/// This resets the mass properties to the sum of the mass properties of the fixtures.
/// This normally does not need to be called unless you called SetMassData to override
/// the mass and you later want to reset the mass.
public void ResetMassData()
{
// Compute mass data from shapes. Each shape has its own density.
_mass = 0.0f;
_invMass = 0.0f;
_I = 0.0f;
_invI = 0.0f;
_sweep.localCenter = Vector2.Zero;
// Static and kinematic bodies have zero mass.
if (_type == BodyType.Static || _type == BodyType.Kinematic)
{
_sweep.c0 = _sweep.c = _xf.Position;
return;
}
Debug.Assert(_type == BodyType.Dynamic);
// Accumulate mass over all fixtures.
Vector2 center = Vector2.Zero;
for (Fixture f = _fixtureList; f != null; f = f._next)
{
if (f._density == 0.0f)
{
continue;
}
MassData massData;
f.GetMassData(out massData);
_mass += massData.mass;
center += massData.mass * massData.center;
_I += massData.I;
}
// Compute center of mass.
if (_mass > 0.0f)
{
_invMass = 1.0f / _mass;
center *= _invMass;
}
else
{
// Force all dynamic bodies to have a positive mass.
_mass = 1.0f;
_invMass = 1.0f;
}
if (_I > 0.0f && (_flags & BodyFlags.FixedRotation) == 0)
{
// Center the inertia about the center of mass.
_I -= _mass * Vector2.Dot(center, center);
Debug.Assert(_I > 0.0f);
_invI = 1.0f / _I;
}
else
{
_I = 0.0f;
_invI = 0.0f;
}
// Move center of mass.
Vector2 oldCenter = _sweep.c;
_sweep.localCenter = center;
_sweep.c0 = _sweep.c = MathUtils.Multiply(ref _xf, _sweep.localCenter);
// Update center of mass velocity.
_linearVelocity += MathUtils.Cross(_angularVelocity, _sweep.c - oldCenter);
}
