Re: [Algorithms] Colliding against polygon soup

[Conor S. <cs...@tp...>]

> At 09:46 AM 12/7/00 +0800, Conor Stokes wrote:
> >OBB-Trees can apply to interiors rather well actually. Heightmaps are
> >special cases anyway, and suited to quadtrees much better (they are a
very
> >2d collision problem.)
>
> I dislike the assumption that a terrain = heightmap.  I'd like to use a
> generalized mesh to represent a terrain region, say something like you'd
> say in the old Dagoth Moor demo that shipped with the GeForce.  Overhangs,
> caves, etc.

Well, in many cases maps like that can be treated as a heightmap + models :)

Anyway, a height segmented quadtree can do a good job there. Still, there is
a good reason why people like to use heightmaps :)

>
> So if you're building an interior with OBB-Trees, how do you do it?  I
> mean, not the technical stuff, I'm talking about the logical stuff -- do
> you end up building it as discrete pieces (column 0, dais, stairs, rail,
> etc.) or as a single monolithic mesh and there's some magic OBB-Tree
> creation algorithm I'm unaware of that automatically takes a mesh and
> decomposes it into sane OBBs?

Well, actually, you can do either ways, or a combination of both.  There are
sane OBB algorithms, but I prefer objects and building the tree backwards
from a set of objects. (I also went down the objects, as they could contain
a reasonable amount of triangles).

> I'm having a hard time visualizing this...what's an example of this?  Do
> you mean the case where the sphere is going into a "V" and pushing off of
> one triangle forces it into the other?

That is one of the cases that can happen. Another case is simply that you
have two collisions occuring at once (say in a right angled corner) that
both need to be taken care of.

Conor Stokes