Documentation

Following is just like Trail' Line V2, except that it has a different Monoid instance. Following values are concatenated, just like regular lines, except that they are also rotated so the tangents match at the join point. In addition, they are normalized so the tangent at the start point is in the direction of the positive x axis (essentially we are considering trails equivalent up to rotation).

Pro tip: you can concatenate a list of trails so their tangents match using ala from Control.Lens, like so:

ala follow foldMap :: [Trail' Line V2 n] -> Trail' Line V2 n

This is illustrated in the example below.

import Control.Lens (ala)
import Diagrams.TwoD.Path.Follow

wibble :: Trail' Line V2 Double
wibble = hrule 1 <> hrule 0.5 # rotateBy (1/6) <> hrule 0.5 # rotateBy (-1/6) <> a
  where a = arc (xDir # rotateBy (-1/4)) (1/5 @@ turn)
          # scale 0.7

followExample =
  [ wibble
  , wibble
    # replicate 5
    # ala follow foldMap
  ]
  # map stroke
  # map centerXY
  # vsep 1
  # frame 0.5

Create a Following from a line, normalizing it (by rotation) so that it starts in the positive x direction.

Project out the line from a Following.

If trails are considered equivalent up to rotation, then unfollow and follow are inverse.