示例#1
0
  @Override
  public void solveVelocityConstraints(TimeStep step) {
    Body b = m_bodyB;

    Vec2 r = pool.popVec2();

    r.set(m_localAnchor).subLocal(b.getLocalCenter());
    Mat22.mulToOut(b.getTransform().R, r, r);

    // Cdot = v + cross(w, r)
    Vec2 Cdot = pool.popVec2();
    Vec2.crossToOut(b.m_angularVelocity, r, Cdot);
    Cdot.addLocal(b.m_linearVelocity);

    Vec2 impulse = pool.popVec2();
    Vec2 temp = pool.popVec2();

    // Mul(m_mass, -(Cdot + m_beta * m_C + m_gamma * m_impulse));
    impulse.set(m_C).mulLocal(m_beta);
    temp.set(m_impulse).mulLocal(m_gamma);
    temp.addLocal(impulse).addLocal(Cdot).mulLocal(-1);
    Mat22.mulToOut(m_mass, temp, impulse);

    Vec2 oldImpulse = temp;
    oldImpulse.set(m_impulse);
    m_impulse.addLocal(impulse);
    float maxImpulse = step.dt * m_maxForce;
    if (m_impulse.lengthSquared() > maxImpulse * maxImpulse) {
      m_impulse.mulLocal(maxImpulse / m_impulse.length());
    }
    impulse.set(m_impulse).subLocal(oldImpulse);

    // pooling
    oldImpulse.set(impulse).mulLocal(b.m_invMass);
    b.m_linearVelocity.addLocal(oldImpulse);
    b.m_angularVelocity += b.m_invI * Vec2.cross(r, impulse);

    pool.pushVec2(4);
  }
示例#2
0
  @Override
  public void initVelocityConstraints(TimeStep step) {
    Body b = m_bodyB;

    float mass = b.getMass();

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

    // Damping coefficient
    float d = 2.0f * mass * m_dampingRatio * omega;

    // Spring stiffness
    float k = mass * (omega * omega);

    // magic formulas
    // gamma has units of inverse mass.
    // beta has units of inverse time.
    assert (d + step.dt * k > Settings.EPSILON);
    m_gamma = step.dt * (d + step.dt * k);
    if (m_gamma != 0.0f) {
      m_gamma = 1.0f / m_gamma;
    }
    m_beta = step.dt * k * m_gamma;

    Vec2 r = pool.popVec2();

    // Compute the effective mass matrix.
    // Vec2 r = Mul(b.getTransform().R, m_localAnchor - b.getLocalCenter());
    r.set(m_localAnchor).subLocal(b.getLocalCenter());
    Mat22.mulToOut(b.getTransform().R, r, r);

    // K    = [(1/m1 + 1/m2) * eye(2) - skew(r1) * invI1 * skew(r1) - skew(r2) * invI2 * skew(r2)]
    //      = [1/m1+1/m2     0    ] + invI1 * [r1.y*r1.y -r1.x*r1.y] + invI2 * [r1.y*r1.y
    // -r1.x*r1.y]
    //        [    0     1/m1+1/m2]           [-r1.x*r1.y r1.x*r1.x]           [-r1.x*r1.y
    // r1.x*r1.x]
    float invMass = b.m_invMass;
    float invI = b.m_invI;

    Mat22 K1 = pool.popMat22();
    K1.m11 = invMass;
    K1.m21 = 0.0f;
    K1.m12 = 0.0f;
    K1.m22 = invMass;

    Mat22 K2 = pool.popMat22();
    K2.m11 = invI * r.y * r.y;
    K2.m21 = -invI * r.x * r.y;
    K2.m12 = -invI * r.x * r.y;
    K2.m22 = invI * r.x * r.x;

    Mat22 K = pool.popMat22();
    K.set(K1).addLocal(K2);
    K.m11 += m_gamma;
    K.m22 += m_gamma;

    K.invertToOut(m_mass);

    m_C.set(b.m_sweep.c).addLocal(r).subLocal(m_target);

    // Cheat with some damping
    b.m_angularVelocity *= 0.98f;

    // Warm starting.
    m_impulse.mulLocal(step.dtRatio);
    // pool
    Vec2 temp = pool.popVec2();
    temp.set(m_impulse).mulLocal(invMass);
    b.m_linearVelocity.addLocal(temp);
    b.m_angularVelocity += invI * Vec2.cross(r, m_impulse);

    pool.pushVec2(2);
    pool.pushMat22(3);
  }