A scene description file represents a three-dimensional physical environment in Cartesian (rectilinear) world coordinates. It is stored as ascii text, with the following basic format:
# comment
modifier type identifier
n S1 S2 S3 .. Sn
0
m R1 R2 R3 .. Rm
modifier alias identifier reference
! command
...
A comment line begins with a pound sign, `#'.
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 (ie. sequence of non-blank characters).
The arguments associated with a primitive can be strings or real numbers.
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.
mod source id
0
0
4 xdir ydir zdir angle
mod sphere id
0
0
4 xcent ycent zcent radius
mod polygon id
0
0
3n
x1 y1 z1
x2 y2 z2
...
xn yn zn
mod cone id
0
0
8
x0 y0 z0
x1 y1 z1
r0 r1
mod cylinder id
0
0
7
x0 y0 z0
x1 y1 z1
rad
mod ring id
0
0
8
xcent ycent zcent
xdir ydir zdir
r0 r1
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.
mod light id
0
0
3 red green blue
mod illum id
1 material
0
3 red green blue
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.
mod spotlight id
0
0
7 red green blue angle xdir ydir zdir
mod mirror id
1 material
0
3 red green blue
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.
mod direct1 id
9+ coef1 dx1 dy1 dz1 coef2 dx2 dy2 dz2 funcfile transform
0
n A1 A2 .. An
mod plastic id
0
0
5 red green blue spec rough
mod trans id
0
0
7 red green blue spec rough trans tspec
mod plastic2 id
4+ ux uy uz funcfile transform
0
6 red green blue spec urough vrough
mod trans2 id
4+ ux uy uz funcfile transform
0
8 red green blue spec urough vrough trans tspec
mod dielectric id
0
0
5 rtn gtn btn n hc
mod interface id
0
0
8 rtn1 gtn1 btn1 n1 rtn2 gtn2 btn2 n2
mod glass id
0
0
3 rtn gtn btn
mod plasfunc id
2+ refl funcfile transform
0
4+ red green blue spec A5 ..
The function refl must take three arguments, the x, y and z direction towards the incident light,
and should integrate to 1 over the projected hemisphere.
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.
mod transfunc id
2+ brtd funcfile transform
0
4+ 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.
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
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.
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.
The data function (func) takes four variables, the interpolated value from the n-dimensional data file,
followed by the x, y and z direction to the incident light.
The light source direction may of course be ignored by the function.
mod transdata id
3+n+
func datafile
funcfile x1 x2 .. xn transform
0
6+ red green blue rspec trans tspec A7 ..
mod antimatter id
N mod1 mod2 .. modN
0
0
The first modifier will 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.
mod texfunc id
4+ xpert ypert zpert funcfile transform
0
n A1 A2 .. An
mod texdata id
8+ xfunc yfunc zfunc xdfname ydfname zdfname vfname x0 x1 .. xf
0
n A1 A2 .. An
mod colorfunc id
4+ red green blue funcfile transform
0
n A1 A2 .. An
mod brightfunc id
2+ refl funcfile transform
0
n A1 A2 .. An
mod colordata id
7+n+
rfunc gfunc bfunc rdatafile gdatafile bdatafile
funcfile x1 x2 .. xn transform
0
m A1 A2 .. Am
mod brightdata id
3+n+
func datafile
funcfile x1 x2 .. xn transform
0
m A1 A2 .. Am
mod colorpict id
7+
rfunc gfunc bfunc pictfile
funcfile u v transform
0
m A1 A2 .. Am
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]
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).
mod mixfunc id
4+ foreground background vname funcfile transform
0
n A1 A2 .. An
Foreground and background are modifier names that must be uniquely defined in the scene description.
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.
mod mixdata id
5+n+
foreground background func datafile
funcfile x1 x2 .. xn transform
0
m A1 A2 .. Am
mod mixtext id
4 foreground background fontfile textfile
0
9+
Ox Oy Oz
Rx Ry Rz
Dx Dy Dz
[spacing]
or:
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) ;
Many variables and functions are already defined by the program, and they are listed in the file rayinit.cal.
The following variables are particularly important:
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
For BRDF types, the following variables are defined as well:
NxP, NyP, NzP - perturbed surface normal
RdotP - perturbed dot product
CrP, CgP, CbP - perturbed material color
A unique context is set up for each file so that the same variable may appear in different function files without conflict.
The variables listed above and any others defined in rayinit.cal are available globally.
If no file is needed by a given primitive because all the required variables are global,
a period (`.') can be given in place of the file name.
It is also possible to give an expression instead of a straight variable name in a scene file,
although such expressions should be kept simple as they cannot contain any white space.
Also, functions (requiring parameters) must be given as names and not as expressions.
Constant expressions are used as an optimization in function files. They are replaced wherever they occur in an expression by their value. Constant expressions are evaluated only once, so they must not contain any variables or values that can change, such as the ray variables Px and Ny or the primitive argument function arg(). All the math library functions such as sqrt() and cos() have the constant attribute, so they will be replaced by immediate values whenever they are given constant arguments. Thus, the subexpression cos(PI*sqrt(2)) is immediately replaced by its value, -.266255342, and does not cause any additional overhead in the calculation.
It is generally a good idea to define constants and variables before they are referred to in a function file. Although evaluation does not take place until later, the interpreter does variable scoping and constant subexpression evaluation based on what it has compiled already. For example, a variable that is defined globally in rayinit.cal then referenced in the local context of a function file cannot subsequently be redefined in the same file because the compiler has already determined the scope of the referenced variable as global. To avoid such conflicts, one can state the scope of a variable explicitly by preceding the variable name with a context mark (a back-quote) for a local variable, or following the name with a context mark for a global variable.
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.
N is the number of dimensions.
For each dimension, the beginning and ending coordinate values and the dimension size is given.
Alternatively, individual coordinate values can be given when the points are not evenly spaced.
These values must either be increasing or decreasing monotonically.
The data is m1*m2*...*mN real numbers in ascii form.
Comments are not allowed in data files.
code n
x0 y0
x1 y1
...
xn yn
...
The ascii codes can appear in any order. N is the number of vertices, and the last is automatically connected to the first.
Separate polygonal sections are joined by coincident sides.
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).