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Methods to compute more accurate inertia tensor for btCompoundShape and btConvexTriangleMeshShape.

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Thanks to Ole K. for the fixes, see http://www.bulletphysics.com/Bullet/phpBB3/viewtopic.php?f=9&t=2562
This commit is contained in:
erwin.coumans
2008-09-04 18:20:32 +00:00
parent 5d2720d267
commit 7380db7653
5 changed files with 268 additions and 1 deletions
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59
src/BulletCollision/CollisionShapes/btCompoundShape.cpp
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@@ -147,5 +147,62 @@ void btCompoundShape::calculateLocalInertia(btScalar mass,btVector3& inertia) co
}
void btCompoundShape::calculatePrincipalAxisTransform(btScalar* masses, btTransform& principal, btVector3& inertia) const
{
int n = m_children.size();
btScalar totalMass = 0;
btVector3 center(0, 0, 0);
for (int k = 0; k < n; k++)
{
center += m_children[k].m_transform.getOrigin() * masses[k];
totalMass += masses[k];
}
center /= totalMass;
principal.setOrigin(center);
btMatrix3x3 tensor(0, 0, 0, 0, 0, 0, 0, 0, 0);
for (int k = 0; k < n; k++)
{
btVector3 i;
m_children[k].m_childShape->calculateLocalInertia(masses[k], i);
const btTransform& t = m_children[k].m_transform;
btVector3 o = t.getOrigin() - center;
//compute inertia tensor in coordinate system of compound shape
btMatrix3x3 j = t.getBasis().transpose();
j[0] *= i[0];
j[1] *= i[1];
j[2] *= i[2];
j = t.getBasis() * j;
//add inertia tensor
tensor[0] += j[0];
tensor[1] += j[1];
tensor[2] += j[2];
//compute inertia tensor of pointmass at o
btScalar o2 = o.length2();
j[0].setValue(o2, 0, 0);
j[1].setValue(0, o2, 0);
j[2].setValue(0, 0, o2);
j[0] += o * -o.x();
j[1] += o * -o.y();
j[2] += o * -o.z();
//add inertia tensor of pointmass
tensor[0] += masses[k] * j[0];
tensor[1] += masses[k] * j[1];
tensor[2] += masses[k] * j[2];
}
tensor.diagonalize(principal.getBasis(), btScalar(0.00001), 20);
inertia.setValue(tensor[0][0], tensor[1][1], tensor[2][2]);
}