre>
1570     N
1571     beg1 end1 m1
1572     0 0 m2 x2.1 x2.2 x2.3 x2.4 .. x2.m2
1573     ...
1574     begN endN mN
1575     DATA, later dimensions changing faster.
1576     </pre>
1577    
1578     N is the number of dimensions.
1579     For each dimension, the beginning and ending coordinate values and the dimension size is given.
1580     Alternatively, individual coordinate values can be given when the points are not evenly spaced.
1581     These values must either be increasing or decreasing monotonically.
1582     The data is m1*m2*...*mN real numbers in ASCII form.
1583     Comments may appear anywhere in the file, beginning with a pound
1584     sign ('#') and continuing to the end of line.
1585    
1586     <p>
1587    
1588     <h4>
1589     <a NAME="Font">2.2.3. Font Files</a>
1590     </h4>
1591    
1592     A font file lists the polygons which make up a character set.
1593     Comments may appear anywhere in the file, beginning with a pound
1594     sign ('#') and continuing to the end of line.
1595     All numbers are decimal integers:
1596    
1597     <pre>
1598     code n
1599     x0 y0
1600     x1 y1
1601     ...
1602     xn yn
1603     ...
1604     </pre>
1605    
1606     The ASCII codes can appear in any order. N is the number of vertices, and the last is automatically connected to the first.
1607     Separate polygonal sections are joined by coincident sides.
1608     The character coordinate system is a square with lower left corner at (0,0), lower right at (255,0) and upper right at (255,255).
1609    
1610     <p>
1611    
1612     <hr>
1613    
1614     <h3>
1615     <a NAME="Generators">2.3. Generators</a>
1616     </h3>
1617    
1618     A generator is any program that produces a scene description as its output.
1619     They usually appear as commands in a scene description file.
1620     An example of a simple generator is genbox.
1621    
1622     <ul>
1623    
1624     <li>
1625     <a NAME="Genbox" HREF="../man_html/genbox.1.html">
1626     <b>Genbox</b>
1627     </a>
1628     takes the arguments of width, height and depth to produce a parallelepiped description.
1629     <li>
1630     <a NAME="Genprism" HREF="../man_html/genprism.1.html">
1631     <b>Genprism</b>
1632     </a>
1633     takes a list of 2-dimensional coordinates and extrudes them along a vector to
1634     produce a 3-dimensional prism.
1635     <li>
1636     <a NAME="Genrev" HREF="../man_html/genrev.1.html">
1637     <b>Genrev</b>
1638     </a>
1639     is a more sophisticated generator that produces an object of rotation from parametric functions for radius and axis position.
1640     <li>
1641     <a NAME="Gensurf" HREF="../man_html/gensurf.1.html">
1642     <b>Gensurf</b>
1643     </a>
1644     tessellates a surface defined by the parametric functions x(s,t), y(s,t), and z(s,t).
1645     <li>
1646     <a NAME="Genworm" HREF="../man_html/genworm.1.html">
1647     <b>Genworm</b>
1648     </a>
1649     links cylinders and spheres along a curve.
1650     <li>
1651     <a NAME="Gensky" HREF="../man_html/gensky.1.html">
1652     <b>Gensky</b>
1653     </a>
1654     produces a sun and sky distribution corresponding to a given time and date.
1655     <li>
1656     <a NAME="Xform" HREF="../man_html/xform.1.html">
1657     <b>Xform</b>
1658     </a>
1659     is a program that transforms a scene description from one coordinate space to another.
1660     Xform does rotation, translation, scaling, and mirroring.
1661    
1662     </ul>
1663    
1664     <p>
1665     <hr>
1666    
1667     <h2>
1668     <a NAME="Image">3. Image Generation</a>
1669     </h2>
1670    
1671     Once the scene has been described in three-dimensions, it is possible to generate a two-dimensional image from a given perspective.
1672    
1673     <p>
1674     The image generating programs use an <a NAME="octree"><b>octree</b></a> to efficiently trace rays through the scene.
1675     An octree subdivides space into nested octants which contain sets of surfaces.
1676     In RADIANCE, an octree is created from a scene description by <a NAME="oconv1" HREF="../man_html/oconv.1.html"><b>oconv</b></a>.
1677     The details of this process are not important, but the octree will serve as input to the ray-tracing programs and
1678     directs the use of a scene description.
1679     <ul>
1680     <li>
1681 greg 1.3 <a NAME="rvu" HREF="../man_html/rvu.1.html"><b>Rview</b></a> is ray-tracing program for viewing a scene interactively.
1682     When the user specifies a new perspective, rvu quickly displays a rough image on the terminal,
1683 greg 1.1 then progressively increases the resolution as the user looks on.
1684     He can select a particular section of the image to improve, or move to a different view and start over.
1685     This mode of interaction is useful for debugging scenes as well as determining the best view for a final image.
1686    
1687     <li>
1688     <a NAME="rpict" HREF="../man_html/rpict.1.html"><b>Rpict</b></a> produces a high-resolution picture of a scene from a particular perspective.
1689     This program features adaptive sampling, crash recovery and progress reporting, all of which are important for time-consuming images.
1690     </ul>
1691     <p>
1692     A number of <a NAME="filters"><b>filters</b></a> are available for manipulating picture files:
1693     <ul>
1694     <li> <a HREF="../man_html/pfilt.1.html"><b>Pfilt</b></a>
1695     sets the exposure and performs antialiasing.
1696     <li> <a HREF="../man_html/pcompos.1.html"><b>Pcompos</b></a>
1697     composites (cuts and pastes) pictures.
1698     <li> <a HREF="../man_html/pcomb.1.html"><b>Pcomb</b></a>
1699     performs arbitrary math on one or more pictures.
1700     <li> <a HREF="../man_html/pcond.1.html"><b>Pcond</b></a>
1701     conditions a picture for a specific display device.
1702     <li> <a HREF="../man_html/protate.1.html"><b>Protate</b></a>
1703     rotates a picture 90 degrees clockwise.
1704     <li> <a HREF="../man_html/pflip.1.html"><b>Pflip</b></a>
1705     flips a picture horizontally, vertically, or both
1706     (180 degree rotation).
1707     <li> <a HREF="../man_html/pvalue.1.html"><b>Pvalue</b></a>
1708     converts a picture to and from simpler formats.
1709     </ul>
1710    
1711     <p>
1712     Pictures may be displayed directly under X11 using the program
1713     <a HREF="../man_html/ximage.1.html">ximage</a>,
1714     or converted a standard image format using one of the following
1715     <b>translators</b>:
1716     <ul>
1717     <li> <b>Ra_avs</b>
1718     converts to and from AVS image format.
1719     <li> <a HREF="../man_html/ra_pict.1.html"><b>Ra_pict</b></a>
1720     converts to Macintosh 32-bit PICT2 format.
1721     <li> <a HREF="../man_html/ra_ppm.1.html"><b>Ra_ppm</b></a>
1722     converts to and from Poskanzer Portable Pixmap formats.
1723     <li> <a HREF="../man_html/ra_pr.1.html"><b>Ra_pr</b></a>
1724     converts to and from Sun 8-bit rasterfile format.
1725     <li> <a HREF="../man_html/ra_pr24.1.html"><b>Ra_pr24</b></a>
1726     converts to and from Sun 24-bit rasterfile format.
1727     <li> <a HREF="../man_html/ra_ps.1.html"><b>Ra_ps</b></a>
1728     converts to PostScript color and greyscale formats.
1729     <li> <a HREF="../man_html/ra_rgbe.1.html"><b>Ra_rgbe</b></a>
1730     converts to and from Radiance uncompressed picture format.
1731     <li> <a HREF="../man_html/ra_t16.1.html"><b>Ra_t16</b></a>
1732     converts to and from Targa 16 and 24-bit image formats.
1733     <li> <a HREF="../man_html/ra_t8.1.html"><b>Ra_t8</b></a>
1734     converts to and from Targa 8-bit image format.
1735     <li> <a HREF="../man_html/ra_tiff.1.html"><b>Ra_tiff</b></a>
1736     converts to and from TIFF.
1737     <li> <a HREF="../man_html/ra_xyze.1.html"><b>Ra_xyze</b></a>
1738     converts to and from Radiance CIE picture format.
1739     </ul>
1740    
1741     <p>
1742    
1743     <hr>
1744    
1745     <h2>
1746     <a NAME="License">4. License</a>
1747     </h2>
1748    
1749     <pre>
1750     The Radiance Software License, Version 1.0
1751    
1752     Copyright (c) 1990 - 2002 The Regents of the University of California,
1753     through Lawrence Berkeley National Laboratory. All rights reserved.
1754    
1755     Redistribution and use in source and binary forms, with or without
1756     modification, are permitted provided that the following conditions
1757     are met:
1758    
1759     1. Redistributions of source code must retain the above copyright
1760     notice, this list of conditions and the following disclaimer.
1761    
1762     2. Redistributions in binary form must reproduce the above copyright
1763     notice, this list of conditions and the following disclaimer in
1764     the documentation and/or other materials provided with the
1765     distribution.
1766    
1767     3. The end-user documentation included with the redistribution,
1768     if any, must include the following acknowledgment:
1769     &quot;This product includes Radiance software
1770     (<a HREF="http://radsite.lbl.gov/">http://radsite.lbl.gov/</a>)
1771     developed by the Lawrence Berkeley National Laboratory
1772     (<a HREF="http://www.lbl.gov/">http://www.lbl.gov/</a>).&quot;
1773     Alternately, this acknowledgment may appear in the software itself,
1774     if and wherever such third-party acknowledgments normally appear.
1775    
1776     4. The names &quot;Radiance,&quot; &quot;Lawrence Berkeley National Laboratory&quot;
1777     and &quot;The Regents of the University of California&quot; must
1778     not be used to endorse or promote products derived from this
1779     software without prior written permission. For written
1780     permission, please contact [email protected].
1781    
1782     5. Products derived from this software may not be called &quot;Radiance&quot;,
1783     nor may &quot;Radiance&quot; appear in their name, without prior written
1784     permission of Lawrence Berkeley National Laboratory.
1785    
1786     THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
1787     WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
1788     OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
1789     DISCLAIMED. IN NO EVENT SHALL Lawrence Berkeley National Laboratory OR
1790     ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
1791     SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
1792     LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
1793     USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
1794     ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
1795     OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
1796     OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
1797     SUCH DAMAGE.
1798     </pre>
1799    
1800     <hr>
1801    
1802     <h2>
1803     <a NAME="Ack">5. Acknowledgements</a>
1804     </h2>
1805    
1806     This work was supported by the Assistant Secretary of Conservation and Renewable Energy,
1807     Office of Building Energy Research and Development,
1808     Buildings Equipment Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098.
1809    
1810     <p>
1811     Additional work was sponsored by the Swiss federal government
1812     under the Swiss LUMEN Project and was carried out in the
1813     Laboratoire d'Energie Solaire (LESO Group) at the
1814     Ecole Polytechnique Federale de Lausanne (EPFL University) in Lausanne, Switzerland.
1815    
1816     <p>
1817    
1818     <hr>
1819    
1820     <h2>
1821     <a NAME="Ref">6.</a> References
1822     </h2>
1823     <p>
1824     <ul>
1825     <li>Ward, Greg, Elena Eydelberg-Vileshin,
1826 greg 1.2 ``<a HREF="http://viz.cs.berkeley.edu/~gwlarson/papers/egwr02/index.html">Picture Perfect RGB
1827 greg 1.1 Rendering Using Spectral Prefiltering and Sharp Color Primaries</a>,''
1828     Thirteenth Eurographics Workshop on Rendering (2002),
1829     P. Debevec and S. Gibson (Editors), June 2002.
1830     <li>Ward, Gregory,
1831 greg 1.2 ``<a HREF="http://viz.cs.berkeley.edu/~gwlarson/papers/cic01.pdf">High Dynamic Range Imaging</a>,''
1832 greg 1.1 Proceedings of the Ninth Color Imaging Conference, November 2001.
1833     <li>Ward, Gregory and Maryann Simmons,
1834 greg 1.2 ``<a HREF="http://viz.cs.berkeley.edu/~gwlarson/papers/tog99.pdf">
1835 greg 1.1 The Holodeck Ray Cache: An Interactive Rendering System for Global Illumination in Nondiffuse
1836     Environments</a>,'' ACM Transactions on Graphics, 18(4):361-98, October 1999.
1837 greg 1.2 <li>Larson, G.W., ``<a HREF="http://viz.cs.berkeley.edu/~gwlarson/papers/ewp98.pdf">The Holodeck: A Parallel
1838 greg 1.1 Ray-caching Rendering System</a>,'' Proceedings of the Second
1839     Eurographics Workshop on Parallel Graphics and Visualisation,
1840     September 1998.
1841     <li>Larson, G.W. and R.A. Shakespeare,
1842 greg 1.2 <a HREF="http://radsite.lbl.gov/radiance/book/index.html"><em>Rendering with Radiance:
1843 greg 1.1 the Art and Science of Lighting Visualization</em></a>,
1844     Morgan Kaufmann Publishers, 1998.
1845     <li>Larson, G.W., H. Rushmeier, C. Piatko,
1846 greg 1.2 ``<a HREF="http://radsite.lbl.gov/radiance/papers/lbnl39882/tonemap.pdf">A Visibility
1847 greg 1.1 Matching Tone Reproduction Operator for
1848     High Dynamic Range Scenes</a>,'' LBNL Technical Report 39882,
1849     January 1997.
1850 greg 1.2 <li>Ward, G., ``<a HREF="http://radsite.lbl.gov/radiance/papers/erw95.1/paper.html">Making
1851 greg 1.1 Global Illumination User-Friendly</a>,'' Sixth
1852     Eurographics Workshop on Rendering, Springer-Verlag,
1853     Dublin, Ireland, June 1995.</li>
1854     <li>Rushmeier, H., G. Ward, C. Piatko, P. Sanders, B. Rust,
1855     ``<a HREF="http://radsite.lbl.gov/mgf/compare.html">
1856     Comparing Real and Synthetic Images: Some Ideas about
1857     Metrics</a>,'' Sixth Eurographics Workshop on Rendering,
1858     Springer-Verlag, Dublin, Ireland, June 1995.</li>
1859 greg 1.2 <li>Ward, G., ``<a HREF="http://radsite.lbl.gov/radiance/papers/sg94.1/paper.html">The RADIANCE
1860 greg 1.1 Lighting Simulation and Rendering System</a>,'' <em>Computer
1861     Graphics</em>, July 1994.</li>
1862 greg 1.2 <li>Rushmeier, H., G. Ward, ``<a HREF="http://radsite.lbl.gov/radiance/papers/sg94.2/energy.html">Energy
1863 greg 1.1 Preserving Non-Linear Filters</a>,'' <em>Computer
1864     Graphics</em>, July 1994.</li>
1865     <li>Ward, G., ``A Contrast-Based Scalefactor for Luminance
1866     Display,'' <em>Graphics Gems IV</em>, Edited by Paul Heckbert,
1867     Academic Press 1994.</li>
1868 greg 1.2 <li>Ward, G., ``<a HREF="http://radsite.lbl.gov/radiance/papers/sg92/paper.html">Measuring and
1869 greg 1.1 Modeling Anisotropic Reflection</a>,'' <em>Computer
1870     Graphics</em>, Vol. 26, No. 2, July 1992. </li>
1871 greg 1.2 <li>Ward, G., P. Heckbert, ``<a HREF="http://radsite.lbl.gov/radiance/papers/erw92/paper.html">Irradiance
1872 greg 1.1 Gradients</a>,'' Third Annual Eurographics Workshop on
1873     Rendering, Springer-Verlag, May 1992. </li>
1874 greg 1.2 <li>Ward, G., ``<a HREF="http://radsite.lbl.gov/radiance/papers/erw91/erw91.html">Adaptive Shadow
1875 greg 1.1 Testing for Ray Tracing</a>'' Photorealistic Rendering in
1876     Computer Graphics, proceedings of 1991 Eurographics
1877     Rendering Workshop, edited by P. Brunet and F.W. Jansen,
1878     Springer-Verlag. </li>
1879     <li>Ward, G., ``Visualization,'' <em>Lighting Design and
1880     Application</em>, Vol. 20, No. 6, June 1990. </li>
1881 greg 1.2 <li>Ward, G., F. Rubinstein, R. Clear, ``<a HREF="http://radsite.lbl.gov/radiance/papers/sg88/paper.html">A Ray Tracing Solution for
1882 greg 1.1 Diffuse Interreflection</a>,'' <em>Computer Graphics</em>,
1883     Vol. 22, No. 4, August 1988. </li>
1884     <li>Ward, G., F. Rubinstein, ``A New Technique for Computer
1885     Simulation of Illuminated Spaces,'' <em>Journal of the
1886     Illuminating Engineering Society</em>, Vol. 17, No. 1,
1887     Winter 1988. </li>
1888     </ul>
1889     <p>
1890     See the <a HREF="index.html">RADIANCE Reference Materials</a> page
1891     for additional information.
1892     <hr>
1893    
1894     <a NAME="Index"><h2>7. Types Index</h2></a>
1895    
1896     <pre>
1897     <h4>
1898     SURFACES MATERIALS TEXTURES PATTERNS MIXTURES</h4>
1899     <a HREF="#Source">Source</a> <a HREF="#Light">Light</a> <a HREF="#Texfunc">Texfunc</a> <a HREF="#Colorfunc">Colorfunc</a> <a HREF="#Mixfunc">Mixfunc</a>
1900     <a HREF="#Sphere">Sphere</a> <a HREF="#Illum">Illum</a> <a HREF="#Texdata">Texdata</a> <a HREF="#Brightfunc">Brightfunc</a> <a HREF="#Mixdata">Mixdata</a>
1901     <a HREF="#Bubble">Bubble</a> <a HREF="#Glow">Glow</a> <a HREF="#Colordata">Colordata</a> <a HREF="#Mixtext">Mixtext</a>
1902     <a HREF="#Polygon">Polygon</a> <a HREF="#Spotlight">Spotlight</a> <a HREF="#Brightdata">Brightdata</a>
1903     <a HREF="#Cone">Cone</a> <a HREF="#Mirror">Mirror</a> <a HREF="#Colorpict">Colorpict</a>
1904     <a HREF="#Cup">Cup</a> <a HREF="#Prism1">Prism1</a> <a HREF="#Colortext">Colortext</a>
1905     <a HREF="#Cylinder">Cylinder</a> <a HREF="#Prism2">Prism2</a> <a HREF="#Brighttext">Brighttext</a>
1906     <a HREF="#Tube">Tube</a> <a HREF="#Plastic">Plastic</a>
1907     <a HREF="#Ring">Ring</a> <a HREF="#Metal">Metal</a>
1908     <a HREF="#Instance">Instance</a> <a HREF="#Trans">Trans</a>
1909     <a HREF="#Mesh">Mesh</a> <a HREF="#Plastic2">Plastic2</a>
1910     <a HREF="#Metal2">Metal2</a>
1911     <a HREF="#Trans2">Trans2</a>
1912     <a HREF="#Mist">Mist</a>
1913     <a HREF="#Dielectric">Dielectric</a>
1914     <a HREF="#Interface">Interface</a>
1915     <a HREF="#Glass">Glass</a>
1916     <a HREF="#Plasfunc">Plasfunc</a>
1917     <a HREF="#Metfunc">Metfunc</a>
1918     <a HREF="#Transfunc">Transfunc</a>
1919     <a HREF="#BRTDfunc">BRTDfunc</a>
1920     <a HREF="#Plasdata">Plasdata</a>
1921     <a HREF="#Metdata">Metdata</a>
1922     <a HREF="#Transdata">Transdata</a>
1923     <a HREF="#Antimatter">Antimatter</a>
1924    
1925     </pre>
1926    
1927     <p>
1928    
1929    
1930     <hr>
1931     <center>Last Update: October 22, 1997</center>
1932     </body>
1933     </html>
1934