public MouseJoint(MouseJointDef def)
: base(def)
{
_target = def.Target;
_localAnchor = Common.Math.MulT(_body2.GetXForm(), _target);
_maxForce = def.MaxForce;
_impulse.SetZero();
_frequencyHz = def.FrequencyHz;
_dampingRatio = def.DampingRatio;
_beta = 0.0f;
_gamma = 0.0f;
}