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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Mon, 27 Sep 1999 03:22:06 GMT
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Viewed:
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496 times
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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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