Add random floor tiles to floors

src/Geometry.hs

@@ -21,7 +21,7 @@ import Geometry.Intersect
 import Geometry.Bezier
 import Geometry.Vector
 
-import Data.Function
+--import Data.Function
 import Data.List
 import Data.Maybe
 --import Control.Applicative
@@ -143,12 +143,20 @@ isRHS
     a2 = y' - y
     b1 = x'' - x
     b2 = y'' - y
+orderPolygonAround 
+    :: Point2 -- ^ point to order around
+    -> [Point2]
+    -> [Point2]
+orderPolygonAround _ [] = []
+orderPolygonAround cen ps = sortOn (\p -> argV (p -.- cen)) ps
+
+orderAroundFirst :: [Point2] -> [Point2]
+orderAroundFirst [] = []
+orderAroundFirst (a:as) = a : orderPolygonAround a as
 -- | Reorder points to be anticlockwise around their center.
 orderPolygon :: [Point2] -> [Point2]
 orderPolygon [] = []
-orderPolygon ps = sortBy (compare `on` \p -> argV (p -.- cen)) ps
-  where 
-    cen = 1/ fromIntegral (length ps) *.* foldr1 (+.+) ps
+orderPolygon ps = orderPolygonAround (1/ fromIntegral (length ps) *.* foldr1 (+.+) ps) ps
 -- | Adds a point to a convex polygon.
 -- If the point is inside, returns the original.
 -- Points ordered anticlockwise, input not checked.
@@ -158,8 +166,22 @@ addPointPolygon p ps
     | otherwise = orderPolygon $ p : ps
 -- | Creates the convex hull of a set of points.
 convexHull :: [Point2] -> [Point2]
-convexHull (x:y:z:xs) = foldr addPointPolygon (orderPolygon [x,y,z]) xs
-convexHull _ = error "Tried to create the convex hull of two or less points"
+convexHull (x:y:z:xs) = grahamScan $ orderAroundFirst $ sortOn (\(a,b) -> (b,a)) (x:y:z:xs)
+convexHull _ = error "Tried to create the convex hull of two or fewer points"
+
+grahamScan :: [Point2] -> [Point2]
+grahamScan = foldr push []
+  where
+    push point stack = grahamEliminate (point:stack)
+
+-- | Remove second element if top three elements are not counterclockwise.
+-- Repeat if necessary. See 
+-- https://codereview.stackexchange.com/questions/206019/graham-scan-algorithm-in-haskell
+grahamEliminate :: [Point2] -> [Point2]
+grahamEliminate (x:y:z:xs)
+    | isRHS x y z = grahamEliminate (x:z:xs)
+grahamEliminate xs = xs
+
 -- | Return distance between two points.
 dist :: Point2 -> Point2 -> Float
 {-# INLINE dist #-}
@@ -229,7 +251,7 @@ anyPolyssIntersect x y = or $ polysIntersect <$> x <*> y
 -- split a list into triples, forms triangles from a polygon
 polyToTris :: [s] -> [s]
 {-# INLINE polyToTris #-}
-polyToTris (a:b:c:as) = a : intercalate [a] (zipWith (\x y->[x,y]) (init (b:c:as)) (c:as))
+polyToTris (a:b:c:as) = a : intercalate [a] (zipWith (\x y->[x,y]) (b:c:as) (c:as))
 polyToTris _ = []
 
 -- | Return n equidistant points on a circle with a radius of 600.