Clarify circle segment intersection

src/Geometry/Intersect.hs

@@ -7,7 +7,6 @@ module Geometry.Intersect where
 import Control.Applicative
 import Control.Lens
 import Control.Monad
-import Data.List
 import Data.Maybe
 import Geometry.Data
 import Geometry.LHS
@@ -348,18 +347,26 @@ inSegArea a b c = param >= 0 && param <= dotV (b -.- a) (b -.- a)
   where
     param = dotV (b -.- a) (c -.- a)
 
--- I suspect that this may not be correct...
--- it should probably use closestPointOnSeg
-intersectCircSeg :: Point2 -> Float -> Point2 -> Point2 -> [Point2]
-intersectCircSeg c r a b
-    | y < 0 = []
-    | otherwise = nub $ filter (inSegArea a b) [d -.- v, d +.+ v]
+intersectCircSeg :: Point2 -> Float -> Point2 -> Point2 -> (Maybe Point2,Maybe Point2)
+intersectCircSeg c r s e = intersectCircLineAlong c r s e
+    & g
+    & each %~ f
   where
-    d = closestPointOnLine a b c
-    x = dist d c
-    y = r ^ (2 :: Int) - x ^ (2 :: Int)
-    z = sqrt y
-    v = z *.* normalizeV (b -.- a)
+    f (Just x) | x >= 0 && x < 1 = Just $ s + x *^ (e - s)
+    f _ = Nothing
+    g Nothing = (Nothing,Nothing)
+    g (Just (x,y)) = (Just x,Just y)
+        
+--intersectCircSeg :: Point2 -> Float -> Point2 -> Point2 -> [Point2]
+--intersectCircSeg c r a b
+--    | y < 0 = []
+--    | otherwise = nub $ filter (inSegArea a b) [d -.- v, d +.+ v]
+--  where
+--    d = closestPointOnLine a b c
+--    x = dist d c
+--    y = r ^ (2 :: Int) - x ^ (2 :: Int)
+--    z = sqrt y
+--    v = z *.* normalizeV (b -.- a)
 
 intersectCircLineAlong :: Point2 -> Float -> Point2 -> Point2 -> Maybe (Float, Float)
 intersectCircLineAlong p r x y = do
@@ -415,4 +422,4 @@ intersectCircSegTest c r x y =
     z = r *.* vNormal (normalizeV x - y)
 
 intersectCircSegFirst :: Point2 -> Float -> Point2 -> Point2 -> Maybe Point2
-intersectCircSegFirst c r a = listToMaybe . intersectCircSeg c r a
+intersectCircSegFirst c r a = fst . intersectCircSeg c r a