63 lines
1.6 KiB
Haskell
63 lines
1.6 KiB
Haskell
{-# OPTIONS_HADDOCK ignore-exports #-}
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module Algebra.Polygon where
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import Algebra.Vector
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import Data.Maybe
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import Diagrams.TwoD.Types
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import MyPrelude
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-- |Split a polygon by a given segment which must be vertices of the
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-- polygon (returns empty array otherwise).
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splitPoly :: [P2 Double]
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-> (P2 Double, P2 Double)
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-> [[P2 Double]]
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splitPoly pts (a, b)
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| elem a pts && elem b pts =
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[b : takeWhile (/= b) shiftedPoly, a : dropWhile (/= b) shiftedPoly]
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| otherwise = [[]]
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where
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shiftedPoly = shiftM' a pts
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-- |Get all edges of a polygon.
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polySegments :: [P2 Double] -> [(P2 Double, P2 Double)]
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polySegments p@(x':_:_:_) = go p ++ [(last p, x')]
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where
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go (x:y:xs) = (x, y) : go (y:xs)
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go _ = []
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polySegments _ = []
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-- |Check whether the given segment is inside the polygon.
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-- This doesn't check for segments that are completely outside
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-- of the polygon yet.
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isInsidePoly :: [P2 Double] -> (P2 Double, P2 Double) -> Bool
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isInsidePoly pts seg =
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null
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. catMaybes
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. fmap (intersectSeg'' seg)
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$ polySegments pts
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-- |Check whether two points are adjacent vertices of a polygon.
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adjacent :: P2 Double -> P2 Double -> [P2 Double] -> Bool
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adjacent u v = any (\x -> x == (u, v) || x == (v, u)) . polySegments
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-- |Check whether the polygon is a triangle polygon.
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isTrianglePoly :: [P2 Double] -> Bool
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isTrianglePoly [_, _, _] = True
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isTrianglePoly _ = False
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-- |Get all triangle polygons.
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triangleOnly :: [[P2 Double]] -> [[P2 Double]]
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triangleOnly = filter isTrianglePoly
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-- |Get all non-triangle polygons.
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nonTriangleOnly :: [[P2 Double]] -> [[P2 Double]]
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nonTriangleOnly = filter (not . isTrianglePoly)
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