spaceinvaders.elm

import Keyboard
import Window

(gameWidth,gameHeight) = (600,800)
(halfWidth,halfHeight) = (300,400)


type Input = {space:Bool, dir:Int, delta:Time}
type Spaceship = {x:Float, y:Float, rotation:Float}
type Ball = {x:Float, y:Float, vx:Float, vy:Float}
type Game = {spaceship:Spaceship, ball:Ball, state:State}


defaultGame : Game
defaultGame = 
  { spaceship = {x=0, y=-halfHeight+40, rotation=90},
    ball = {x=0, y=-halfHeight+40, vx=100, vy=100},
    state = NotShooting
  }


data State = Shooting | NotShooting

defaultSpaceship : Float -> Spaceship
defaultSpaceship h = {x=0, y=h + 40, rotation=90}

delta = inSeconds <~ fps 35
input = sampleOn delta (Input <~ Keyboard.space
                               ~ lift .x Keyboard.arrows
                               ~ delta)
                               


drawSpaceship : Spaceship -> Color -> Form
drawSpaceship spaceship clr = (rotate (degrees spaceship.rotation) ( move (spaceship.x, spaceship.y) (filled clr (ngon 3 20))))

drawBall : Ball -> Color -> Form
drawBall ball clr = ( move (ball.x, ball.y) (filled clr (circle 8)))


stepGame : Input -> Game -> Game
stepGame ({space, dir, delta} as input) ({spaceship, ball, state} as game) =
      let spaceship' = moveSpaceship spaceship delta dir
          ball' = moveBall ball delta state
          state' = updateState state ball space
      in { game | spaceship <- spaceship',
                  ball      <- ball',
                  state     <- state'}


updateState : State -> Ball -> Bool -> State
updateState state ball isSpacePressed = case (state, ball, isSpacePressed) of
                                    (NotShooting, _, True) -> Shooting
                                    (s, b, _) -> if b.y < halfHeight then s else NotShooting

moveBall : Ball -> Time -> State -> Ball
moveBall ({x,y,vx,vy} as ball) delta state = let y' = if state == Shooting && y < halfHeight then y + vx * delta
                                      else -halfHeight+40
                             in {ball | y <- y'}

moveSpaceship : Spaceship -> Time -> Int -> Spaceship
moveSpaceship spaceship delta angle = let rotation' = spaceship.rotation - ((toFloat angle))
                        in {spaceship | rotation <- rotation'}

gameState : Signal Game
gameState = foldp stepGame defaultGame input

showRotation : Spaceship -> String
showRotation {x, y, rotation} = "Rotation " ++ show rotation

display : (Int, Int) -> Game -> Input -> Element
display (w,h) {spaceship, ball, state} i = collage w h [
                move (0, 0) (filled yellow (rect gameWidth gameHeight)),
                move (0, 0) (filled green (rect 5 5)),
                move (0, 0) (toForm (asText (showRotation spaceship))),
                move (0, -20) (toForm (asText i.dir)),
                (drawSpaceship spaceship red),
                (drawBall ball blue)]

main = lift3 display Window.dimensions gameState input