1 files changed, 72 insertions, 0 deletions
diff --git a/users/grfn/xanthous/src/Xanthous/Data/EntityMap/Graphics.hs b/users/grfn/xanthous/src/Xanthous/Data/EntityMap/Graphics.hs
new file mode 100644
index 000000000000..1398c611cf20
--- /dev/null
+++ b/users/grfn/xanthous/src/Xanthous/Data/EntityMap/Graphics.hs
@@ -0,0 +1,72 @@
+--------------------------------------------------------------------------------
+module Xanthous.Data.EntityMap.Graphics
+  ( visiblePositions
+  , visibleEntities
+  , lineOfSight
+  , 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 entities on the *line of sight* from the first position
+-- to the second position
+lineOfSight
+  :: forall e. Entity e
+  => Position -- ^ Origin
+  -> Position -- ^ Destination
+  -> EntityMap e
+  -> [(Position, Vector (EntityID, e))]
+lineOfSight (view _Position -> origin) (view _Position -> destination) em =
+  takeWhileInclusive (none (view blocksVision . entityAttributes . snd) . snd)
+    $ getPositionedAt <$> line origin destination
+  where
+    getPositionedAt :: V2 Int -> (Position, Vector (EntityID, e))
+    getPositionedAt (review _Position -> p) =
+      (p, over _2 (view positioned) <$> atPositionWithIDs p em)
+
+-- | 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    -- ^ Centerpoint
+  -> Word        -- ^ Radius
+  -> EntityMap e
+  -> [[(Position, Vector (EntityID, e))]]
+linesOfSight pos visionRadius em =
+  radius <&> \edge -> lineOfSight pos (_Position # edge) em
+  where
+    radius = circle (pos ^. _Position) $ fromIntegral visionRadius
+
+-- | 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