[ODE] Tri-collider with current ODE collision code

[Nate W]

I found and fixed the problem with tri-collider in the new ODE code.  

The main problem is that tri-collider uses dCollideBoxPlane, and the geom
that it passes to dCollideBoxPlane must be laid out in memory in a way
that matches dxPlane.  Far as I can tell, that's incompatible with the
dxUserGeom way of doing things - dxUserGeom seems to be putting a
user_data member right where dxPlane puts the first element of the plane's
normal.

So, in dxTriList.h, I put a structure that has a large section of unused
data, to match dxGeom, and has four dReals in the right place to match
dxPlane's normal vector and distance scalar.

struct dxTriangle
{
	char unused [sizeof (dxGeom)];
	dReal x,y,z,d;
};

(I would have simply derived dxTriangle from dxGeom to get the same
effect, but that would require implementing some abstract virtual
functions.)

In dcTriListCollider.cpp, I got rid of the code that used to copy triangle
data into dcTriListCollider::Geometry, and put in this instead:

	for (int i = 0; i < CollisionTriangles.size(); i++) {

		dxTriangle Triangle;
		dcPlane &TriPlane = CollisionTriangles[i].Plane;

		Triangle.x = TriPlane.Normal.x;
		Triangle.y = TriPlane.Normal.y;
		Triangle.z = TriPlane.Normal.z;
		Triangle.d = TriPlane.Distance;

		int ContactCount = dCollideBoxPlane(Box, (dxGeom*) &Triangle, ...

		for (int j = 0; j < ContactCount; j++) {

			BoxContacts[j].g2 = Geometry;

That last bit sets the contact's g2 member to the tri-list geom object
that the user will be expecting, because dCollideBoxPlane will just set it
to the "Triangle" pseudo-geom object.

It seems to work OK.  Anyone want to try these changes and/or comment on
my form? :-)

Erwin, with your blessing and someone's confirmation (perhaps yours) that
this actually works, I'd like to check this into CVS.

-- 

Nate Waddoups
Redmond WA USA
http://www.natew.com