internal override void SolveVelocityConstraints(TimeStep step)
{
Body b1 = _body1;
Body b2 = _body2;
float Cdot = _J.Compute(b1._linearVelocity, b1._angularVelocity, b2._linearVelocity, b2._angularVelocity);
float impulse = _mass * (-Cdot);
_impulse += impulse;
b1._linearVelocity += b1._invMass * impulse * _J.Linear1;
b1._angularVelocity += b1._invI * impulse * _J.Angular1;
b2._linearVelocity += b2._invMass * impulse * _J.Linear2;
b2._angularVelocity += b2._invI * impulse * _J.Angular2;
}