Stairs.fr

module Stairs where

import org.frege.SketchBook (paint)

import fregefx.JavaFxAll (GraphicsContext)
import fregefx.JavaFxUtils (withUI)
import Data.List

--- A point on the canvas.
data Point = P {x, y :: Double}

--- The last four points that we have drawn a line to, latest first.
type Trail = (Point, Point, Point, Point)

--- The initial trail.
--- Note that the starting point is tugged in a little to make the first bearing landing at the right point.
start = ( P (-10) 10, P (-10) (-10), P 10 (-10), P 9.5 9.5 )

--- Return the point that we reach when drawing a line from _start_ to _over_ and extend by 5%.
bearing:: Point -> Point -> Point
bearing start over = P ((over.x - start.x) * 1.05 + start.x ) ((over.y - start.y) * 1.05 + start.y)

--- How to move the trails one step forward.
step :: Trail -> Trail
step (first, second, third, last) = (bearing first last, first, second, third)

--- The infinite production of trails.
trails :: [Trail]
trails = iterate step start

--- Given a trail with a new head, paint the line that connects it to its body (= old head).
connect :: GraphicsContext -> Trail -> IO ()
connect ctx (nextHead,head,_,_) = withUI $ ctx.strokeLine head.x head.y nextHead.x nextHead.y

--- A doodle contains all actions that when applied in sequence make up the picture.
doodle :: GraphicsContext -> [IO ()]
doodle ctx = map (connect ctx) trails

--- Play any function _f_ that returns a list of IO actions
play f = paint $ sequence_ . f

--- Sample usage: paint the doodle at once.
fast = play $ take 300 . doodle

--- Sample usage: make every second action a sleep.
slow = play $ intersperse (Thread.sleep 100) . take 300 . doodle