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, 52 insertions, 0 deletions

diff --git a/users/grfn/xanthous/src/Xanthous/Game/Memo.hs b/users/grfn/xanthous/src/Xanthous/Game/Memo.hs
new file mode 100644
index 000000000000..9e483a8d4af7
--- /dev/null
+++ b/users/grfn/xanthous/src/Xanthous/Game/Memo.hs
@@ -0,0 +1,52 @@
+{-# LANGUAGE TemplateHaskell #-}
+--------------------------------------------------------------------------------
+-- | Memoized versions of calculations
+--------------------------------------------------------------------------------
+module Xanthous.Game.Memo
+  ( MemoState
+  , emptyMemoState
+  , clear
+    -- ** Memo lenses
+  , characterVisiblePositions
+
+    -- * Memoized values
+  , Memoized(UnMemoized)
+  , memoizeWith
+  , getMemoized
+  , runMemoized
+  ) where
+--------------------------------------------------------------------------------
+import Xanthous.Prelude
+--------------------------------------------------------------------------------
+import Data.Aeson (ToJSON, FromJSON)
+import Data.Aeson.Generic.DerivingVia
+import Test.QuickCheck (CoArbitrary, Function, Arbitrary)
+--------------------------------------------------------------------------------
+import Xanthous.Data (Position)
+import Xanthous.Data.Memo
+import Xanthous.Util.QuickCheck (GenericArbitrary(GenericArbitrary))
+--------------------------------------------------------------------------------
+
+-- | Memoized calculations on the game state
+data MemoState = MemoState
+  { -- | Memoized version of 'Xanthous.Game.Lenses.characterVisiblePositions',
+    -- memoized with the position of the character
+    _characterVisiblePositions :: Memoized Position (Set Position)
+  }
+  deriving stock (Show, Eq, Generic)
+  deriving anyclass (NFData, CoArbitrary, Function)
+  deriving Arbitrary via GenericArbitrary MemoState
+  deriving (ToJSON, FromJSON)
+       via WithOptions '[ FieldLabelModifier '[Drop 1] ]
+           MemoState
+makeLenses ''MemoState
+
+emptyMemoState :: MemoState
+emptyMemoState = MemoState { _characterVisiblePositions = UnMemoized }
+{-# INLINE emptyMemoState #-}
+
+clear :: Lens' MemoState (Memoized k v) -> MemoState -> MemoState
+clear = flip set UnMemoized
+{-# INLINE clear #-}
+
+{-# ANN module ("Hlint: ignore Use newtype instead of data" :: String) #-}