cga/Algebra/Polygon.hs

62 lines
1.5 KiB
Haskell

{-# OPTIONS_HADDOCK ignore-exports #-}
module Algebra.Polygon where
import Algebra.Vector
import Data.Maybe
import MyPrelude
-- |Split a polygon by a given segment which must be vertices of the
-- polygon (returns empty array otherwise).
splitPoly :: [PT]
-> Segment
-> [[PT]]
splitPoly pts (a, b)
| elem a pts && elem b pts =
[b : takeWhile (/= b) shiftedPoly, a : dropWhile (/= b) shiftedPoly]
| otherwise = [[]]
where
shiftedPoly = shiftM' a pts
-- |Get all edges of a polygon.
polySegments :: [PT] -> [Segment]
polySegments p@(x':_:_:_) = go p ++ [(last p, x')]
where
go (x:y:xs) = (x, y) : go (y:xs)
go _ = []
polySegments _ = []
-- |Check whether the given segment is inside the polygon.
-- This doesn't check for segments that are completely outside
-- of the polygon yet.
isInsidePoly :: [PT] -> Segment -> Bool
isInsidePoly pts seg =
null
. catMaybes
. fmap (intersectSeg'' seg)
$ polySegments pts
-- |Check whether two points are adjacent vertices of a polygon.
adjacent :: PT -> PT -> [PT] -> Bool
adjacent u v = any (\x -> x == (u, v) || x == (v, u)) . polySegments
-- |Check whether the polygon is a triangle polygon.
isTrianglePoly :: [PT] -> Bool
isTrianglePoly [_, _, _] = True
isTrianglePoly _ = False
-- |Get all triangle polygons.
triangleOnly :: [[PT]] -> [[PT]]
triangleOnly = filter isTrianglePoly
-- |Get all non-triangle polygons.
nonTriangleOnly :: [[PT]] -> [[PT]]
nonTriangleOnly = filter (not . isTrianglePoly)