Subject:
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Re: Hidden surface removal, and vertex order in part/primitive DAT files
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Newsgroups:
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lugnet.cad.dev
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Date:
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Fri, 1 Oct 1999 04:21:39 GMT
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Viewed:
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496 times
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You mentioned that some parts have a "0 CW-Compliant" tag. Could we do
something to make this a standard? Because than I could read this tag in
MLCad and make the drawing faster!!!!!
Tell me what you think!
Mike
> discussion of this. Some parts (mostly done by Steve Bliss) have a "0 CW-
> Compliant" tag, which means you can use backface culling on them.
John VanZwieten wrote in message ...
> In lugnet.cad.dev, Gary Williams writes:
> > I performed some hidden surface removal tests today (I should have been
> > working on other things, like the inventory file cleanup utility...) and • it
> > appears that there isn't a standard order for listing vertices in DAT • files
> > (I only tested a few elements, and my code may be flawed, so I may be
> > wrong).
> >
> > A common technique in the rendering world is to always specify vertices of • a
> > polygon in clockwise order (clockwise as viewed from the outside of the
> > polyhedra that contains it). This cuts the rendering time in half by
> > allowing the rendering algorithm to ignore the polygons that face away • from
> > the observer (assuming there are no transparent polygons through which the
> > observer might see the backside of another polygon).
> >
> > This technique can also cut in half the amount of time required to • determine
> > which polygon the user clicked on when selecting elements in a model, • since
> > you can't click on a polygon that's facing away from you, so half the
> > polygons don't need to be tested.
> >
> > So...I've got half a mind to write a utility that will load every existing
> > part and primitive file and analyze them and automatically tweak the • vertex
> > orders of all the polygons. But I thought I'd mention the idea first.
> >
> > -Gary
>
> If you run a LUGNET search on backface culling, you'll find extensive
> discussion of this. Some parts (mostly done by Steve Bliss) have a "0 CW-
> Compliant" tag, which means you can use backface culling on them.
>
> It would be pretty amazing if you could create a utility to automatically • fix
> other parts. Even if you fix the vertex order of polygons, you have to • worry
> about the transformations applied to primitives and subparts in a part • file.
> And then you'd have to adjust for transformations applied to parts and
> submodels in a model file.
>
> Would be great to save 1/2 the rendering time, though.
>
> -John Van
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