[ODE] Very close to solving trimesh problem (Normals question).

[Alen Ladavac]

> > 2) for each triangle, add it in both the current winding order, and the
> > reverse winding order
> >
>
> Well in my experience, there's quite a problem with this. Anytime I've
> ever tried to have a paper-thin trimesh (say I want collision for a
> 'fence') and add triangles to both sides (same vertex positions, opposite
> normals), if any moving body came along and collided with that fence,
> during the first timestep, it will be partially intersecting with
> triangles on the front and back of the fence. Then the simulator has no
> idea how to deal with this condition, and the body is pushed in two
> opposite directions at once.

If you are going to do that, then you need to take care in the collider to
ignore penetration into a triangle deeper than half of the penetrating
object. Then you won't have the problem you see. But I'd recommend the
"create your art correctly", plus special collider handling for specially
flagged "double-sided" triangles. If you want to do fences that way.

HTH,
Alen