anchor.diff:  ;; newtonworldconvexcast
   ;; newtonworldconvexcastreturninfo
   ;;
  -;; newtonworldforeachbodyinaabbdo
  -;; newtonworldforeachjointdo
  +
  +
   ;; newtonworldgetbodycount
   ;; newtonworldgetconstraintcount
   ;; newtonworldgetfirstmaterial
  
positive.code:     (setf (world-solver-model world) solve-model)
      (setf (world-friction-model world) friction-model)
      world))
  
  ;;------------------------------------------------------------
  
  
negative.code: ;;------------------------------------------------------------
  
  ;; newtonworldgetnextbody
  ;; newtonworldgetfirstbody
  ;; newtonworldforeachjointdo
  ;; newtonworldforeachbodyinaabbdo
  
  ;;------------------------------------------------------------
  
  