Bresenham's line drawing algorithm
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import List (sort,unfoldr)
type Point = (Integer,Integer)
line :: Point -> Point -> [Point]
line pa@(xa,ya) pb@(xb,yb) = map maySwitch . unfoldr go $ (x1,y1,0)
where
steep = abs (yb - ya) > abs (xb - xa)
maySwitch = if steep then (\(x,y) -> (y,x)) else id
[(x1,y1),(x2,y2)] = sort [maySwitch pa, maySwitch pb]
deltax = x2 - x1
deltay = abs (y2 - y1)
ystep = if y1 < y2 then 1 else -1
go (xTemp, yTemp, error)
| xTemp > x2 = Nothing
| otherwise = Just ((xTemp, yTemp), (xTemp + 1, newY, newError))
where
tempError = error + deltay
(newY, newError) = if (2*tempError) >= deltax
then (yTemp+ystep,tempError-deltax)
else (yTemp,tempError)
Thanks to Cheddai Fouche for the above implementation.
The core logic is in the "go" function which is passed to unfoldr.