# Difference between revisions of "Bresenham's line drawing algorithm"

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The core logic is in the "go" function which is passed to unfoldr. | The core logic is in the "go" function which is passed to unfoldr. | ||

+ | |||

+ | And here is an implementation of generalized Bresenham's line drawing algorithm, in terms of balanced words: https://github.com/LambdaHack/LambdaHack/blob/2f031f8a09d07d46b8e0dfeff1d9653d31ea19cc/Game/LambdaHack/Common/Point.hs#L112 |

## Revision as of 09:59, 13 April 2018

```
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.

And here is an implementation of generalized Bresenham's line drawing algorithm, in terms of balanced words: https://github.com/LambdaHack/LambdaHack/blob/2f031f8a09d07d46b8e0dfeff1d9653d31ea19cc/Game/LambdaHack/Common/Point.hs#L112