anchor: Joint:getAnchors
  Get the anchor points of the joint.
  x1, y1, x2, y2 = Joint:getAnchors()
  x1 number The x-component of the anchor on Body 1.
  y1 number The y-component of the anchor on Body 1.
  x2 number The x-component of the anchor on Body 2.
  y2 number The y-component of the anchor on Body 2.