[ODE] Terrain + ODE ... again

[Paul Cheyrou-Lagreze]

> So, can someone who already have made it to explain a good way to have  
> terrain collision?

Because there is many ways to handle this, Benoit CHAPEROT implementation,  
transform terrain into a trimesh, Create a new Ode object as in slickworm  
http://slickworm.sourceforge.net/, etc.

> Heh... ODE is i nice stuff.. i don't understand why nobody write  
> something strong for this,... a

So here's another one, surely the easiest to test... (don't know if it's  
the best one...)

I use "Sliding Planes", that is ode plane appears under entities according  
to terrain normals at the entity position.

Here's one (in C++),
that just need a GetHeightAt function in you terrain algos :

/////code
const dReal *pos_bod = dBodyGetPosition (entity->getBody ());

float objheight = (float) pos_bod[1]; // pos_bod[1] is  entity y pos

Vector3 pos = Vector3 ((Real) pos_bod[0],
                        (Real) pos_bod[1],
                        (Real) pos_bod[2]);

getHeightAt (pos); // does modify pos.y according to terrain height at  
this position

// if test is true, then there is some collision
// therefore, we create a "sliding plane"
if  (pos.y > objheight)
{
   Vector3 vecz = pos;
   Vector3 vecx = pos;


  vecx.x = vecx.x + SHIFT_POS;
  activetempentity->getHeightAt (vecx);

  vecz.z = vecz.z + SHIFT_POS;
  activetempentity->getHeightAt (vecz);

  Vector3 kEdge1 = pos - vecx;
  Vector3 kEdge2 = vecz - vecx;
  Vector3 normal = kEdge1.crossProduct (kEdge2);

  normal.normalise();
  Real distance = normal.dotProduct (pos);

  dPlane temp  (space,
		   (dReal) normal.x, (dReal) normal.y, (dReal) normal.z,
		   (dReal) distance);

  dContact contact[NUM_CONTACTS];
  if (int numc = dCollide (entity->getGeom (),  temp.id (), NUM_CONTACTS,  
&contact[0].geom, sizeof(dContact)))
   {
      for (int i=0; i < numc; i++)
      {		
  	[...]// usual Ode contact stuff
      }	
   }
}
/////end of code

- SHIFT_POS must be equal to object width or height...
- Vector3, Vector3::normalise and Vector3::dotProduct comes from OGRE  
engine. but surely you have same objects or functions somewhere in your  
code. (perhaps there is some in Ode's?)

...