anchor.diff:  
   (defun flip-alu-p (alu)
     "Determine if this alu represents XOR drawing."
  -  #+clim (eq alu :flipping)
  -  #-clim
  -  (not (cond ((numberp alu) (= alu tv:alu-xor))	; Black and white.
  -	     ((symbolp alu) (eq alu :flip))	
  -	     ((scl:instancep alu) (= (scl:send alu :alu) tv:alu-xor)))))	; Color
  +  (eq alu :flipping))	; Color
   
   (defun DEVICE-DRAW-LINE (stream x1 y1 x2 y2 
   			 &key (alu %alu) (dash-pattern %dash-pattern)
  
positive.code:        (with-clipping-screen-rectangle (,stream .le. .re. .te. .be.)	; -y
  	 ,@body))))
  
  #+clim
  (defvar *clim-clip-rectangle* 
      #-clim-2 (make-rectangle* 0 0 1 1)
      #+clim-2 (make-bounding-rectangle 0 0 1 1) 
    "Reused by with-clipping-internal to reduce consing.")
  
  (defmacro WITH-CLIPPING-INTERNAL ((stream) &body body)
  
negative.code:   (multiple-value-setq (u v) (uv-to-screen stream u v))
    (when (point-in-clip-rectangle-p u v)
      (draw-point u v :stream stream :alu alu)))
  
  
  