Move toward indexed external placements

src/Geometry.hs

@@ -22,6 +22,7 @@ import Geometry.Intersect
 import Geometry.Bezier
 import Geometry.Vector
 import Geometry.LHS
+import Geometry.ConvexPoly
 
 import Data.Maybe
 import Data.List
@@ -132,7 +133,8 @@ orderAroundFirst (a:as) = a : orderPolygonAround a as
 -- | Reorder points to be anticlockwise around their center.
 orderPolygon :: [Point2] -> [Point2]
 orderPolygon [] = []
-orderPolygon ps = orderPolygonAround (1/ fromIntegral (length ps) *.* foldr1 (+.+) ps) ps
+--orderPolygon ps = orderPolygonAround (1/ fromIntegral (length ps) *.* foldr1 (+.+) ps) ps
+orderPolygon ps = orderPolygonAround (centroid ps) ps
 -- | Adds a point to a convex polygon.
 -- If the point is inside, returns the original.
 -- Points ordered anticlockwise, input not checked.
@@ -447,6 +449,13 @@ arcStepwisePositive ssize a cen v = (cen +.+) . (`rotateV` v) <$> rots
     n :: Int
     n = ceiling (a * magV v / ssize)
 
+-- | Given a list of points, returns pairs of points linking the points into a
+-- loop.
+chainPairs :: [Point2] -> [(Point2,Point2)]
+chainPairs [] = error "tried to make chain with empty list of points"
+chainPairs [_] = error "tried to make chain with singleton list of points"
+chainPairs xs = zip xs $ tail xs
+
 -- | Given a list of points, returns pairs of points linking the points into a
 -- loop.
 loopPairs :: [Point2] -> [(Point2,Point2)]