Charles Paik (cpaik++at++mdc.com)
Wed, 29 Jul 1998 12:58:46 -0500
My trees are currenly modeled very similar to Billboards. They are quads
with an texture of a tree. They are not billboards because they do not
rotate with the view of the eye. Instead, my trees are modeled with 2
intersecting quads. From above, it looks like an X. This gives the trees
a 3-D look. Even though they are really 2D. They are very similar to
billboards, but they have an extra quad, and they do not rotate.
I do not have transformations for my trees. The quads are individually
placed. (At least that's how I think the database was developed from
my best interpretation of the database.)
App and Cull stages are extremely light relative to my Draw Stage.
I suppose making the trees billboards, will reduce the number of
polygons by 1/2 since I will not need the intersecting quad.
But my real question of dicussion on this topic is: if the trees were
modeled similarly (for example, the trees are both textures on a quad), is
there a significant performance advantage using a billboard approach?
And what are the key issues?
And my ultimate question would be: what would be a good trick for
drawing a ton of trees?
Thanks for all the feed back thus far.
>>> "Alejandro Saez" <cano++at++krusty> 10/23/97 01:38pm >>>
On Jul 29, 10:44am, Charles Paik wrote:
> Subject: Billboard Performance
> I have a database full of trees. In fact, the trees are taking up more
than
> 50% of the time to render the scene. The trees are not modeled as
> billboards. Can I get significant performance increases by changing my
> database to model the trees as billboards?
>
> -or- Are there any good suggestions on improving performance when
> you have to render a ton of trees?
>
> --
> Charles Paik
> charles.c.paik++at++boeing.com
>
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>-- End of excerpt from Charles Paik
How are you representing trees now? I'm assuming you are using a 3D
solid model
of a tree, and with that in mind the answer, most of the time is yes but
then
you should ask where is that 50% of time actually being spent. Using
billboards
has a trade off, in one hand you are most probably reducing the number
of polys
being drawn (how many triangles has a modeled tree, 50-100? a
billboard will be
2 traingles or a quad)
which is good for the draw stage but then you are adding an extra
burden to
your app because you have to compute the orientation ot the billboards.
If you
have plenty of time left in your app. and it is also geometry limeted then
probably billboards are the way to go. There is still another way of
lightening
the draw stage by using LODs for the trees, this is also adding extra app
time
to compute the correct LOD. Another thing to consider is .. are you
cloning a
single tree. if this is the case then bear in mind that each cloned tree has
a
translation matrix associated that must be computed for each tree, if this
is
your case then try copying at an extra memory consuption fee.
--
------------------------------------------------------------------------
Alejandro Saez
Software Engineer
Silicon Chile S.A.
Avda. Santa Maria 2560
E-mail: asaez++at++silicon.cl Providencia
Phone: +56 (2) 203 3371 Ext. 107 Santiago
Fax: +56 (2) 203 3370 Chile
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