refactor(users/glittershark): Rename to grfn

Rename my //users directory and all places that refer to glittershark to
grfn, including nix references and documentation.

This may require some extra attention inside of gerrit's database after
it lands to allow me to actually push things.

Change-Id: I4728b7ec2c60024392c1c1fa6e0d4a59b3e266fa
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2933
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: lukegb <lukegb@tvl.fyi>
Reviewed-by: glittershark <grfn@gws.fyi>

users/grfn/xanthous/src/Xanthous/Data/EntityMap/Graphics.hs

@@ -0,0 +1,64 @@
+--------------------------------------------------------------------------------
+module Xanthous.Data.EntityMap.Graphics
+  ( visiblePositions
+  , visibleEntities
+  , linesOfSight
+  , canSee
+  ) where
+--------------------------------------------------------------------------------
+import Xanthous.Prelude hiding (lines)
+--------------------------------------------------------------------------------
+import Xanthous.Util (takeWhileInclusive)
+import Xanthous.Data
+import Xanthous.Data.Entities
+import Xanthous.Data.EntityMap
+import Xanthous.Game.State
+import Xanthous.Util.Graphics (circle, line)
+--------------------------------------------------------------------------------
+
+-- | Returns a set of positions that are visible, when taking into account
+-- 'blocksVision', from the given position, within the given radius.
+visiblePositions
+  :: Entity e
+  => Position
+  -> Word -- ^ Vision radius
+  -> EntityMap e
+  -> Set Position
+visiblePositions pos radius
+  = setFromList . positions . visibleEntities pos radius
+
+-- | Returns a list of individual lines of sight, each of which is a list of
+-- entities at positions on that line of sight
+linesOfSight
+  :: forall e. Entity e
+  => Position
+  -> Word
+  -> EntityMap e
+  -> [[(Position, Vector (EntityID, e))]]
+linesOfSight (view _Position -> pos) visionRadius em
+  = entitiesOnLines
+  <&> takeWhileInclusive
+      (none (view blocksVision . entityAttributes . snd) . snd)
+  where
+    radius = circle pos $ fromIntegral visionRadius
+    lines = line pos <$> radius
+    entitiesOnLines :: [[(Position, Vector (EntityID, e))]]
+    entitiesOnLines = lines <&> map getPositionedAt
+    getPositionedAt :: V2 Int -> (Position, Vector (EntityID, e))
+    getPositionedAt p =
+      let ppos = _Position # p
+      in (ppos, over _2 (view positioned) <$> atPositionWithIDs ppos em)
+
+-- | Given a point and a radius of vision, returns a list of all entities that
+-- are *visible* (eg, not blocked by an entity that obscures vision) from that
+-- point
+visibleEntities :: Entity e => Position -> Word -> EntityMap e -> EntityMap e
+visibleEntities pos visionRadius
+  = fromEIDsAndPositioned
+  . foldMap (\(p, es) -> over _2 (Positioned p) <$> es)
+  . fold
+  . linesOfSight pos visionRadius
+
+canSee :: Entity e => (e -> Bool) -> Position -> Word -> EntityMap e -> Bool
+canSee match pos radius = any match . visibleEntities pos radius
+-- ^ this might be optimizable