public HingeJoint(Body body1, Body body2, Vector2D anchor, Lifespan lifetime)
: base(lifetime)
{
if (body1 == null) { throw new ArgumentNullException("body1"); }
if (body2 == null) { throw new ArgumentNullException("body2"); }
this.body1 = body1;
this.body2 = body2;
body1.ApplyMatrix();
body2.ApplyMatrix();
Matrix3x3 matrix1 = body1.Shape.MatrixInv.VertexMatrix;
Matrix3x3 matrix2 = body2.Shape.MatrixInv.VertexMatrix;
Vector2D.Transform(ref matrix1, ref anchor, out localAnchor1);
Vector2D.Transform(ref matrix2, ref anchor, out localAnchor2);
relaxation = 1.0f;
biasFactor = .1f;
}