Yampa.hs

module Graphics.Gloss.Interface.FRP.Yampa (playYampa, InputEvent) where

import Control.Monad (when)
import Data.IORef (newIORef, writeIORef, readIORef)
import Graphics.Gloss (Display, Color, Picture, blank)
import Graphics.Gloss.Interface.IO.Game (playIO)
import FRP.Yampa (Event(..), SF, reactInit, react)

import Types (InputEvent)

-- | Play the game in a window, updating when the value of the provided 
playYampa :: Display -- ^ The display method
          -> Color   -- ^ The background color
          -> Int     -- ^ The refresh rate, in Hertz
          -> SF (Event InputEvent) Picture
          -> IO ()
playYampa display color frequency mainSF = do
    picRef <- newIORef blank

    handle <- reactInit
      (return NoEvent)
      (\_ updated pic -> when updated (picRef `writeIORef` pic) >> return False)
      mainSF

    playIO display
           color
           frequency
           0
           (const $ readIORef picRef) -- An action to convert the world to a picture
           (\e t -> react handle (delta, Just (Event e)) >> return (t + delta)) -- A function to handle input events
           (\d t -> let delta' = realToFrac d - t
                   in if delta' > 0
                        then react handle (delta', Just NoEvent) >> return 0.0
                        else return (-delta')) -- A function to step the world one iteration. It is passed the period of time (in seconds) needing to be advanced
  where
    delta = 0.01 / fromIntegral frequency