Drop Rasterific for non-filled circles

Rasterific appears to generate some pretty surprising, if  not
completely wrong, circles at especially low sizes - this was resulting
in unexpected behavior with vision calculation, including the character
never being able to see directly to the left of them, among other
things. This moves back to the old midpoint circle algorithm I pulled
off of rosetta code, but only for the non-filled circle. The filled
circle is still using the wonky algorithm for now, but at some point I'd
love to refactor it such that empty circles are eg always a subset of
non-filled circles.

3 files changed, 61 insertions, 17 deletions

diff --git a/src/Xanthous/Data.hs b/src/Xanthous/Data.hs
index 1874b45e9047..2cfb8204d58c 100644
--- a/src/Xanthous/Data.hs
+++ b/src/Xanthous/Data.hs
@@ -68,6 +68,7 @@ module Xanthous.Data
   , move
   , asPosition
   , directionOf
+  , Cardinal(..)
 
     -- *
   , Corner(..)
@@ -86,12 +87,12 @@ module Xanthous.Data
   , Hitpoints(..)
   ) where
 --------------------------------------------------------------------------------
-import           Xanthous.Prelude hiding (Left, Down, Right, (.=))
+import           Xanthous.Prelude hiding (Left, Down, Right, (.=), elements)
 --------------------------------------------------------------------------------
 import           Linear.V2 hiding (_x, _y)
 import qualified Linear.V2 as L
 import           Linear.V4 hiding (_x, _y)
-import           Test.QuickCheck (Arbitrary, CoArbitrary, Function)
+import           Test.QuickCheck (Arbitrary, CoArbitrary, Function, elements)
 import           Test.QuickCheck.Arbitrary.Generic
 import           Data.Group
 import           Brick (Location(Location), Edges(..))
@@ -267,11 +268,9 @@ data Direction where
   DownLeft  :: Direction
   DownRight :: Direction
   Here      :: Direction
-  deriving stock (Show, Eq, Generic)
-
-instance Arbitrary Direction where
-  arbitrary = genericArbitrary
-  shrink = genericShrink
+  deriving stock (Show, Eq, Ord, Generic)
+  deriving anyclass (CoArbitrary, Function, NFData)
+  deriving Arbitrary via GenericArbitrary Direction
 
 instance Opposite Direction where
   opposite Up        = Down
@@ -330,6 +329,16 @@ stepTowards (view _Position -> p₁) (view _Position -> p₂)
     let (_:p:_) = line p₁ p₂
     in _Position # p
 
+-- | Newtype controlling arbitrary generation to only include cardinal
+-- directions ('Up', 'Down', 'Left', 'Right')
+newtype Cardinal = Cardinal { getCardinal :: Direction }
+  deriving stock (Eq, Show, Ord, Generic)
+  deriving anyclass (NFData, Function, CoArbitrary)
+  deriving newtype (Opposite)
+
+instance Arbitrary Cardinal where
+  arbitrary = Cardinal <$> elements [Up, Down, Left, Right]
+
 --------------------------------------------------------------------------------
 
 data Corner
diff --git a/src/Xanthous/Data/EntityMap/Graphics.hs b/src/Xanthous/Data/EntityMap/Graphics.hs
index 9064855bdbae..d523c0555e4f 100644
--- a/src/Xanthous/Data/EntityMap/Graphics.hs
+++ b/src/Xanthous/Data/EntityMap/Graphics.hs
@@ -17,8 +17,16 @@ import Xanthous.Game.State
 import Xanthous.Util.Graphics (circle, line)
 --------------------------------------------------------------------------------
 
-visiblePositions :: Entity e => Position -> Word -> EntityMap e -> Set Position
-visiblePositions pos radius = setFromList . positions . visibleEntities pos radius
+-- | 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
diff --git a/src/Xanthous/Util/Graphics.hs b/src/Xanthous/Util/Graphics.hs
index fc704abf64fd..ea1dbffe839b 100644
--- a/src/Xanthous/Util/Graphics.hs
+++ b/src/Xanthous/Util/Graphics.hs
@@ -30,16 +30,45 @@ import           Linear.V2
 --------------------------------------------------------------------------------
 
 
-circle :: (Num i, Integral i, Ix i)
+-- | Generate a circle centered at the given point and with the given radius
+-- using the <midpoint circle algorithm
+-- https://en.wikipedia.org/wiki/Midpoint_circle_algorithm>.
+--
+-- Code taken from <https://rosettacode.org/wiki/Bitmap/Midpoint_circle_algorithm#Haskell>
+circle :: (Num i, Ord i)
        => (i, i) -- ^ center
        -> i      -- ^ radius
        -> [(i, i)]
-circle (ox, oy) radius
-  = pointsFromRaster (ox + radius) (oy + radius)
-  $ stroke 1 JoinRound (CapRound, CapRound)
-  $ Raster.circle (Raster.V2 (fromIntegral ox) (fromIntegral oy))
-  $ fromIntegral radius
+circle (x₀, y₀) radius
+  -- Four initial points, plus the generated points
+  = (x₀, y₀ + radius) : (x₀, y₀ - radius) : (x₀ + radius, y₀) : (x₀ - radius, y₀) : points
+    where
+      -- Creates the (x, y) octet offsets, then maps them to absolute points in all octets.
+      points = concatMap generatePoints $ unfoldr step initialValues
+
+      generatePoints (x, y)
+        = [ (x₀ `xop` x', y₀ `yop` y')
+          | (x', y') <- [(x, y), (y, x)]
+          , xop <- [(+), (-)]
+          , yop <- [(+), (-)]
+          ]
 
+      initialValues = (1 - radius, 1, (-2) * radius, 0, radius)
+
+      step (f, ddf_x, ddf_y, x, y)
+        | x >= y = Nothing
+        | otherwise = Just ((x', y'), (f', ddf_x', ddf_y', x', y'))
+        where
+          (f', ddf_y', y') | f >= 0 = (f + ddf_y' + ddf_x', ddf_y + 2, y - 1)
+                           | otherwise = (f + ddf_x, ddf_y, y)
+          ddf_x' = ddf_x + 2
+          x' = x + 1
+
+
+-- | Generate a *filled* circle centered at the given point and with the given
+-- radius using the Rasterific package. Note that since this uses a different
+-- implementation, this is not a strict superset of the 'circle' function
+-- (unfortunately - would like to make that not the case!)
 filledCircle :: (Num i, Integral i, Ix i)
              => (i, i) -- ^ center
              -> i      -- ^ radius
@@ -72,8 +101,6 @@ pointsFromRaster w h raster
            $ renderDrawing @Word8 (fromIntegral w) (fromIntegral h) 0
            $ withTexture (uniformTexture 1) raster
 
-
-
 -- | Draw a line between two points using Bresenham's line drawing algorithm
 --
 -- Code taken from <https://wiki.haskell.org/Bresenham%27s_line_drawing_algorithm>