anchor.diff:  0 VALUE screen-height
   0 VALUE screen-width
   0 VALUE screen-depth
  +0 VALUE screen-line-bytes
   0 VALUE window-top
   0 VALUE window-left
   
  
positive.code: : fb8-install ( width height #columns #lines -- )
  	1 to screen-depth
  	2swap  to screen-height  to screen-width
  	screen-#rows min to #lines
  	screen-#columns min to #columns
  	screen-height char-height #lines * - 2/ to window-top
  
negative.code: 
  : fb8-toggle-cursor ( -- )
  	line# fb8-line2addr column# fb8-columns2bytes +
  	char-height 2 - screen-line-bytes * +
  	2 0 ?DO
  		dup char-width screen-depth * invert-region
  		screen-line-bytes +
  	LOOP drop
  ;
  
  