Progressively reveal the map to the player

As the character walks around the map, progressively reveal the entities
on the map to them, using an algorithm based on well known
circle-rasterizing and line-rasterizing algorithms to calculate lines of
sight that are potentially obscured by walls.

1 files changed, 13 insertions, 3 deletions

diff --git a/src/Xanthous/Entities.hs b/src/Xanthous/Entities.hs
index bd52ae62b2..223c8d769b 100644
--- a/src/Xanthous/Entities.hs
+++ b/src/Xanthous/Entities.hs
@@ -7,7 +7,7 @@ module Xanthous.Entities
   ( Draw(..)
   , DrawCharacter(..)
   , DrawStyledCharacter(..)
-  , Entity
+  , Entity(..)
   , SomeEntity(..)
   , downcastEntity
   , entityIs
@@ -29,8 +29,11 @@ import           Data.Aeson
 import           Xanthous.Data
 --------------------------------------------------------------------------------
 
-class (Show a, Eq a, Draw a) => Entity a
-instance (Show a, Eq a, Draw a) => Entity a
+class (Show a, Eq a, Draw a) => Entity a where
+  blocksVision :: a -> Bool
+
+instance Entity a => Entity (Positioned a) where
+  blocksVision (Positioned _ ent) = blocksVision ent
 
 --------------------------------------------------------------------------------
 data SomeEntity where
@@ -47,6 +50,9 @@ instance Eq SomeEntity where
 instance Draw SomeEntity where
   drawWithNeighbors ns (SomeEntity ent) = drawWithNeighbors ns ent
 
+instance Entity SomeEntity where
+  blocksVision (SomeEntity ent) = blocksVision ent
+
 downcastEntity :: (Entity a, Typeable a) => SomeEntity -> Maybe a
 downcastEntity (SomeEntity e) = cast e
 
@@ -61,6 +67,10 @@ class Draw a where
   draw :: a -> Widget n
   draw = drawWithNeighbors $ pure mempty
 
+instance Draw a => Draw (Positioned a) where
+  drawWithNeighbors ns (Positioned _ a) = drawWithNeighbors ns a
+  draw (Positioned _ a) = draw a
+
 newtype DrawCharacter (char :: Symbol) (a :: Type) where
   DrawCharacter :: a -> DrawCharacter char a