How to get a correct AABB for a collision shape?

[Julio Jerez]

Function NewtonCollisionCalculateAABB() return and AABB designed for fast determination of colliding pairs.
The AABB in must case will fix the collision shape, but in some other cases it will be just an approximation of the shape.
For example this function will calculate a fitting box for a cylinder but will not do so if this cylinder has an offset matrix or and scaled matrix.
As long as the box is larger than the shape this is not problem for the physic engine, but will report inacurate result to the client application.

if an application requires a tight fitting bounding box, the application should use function SupportVertex, here it is a function to do that

Code: Select all

void CalculteLocalAABB (const dMatrix& matrix, NewtonCollision *collision, dVector& p0, dVector& p1)
{
   for (int i = 0; i < 3; i ++) {
      dVector dir (0.0f, 0.0f, 0.0f, 0.0f);

      dir[i] = 1.0f;
      dir = matrix.RotateVector (dir);
      NewtonCollisionSupportVertex (collision, &dir[0], &p1[0]);

      dir = dir.Scale (-1.0f);
      NewtonCollisionSupportVertex (collision, &dir[0], &p0[0]);
   }
}

This function is accurate for all shape, and it calculates a generic AABB,
by setting matrix to identity you get the local aabb.
if you want a global AABB you just the matrix of the object an pass the inverse to the functions.

[Delfi]

I already put warnings about that in calculateAABB wiki page, directing people to NewtonCollisionSupportVertex page, which already has a example how to calculate a proper tight AABB from one of your older posts, i'll add this local aabb there aswell (function there is for global aabb only).