The Persistence of Vision Raytracer (POV-Ray).
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Opened by Mike H - 2010-06-11
Last edited by Thorsten Fröhlich - 2010-06-20
FS#130 - Master scene unit system variable
Currently, many POV scenes/include files behave differently depending on the basic units used within the scene. Scaling them differently can affect things like ior and media. A master system variable that users can set to configure the scene’s units would be beneficial for sharing and collaboration purposes, so that person A’s glass interior works correctly in person B’s wine glass scene. Just like the #version system variable, it should have a default value but should be possible to explicitly override.
Sunday, 20 June 2010, 06:11 GMT
Reason for closing: Won't implement
Additional comments about closing:
This will not be implemented. POV-Ray is
unit-less by design.
This could also be used to force consistency within the sample scenes/include files that come with the POV-Ray distribution.
It would also make developing/using third-party tools like LightSys easier and more intuitive.
How is IOR impacted by the choice of dimensional unit ?
(I can figure that for media, not for IOR)
If it is a "MASTER" unit, what is the meaning of allowing override inside SDL ?
As a master value, it should be readable from SDL, but setting only in command-line & ini files.
What would be meaning of the value ?
It could be the "actual" size of a pov unit (1 cm, 1 m, 1 inch, 1 furlong... but what would be the reference 1:1 value ?) or better, could provide a ratio from actual size to pov unit.
A serie of variables/keyword (tuned by a master setting could be provided so as to be able to write:
1 * meter, 4 * inch, 3 * feet, 4 * kilometer, 8 * centimeter (cm ?), 2.566 * decimeter, 6 * decameter, 9 * hectameter, 8559 * micron, 232 * millimeter
(metric system is easy to have unambiguous multiple, for the inch/foot/... I wonder if there is a difference between the various imperial length units, like there is for the canadian/US gallon ?): both imperial & metric should be provided, to make both side of the pond happy.
IMHO, it make more senses to introduces a set of length-units that can be used on an object/scene, rather than applying some adjustment to declaration based on #loony_length inside each portion of many files. It also avoid the issue of handling side-effect-include (when an include sets but does not restores the values)
Moreover, it can be made backward compatible with a simple #include file providing the variables.
The variable is especially meant to standardize things like ior and media, since otherwise they are a serious pain to port from one scene to another.
Allowing people to modify the variable would be necessary if one person's scene is rendered in inches, and another person's is in cm.
Explicit unit lengths (e.g. "1in", "7cm", "4ft", etc.) would make this unnecessary as you state, but would be more difficult to make backwards-compatible due to the new syntax that didn't exist before.