anchor.diff:  				       user-pixmap-x2 user-pixmap-y2))
   			 (set-native sheet-transform
   				     current-sheet-region
  -				     sheet)))
  +				     msheet)))
   		  (copy-from-pixmap pixmap 0 0
  -				    pixmap-width pixmap-height sheet
  -				    user-pixmap-x1 user-pixmap-y1)
  +				    pixmap-width pixmap-height msheet
  +				    pixmap-x1 pixmap-y1)
   		  (deallocate-pixmap pixmap))))))))))
   
   (defmacro with-double-buffering (((sheet &rest bounds-args)
  
positive.code: 							    user-pixmap-y1
  							    user-pixmap-x2
  							    user-pixmap-y2)))
  			      (set-native sheet-native pixmap-region  sheet)
  			      ;(break)
  			      (with-drawing-options
  				  (medium :ink (medium-background medium))
  
negative.code: 	       (pixmap-y2 (ceiling sheet-y2))
  	       (pixmap-width (- pixmap-x2 pixmap-x1))
  	       (pixmap-height (- pixmap-y2 pixmap-y1))
  	       (current-sheet-region (sheet-region msheet))
  	       (sheet-native (compose-transformation-with-translation
  			      sheet-transform
  			      (- pixmap-x1)
  			      (- pixmap-y1)))
  	       (pixmap (allocate-pixmap msheet pixmap-width pixmap-height))
  	       )
  	  (unless pixmap
  	    (error "Couldn't allocate pixmap")) 
  