Steve Baker (sbaker++at++link.com)
Tue, 23 Jun 1998 15:43:14 -0500 (CDT)
> Both affect the cull pretty much the same.
Perhaps - I thought billboards were still a little worse because you
can't pfFlatten them - but with all the newer pfSprite stuff, that
could well have changed.
> Cross trees hit your draw harder because you are essentially drawing
> 8 triangles vs. 2 for billboards.
Well, if you flag the polygons of the cross trees so that GL doesn't
have to backface cull them, then you only need 4 triangles.
If you are not horribly fill limited (and certainly at longer ranges),
you can go to two triangles for a cross tree and just one for the Billboard
(the point of the triangle being buried slightly underground and the top
of the triangle sized to be large enough to encompass the crown).
The nastiest things about both kinds of trees is that they don't T-mesh
at all well. If you can cope with it, it's much better to go with modelling
clumps of trees (at least at longer ranges).
> Billboarded trees look better and don't hit your draw as hard, but
> you have to spend time in the app rotating them toward your eyepoint.
(I think that happens in CULL - or now, with pfSprites and GL_SGIX_sprite
extensions to OpenGL, it's probably happening down in the geometry engine)
> What I am interested in knowing is:
> 1. Has anybody documented performance differences between Billboards
> vs. Cross trees?
> 2. Has anybody tried using a billboard as the highest level of detail
> for a cross tree and would this be a feasible solution?
If anything, you need to do the reverse. The problem with billboarded
trees is that you can see them spinning as you get close to them - especially
in a wide field of view - or if you are in some kind of aircraft and
can look down on them from above...go into a steep dive and do a 360 roll
and see what I mean!
Rendering good trees in a large enough quantity to be convincing
is a really hard problem - it can be done - but it takes a LOT of
sneaky tricks.
Steve Baker (817)619-8776 (Vox/Vox-Mail)
Raytheon Systems Inc. (817)619-4028 (Fax)
Work: SBaker++at++link.com http://www.hti.com
Home: SJBaker1++at++airmail.net http://web2.airmail.net/sjbaker1
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