Method ResetMassData

DynamicsB2Body.go:714–779

()

}

func (body *B2Body) ResetMassData() {

	// Compute mass data from shapes. Each shape has its own density.
	body.M_mass = 0.0
	body.M_invMass = 0.0
	body.M_I = 0.0
	body.M_invI = 0.0
	body.M_sweep.LocalCenter.SetZero()

	// Static and kinematic bodies have zero mass.
	if body.M_type == B2BodyType.B2_staticBody || body.M_type == B2BodyType.B2_kinematicBody {
		body.M_sweep.C0 = body.M_xf.P
		body.M_sweep.C = body.M_xf.P
		body.M_sweep.A0 = body.M_sweep.A
		return
	}

	B2Assert(body.M_type == B2BodyType.B2_dynamicBody)

	// Accumulate mass over all fixtures.
	localCenter := MakeB2Vec2(0, 0)
	for f := body.M_fixtureList; f != nil; f = f.M_next {
		if f.M_density == 0.0 {
			continue
		}

		massData := NewMassData()
		f.GetMassData(massData)
		body.M_mass += massData.Mass
		localCenter.OperatorPlusInplace(B2Vec2MulScalar(massData.Mass, massData.Center))
		body.M_I += massData.I
	}

	// Compute center of mass.
	if body.M_mass > 0.0 {
		body.M_invMass = 1.0 / body.M_mass
		localCenter.OperatorScalarMulInplace(body.M_invMass)
	} else {
		// Force all dynamic bodies to have a positive mass.
		body.M_mass = 1.0
		body.M_invMass = 1.0
	}

	if body.M_I > 0.0 && (body.M_flags&B2Body_Flags.E_fixedRotationFlag) == 0 {
		// Center the inertia about the center of mass.
		body.M_I -= body.M_mass * B2Vec2Dot(localCenter, localCenter)
		B2Assert(body.M_I > 0.0)
		body.M_invI = 1.0 / body.M_I

	} else {
		body.M_I = 0.0
		body.M_invI = 0.0
	}

	// Move center of mass.
	oldCenter := body.M_sweep.C
	body.M_sweep.LocalCenter = localCenter
	body.M_sweep.C0 = B2TransformVec2Mul(body.M_xf, body.M_sweep.LocalCenter)