The RADIANCE 3.1 Synthetic Imaging System

Overview

1. Introduction
2. Scene Description
   1. Primitive Types
      1. Surfaces
      2. Materials
      3. Textures
      4. Patterns
      5. Mixtures
   2. Auxiliary Files
      1. Function Files
      2. Data Files
      3. Font Files
   3. Generators
3. Image Generation
4. License
5. Acknowledgements
6. References
7. Types Index

1. Introduction

Figure 1

The diagram in Figure 1 shows the flow between programs (boxes) and data (ovals). The central program is rpict, which produces a picture from a scene description. Rview is a variation of rpict that computes and displays images interactively.

A scene description file lists the surfaces and materials that make up a specific environment. The current surface types are spheres, polygons, cones, and cylinders. They can be made from materials such as plastic, metal, and glass. Light sources can be distant disks as well as local spheres, discs and polygons.

From a three-dimensional scene description and a specified view, rpict produces a two-dimensional image. A picture file is a compressed binary representation of the pixels in the image. This picture can be scaled in size and brightness, anti-aliased, and sent to a graphics output device.

A header in each picture file lists the program(s) and parameters that produced it. This is useful for identifying a picture without having to display it. The information can be read by the program getinfo.

2. Scene Description

        # comment

        modifier type identifier
        n S1 S2 S3 .. Sn
        0
        m R1 R2 R3 .. Rm

        modifier alias identifier reference

        ! command

         ...

The scene description primitives all have the same general format, and can be either surfaces or modifiers. A primitive has a modifier, a type, and an identifier.

A modifier is either the identifier of a previously defined primitive, or "void".
[ The most recent definition of a modifier is the one used, and later definitions do not cause relinking of loaded primitives. Thus, the same identifier may be used repeatedly, and each new definition will apply to the primitives following it. ]

An identifier can be any string (i.e. sequence of non-blank characters).

The arguments associated with a primitive can be strings or real numbers.

• The first integer following the identifier is the number of string arguments, and it is followed by the arguments themselves (separated by white space).
• The next integer is the number of integer arguments, and is followed by the integer arguments. (There are currently no primitives that use them, however.)
• The next integer is the real argument count, and it is followed by the real arguments.

An alias gets its type and arguments from a previously defined primitive. This is useful when the same material is used with a different modifier, or as a convenient naming mechanism. Surfaces cannot be aliased.

A line beginning with an exclamation point, `!', is interpreted as a command. It is executed by the shell, and its output is read as input to the program. The command must not try to read from its standard input, or confusion will result. A command may be continued over multiple lines using a backslash, `\', to escape the newline.

Blank space is generally ignored, except as a separator. The exception is the newline character after a command or comment. Commands, comments and primitives may appear in any combination, so long as they are not intermingled.

2.1. Primitive Types

2.1.1. Surfaces

A scene description will consist mostly of surfaces. The basic types are given below.

Source

A source is not really a surface, but a solid angle. It is used for specifying light sources that are very distant. The direction to the center of the source and the number of degrees subtended by its disk are given as follows:

	mod source id
	0
	0
	4 xdir ydir zdir angle

Sphere

A sphere is given by its center and radius:

        mod sphere id
        0
        0
        4 xcent ycent zcent radius

Bubble

A bubble is simply a sphere whose surface normal points inward.

Polygon

A polygon is given by a list of three-dimensional vertices, which are ordered counter-clockwise as viewed from the front side (into the surface normal). The last vertex is automatically connected to the first. Holes are represented in polygons as interior vertices connected to the outer perimeter by coincident edges (seams).

        mod polygon id
        0
        0
        3n
                x1      y1      z1
                x2      y2      z2
                ...
                xn      yn      zn

Cone

A cone is a megaphone-shaped object. It is truncated by two planes perpendicular to its axis, and one of its ends may come to a point. It is given as two axis endpoints, and the starting and ending radii:

        mod cone id
        0
        0
        8
                x0      y0      z0
                x1      y1      z1
                r0      r1

Cup

A cup is an inverted cone (i.e. has an inward surface normal).

Cylinder

A cylinder is like a cone, but its starting and ending radii are equal.

        mod cylinder id
        0
        0
        7
                x0      y0      z0
                x1      y1      z1
                rad

Tube

A tube is an inverted cylinder.

Ring

A ring is a circular disk given by its center, surface normal, and inner and outer radii:

        mod ring id
        0
        0
        8
                xcent   ycent   zcent
                xdir    ydir    zdir
                r0      r1

Instance

An instance is a compound surface, given by the contents of an octree file (created by oconv).

        mod instance id
        1+ octree transform
        0
        0

If the modifier is "void", then surfaces will use the modifiers given in the original description. Otherwise, the modifier specified is used in their place. The transform moves the octree to the desired location in the scene. Multiple instances using the same octree take little extra memory, hence very complex descriptions can be rendered using this primitive.

There are a number of important limitations to be aware of when using instances. First, the scene description used to generate the octree must stand on its own, without referring to modifiers in the parent description. This is necessary for oconv to create the octree. Second, light sources in the octree will not be incorporated correctly in the calculation, and they are not recommended. Finally, there is no advantage (other than convenience) to using a single instance of an octree, or an octree containing only a few surfaces. An xform command on the subordinate description is prefered in such cases.

2.1.2. Materials

Light

Light is the basic material for self-luminous surfaces (i.e. light sources). In addition to the source surface type, spheres, discs (rings with zero inner radius), cylinders (provided they are long enough), and polygons can act as light sources. Polygons work best when they are rectangular. Cones cannot be used at this time. A pattern may be used to specify a light output distribution. Light is defined simply as a RGB radiance value (watts/steradian/m2):

        mod light id
        0
        0
        3 red green blue

Illum

Illum is used for secondary light sources with broad distributions. A secondary light source is treated like any other light source, except when viewed directly. It then acts like it is made of a different material (indicated by the string argument), or becomes invisible (if no string argument is given, or the argument is "void"). Secondary sources are useful when modeling windows or brightly illuminated surfaces.

        mod illum id
        1 material
        0
        3 red green blue

Glow

Glow is used for surfaces that are self-luminous, but limited in their effect. In addition to the radiance value, a maximum radius for shadow testing is given:

        mod glow id
        0
        0
        4 red green blue maxrad

If maxrad is zero, then the surface will never be tested for shadow, although it may participate in an interreflection calculation. If maxrad is negative, then the surface will never contribute to scene illumination. Glow sources will never illuminate objects on the other side of an illum surface. This provides a convenient way to illuminate local light fixture geometry without overlighting nearby objects.

Spotlight

Spotlight is used for self-luminous surfaces having directed output. As well as radiance, the full cone angle (in degrees) and orientation (output direction) vector are given. The length of the orientation vector is the distance of the effective focus behind the source center (i.e. the focal length).

        mod spotlight id
        0
        0
        7 red green blue angle xdir ydir zdir

Mirror

Mirror is used for planar surfaces that produce secondary source reflections. 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. This material is only supported for flat surfaces such as polygons and rings. The arguments are simply the RGB reflectance values, which should be between 0 and 1. An optional string argument may be used like the illum type to specify a different material to be used for shading non-source rays. If this alternate material is given as "void", then the mirror surface will be invisible. This is only appropriate if the surface hides other (more detailed) geometry with the same overall reflectance.

        mod mirror id
        1 material
        0
        3 red green blue

Prism1

The prism1 material is for general light redirection from prismatic glazings, generating secondary light sources. It can only be used to modify a planar surface (i.e. a polygon or disk) and should not result in either light concentration or scattering. The new direction of the ray can be on either side of the material, and the definitions must have the correct bidirectional properties to work properly with secondary light sources. The arguments give the coefficient for the redirected light and its direction.

        mod prism1 id
        5+ coef dx dy dz funcfile transform
        0
        n A1 A2 .. An

The new direction variables dx, dy and dz need not produce a normalized vector. For convenience, the variables DxA, DyA and DzA are defined as the normalized direction to the target light source. See section 2.2.1 on function files for further information.

Prism2

The material prism2 is identical to prism1 except that it provides for two ray redirections rather than one.

        mod prism2 id
        9+ coef1 dx1 dy1 dz1 coef2 dx2 dy2 dz2 funcfile transform
        0
        n A1 A2 .. An

Mist

Mist is a virtual material used to delineate a volume of participating atmosphere. A list of important light sources may be given, along with an extinction coefficient, scattering albedo and scattering eccentricity parameter. The light sources named by the string argument list will be tested for scattering within the volume. Sources are identified by name, and virtual light sources may be indicated by giving the relaying object followed by '>' followed by the source, i.e:

	3  source1  mirror1>source10  mirror2>mirror1>source3

Normally, only one source is given per mist material, and there is an upper limit of 32 to the total number of active scattering sources. The extinction coefficient, if given, is added the the global coefficient set on the command line. Extinction is in units of 1/distance (distance based on the world coordinates), and indicates the proportional loss of radiance over one unit distance. The scattering albedo, if present, will override the global setting within the volume. An albedo of 0 0 0 means a perfectly absorbing medium, and an albedo of 1 1 1 means a perfectly scattering medium (no absorption). The scattering eccentricity parameter will likewise override the global setting if it is present. Scattering eccentricity indicates how much scattered light favors the forward direction, as fit by the Heyney-Greenstein function:

	P(theta) = (1 - g*g) / (1 + g*g - 2*g*cos(theta))^1.5

A perfectly isotropic scattering medium has a g parameter of 0, and a highly directional material has a g parameter close to 1. Fits to the g parameter may be found along with typical extinction coefficients and scattering albedos for various atmospheres and cloud types in USGS meteorological tables. (A pattern will be applied to the extinction values.)

	mod mist id
	N src1 src2 .. srcN
	0
	0|3|6|7 [ rext gext bext [ ralb galb balb [ g ] ] ]

There are two usual uses of the mist type. One is to surround a beam from a spotlight or laser so that it is visible during rendering. For this application, it is important to use a cone (or cylinder) that is long enough and wide enough to contain the important visible portion. Light source photometry and intervening objects will have the desired effect, and crossing beams will result in additive scattering. For this application, it is best to leave off the real arguments, and use the global rendering parameters to control the atmosphere. The second application is to model clouds or other localized media. Complex boundary geometry may be used to give shape to a uniform medium, so long as the boundary encloses a proper volume. Alternatively, a pattern may be used to set the line integral value through the cloud for a ray entering or exiting a point in a given direction. For this application, it is best if cloud volumes do not overlap each other, and opaque objects contained within them may not be illuminated correctly unless the line integrals consider enclosed geometry.

Plastic

Plastic is a material with uncolored highlights. It is given by its RGB reflectance, its fraction of specularity, and its roughness value. Roughness is specified as the rms slope of surface facets. A value of 0 corresponds to a perfectly smooth surface, and a value of 1 would be a very rough surface. Specularity fractions greater than 0.1 and roughness values greater than 0.2 are not very realistic. (A pattern modifying plastic will affect the material color.)

        mod plastic id
        0
        0
        5 red green blue spec rough

Metal

Metal is similar to plastic, but specular highlights are modified by the material color. Specularity of metals is usually .9 or greater. As for plastic, roughness values above .2 are uncommon.

Trans

Trans is a translucent material, similar to plastic. The transmissivity is the fraction of penetrating light that travels all the way through the material. The transmitted specular component is the fraction of transmitted light that is not diffusely scattered. Transmitted and diffusely reflected light is modified by the material color. Translucent objects are infinitely thin.

        mod trans id
        0
        0
        7 red green blue spec rough trans tspec

Plastic2

Plastic2 is similar to plastic, but with anisotropic roughness. This means that highlights in the surface will appear elliptical rather than round. The orientation of the anisotropy is determined by the unnormalized direction vector ux uy uz. These three expressions (separated by white space) are evaluated in the context of the function file funcfile. If no function file is required (i.e. no special variables or functions are required), a period (`.') may be given in its place. (See the discussion of Function Files in the Auxiliary Files section). The urough value defines the roughness along the u vector given projected onto the surface. The vrough value defines the roughness perpendicular to this vector. Note that the highlight will be narrower in the direction of the smaller roughness value. Roughness values of zero are not allowed for efficiency reasons since the behavior would be the same as regular plastic in that case.

        mod plastic2 id
        4+ ux uy uz funcfile transform
        0
        6 red green blue spec urough vrough

Metal2

Metal2 is the same as plastic2, except that the highlights are modified by the material color.

Trans2

Trans2 is the anisotropic version of trans. 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.

        mod trans2 id
        4+ ux uy uz funcfile transform
        0
        8 red green blue spec urough vrough trans tspec

Dielectric

A dielectric material is transparent, and it refracts light as well as reflecting it. Its behavior is determined by the index of refraction and transmission coefficient in each wavelength band per unit length. Common glass has a index of refraction (n) around 1.5, and a transmission coefficient of roughly 0.92 over an inch. An additional number, the Hartmann constant, describes how the index of refraction changes as a function of wavelength. It is usually zero. (A pattern modifies only the refracted value.)

        mod dielectric id
        0
        0
        5 rtn gtn btn n hc

Interface

An interface is a boundary between two dielectrics. The first transmission coefficient and refractive index are for the inside; the second ones are for the outside. Ordinary dielectrics are surrounded by a vacuum (1 1 1 1).

        mod interface id
        0
        0
        8 rtn1 gtn1 btn1 n1 rtn2 gtn2 btn2 n2

Glass

Glass is similar to dielectric, but it is optimized for thin glass surfaces (n = 1.52). One transmitted ray and one reflected ray is produced. By using a single surface is in place of two, internal reflections are avoided. The surface orientation is irrelevant, as it is for plastic, metal, and trans. The only specification required is the transmissivity at normal incidence. (Transmissivity is the amount of light not absorbed in one traversal of the material. Transmittance -- the value usually measured -- is the total light transmitted through the pane including multiple reflections.) To compute transmissivity (tn) from transmittance (Tn) use:

        tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn

Standard 88% transmittance glass has a transmissivity of 0.96. (A pattern modifying glass will affect the transmissivity.) If a fourth real argument is given, it is interpreted as the index of refraction to use instead of 1.52.

        mod glass id
        0
        0
        3 rtn gtn btn

Plasfunc

Plasfunc in used for the procedural definition of plastic-like materials with arbitrary bidirectional reflectance distribution functions (BRDF's). The arguments to this material include the color and specularity, as well as the function defining the specular distribution and the auxiliary file where it may be found.

        mod plasfunc id
        2+ refl funcfile transform
        0
        4+ red green blue spec A5 ..

The function refl takes four arguments, the x, y and z direction towards the incident light, and the solid angle subtended by the source. The solid angle is provided to facilitate averaging, and is usually ignored. The refl function should integrate to 1 over the projected hemisphere to maintain energy balance. At least four real arguments must be given, and these are made available along with any additional values to the reflectance function. Currently, only the contribution from direct light sources is considered in the specular calculation. As in most material types, the surface normal is always altered to face the incoming ray.

Metfunc

Metfunc is identical to plasfunc and takes the same arguments, but the specular component is multiplied also by the material color.

Transfunc

Transfunc is similar to plasfunc but with an arbitrary bidirectional transmittance distribution as well as a reflectance distribution. Both reflectance and transmittance are specified with the same function.

        mod transfunc id
        2+ brtd funcfile transform
        0
        6+ red green blue rspec trans tspec A7 ..

Where trans is the total light transmitted and tspec is the non-Lambertian fraction of transmitted light. The function brtd should integrate to 1 over each projected hemisphere.

BRTDfunc

The material BRTDfunc gives the maximum flexibility over surface reflectance and transmittance, providing for spectrally-dependent specular rays and reflectance and transmittance distribution functions.

        mod BRTDfunc id
        10+  rrefl  grefl  brefl
             rtrns  gtrns  btrns
             rbrtd  gbrtd  bbrtd
             funcfile  transform
        0
        9+   rfdif gfdif bfdif
             rbdif gbdif bbdif
             rtdif gtdif btdif
             A10 ..

The variables rrefl, grefl and brefl specify the color coefficients for the ideal specular (mirror) reflection of the surface. The variables rtrns, gtrns and btrns specify the color coefficients for the ideal specular transmission. The functions rbrtd, gbrtd and bbrtd take the direction to the incident light (and its solid angle) and compute the color coefficients for the directional diffuse part of reflection and transmission. As a special case, three identical values of '0' may be given in place of these function names to indicate no directional diffuse component.

Unlike most other material types, the surface normal is not altered to face the incoming ray. Thus, functions and variables must pay attention to the orientation of the surface and make adjustments appropriately. However, the special variables for the perturbed dot product and surface normal, RdotP, NxP, NyP and NzP are reoriented as if the ray hit the front surface for convenience.

A diffuse reflection component may be given for the front side with rfdif, gfdif and bfdif for the front side of the surface or rbdif, gbdif and bbdif for the back side. The diffuse transmittance (must be the same for both sides by physical law) is given by rtdif, gtdif and btdif. A pattern will modify these diffuse scattering values, and will be available through the special variables CrP, CgP and CbP.

Care must be taken when using this material type to produce a physically valid reflection model. The reflectance functions should be bidirectional, and under no circumstances should the sum of reflected diffuse, transmitted diffuse, reflected specular, transmitted specular and the integrated directional diffuse component be greater than one.

Plasdata

Plasdata is used for arbitrary BRDF's that are most conveniently given as interpolated data. The arguments to this material are the data file and coordinate index functions, as well as a function to optionally modify the data values.

        mod plasdata id
        3+n+
                func datafile
                funcfile x1 x2 .. xn transform
        0
        4+ red green blue spec A5 ..

The coordinate indices (x1, x2, etc.) are themselves functions of the x, y and z direction to the incident light, plus the solid angle subtended by the light source (usually ignored). The data function (func) takes five variables, the interpolated value from the n-dimensional data file, followed by the x, y and z direction to the incident light and the solid angle of the source. The light source direction and size may of course be ignored by the function.

Metdata

As metfunc is to plasfunc, metdata is to plasdata. Metdata takes the same arguments as plasdata, but the specular component is modified by the given material color.

Transdata

Transdata is like plasdata but the specification includes transmittance as well as reflectance. The parameters are as follows.

        mod transdata id
        3+n+
                func datafile
                funcfile x1 x2 .. xn transform
        0
        6+ red green blue rspec trans tspec A7 ..

Antimatter

Antimatter is a material that can "subtract" volumes from other volumes. A ray passing into an antimatter object becomes blind to all the specified modifiers:

        mod antimatter id
        N mod1 mod2 .. modN
        0
        0

The first modifier will also be used to shade the area leaving the antimatter volume and entering the regular volume. If mod1 is void, the antimatter volume is completely invisible. Antimatter does not work properly with the material type "trans", and multiple antimatter surfaces should be disjoint. The viewpoint must be outside all volumes concerned for a correct rendering.

2.1.3. Textures

Texfunc

A texfunc uses an auxiliary function file to specify a procedural texture:

        mod texfunc id
        4+ xpert ypert zpert funcfile transform
        0
        n A1 A2 .. An

Texdata

A texdata texture uses three data files to get the surface normal perturbations. The variables xfunc, yfunc and zfunc take three arguments each from the interpolated values in xdfname, ydfname and zdfname.

        mod texdata id
        8+ xfunc yfunc zfunc xdfname ydfname zdfname vfname x0 x1 .. xf
        0
        n A1 A2 .. An

2.1.4. Patterns

Colorfunc

A colorfunc is a procedurally defined color pattern. It is specified as follows:

        mod colorfunc id
        4+ red green blue funcfile transform
        0
        n A1 A2 .. An

Brightfunc

A brightfunc is the same as a colorfunc, except it is monochromatic.

        mod brightfunc id
        2+ refl funcfile transform
        0
        n A1 A2 .. An

Colordata

Colordata uses an interpolated data map to modify a material's color. The map is n-dimensional, and is stored in three auxiliary files, one for each color. The coordinates used to look up and interpolate the data are defined in another auxiliary file. The interpolated data values are modified by functions of one or three variables. If the functions are of one variable, then they are passed the corresponding color component (red or green or blue). If the functions are of three variables, then they are passed the original red, green, and blue values as parameters.

        mod colordata id
        7+n+
                rfunc gfunc bfunc rdatafile gdatafile bdatafile
                funcfile x1 x2 .. xn transform
        0
        m A1 A2 .. Am

Brightdata

Brightdata is like colordata, except monochromatic.

        mod brightdata id
        3+n+
                func datafile
                funcfile x1 x2 .. xn transform
        0
        m A1 A2 .. Am

Colorpict

Colorpict is a special case of colordata, where the pattern is a two-dimensional image stored in the RADIANCE picture format. The dimensions of the image data are determined by the picture such that the smaller dimension is always 1, and the other is the ratio between the larger and the smaller. For example, a 500x338 picture would have coordinates (u,v) in the rectangle between (0,0) and (1.48,1).

        mod colorpict id
        7+
                rfunc gfunc bfunc pictfile
                funcfile u v transform
        0
        m A1 A2 .. Am

Colortext

Colortext is dichromatic writing in a polygonal font. The font is defined in an auxiliary file, such as helvet.fnt. The text itself is also specified in a separate file, or can be part of the material arguments. The character size, orientation, aspect ratio and slant is determined by right and down motion vectors. The upper left origin for the text block as well as the foreground and background colors must also be given.

        mod colortext id
        2 fontfile textfile
        0
        15+
                Ox Oy Oz
                Rx Ry Rz
                Dx Dy Dz
                rfore gfore bfore
                rback gback bback
                [spacing]

or:

        mod colortext id
        2+N fontfile . This is a line with N words ...
        0
        15+
                Ox Oy Oz
                Rx Ry Rz
                Dx Dy Dz
                rfore gfore bfore
                rback gback bback
                [spacing]

Brighttext

Brighttext is like colortext, but the writing is monochromatic.

        mod brighttext id
        2 fontfile textfile
        0
        11+
                Ox Oy Oz
                Rx Ry Rz
                Dx Dy Dz
                foreground background
                [spacing]

or:

        mod brighttext id
        2+N fontfile . This is a line with N words ...
        0
        11+
                Ox Oy Oz
                Rx Ry Rz
                Dx Dy Dz
                foreground background
                [spacing]

By default, a uniform spacing algorithm is used that guarantees every character will appear in a precisely determined position. Unfortunately, such a scheme results in rather unattractive and difficult to read text with most fonts. The optional spacing value defines the distance between characters for proportional spacing. A positive value selects a spacing algorithm that preserves right margins and indentation, but does not provide the ultimate in proportionally spaced text. A negative value insures that characters are properly spaced, but the placement of words then varies unpredictably. The choice depends on the relative importance of spacing versus formatting. When presenting a section of formatted text, a positive spacing value is usually preferred. A single line of text will often be accompanied by a negative spacing value. A section of text meant to depict a picture, perhaps using a special purpose font such as hexbit4x1.fnt, calls for uniform spacing. Reasonable magnitudes for proportional spacing are between 0.1 (for tightly spaced characters) and 0.3 (for wide spacing).

2.1.5. Mixtures

Mixfunc

A mixfunc mixes two modifiers procedurally. It is specified as follows:

        mod mixfunc id
        4+ foreground background vname funcfile transform
        0
        n A1 A2 .. An

Foreground and background are modifier names that must be defined earlier in the scene description. If one of these is a material, then the modifier of the mixfunc must be "void". (Either the foreground or background modifier may be "void", which serves as a form of opacity control when used with a material.) Vname is the coefficient defined in funcfile that determines the influence of foreground. The background coefficient is always (1-vname). Since the references are not resolved until run-time, the last definitions of the modifier id's will be used. This can result in modifier loops, which are detected by the renderer.

Mixdata

Mixdata combines two modifiers using an auxiliary data file:

        mod mixdata id
        5+n+
                foreground background func datafile
                funcfile x1 x2 .. xn transform
        0
        m A1 A2 .. Am

Mixpict

Mixpict combines two modifiers based on a picture:

        mod mixpict id
        7+
                foreground background func pictfile
                funcfile u v transform
        0
        m A1 A2 .. Am

The mixing coefficient function "func" takes three arguments, the red, green and blue values corresponding to the pixel at (u,v).

        mod mixtext id
        4 foreground background fontfile textfile
        0
        9+
                Ox Oy Oz
                Rx Ry Rz
                Dx Dy Dz
                [spacing]

        mod mixtext id
        4+N
                foreground background fontfile .
                This is a line with N words ...
        0
        9+
                Ox Oy Oz
                Rx Ry Rz
                Dx Dy Dz
                [spacing]

        {
                This is a comment, enclosed in curly braces.
                {Comments can be nested.}
        }
                                { standard expressions use +,-,*,/,^,(,) }
        vname = Ny * func(A1) ;
                                { constants are defined with a colon }
        const : sqrt(PI/2) ;
                                { user-defined functions add to library }
        func(x) = 5 + A1*sin(x/3) ;
                                { functions may be passed and recursive }
        rfunc(f,x) = if(x,f(x),f(-x)*rfunc(f,x+1)) ;
                                { constant functions may also be defined }
        cfunc(x) : 10*x / sqrt(x) ;

                Dx, Dy, Dz              - incident ray direction
                Px, Py, Pz              - intersection point
                Nx, Ny, Nz              - surface normal at intersection point
                Rdot                    - cosine between ray and normal
                arg(0)                  - number of real arguments
                arg(i)                  - i'th real argument

                NxP, NyP, NzP           - perturbed surface normal
                RdotP                   - perturbed dot product
                CrP, CgP, CbP           - perturbed material color

        N
        beg1 end1 m1
        0 0 m2 x2.1 x2.2 x2.3 x2.4 .. x2.m2
         ...
        begN endN mN
        DATA, later dimensions changing faster.

        code n
                x0 y0
                x1 y1
                 ...
                xn yn
         ...

SURFACES	MATERIALS	TEXTURES	PATTERNS	MIXTURES
Source		Light		Texfunc		Colorfunc	Mixfunc
Sphere		Illum		Texdata		Brightfunc	Mixdata
Bubble		Glow				Colordata	Mixtext
Polygon		Spotlight			Brightdata
Cone		Mirror				Colorpict
Cup		Prism1				Colortext
Cylinder	Prism2				Brighttext
Tube		Plastic
Ring		Metal
Instance	Trans
		Plastic2
		Metal2
		Trans2
		Mist
		Dielectric
		Interface
		Glass
		Plasfunc
		Metfunc
		Transfunc
		BRTDfunc
		Plasdata
		Metdata
		Transdata
		Antimatter