/// 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 ResetMass() { // Compute mass data from shapes. Each shape has its own density. _mass = 0.0f; _invMass = 0.0f; _I = 0.0f; _invI = 0.0f; Vec2 center = Vec2.Zero; for (Fixture f = _fixtureList; f != null; f = f._next) { MassData massData = f.GetMassData(); _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; } if (_I > 0.0f && (_flags & BodyFlags.FixedRotation) == 0) { // Center the inertia about the center of mass. _I -= _mass * Vec2.Dot(center, center); Box2DXDebug.Assert(_I > 0.0f); _invI = 1.0f / _I; } else { _I = 0.0f; _invI = 0.0f; } // Move center of mass. Vec2 oldCenter = _sweep.C; _sweep.LocalCenter = center; _sweep.C0 = _sweep.C = Math.Mul(_xf, _sweep.LocalCenter); // Update center of mass velocity. _linearVelocity += Vec2.Cross(_angularVelocity, _sweep.C - oldCenter); // Determine the new body type. BodyType oldType = _type; if (_invMass == 0.0f && _invI == 0.0f) { _type = BodyType.Static; } else { _type = BodyType.Dynamic; } // If the body type changed, we need to flag contacts for filtering. if (oldType != _type) { for (ContactEdge ce = _contactList; ce != null; ce = ce.Next) { ce.Contact.FlagForFiltering(); } } }