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, 4 insertions, 0 deletions

diff --git a/users/grfn/xanthous/src/Xanthous/Game/State.hs b/users/grfn/xanthous/src/Xanthous/Game/State.hs
index f614cad47339..cdaf23edcd48 100644
--- a/users/grfn/xanthous/src/Xanthous/Game/State.hs
+++ b/users/grfn/xanthous/src/Xanthous/Game/State.hs
@@ -16,6 +16,7 @@ module Xanthous.Game.State
   , promptState
   , characterEntityID
   , autocommand
+  , memo
   , GamePromptState(..)
 
     -- * Game Level
@@ -107,6 +108,7 @@ import           Xanthous.Data.Entities
 import           Xanthous.Orphans ()
 import           Xanthous.Game.Prompt
 import           Xanthous.Game.Env
+import           Xanthous.Game.Memo (MemoState)
 --------------------------------------------------------------------------------
 
 data MessageHistory
@@ -502,6 +504,8 @@ data GameState = GameState
   , _promptState       :: !(GamePromptState AppM)
   , _debugState        :: !DebugState
   , _autocommand       :: !AutocommandState
+
+  , _memo              :: MemoState
   }
   deriving stock (Show, Generic)
   deriving anyclass (NFData)