feat(xanthous): Memoize characterVisiblePositions r/2653

Memoize the return value of characterVisiblePositions to a new,
semi-abstracted "memo" field on the GameState, recalcuclated if the
character position ever changes. I'm 90% sure that the perf issues we
were encountering were actually caused by characterVisiblePositions
getting called once for *every tile* on draw, but this slightly larger
change also makes the game perform relatively-usably again.

Since this is only recalculated if the character position changes, if we
ever get non-transparent entities moving around without the characters
influence (maybe something building or knocking down walls?) we'll have
an issue there where the vision won't be updated as a result of those
changes if they happen while the character is taking a non-moving action
- but we can cross that bridge when we come to it.

Change-Id: I3fc745ddf0014d6f164f735ad7e5080da779b92a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3185
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

1 files changed, 1 insertions, 0 deletions

diff --git a/users/grfn/xanthous/src/Xanthous/Prelude.hs b/users/grfn/xanthous/src/Xanthous/Prelude.hs
index 4d79b026f14a..2cb4299303ba 100644
--- a/users/grfn/xanthous/src/Xanthous/Prelude.hs
+++ b/users/grfn/xanthous/src/Xanthous/Prelude.hs
@@ -21,6 +21,7 @@ module Xanthous.Prelude
 import ClassyPrelude hiding
   ( return, (<|), unsnoc, uncons, cons, snoc, index, (<.>), Index, say
   , catMaybes, filter, mapMaybe, hashNub, ordNub
+  , Memoized, runMemoized
   )
 import Data.Kind
 import GHC.TypeLits hiding (Text)