needs-update

Typically called (indirectly) by a snip within the editor to force the editor to be redrawn.

For text% objects, calling this method may force the recalculation of location information if a maximum width is set for the editor, even if the editor currently has delayed refreshing (see refresh-delayed?).

• (send an-editor needs-update snip localx localy w h) -> void
      snip : snip% object
      localx : real number
      localy : real number
      w : non-negative real number
      h : non-negative real number

  The localx, localy, width, and height arguments specify the area that needs repainting in the coordinate system of snip.