Smooth out slime splitting

There are probably possible errors from the use of cutPoly

src/Geometry/Intersect.hs

@@ -4,6 +4,7 @@
 {- Testing for and finding intersection points.  -}
 module Geometry.Intersect where
 
+import Data.Monoid
 import Data.List (sortOn)
 import Control.Applicative
 import Control.Lens
@@ -272,6 +273,12 @@ intersectLinePoly a b (p:ps) = sortOn (dotV (b - a))
     $ zipWith (\x y -> intersectSegLine x y a b) (p:ps) (ps ++[p])
 intersectLinePoly _ _ [] = error "intersectLinePoly empty polygon"
 
+intersectRayPoly :: Point2 -> Point2 -> [Point2] -> Maybe Point2
+intersectRayPoly a b (p:ps) = getFirst . mconcat $ zipWith f (p:ps) (ps++[p])
+  where
+    f x y = First $ intersectSegRay x y a b
+intersectRayPoly _ _ _ = error "intersectRayPoly: polygon too small"
+
 
 {- | Given a line and a point return the point on the line closest to the
  point.