public DistanceJoint(DistanceJointDef def)
: base(def)
{
_localAnchor1 = def.LocalAnchor1;
_localAnchor2 = def.LocalAnchor2;
_length = def.Length;
_frequencyHz = def.FrequencyHz;
_dampingRatio = def.DampingRatio;
_impulse = 0.0f;
_gamma = 0.0f;
_bias = 0.0f;
}