Box2D.Dynamics.Joints.DistanceJoint.InitVelocityConstraints C# (CSharp) Method

        public override void InitVelocityConstraints(SolverData data)
        {
            IndexA = BodyA.IslandIndex;
            IndexB = BodyB.IslandIndex;
            LocalCenterA.Set(BodyA.Sweep.LocalCenter);
            LocalCenterB.Set(BodyB.Sweep.LocalCenter);
            InvMassA = BodyA.InvMass;
            InvMassB = BodyB.InvMass;
            InvIA = BodyA.InvI;
            InvIB = BodyB.InvI;

            Vec2 cA = data.Positions[IndexA].C;
            float aA = data.Positions[IndexA].A;
            Vec2 vA = data.Velocities[IndexA].V;
            float wA = data.Velocities[IndexA].W;

            Vec2 cB = data.Positions[IndexB].C;
            float aB = data.Positions[IndexB].A;
            Vec2 vB = data.Velocities[IndexB].V;
            float wB = data.Velocities[IndexB].W;

            Rot qA = Pool.PopRot();
            Rot qB = Pool.PopRot();

            qA.Set(aA);
            qB.Set(aB);

            // use m_u as temporary variable
            Rot.MulToOutUnsafe(qA, U.Set(LocalAnchorA).SubLocal(LocalCenterA), RA);
            Rot.MulToOutUnsafe(qB, U.Set(LocalAnchorB).SubLocal(LocalCenterB), RB);
            U.Set(cB).AddLocal(RB).SubLocal(cA).SubLocal(RA);

            Pool.PushRot(2);

            // Handle singularity.
            float length = U.Length();
            if (length > Settings.LINEAR_SLOP)
            {
                U.X *= 1.0f / length;
                U.Y *= 1.0f / length;
            }
            else
            {
                U.Set(0.0f, 0.0f);
            }

            float crAu = Vec2.Cross(RA, U);
            float crBu = Vec2.Cross(RB, U);
            float invMass = InvMassA + InvIA * crAu * crAu + InvMassB + InvIB * crBu * crBu;

            // Compute the effective mass matrix.
            Mass = invMass != 0.0f ? 1.0f / invMass : 0.0f;

            if (FrequencyHz > 0.0f)
            {
                float C = length - Length;

                // Frequency
                float omega = 2.0f * MathUtils.PI * FrequencyHz;

                // Damping coefficient
                float d = 2.0f * Mass * DampingRatio * omega;

                // Spring stiffness
                float k = Mass * omega * omega;

                // magic formulas
                float h = data.Step.Dt;
                Gamma = h * (d + h * k);
                Gamma = Gamma != 0.0f ? 1.0f / Gamma : 0.0f;
                Bias = C * h * k * Gamma;

                invMass += Gamma;
                Mass = invMass != 0.0f ? 1.0f / invMass : 0.0f;
            }
            else
            {
                Gamma = 0.0f;
                Bias = 0.0f;
            }
            if (data.Step.WarmStarting)
            {

                // Scale the impulse to support a variable time step.
                Impulse *= data.Step.DtRatio;

                Vec2 P = Pool.PopVec2();
                P.Set(U).MulLocal(Impulse);

                vA.X -= InvMassA * P.X;
                vA.Y -= InvMassA * P.Y;
                wA -= InvIA * Vec2.Cross(RA, P);

                vB.X += InvMassB * P.X;
                vB.Y += InvMassB * P.Y;
                wB += InvIB * Vec2.Cross(RB, P);

                Pool.PushVec2(1);
            }
            else
            {
                Impulse = 0.0f;
            }
            data.Velocities[IndexA].V.Set(vA);
            data.Velocities[IndexA].W = wA;
            data.Velocities[IndexB].V.Set(vB);
            data.Velocities[IndexB].W = wB;
        }