anchor.diff:  							    user-pixmap-y1
   							    user-pixmap-x2
   							    user-pixmap-y2)))
  -			      (set-native sheet-native pixmap-region  sheet)
  +			      (set-native sheet-native pixmap-region  msheet)
   			      ;(break)
   			      (with-drawing-options
   				  (medium :ink (medium-background medium))
  
positive.code:              (replay-output-record ,record ,sheet))))))
  
  (defun invoke-with-double-buffering (sheet continuation x1 y1 x2 y2)
    (let* ((medium (sheet-medium sheet))
  	 (sheet-transform (sheet-native-transformation sheet))
  	 (medium-transform (medium-transformation (sheet-medium sheet)))
  	 (world-transform (compose-transformations sheet-transform
  						   medium-transform)))
      (multiple-value-bind (sheet-x1 sheet-y1)
  	(transform-position world-transform x1 y1)
        (multiple-value-bind (sheet-x2 sheet-y2)
  
negative.code: 				       user-pixmap-x2 user-pixmap-y2))
  			 (set-native sheet-transform
  				     current-sheet-region
  				     msheet)))
  		  (copy-from-pixmap pixmap 0 0
  				    pixmap-width pixmap-height msheet
  				    pixmap-x1 pixmap-y1)
  		  (deallocate-pixmap pixmap))))))))))
  
  (defmacro with-double-buffering (((sheet &rest bounds-args)
  