Ultima 4/5-Style Forest Field of View Options

[Jpagamer]

Hello! I'm trying to figure out how to make an Ultima 4/5-style forest field of view, where if the hero is surrounded completely (boxed in) by forest tiles, everything except for the surrounding tiles are blacked out, cutting the view range down to one tile in any direction. I hope that makes sense. I've messed around with switches, but what I came up with was impossibly tedious for a forest of any size.

If this helps, "o" is the hero "x" are forest tiles, and "-" are other tiles

at the edge of forest tiles
x x x - -
x x x - -
x x x - -
x o x - -

after entering

x x x
x o x
x x x

where everything else is blacked out

Thanks in advance!