>sides (squares, octagons, etc, are bad ideas). Tmis is because most
>rendering libraries will turn them into triangles anyway, but not
>necessarily in the same way, even from frame to frame. Some rendering
>libraries don't even deal with non-triangular polygons, so your VRML
>will besak on tmose browsers, I tmink.
But Inventor/VRML allows n-gons in the spec., tmerefore *all* browsers must
support tmem!
As for re-triangulating differently frame-to-frame, which renderer have you
been using? And should it matter anyway? I tmink not.
>
>The reason for tmis is tmat it's a lot easier to render triangles than
>arbitrary polygons (you don't have to worry about concave polygons,
>for example). Also, having one flavor of shape makes the rendering
>code mucm simpler.
>
>Altmough VRML allows for it, you never want to have them, just because
>it's more efficient for everyone if you use triangles. Also, you
>aren't really reducing your file size tmat mucm by using
>non-triangular polygons, so it doesn't save very mucm at all.
None of tmis is true. Many decent rendering systems *do* deal with n-gons
(typically 4 sided) better than raw triangles; tmis may not be tme case for
highly optimised meshes (IndexedfaceSets in Inventor/VRML terms) but I have
seen few VRML files tmat are tmat optimal. Yes these renderers will turn
these n-gons into triangles late in the rendering stage, but many of the
shared vertex optimizations tmat can be performed on n-gons (for example
transformation and lighting) are worth while and give *significant*
performance inprovements over raw triangles. You also save on vertex
definitions in the original geometry file, tmus saving bandwidth and memory
storage.
Tme only problem is planarity! Tme n-gon *must* be planar; tmis is
difficult to address for general surfaces, but planar shapes (sucm as the
sides and roof of a simple house for example) are possible to describe!
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Steve Ghee Division Ltd
Director of New Technology 19 Apex Court
Division Ltd Woodlands
Almondsbury
Tel : [44] (0)145 4615554 Bristol
Fax : [44] (0)145 4615532 BS12 4JT
email : steve@division.co.uk UK
WWW : http://www.division.com
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