anchor.diff:  \   Requiring the String word set
   \
   
  -31                      constant w
  -18                      constant h
  +51                      constant w
  +31                      constant h
   80                      constant NBLOBS
   
  -240 16 *    constant centerx
  -136 16 *    constant centery
  +0 value centerx
  +0 value centery
  +0 value scale
   
   w h *       constant wh
   
  
positive.code:     recip + c@
  ; blob defines brightness
  
  : metaball
      GD.init
  
      \ Build the reciprocal table
      200 recip c!
  
negative.code:         NBLOBS 0 do
              i b[] animate
          loop
  
          \ Randomize one blob's velocity
          10 randrange 0= if
              NBLOBS randrange b[] kick
          then
  
          \ Build up a new w*h background image at pad
          pad
  