Tweak wall cutting, removes inverse walls

src/Geometry.hs

@@ -164,6 +164,19 @@ orderPolygon ps = sortBy (compare `on` \p -> argV (p -.- cen)) ps
   where 
     cen = 1/ fromIntegral (length ps) *.* foldr1 (+.+) ps
 
+-- | Adds a point to a convex polygon.
+-- If the point is inside, returns the original.
+-- Points ordered anticlockwise, input not checked.
+addPointPolygon :: Point2 -> [Point2] -> [Point2]
+addPointPolygon p ps
+    | pointInOrOnPolygon p ps = 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"
+
 -- | Return distance between two points.
 dist :: Point2 -> Point2 -> Float
 {-# INLINE dist #-}