Add support for clamping pictures to be inside screen

src/Geometry/Intersect.hs

@@ -178,3 +178,11 @@ intersectSegsSeg = undefined
 -- | Placeholder: should intersect a segment with a bezier curve.
 intersectSegBezquad :: Point2 -> Point2 -> Point2 -> Point2 -> Point2 -> [Point2]
 intersectSegBezquad = undefined
+
+-- | finds one (if any) of the points of intersection between a segment and a
+-- polygon.
+-- Can almost certainly be optimised.
+intersectSegPolyFirst :: Point2 -> Point2 -> [Point2] -> Maybe Point2
+intersectSegPolyFirst a b xs = foldr (<|>) Nothing $ zipWith lineColl xs (tail xs ++ [head xs])
+  where
+    lineColl = intersectSegSeg a b