Add function for cutting polygons

src/Geometry/Intersect.hs

@@ -4,6 +4,7 @@
 {- Testing for and finding intersection points.  -}
 module Geometry.Intersect where
 
+import Data.List (sortOn)
 import Control.Applicative
 import Control.Lens
 import Control.Monad
@@ -264,6 +265,14 @@ intersectSegPolyFirst a b xs = foldr (<|>) Nothing $ zipWith lineColl xs (tail x
   where
     lineColl = intersectSegSeg a b
 
+-- orders intersecting points according to the line
+intersectLinePoly :: Point2 -> Point2 -> [Point2] -> [Point2]
+intersectLinePoly a b (p:ps) = sortOn (dotV (b - a)) 
+    . catMaybes
+    $ zipWith (\x y -> intersectSegLine x y a b) (p:ps) (ps ++[p])
+intersectLinePoly _ _ [] = error "intersectLinePoly empty polygon"
+
+
 {- | Given a line and a point return the point on the line closest to the
  point.
 -}