GearJoint constructor

GearJoint(GearJointDef<Body, Body> def)

Implementation

GearJoint(GearJointDef def)
    : _joint1 = def.joint1,
      _joint2 = def.joint2,
      _bodyC = def.joint1.bodyA,
      _bodyD = def.joint2.bodyA,
      super(def) {
  assert(
    (_joint1 is RevoluteJoint || _joint1 is PrismaticJoint) &&
        (_joint2 is RevoluteJoint || _joint2 is PrismaticJoint),
    'A GearJoint can only be joint with RevoluteJoint and/or PrismaticJoint.',
  );

  double coordinateA;
  double coordinateB;

  // TODO_ERIN there might be some problem with the joint edges in Joint.
  bodyA = _joint1.bodyB;

  // Get geometry of joint1
  final xfA = bodyA.transform;
  final aA = bodyA.sweep.a;
  final xfC = _bodyC.transform;
  final aC = _bodyC.sweep.a;

  if (_joint1 is RevoluteJoint) {
    final revolute = def.joint1 as RevoluteJoint;
    _localAnchorC.setFrom(revolute.localAnchorA);
    localAnchorA.setFrom(revolute.localAnchorB);
    _referenceAngleA = revolute.referenceAngle;
    _localAxisC.setZero();

    coordinateA = aA - aC - _referenceAngleA;
  } else {
    final pA = Vector2.zero();
    final temp = Vector2.zero();
    final prismatic = def.joint1 as PrismaticJoint;
    _localAnchorC.setFrom(prismatic.localAnchorA);
    localAnchorA.setFrom(prismatic.localAnchorB);
    _referenceAngleA = prismatic.referenceAngle;
    _localAxisC.setFrom(prismatic.localXAxisA);

    final pC = _localAnchorC;
    temp
      ..setFrom(Rot.mulVec2(xfA.q, localAnchorA))
      ..add(xfA.p)
      ..sub(xfC.p);
    pA.setFrom(Rot.mulTransVec2(xfC.q, temp));
    coordinateA = (pA..sub(pC)).dot(_localAxisC);
  }

  bodyB = _joint2.bodyB;

  // Get geometry of joint2
  final xfB = bodyB.transform;
  final aB = bodyB.sweep.a;
  final xfD = _bodyD.transform;
  final aD = _bodyD.sweep.a;

  if (_joint2 is RevoluteJoint) {
    final revolute = def.joint2 as RevoluteJoint;
    _localAnchorD.setFrom(revolute.localAnchorA);
    localAnchorB.setFrom(revolute.localAnchorB);
    _referenceAngleB = revolute.referenceAngle;
    _localAxisD.setZero();

    coordinateB = aB - aD - _referenceAngleB;
  } else {
    final pB = Vector2.zero();
    final temp = Vector2.zero();
    final prismatic = def.joint2 as PrismaticJoint;
    _localAnchorD.setFrom(prismatic.localAnchorA);
    localAnchorB.setFrom(prismatic.localAnchorB);
    _referenceAngleB = prismatic.referenceAngle;
    _localAxisD.setFrom(prismatic.localXAxisA);

    final pD = _localAnchorD;
    temp
      ..setFrom(Rot.mulVec2(xfB.q, localAnchorB))
      ..add(xfB.p)
      ..sub(xfD.p);
    pB.setFrom(Rot.mulTransVec2(xfD.q, temp));
    coordinateB = (pB..sub(pD)).dot(_localAxisD);
  }

  ratio = def.ratio;
  _constant = coordinateA + ratio * coordinateB;
  _impulse = 0.0;
}