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Each entity is given by a short keyword, followed by space- or tab- |
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delimited arguments on a single line. A single entity may be extended |
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over multiple lines using a backslash ('\') character right before the |
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end of line, though no extended line may exceed 512 characters in total |
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length. (Given the current set of entities, even approaching 80 |
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characters would be highly unusual.) |
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end of line, though no extended line may exceed 4096 characters in total |
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length. |
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Entities and Contexts |
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===================== |
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Note that this is strictly for ease of identification, and has no |
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real meaning as far as the geometric description goes. In contrast, |
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the transform entity is very significant as it determines how enclosing |
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< |
objects are to be scaled and placed in the final description. |
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> |
objects are to be scaled and placed in the final description. Hierarchical |
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contexts may be nested in any way, but should not overlap. |
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Without further ado, here are the proposed entities and their interpretations: |
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c [id [= [template]]] get/set color context |
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cxy x y set CIE (x,y) chromaticity for current color |
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cspec l_min l_max v1 v2 .. set relative spectrum for current color |
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+ |
cct temperature set spectrum based on black body temperature |
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cmix w1 c1 w2 c2 .. mix named colors to make current color |
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m [id [= [template]]] get/set material context |
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sides {1|2} set number of sides for current material |
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sph vc radius sphere |
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cyl v1 radius v2 truncated right cylinder (open-ended) |
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cone v1 rad1 v2 rad2 truncated right cone (open-ended) |
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prism v1 v2 v3 .. length right prism (closed solid) |
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> |
prism v1 v2 v3 .. length truncated right prism (closed solid) |
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ring vc rmin rmax circular ring with inner and outer radii |
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torus vc rmin rmax circular torus with inner and outer radii |
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xf [xform] begin/end transformation context |
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That is, with the thumb of the right hand pointing in the direction |
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of the axis, rotation follows the curl of the fingers. |
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|
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< |
The transform command itself is also cumulative, and a transform |
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< |
command with no arguments is used to return to the previous |
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< |
condition. It is necessary that transforms and their end statements |
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< |
("xf" by itself) be balanced in a file, so that later or enclosing |
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< |
files are not affected. |
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> |
The transform command itself is also cumulative, but in the reverse |
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order. That is, later transformations (i.e. enclosed transformations) |
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> |
are prepended to existing (i.e. enclosing) ones. A transform command |
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> |
with no arguments is used to return to the previous condition. It is |
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> |
necessary that transforms and their end statements ("xf" by itself) be |
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> |
balanced in a file, so that later or enclosing files are not affected. |
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|
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Transformations apply only to geometric types, e.g. polygons, spheres, etc. |
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Vertices and the components that go into geometry are not directly affected. |
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included in the other material parameters. All colors are absolute, |
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e.g. spectral reflectance or transmittance under uniform white light. |
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|
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A CIE xy chromaticity pair is the most basic color specification. |
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A full spectrum is the most general specification, and the starting |
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(i.e. minimum) and ending (i.e. maximum) wavelengths are given along |
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< |
with a set of evenly spaced values. Wavelengths are given in nanometers, |
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< |
and must be within the range of 380-780. The spectral values themselves |
| 218 |
< |
are located starting at the first wavelength and proceeding at even |
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< |
increments to the ending wavelength. The values in between will be |
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interpolated as necessary, so there must be at least two specified points. |
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< |
The color mixing entity is intended not only for the mixing of named |
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colors, but also for color specifications using an arbitrary set |
| 223 |
< |
of basis functions. The actual totals for spectral and mixing |
| 224 |
< |
coefficients is irrelevant, since the results will be normalized. |
| 213 |
> |
A CIE xy chromaticity pair is the most basic color specification. A |
| 214 |
> |
full spectrum is the most general specification, and the starting (i.e. |
| 215 |
> |
minimum) and ending (i.e. maximum) wavelengths are given along with a |
| 216 |
> |
set of evenly spaced values. Wavelengths are given in nanometers, and |
| 217 |
> |
should be within the range of 380-780. The spectral values themselves, |
| 218 |
> |
which can be thought of as relative power density per nanometer, start |
| 219 |
> |
at the first wavelength and proceed at even increments to the last |
| 220 |
> |
wavelength. The values in between will be interpolated as necessary, |
| 221 |
> |
so there must be at least two specified points. The color temperature |
| 222 |
> |
entity corresponds to the spectrum of a black body at the specified |
| 223 |
> |
temperature (in degrees Kelvin). The color mixing entity is intended |
| 224 |
> |
not only for the mixing of named colors, but also for color |
| 225 |
> |
specifications using an arbitrary set of basis functions. The mixing |
| 226 |
> |
coefficients are in effect relative luminances for each color |
| 227 |
> |
"primary." The actual total of the mixing coefficients or spectral |
| 228 |
> |
values is irrelevant, since the results will always be normalized. |
| 229 |
|
|
| 230 |
|
Diffuse emittance is always given in SI units of lumens/meter^2. Note that |
| 231 |
|
this is emittance, not exitance, and does not include light reflected or |
| 267 |
|
and a length value. The prism will be extruded so that the end-face |
| 268 |
|
points outward, unless the length value is negative, in which case the |
| 269 |
|
object is extruded in the opposite direction, resulting in inward- |
| 270 |
< |
directed surface normals. |
| 270 |
> |
directed surface normals. If surface normals are specified for the |
| 271 |
> |
vertices, they will be applied to the side faces but not the end |
| 272 |
> |
faces, and they must generally point in the appropriate direction |
| 273 |
> |
(i.e. in or out depending on whether extrusion is negative or positive). |
| 274 |
|
|
| 275 |
|
A sphere, cylinder or cone with negative radii is interpreted as having |
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|
an inward facing surface normal. Otherwise, the normal is assumed |
