Beispiel #1
0
  /* (non-Javadoc)
   * @see org.dyn4j.dynamics.joint.Joint#solveVelocityConstraints(org.dyn4j.dynamics.Step, org.dyn4j.dynamics.Settings)
   */
  @Override
  public void solveVelocityConstraints(Step step, Settings settings) {
    Transform t1 = body1.getTransform();
    Transform t2 = body2.getTransform();
    Mass m1 = body1.getMass();
    Mass m2 = body2.getMass();

    double invM1 = m1.getInverseMass();
    double invM2 = m2.getInverseMass();
    double invI1 = m1.getInverseInertia();
    double invI2 = m2.getInverseInertia();

    // compute r1 and r2
    Vector2 r1 = t1.getTransformedR(this.body1.getLocalCenter().to(this.localAnchor1));
    Vector2 r2 = t2.getTransformedR(this.body2.getLocalCenter().to(this.localAnchor2));

    // compute the relative velocity
    Vector2 v1 = body1.getLinearVelocity().sum(r1.cross(body1.getAngularVelocity()));
    Vector2 v2 = body2.getLinearVelocity().sum(r2.cross(body2.getAngularVelocity()));

    // compute Jv
    double Jv = n.dot(v1.difference(v2));

    // compute lambda (the magnitude of the impulse)
    double j = -this.invK * (Jv + this.bias + this.gamma * this.impulse);
    this.impulse += j;

    // apply the impulse
    Vector2 J = n.product(j);
    body1.getLinearVelocity().add(J.product(invM1));
    body1.setAngularVelocity(body1.getAngularVelocity() + invI1 * r1.cross(J));
    body2.getLinearVelocity().subtract(J.product(invM2));
    body2.setAngularVelocity(body2.getAngularVelocity() - invI2 * r2.cross(J));
  }
Beispiel #2
0
  /* (non-Javadoc)
   * @see org.dyn4j.dynamics.joint.Joint#solvePositionConstraints(org.dyn4j.dynamics.Step, org.dyn4j.dynamics.Settings)
   */
  @Override
  public boolean solvePositionConstraints(Step step, Settings settings) {
    // check if this is a spring damper
    if (this.frequency > 0.0) {
      // don't solve position constraints for spring damper
      return true;
    }

    double linearTolerance = settings.getLinearTolerance();
    double maxLinearCorrection = settings.getMaximumLinearCorrection();

    Transform t1 = body1.getTransform();
    Transform t2 = body2.getTransform();
    Mass m1 = body1.getMass();
    Mass m2 = body2.getMass();

    double invM1 = m1.getInverseMass();
    double invM2 = m2.getInverseMass();
    double invI1 = m1.getInverseInertia();
    double invI2 = m2.getInverseInertia();

    Vector2 c1 = body1.getWorldCenter();
    Vector2 c2 = body2.getWorldCenter();

    // recompute n since it may have changed after integration
    Vector2 r1 = t1.getTransformedR(this.body1.getLocalCenter().to(this.localAnchor1));
    Vector2 r2 = t2.getTransformedR(this.body2.getLocalCenter().to(this.localAnchor2));
    n = r1.sum(body1.getWorldCenter()).subtract(r2.sum(body2.getWorldCenter()));

    // solve the position constraint
    double l = n.normalize();
    double C = l - this.distance;
    C = Interval.clamp(C, -maxLinearCorrection, maxLinearCorrection);

    double impulse = -this.invK * C;

    Vector2 J = n.product(impulse);

    // translate and rotate the objects
    body1.translate(J.product(invM1));
    body1.rotate(invI1 * r1.cross(J), c1);

    body2.translate(J.product(-invM2));
    body2.rotate(-invI2 * r2.cross(J), c2);

    return Math.abs(C) < linearTolerance;
  }
Beispiel #3
0
  /* (non-Javadoc)
   * @see org.dyn4j.dynamics.joint.Joint#initializeConstraints(org.dyn4j.dynamics.Step, org.dyn4j.dynamics.Settings)
   */
  @Override
  public void initializeConstraints(Step step, Settings settings) {
    double linearTolerance = settings.getLinearTolerance();

    Transform t1 = body1.getTransform();
    Transform t2 = body2.getTransform();
    Mass m1 = body1.getMass();
    Mass m2 = body2.getMass();

    double invM1 = m1.getInverseMass();
    double invM2 = m2.getInverseMass();
    double invI1 = m1.getInverseInertia();
    double invI2 = m2.getInverseInertia();

    // compute the normal
    Vector2 r1 = t1.getTransformedR(this.body1.getLocalCenter().to(this.localAnchor1));
    Vector2 r2 = t2.getTransformedR(this.body2.getLocalCenter().to(this.localAnchor2));
    this.n = r1.sum(this.body1.getWorldCenter()).subtract(r2.sum(this.body2.getWorldCenter()));

    // get the current length
    double length = this.n.getMagnitude();
    // check for the tolerance
    if (length < linearTolerance) {
      this.n.zero();
    } else {
      // normalize it
      this.n.multiply(1.0 / length);
    }

    // compute K inverse
    double cr1n = r1.cross(this.n);
    double cr2n = r2.cross(this.n);
    double invMass = invM1 + invI1 * cr1n * cr1n;
    invMass += invM2 + invI2 * cr2n * cr2n;

    // check for zero before inverting
    this.invK = invMass <= Epsilon.E ? 0.0 : 1.0 / invMass;

    // see if we need to compute spring damping
    if (this.frequency > 0.0) {
      double dt = step.getDeltaTime();
      // get the current compression/extension of the spring
      double x = length - this.distance;
      // compute the natural frequency; f = w / (2 * pi) -> w = 2 * pi * f
      double w = Geometry.TWO_PI * this.frequency;
      // compute the damping coefficient; dRatio = d / (2 * m * w) -> d = 2 * m * w * dRatio
      double d = 2.0 * this.invK * this.dampingRatio * w;
      // compute the spring constant; w = sqrt(k / m) -> k = m * w * w
      double k = this.invK * w * w;

      // compute gamma = CMF = 1 / (hk + d)
      this.gamma = dt * (d + dt * k);
      // check for zero before inverting
      this.gamma = this.gamma <= Epsilon.E ? 0.0 : 1.0 / this.gamma;
      // compute the bias = x * ERP where ERP = hk / (hk + d)
      this.bias = x * dt * k * this.gamma;

      // compute the effective mass
      invMass += this.gamma;
      // check for zero before inverting
      this.invK = invMass <= Epsilon.E ? 0.0 : 1.0 / invMass;
    } else {
      this.gamma = 0.0;
      this.bias = 0.0;
    }

    // warm start
    impulse *= step.getDeltaTimeRatio();

    Vector2 J = n.product(impulse);
    body1.getLinearVelocity().add(J.product(invM1));
    body1.setAngularVelocity(body1.getAngularVelocity() + invI1 * r1.cross(J));
    body2.getLinearVelocity().subtract(J.product(invM2));
    body2.setAngularVelocity(body2.getAngularVelocity() - invI2 * r2.cross(J));
  }