Subject:
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Re: L3P user primitive substitution
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Newsgroups:
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lugnet.cad.dev
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Date:
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Mon, 17 Dec 2001 22:03:27 GMT
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Viewed:
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1360 times
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Dear All,
Currently, there are a number of files on the Parts Tracker which include
embedded POV-Ray, using the 0 L3P meta-statement.
I've been emailing with Lars, Paul and Chris about some concerns I have with
this approach. Basically, before we allowed this approach in the official
parts library, I wanted to be sure we were taking the best approach.
Through the email, I've been convinced that embedding POV-Ray code in part
files is a good idea. The alternatives would be:
1. Not address the issue at all, and not support any method for substituting
solid-modeling code for LDraw code.
2. Maintain a separate library of POV-Ray files, or at least a separate
library POV-Ray enhanced LDraw files.
I don't think either of these alternatives is desireable.
One issue I still have is with the specific syntax used. I think the
current syntax is too specific to L3P. What would be better is a more
generic meta-statement, that could be used for other purposes in the future.
So I'd like to propose that the current syntax be replaced with the following:
> 0 IFDEF <tag>
> Conditional section begin
> Begin non-LDraw statements in comment statement fields
>
> 0 IFNDEF <tag>
> Conditional section begin
> Begin DAT statements
>
> 0 ELSE
> Switch between above section modes
>
> 0 ENDIF
> Terminate conditional section
In the current situation, <tag> would always be POVRAY. In the future,
other possible tag-values may be determined, such as level-of-detail settings.
So, that's all I've got to say for now. Comments, anyone?
Steve
In lugnet.cad.ray, 12 months ago, Chuck Sommerville writes:
> Awhile back, I persuaded Lars Hassing to add a feature to L3P. I wanted the
> ability to substutite POV language commands in the comments of a .DAT file
> that could be used in place of the DAT primitives when rendering through
> POV. This would allow users to add native POV commands that could render
> better than the triangles and polygons defined in DAT files. Since the
> commands are inbedded in comment fields, and only recognized by L3P, they
> have no effect of any other tools. Lars was waiting untill I tested the
> commands to announce the feature. The good news, is you probably already
> have the ability to use these features. He built them into Version 1.2
> 20000616.
>
> The commands are
> 0 L3P IFPOV
> Conditional section begin
> Begin POV statements in comment statement fields
>
> 0 L3P IFNOTPOV
> Conditional section begin
> Begin DAT statements
>
> 0 L3P ELSEPOV
> Switch between above section modes
>
> 0 L3P ENDPOV
> Terminate conditional section
>
> After running L3P, you can see in the POV file conditionals like
> if(0) or if(1)
> To see the alternate version for comparison, just change the constant in
> these conditionals.
>
> If you don't understand any of this, don't worry, I am following this post
> up with some examples. Remember to get L3P V1.2 or latter to use thse.
>
> -Chuck
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Message has 2 Replies:
 | | Re: L3P user primitive substitution
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| (...) Just a thought. If the POVRAY (or whatever) sections get too big, would it make sense to add 0 INCLUDE meta-command so the LDRAW only programs don't waste time parsing? Then the POV specific versions could be distributed separately from the (...) (25 years ago, 17-Dec-01, to lugnet.cad.dev)
| | | Re: L3P user primitive substitution
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| Since there hasn't been discussion of this topic, and more than two weeks have elapsed, can we assume that: A) The proposed revision is acceptable B) The proposed revision is un-acceptable C) No one knows LMKWYT, Steve (...) (25 years ago, 3-Jan-02, to lugnet.cad.dev)
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