Subject:
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Re: Maximum depth of ldraw models?
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Newsgroups:
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lugnet.cad.dev
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Date:
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Thu, 7 Sep 2006 04:54:07 GMT
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Viewed:
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2525 times
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Erik Olson wrote:
> In lugnet.cad.dev, Steve Bliss wrote:
> > In lugnet.cad.dev, Mark Tarrabain wrote:
> > > I notice that no maximum depth is given by the standard. How
> > > potentially non-compliant would a renderer be if it fails because parts
> > > in a model are too deeply nested (a maximum of as little as 16 on some
> > > OpenGL implementations). I notice that no existing parts are nested
> > > more than 7 files deep, but I want to be sure.
> > Hmm. I use MPD models a lot, there can be several levels of nesting within a
> > single .mpd file, and I have been known to refer to .mpd files from other .mpd
> > files.
> >
> > I'm not sure how deep my nesting of model files goes, but I'd be a little
> > concerned about a limit of 16 levels. I wonder if ldraw renderers tend to
> > flatten out the nesting in part files?
>
> I tested the performance of, and saw a decent gain from flattening part
> geometry. (Perhaps 15% in BrickDraw3D for QuickDraw3D or OpenGL.)
Okay... 15% speedup is substantial... that means that it's better to
pre-transform the subfiles when generating the operations for the
current file. I won't worry about the maximum depth any more then.
> What this means is that when a part is prepared into a drawing list, it is not a
> list of calls to primitives with a transformation, but instead the primitives
> are copied out and all coordinates pre-transformed, all the way down. (With the
> exception of studs and changes of color.)
How does a renderer know which parts are studs anyways? Are the
filename(s) for studs manually hardcoded into the renderer?
> Or, a part is created as a single mesh
> with an attempt to join triangles into triangle mesh and to join line segments
> into line primitives.
>
> This can speed up rendering by eliminating a large number of camera stack
> operations, eliminating duplicate vertices, and by increasing the memory cache
> hit rate, at the cost of a reasonable amount of extra memory used.
Hmmm... I can't see any way of using compiled vertex arrays for an
object without potentially decoupling the order of opengl operations for
the object from the actual order of ldraw commands as they appear in the
DAT file. That would make editing awkward, wouldn't it?
>> Mark
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Message has 1 Reply:
 | | Re: Maximum depth of ldraw models?
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| The thread seems to be splitting from the original point, It is a fact that OpenGL generally places a depth of 16 on any transforms. If an LDRAW model in MPD format was presented to OpenGL as a raw data block I suspect that OpenGL would easily hit (...) (18 years ago, 8-Sep-06, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: Maximum depth of ldraw models?
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| (...) I tested the performance of, and saw a decent gain from flattening part geometry. (Perhaps 15% in BrickDraw3D for QuickDraw3D or OpenGL.) What this means is that when a part is prepared into a drawing list, it is not a list of calls to (...) (18 years ago, 7-Sep-06, to lugnet.cad.dev)
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