smooth ball-following in elm

smooth-follow.elm

import Either
import Mouse
import Window

-- updates for movement
data Update = Click (Int,Int) | TimeDelta Time


-- control
-- merges the Click
input = let clickPos = Mouse.position
        in  merge (Click <~ clickPos)
                  (TimeDelta <~ (40 `fpsWhen` (second `since` clickPos)))

-- steps
step inp ((tx,ty),(x,y)) =
    case inp of
      Click t  -> (t, (x,y))
      TimeDelta d -> ((tx,ty), ( x + (tx-x) * (d/100) ,
                                 y + (ty-y) * (d/100) ))   
            
-- MODEL
data Update = Click (Int,Int) | TimeDelta Time

-- view
ball (w,h) (endpos,(x,y)) = 
  collage w h [ circle 10  |> filled blue
                           |> move (x- toFloat w/2, toFloat h/2-y) ]

main = ball <~ Window.dimensions
             ~ foldp step ((0,0),(0,0)) input