Typically called (indirectly) by a snip within the buffer to force the
buffer to be redrawn.
(send a-wx:media-buffer needs-update sniplocalxlocalywh)->void snip : wx:snip% object localx : inexact real localy : inexact real w : inexact real h : inexact real
The localx, localy, width, and height
arguments specify the area that needs repainting in the coordinate
system of snip.