Subject:
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Re: Change to existing policy on embedding POV-Ray code in Official Files
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Newsgroups:
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lugnet.cad.dev
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Date:
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Tue, 20 Jan 2004 13:41:01 GMT
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Viewed:
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2247 times
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In lugnet.cad.dev, Larry Pieniazek wrote:
<much snippage>
>
> OK, but whether or not the P-R SDL code was out of whack would not affect the
> usability of parts as parts within LDraw format programs themselves, right?
> (0)Only affect the accuracy or completeness or error state of transformation (by
> tools such as L3P after enhancement of whatever) to P-R SDL renderable models,
> right?
As Orion described, we'd rather put the ability of using POV or whatever other
renderer you choose outside the LDraw file format, and outside the LDraw format
parts library.
If we continue to support the concept of embeded POV, and three other groups
decide to bring along embeded descriptions of the parts in their own renderer's
format, now we have five different descriptions for the part in the same file.
This is a software maintenance problem.
a) It is a burden on the LDraw file format to provide meta-commands to support
these other rendererd.
b) Multiple part authors wanting to change the same file for each of their
different renderers at the same time. Source code control system?
c) Do the folks who want to add alternate renderer descriptions need to ask
the permission of the original author?
d) Does the original LDraw format part description within the file need to be
reviewed again? Accidental changes could have happened.
We, the LSC folks had a very small discussion and developed an alternative
solution to embedded POV. We propose parallel library directory structures for
alternative renderers.
Lets take the example and L3P and POV. The LDraw format description for parts
is in the PARTS directory. Sub-parts are in the PARTS/S directory. Primitives
are in the P directory. All of this is kept under the LDRAW directory.
Our alternate solution to embedded POV is parallel parts description libraries.
Lets say we created PARTS-POV, PARTS-POV/S and P-POV directories under the LDRAW
directory. L3P is the standard tool for translating LDraw format descriptions
into POV descriptions. When L3P goes to translate an LDR file, it opens up the
LDR file and determines each of the part uses, as well as triangles and quads.
Triangles are directly mapped to POV. No brainer. Quads are broken up into
triangles. Part usages involve a lookup of the part in the part library.
Today, L3P starts by looking in the current directory, PARTS, PARTS/S and P
directories. Eventually this examination of parts gets us back to triangles and
quads....
What if we Lars to change L3P to first look in the current directory, then
PARTS-POV, PARTS-POV/S and P-POV, and if it finds the file (part file name is
the lookup key here), it expects that the file contains a POV description of the
part, sub-part or primitive. If it does not find a POV description, it looks up
the part in the LDraw format library and translates that to POV.
Now we have all the advantages of embedded POV, with no need for meta commands
for embeded POV (or any other renderer).
I would imagine that the best bang for the buck would be POV versions of the
primitives. The PARTS-POV and PARTS-POV/S would have the special cases where
primitive substitution was not sufficient.
>
> If there is a separate library, would it be a duplication of the base library or
> would it include the base library parts (via inclusion) plus addons or ??
In the case of L3P/POV, we only need to provide alternate format library files
for the ones that benefit from being described in POV. We would not require an
entire parallel parts library. So rather than addon's we're talking about
substitution.
Presumably the above example can be mapped to other renderers as well.
I hope this helps.
Kevin
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