src/RMCA/Global/Clock.hs

   1 module RMCA.Global.Clock where
   2
   3 import Control.Concurrent
   4 import Control.Monad
   5 import Data.CBMVar
   6 import Data.ReactiveValue
   7 import FRP.Yampa
   8 import RMCA.Auxiliary
   9 import RMCA.Semantics
  10
  11 -- The initial value is arbitrary but never appears because the switch
  12 -- is immediate.
  13 metronome :: SF Tempo (Event Beat)
  14 metronome = switch (repeatedly (tempoToQNoteIvl 120) ()
  15                     &&&
  16                     onChange') metronome'
  17   where metronome' :: Tempo -> SF Tempo (Event Beat)
  18         metronome' t = switch (repeatedly (tempoToQNoteIvl t) ()
  19                                &&&
  20                                onChange) metronome'
  21
  22 -- Tempo is the number of quarter notes per minute.
  23 tempoToQNoteIvl :: Tempo -> DTime
  24 tempoToQNoteIvl = (15/) . fromIntegral
  25
  26 type TickingClock = (CBMVar (), ThreadId)
  27
  28 -- Make a clock that will execute any IO when it updates.
  29 mkClockGeneric :: IO () -> DTime -> IO TickingClock
  30 mkClockGeneric io d = do
  31   n <- newCBMVar ()
  32   tid <- forkIO $ forever $  do
  33     threadDelay dInt
  34     modifyCBMVar n return
  35     io
  36   return (n, tid)
  37   where dInt = floor $ d * 1000
  38
  39 -- Ticking clock in the IO monad, sending callbacks every t milliseconds.
  40 mkClock :: DTime -> IO TickingClock
  41 mkClock = mkClockGeneric (return ())
  42
  43 -- For debugging purposes.
  44 mkClockDebug :: DTime -> IO TickingClock
  45 mkClockDebug = mkClockGeneric (putStrLn "Ping !")
  46
  47 clockRV :: TickingClock -> ReactiveFieldRead IO ThreadId
  48 clockRV (mvar, tid) = ReactiveFieldRead (return tid)
  49                       (installCallbackCBMVar mvar)
  50
  51 mkClockRV :: DTime -> IO (ReactiveFieldRead IO ThreadId)
  52 mkClockRV d = clockRV <$> mkClock d
  53
  54 stopClock :: TickingClock -> IO ()
  55 stopClock (_,t) = killThread t