前言
经过 3 个月的大量网站挖掘和一些小项目的尝试后，我终于以一种非常非常不同的方式实现了一款极简主义游戏（或者是吗？）。此示例仅用于演示用 Haskell 编写的游戏的一种可能结构，并且应该很容易扩展以处理更复杂的逻辑和游戏玩法。
https://github.com/carldong/HMovePad-Tutorial上提供了完整的代码和教程
抽象的
这个小游戏只有一个矩形，玩家可以通过左右键左右移动，这就是整个“游戏”。
游戏使用netwire-5.0.1,SDL处理图形实现。如果我理解正确，该架构是功能齐全的反应式。几乎所有东西都是由 Arrow 组合实现的，只有一个函数暴露在IO. 因此，我希望读者对 Haskell 的箭头语法有基本的了解，因为它被广泛使用。
选择这个游戏的实现顺序是为了方便调试，选择实现本身是为了netwire尽可能多的演示不同的用法。
连续时间语义用于 I/O，但离散事件用于处理游戏逻辑中的游戏事件。
设置 SDL
第一步是确保 SDL 正常工作。来源很简单：
module Main where
import qualified Graphics.UI.SDL as SDL
main :: IO ()
main = do
SDL.init [SDL.InitEverything]
w <- SDL.setVideoMode 800 600 32 [SDL.SWSurface]
s <- SDL.createRGBSurfaceEndian [SDL.SWSurface] 800 600 32
SDL.fillRect s (Just testRect) (SDL.Pixel 0xFFFFFFFF)
SDL.blitSurface s (Nothing) w (Nothing)
SDL.flip w
testLoop
SDL.quit
where
testLoop = testLoop
testRect = SDL.Rect 350 500 100 50
如果一切正常，窗口底部应该会出现一个白色矩形。请注意，单击x不会关闭窗口。它必须通过Ctrl+C或杀死来关闭。
设置输出线
由于我们不想一直执行到最后一步，发现屏幕上什么都画不出来，所以我们先做输出部分。
我们需要箭头语法：
{-# LANGUAGE Arrows #-}
另外，我们需要导入一些东西：
import Prelude hiding ((.), id)
import Control.Wire
import Control.Arrow
import Control.Monad
import Data.Monoid
import qualified Graphics.UI.SDL as SDL
我们需要了解如何构建 Kleisli Wires：Netwire 5 中的 Kleisli Arrow？. 此示例显示了使用 Kleisli Wires 的交互式程序的基本结构：Netwire 中的控制台交互性？. 要从任何 type 构造 Kleisli Wire a -> m b，我们需要：
mkKleisli :: (Monad m, Monoid e) => (a -> m b) -> Wire s e m a b
mkKleisli f = mkGen_ $ \a -> liftM Right $ f a
然后，由于我没有trace在 Arrow 进程下工作，因此使用调试线将对象打印到控制台：
wDebug :: (Show a, Monoid e) => Wire s e IO a ()
wDebug = mkKleisli $ \a -> putStrLn $ show a
现在是时候编写一些要提升到连线中的函数了。对于输出，我们需要一个函数，它返回一个SDL.Surface在给定焊盘 X 坐标的情况下绘制正确矩形的函数：
padSurf :: SDL.Surface
-> Int
-> IO SDL.Surface
padSurf surf x' = do
let rect' = SDL.Rect x' 500 100 50
clipRect <- SDL.getClipRect surf
SDL.fillRect surf (Just clipRect) (SDL.Pixel 0x00000000)
SDL.fillRect surf (Just rect') (SDL.Pixel 0xFFFFFFFF)
return surf
请注意，此功能会进行破坏性更新。传入的表面稍后将被 blitted 到窗口表面上。
现在我们有了表面。然后输出线很简单：
wTestOutput :: SDL.Surface -> Wire s () IO () SDL.Surface
wTestOutput surf = mkKleisli $ \_ -> testPad
where
testPad = padSurf surf 350
然后，我们把电线放在一起，玩一下：
gameWire :: SDL.Surface
-> Wire s () IO () SDL.Surface
gameWire w = proc _ -> do
finalSurf <- wTestOutput w -< ()
wDebug -< "Try a debug message"
returnA -< finalSurf
最后，我们main正确地改变和驱动电线：
main :: IO ()
main = do
SDL.init [SDL.InitEverything]
w <- SDL.setVideoMode 800 600 32 [SDL.SWSurface]
s <- SDL.createRGBSurfaceEndian [SDL.SWSurface] 800 600 32
run w (countSession_ 1) $ gameWire w
SDL.quit
run ::SDL.Surface -> Session IO s -> Wire s () IO () SDL.Surface -> IO ()
run mainSurf s w = do
(ds, s') <- stepSession s
(eSrcSurf, w') <- stepWire w ds (Right ())
case eSrcSurf of
Right srcSurf -> do
SDL.blitSurface srcSurf (Nothing) mainSurf (Nothing)
SDL.flip mainSurf
SDL.delay 30
run mainSurf s' w'
_ -> return ()
请注意，如果您愿意，您也可以制作另一条线来处理主窗口表面（它比我当前的实现更简单且更好），但我太晚了，懒得添加它。查看我上面提到的交互式示例，看看run可以变得多么简单（如果使用抑制而不是quitWire在该示例中，它会变得更加简单）。
当程序运行时，它的外观应该和以前一样。
这是完整的代码：
{-|
01-OutputWires.hs: This step, the output wires are constructed first for
easy debugging
-}
{-# LANGUAGE Arrows #-}
module Main where
import Prelude hiding ((.), id)
import Control.Wire
import Control.Arrow
import Control.Monad
import Data.Monoid
import qualified Graphics.UI.SDL as SDL
{- Wire Utilities -}
-- | Make a Kleisli wire
mkKleisli :: (Monad m, Monoid e) => (a -> m b) -> Wire s e m a b
mkKleisli f = mkGen_ $ \a -> liftM Right $ f a
-- | The debug wire
wDebug :: (Show a, Monoid e) => Wire s e IO a ()
wDebug = mkKleisli $ \a -> putStrLn $ show a
{- Functions to be lifted -}
padSurf :: SDL.Surface
-- ^ Previous state of surface
-> Int
-- ^ X'
-- | New state
-> IO SDL.Surface
padSurf surf x' = do
let rect' = SDL.Rect x' 500 100 50
clipRect <- SDL.getClipRect surf
SDL.fillRect surf (Just clipRect) (SDL.Pixel 0x00000000)
SDL.fillRect surf (Just rect') (SDL.Pixel 0xFFFFFFFF)
return surf
{- Wires -}
wTestOutput :: SDL.Surface -> Wire s () IO () SDL.Surface
wTestOutput surf = mkKleisli $ \_ -> testPad
where
testPad = padSurf surf 350
-- | This is the main game wire
gameWire :: SDL.Surface
-- ^ The main surface (i.e. the window)
-> Wire s () IO () SDL.Surface
gameWire w = proc _ -> do
finalSurf <- wTestOutput w -< ()
wDebug -< "Try a debug message"
returnA -< finalSurf
main :: IO ()
main = do
SDL.init [SDL.InitEverything]
w <- SDL.setVideoMode 800 600 32 [SDL.SWSurface]
s <- SDL.createRGBSurfaceEndian [SDL.SWSurface] 800 600 32
run w (countSession_ 1) $ gameWire w
SDL.quit
run ::SDL.Surface -> Session IO s -> Wire s () IO () SDL.Surface -> IO ()
run mainSurf s w = do
(ds, s') <- stepSession s
(eSrcSurf, w') <- stepWire w ds (Right ())
case eSrcSurf of
Right srcSurf -> do
SDL.blitSurface srcSurf (Nothing) mainSurf (Nothing)
SDL.flip mainSurf
SDL.delay 30
run mainSurf s' w'
_ -> return ()
输入线
在本节中，我们将构建让玩家输入到程序中的连线。
由于我们将在逻辑部分使用离散事件，因此我们需要游戏事件的数据类型：
data GameEvent = MoveR
| MoveL
| NoEvent
deriving (Show, Eq)
-- | Make it Monoid so that game events can be combined
-- (Only applicable in this "game"!)
instance Monoid GameEvent where
mempty = NoEvent
-- | Simultaneously moving left and right is just nothing
MoveR `mappend` MoveL = NoEvent
MoveL `mappend` MoveR = NoEvent
-- | NoEvent is the identity
NoEvent `mappend` x = x
x `mappend` NoEvent = x
x `mappend` y
-- | Make sure identical events return same events
| x == y = x
-- | Otherwise, no event
| otherwise = NoEvent
正如评论所建议的，该Monoid实例仅适用于该特定游戏，因为它只有两个相反的操作：左和右。
首先，我们将从 SDL 轮询事件：
pollEvents :: [SDL.Event] -> IO (Either () ([SDL.Event]))
pollEvents es = do
e <- SDL.pollEvent
case e of
SDL.NoEvent -> return $ Right es
SDL.Quit -> return $ Left ()
_ -> pollEvents $ e:es
显然，这个函数以列表的形式从 SDL 轮询事件，并在收到事件时禁止Quit。
接下来，我们需要检查一个事件是否是键盘事件：
isKeyEvent :: SDL.Event -> Bool
isKeyEvent (SDL.KeyDown k) = True
isKeyEvent (SDL.KeyUp k) = True
isKeyEvent _ = False
我们将有一个当前按下的键的列表，它应该在键盘事件发生时更新。简而言之，当一个键按下时，将该键插入到列表中，反之亦然：
keyStatus :: [SDL.Keysym] -> [SDL.Event] -> [SDL.Keysym]
keyStatus keysDown (e:es) =
case e of
-- | If a KeyDown is detected, add key to list
SDL.KeyDown k -> keyStatus (k:keysDown) es
-- | If a KeyUp is detected, remove key from list
SDL.KeyUp k -> keyStatus (filter (/= k) keysDown) es
_ -> keyStatus keysDown es
keyStatus keysDown [] = keysDown
接下来，我们编写一个将键盘事件转换为游戏事件的函数：
toGameEv :: SDL.Keysym -> GameEvent
toGameEv (SDL.Keysym SDL.SDLK_RIGHT _ _) = MoveR
toGameEv (SDL.Keysym SDL.SDLK_LEFT _ _) = MoveL
toGameEv _ = NoEvent
我们折叠游戏事件并获得一个事件（真的，真的，特定于游戏！）：
fireGameEv :: [SDL.Keysym] -> GameEvent
fireGameEv ks = foldl mappend NoEvent $ fmap toGameEv ks
现在我们可以开始制作电线了。
首先，我们需要一个轮询事件的线路：
wPollEvents :: Wire s () IO () [SDL.Event]
wPollEvents = mkGen_ $ \_ -> pollEvents []
请注意，这mkKleisli使得线不禁止，但我们希望在这条线上禁止，因为程序应该在它应该退出的时候退出。因此，我们mkGen_在这里使用。
然后，我们需要过滤事件。首先，制作一个制作连续时间过滤线的辅助函数：
mkFW_ :: (Monad m, Monoid e) => (a -> Bool) -> Wire s e m [a] [a]
mkFW_ f = mkSF_ $ filter f
用于mkFW_制作过滤器：
wKeyEvents :: (Monad m, Monoid e) => Wire s e m [SDL.Event] [SDL.Event]
wKeyEvents = mkFW_ isKeyEvent
然后，我们需要另一个方便的函数来从 type 的有状态函数创建有状态连接b -> a -> b：
mkSW_ :: (Monad m, Monoid e) => b -> (b->a->b) -> Wire s e m a b
mkSW_ b0 f = mkSFN $ g b0
where
g b0 a = let b1 = f b0 a in
(b1, mkSW_ b1 f)
接下来，构建一个有状态的线来记住所有关键状态：
wKeyStatus :: (Monad m, Monoid e) => Wire s e m [SDL.Event] [SDL.Keysym]
wKeyStatus = mkSW_ empty keyStatus
最后一段线段触发游戏事件：
wFireGameEv :: (Monad m, Monoid e) => Wire s e m [SDL.Keysym] (GameEvent)
wFireGameEv = arr fireGameEv
要主动触发包含游戏事件的离散事件（netwire 事件），我们需要稍微修改一下 netwire（我认为它仍然很不完整），因为它不提供始终触发事件的线路：
always :: (Monad m, Monoid e) => Wire s e m a (Event a)
always = mkSFN $ \x -> (WE.Event x, always)
与 的实现相比now，唯一的区别是never和always。
最后，一条大线，将上面所有的输入线组合在一起：
wGameInput :: Wire s () IO () (Event GameEvent)
wGameInput = proc _ -> do
ge <- wFireGameEv <<< wKeyStatus
<<< wKeyEvents <<< wPollEvents -< ()
e <- always -< ge
-- Debug!
case e of
WE.NoEvent -> wDebug -< "No Event?!!"
WE.Event g -> wDebug -< "Game Event: " ++ show g
-- End Debug
returnA -< e
该线路还显示了一个调试示例。
要与主程序交互，请修改gameWire以使用输入：
gameWire w = proc _ -> do
ev <- wGameInput -< ()
finalSurf <- wTestOutput w -< ()
returnA -< finalSurf
没有其他东西需要改变。嗯，很有趣，不是吗？
程序运行时，控制台会提供大量输出，显示当前正在触发的游戏事件。尝试按左键和右键，以及它们的组合，看看行为是否符合预期。当然，矩形不会移动。
这是一个巨大的代码块：
{-|
02-InputWires.hs: This step, input wires are constructed and
debugged by using wDebug
-}
{-# LANGUAGE Arrows #-}
module Main where
import Prelude hiding ((.), id)
import Control.Wire
import Control.Arrow
import Control.Monad
import Data.Monoid
import qualified Graphics.UI.SDL as SDL
import qualified Control.Wire.Unsafe.Event as WE
{- Data types -}
-- | The unified datatype of game events
data GameEvent = MoveR
| MoveL
| NoEvent
deriving (Show, Eq)
-- | Make it Monoid so that game events can be combined
-- (Only applicable in this "game"!)
instance Monoid GameEvent where
mempty = NoEvent
-- | Simultaneously moving left and right is just nothing
MoveR `mappend` MoveL = NoEvent
MoveL `mappend` MoveR = NoEvent
-- | NoEvent is the identity
NoEvent `mappend` x = x
x `mappend` NoEvent = x
x `mappend` y
-- | Make sure identical events return same events
| x == y = x
-- | Otherwise, no event
| otherwise = NoEvent
{- Wire Utilities -}
-- | Make a stateless filter wire
mkFW_ :: (Monad m, Monoid e) => (a -> Bool) -> Wire s e m [a] [a]
mkFW_ f = mkSF_ $ filter f
-- -- | Make a stateful wire from a chained stateful function and initial value
-- -- The function (a -> b -> a) takes in an old state /a/, and returns state
-- -- transition function (b -> a).
mkSW_ :: (Monad m, Monoid e) => b -> (b->a->b) -> Wire s e m a b
mkSW_ b0 f = mkSFN $ g b0
where
g b0 a = let b1 = f b0 a in
(b1, mkSW_ b1 f)
-- | Make a Kleisli wire
mkKleisli :: (Monad m, Monoid e) => (a -> m b) -> Wire s e m a b
mkKleisli f = mkGen_ $ \a -> liftM Right $ f a
-- | The debug wire
wDebug :: (Show a, Monoid e) => Wire s e IO a ()
wDebug = mkKleisli $ \a -> putStrLn $ show a
-- | The "always" wire
always :: (Monad m, Monoid e) => Wire s e m a (Event a)
always = mkSFN $ \x -> (WE.Event x, always)
{- Functions to be lifted -}
-- | This is the pad surface whose X coordinate can be updated
padSurf :: SDL.Surface
-- ^ Previous state of surface
-> Int
-- ^ X'
-- | New state
-> IO SDL.Surface
padSurf surf x' = do
let rect' = SDL.Rect x' 500 100 50
clipRect <- SDL.getClipRect surf
SDL.fillRect surf (Just clipRect) (SDL.Pixel 0x00000000)
SDL.fillRect surf (Just rect') (SDL.Pixel 0xFFFFFFFF)
return surf
-- | The function to poll events and add to a list of events
pollEvents :: [SDL.Event] -> IO (Either () ([SDL.Event]))
pollEvents es = do
e <- SDL.pollEvent
case e of
SDL.NoEvent -> return $ Right es
SDL.Quit -> return $ Left ()
_ -> pollEvents $ e:es
-- | Checks whether one SDL.Event is a keyboard event
isKeyEvent :: SDL.Event -> Bool
isKeyEvent (SDL.KeyDown k) = True
isKeyEvent (SDL.KeyUp k) = True
isKeyEvent _ = False
-- | The raw function to process key status from events
keyStatus :: [SDL.Keysym] -> [SDL.Event] -> [SDL.Keysym]
keyStatus keysDown (e:es) =
case e of
-- | If a KeyDown is detected, add key to list
SDL.KeyDown k -> keyStatus (k:keysDown) es
-- | If a KeyUp is detected, remove key from list
SDL.KeyUp k -> keyStatus (filter (/= k) keysDown) es
_ -> keyStatus keysDown es
-- | If all events are processed, return
keyStatus keysDown [] = keysDown
-- | Convert a SDL Keysym into "standard" game events
toGameEv :: SDL.Keysym -> GameEvent
toGameEv (SDL.Keysym SDL.SDLK_RIGHT _ _) = MoveR
toGameEv (SDL.Keysym SDL.SDLK_LEFT _ _) = MoveL
toGameEv _ = NoEvent
-- | Combine all game events to get one single firing
fireGameEv :: [SDL.Keysym] -> GameEvent
fireGameEv ks = foldl mappend NoEvent $ fmap toGameEv ks
{- Wires -}
-- | The Kleisli wire to poll events
wPollEvents :: Wire s () IO () [SDL.Event]
wPollEvents = mkGen_ $ \_ -> pollEvents []
-- | A stateless wire that filters out keyboard events
wKeyEvents :: (Monad m, Monoid e) => Wire s e m [SDL.Event] [SDL.Event]
wKeyEvents = mkFW_ isKeyEvent
-- | A stateful wire to keep track of key status
wKeyStatus :: (Monad m, Monoid e) => Wire s e m [SDL.Event] [SDL.Keysym]
wKeyStatus = mkSW_ empty keyStatus
-- | A wire to fire game events from SDL events
wFireGameEv :: (Monad m, Monoid e) => Wire s e m [SDL.Keysym] (GameEvent)
wFireGameEv = arr fireGameEv
-- | This is the connected wire for the entire game input
wGameInput :: Wire s () IO () (Event GameEvent)
wGameInput = proc _ -> do
ge <- wFireGameEv <<< wKeyStatus
<<< wKeyEvents <<< wPollEvents -< ()
e <- always -< ge
-- Debug!
case e of
WE.NoEvent -> wDebug -< "No Event?!!"
WE.Event g -> wDebug -< "Game Event: " ++ show g
-- End Debug
returnA -< e
-- | The wire to test output
wTestOutput :: SDL.Surface -> Wire s () IO () SDL.Surface
wTestOutput surf = mkKleisli $ \_ -> testPad
where
testPad = padSurf surf 350
-- | This is the main game wire
gameWire :: SDL.Surface
-- ^ The main surface (i.e. the window)
-> Wire s () IO () SDL.Surface
gameWire w = proc _ -> do
ev <- wGameInput -< ()
finalSurf <- wTestOutput w -< ()
returnA -< finalSurf
main :: IO ()
main = do
SDL.init [SDL.InitEverything]
w <- SDL.setVideoMode 800 600 32 [SDL.SWSurface]
s <- SDL.createRGBSurfaceEndian [SDL.SWSurface] 800 600 32
run w (countSession_ 1) $ gameWire w
SDL.quit
run ::SDL.Surface -> Session IO s -> Wire s () IO () SDL.Surface -> IO ()
run mainSurf s w = do
(ds, s') <- stepSession s
(eSrcSurf, w') <- stepWire w ds (Right ())
case eSrcSurf of
Right srcSurf -> do
SDL.blitSurface srcSurf (Nothing) mainSurf (Nothing)
SDL.flip mainSurf
SDL.delay 30
run mainSurf s' w'
_ -> return ()
“游戏”逻辑——终于把所有东西放在一起！
首先，我们写一个焊盘X位置的积分函数：
padDX :: Int -> GameEvent -> Int
padDX x0 e
| x > 700 = 700
| x < 0 = 0
| otherwise = x
where
x = x0 + go e
go MoveR = dx
go MoveL = -dx
go _ = 0
dx = 15
我对所有内容都进行了硬编码，但对于这个简约的示例来说，这些并不重要。它应该是直截了当的。
然后，我们创建代表焊盘当前位置的连线：
wPadX :: (Monad m, Monoid e) => Wire s e m (Event GameEvent) Int
wPadX = accumE padDX 400 >>> hold
hold保持离散事件流的最新值。
接下来，我们将所有逻辑的东西放在一条大逻辑线上：
wGameLogic :: Wire s () IO (Event GameEvent) Int
wGameLogic = proc ev -> do
x' <- wPadX -< ev
returnA -< x'
由于我们有一个关于 X 坐标的状态，我们需要修改输出线：
wGameOutput :: SDL.Surface -> Wire s () IO Int SDL.Surface
wGameOutput surf = mkKleisli $ testPad
where
testPad = padSurf surf
最后，我们将所有内容链接在gameWire：
gameWire w = proc _ -> do
ev <- wGameInput -< ()
x <- wGameLogic -< ev
finalSurf <- wGameOutput w -< x
returnA -< finalSurf
main和中无需更改任何内容run。哇！
就是这样！运行它，你就可以左右移动矩形了！
一个巨大的代码块（我很好奇做同样事情的 C++ 程序会持续多久）：
{-|
03-GameLogic.hs: The final product!
-}
{-# LANGUAGE Arrows #-}
module Main where
import Prelude hiding ((.), id)
import Control.Wire
import Control.Arrow
import Control.Monad
import Data.Monoid
import qualified Graphics.UI.SDL as SDL
import qualified Control.Wire.Unsafe.Event as WE
{- Data types -}
-- | The unified datatype of game events
data GameEvent = MoveR
| MoveL
| NoEvent
deriving (Show, Eq)
-- | Make it Monoid so that game events can be combined
-- (Only applicable in this "game"!)
instance Monoid GameEvent where
mempty = NoEvent
-- | Simultaneously moving left and right is just nothing
MoveR `mappend` MoveL = NoEvent
MoveL `mappend` MoveR = NoEvent
-- | NoEvent is the identity
NoEvent `mappend` x = x
x `mappend` NoEvent = x
x `mappend` y
-- | Make sure identical events return same events
| x == y = x
-- | Otherwise, no event
| otherwise = NoEvent
{- Wire Utilities -}
-- | Make a stateless filter wire
mkFW_ :: (Monad m, Monoid e) => (a -> Bool) -> Wire s e m [a] [a]
mkFW_ f = mkSF_ $ filter f
-- -- | Make a stateful wire from a chained stateful function and initial value
-- -- The function (a -> b -> a) takes in an old state /a/, and returns state
-- -- transition function (b -> a).
mkSW_ :: (Monad m, Monoid e) => b -> (b->a->b) -> Wire s e m a b
mkSW_ b0 f = mkSFN $ g b0
where
g b0 a = let b1 = f b0 a in
(b1, mkSW_ b1 f)
-- | Make a Kleisli wire
mkKleisli :: (Monad m, Monoid e) => (a -> m b) -> Wire s e m a b
mkKleisli f = mkGen_ $ \a -> liftM Right $ f a
-- | The debug wire
wDebug :: (Show a, Monoid e) => Wire s e IO a ()
wDebug = mkKleisli $ \a -> putStrLn $ show a
-- | The "always" wire
always :: (Monad m, Monoid e) => Wire s e m a (Event a)
always = mkSFN $ \x -> (WE.Event x, always)
{- Functions to be lifted -}
-- | This is the pad surface whose X coordinate can be updated
padSurf :: SDL.Surface
-- ^ Previous state of surface
-> Int
-- ^ X'
-- | New state
-> IO SDL.Surface
padSurf surf x' = do
let rect' = SDL.Rect x' 500 100 50
clipRect <- SDL.getClipRect surf
SDL.fillRect surf (Just clipRect) (SDL.Pixel 0x00000000)
SDL.fillRect surf (Just rect') (SDL.Pixel 0xFFFFFFFF)
return surf
-- | The function to poll events and add to a list of events
pollEvents :: [SDL.Event] -> IO (Either () ([SDL.Event]))
pollEvents es = do
e <- SDL.pollEvent
case e of
SDL.NoEvent -> return $ Right es
SDL.Quit -> return $ Left ()
_ -> pollEvents $ e:es
-- | Checks whether one SDL.Event is a keyboard event
isKeyEvent :: SDL.Event -> Bool
isKeyEvent (SDL.KeyDown k) = True
isKeyEvent (SDL.KeyUp k) = True
isKeyEvent _ = False
-- | The raw function to process key status from events
keyStatus :: [SDL.Keysym] -> [SDL.Event] -> [SDL.Keysym]
keyStatus keysDown (e:es) =
case e of
-- | If a KeyDown is detected, add key to list
SDL.KeyDown k -> keyStatus (k:keysDown) es
-- | If a KeyUp is detected, remove key from list
SDL.KeyUp k -> keyStatus (filter (/= k) keysDown) es
_ -> keyStatus keysDown es
-- | If all events are processed, return
keyStatus keysDown [] = keysDown
-- | Convert a SDL Keysym into "standard" game events
toGameEv :: SDL.Keysym -> GameEvent
toGameEv (SDL.Keysym SDL.SDLK_RIGHT _ _) = MoveR
toGameEv (SDL.Keysym SDL.SDLK_LEFT _ _) = MoveL
toGameEv _ = NoEvent
-- | Combine all game events to get one single firing
fireGameEv :: [SDL.Keysym] -> GameEvent
fireGameEv ks = foldl mappend NoEvent $ fmap toGameEv ks
-- | The integrator of X position of pad
padDX :: Int -> GameEvent -> Int
padDX x0 e
| x > 700 = 700
| x < 0 = 0
| otherwise = x
where
x = x0 + go e
go MoveR = dx
go MoveL = -dx
go _ = 0
dx = 15
{- Wires -}
-- | The Kleisli wire to poll events
wPollEvents :: Wire s () IO () [SDL.Event]
wPollEvents = mkGen_ $ \_ -> pollEvents []
-- | A stateless wire that filters out keyboard events
wKeyEvents :: (Monad m, Monoid e) => Wire s e m [SDL.Event] [SDL.Event]
wKeyEvents = mkFW_ isKeyEvent
-- | A stateful wire to keep track of key status
wKeyStatus :: (Monad m, Monoid e) => Wire s e m [SDL.Event] [SDL.Keysym]
wKeyStatus = mkSW_ empty keyStatus
-- | A wire to fire game events from SDL events
wFireGameEv :: (Monad m, Monoid e) => Wire s e m [SDL.Keysym] (GameEvent)
wFireGameEv = arr fireGameEv
-- | This is the connected wire for the entire game input
wGameInput :: Wire s () IO () (Event GameEvent)
wGameInput = proc _ -> do
ge <- wFireGameEv <<< wKeyStatus
<<< wKeyEvents <<< wPollEvents -< ()
e <- always -< ge
returnA -< e
-- | The stateful wire of X position of pad
wPadX :: (Monad m, Monoid e) => Wire s e m (Event GameEvent) Int
wPadX = accumE padDX 400 >>> hold
-- | This is the connected wire for the entire game logic
wGameLogic :: Wire s () IO (Event GameEvent) Int
wGameLogic = proc ev -> do
x' <- wPadX -< ev
returnA -< x'
-- | The wire of output
wGameOutput :: SDL.Surface -> Wire s () IO Int SDL.Surface
wGameOutput surf = mkKleisli $ testPad
where
testPad = padSurf surf
-- | This is the main game wire
gameWire :: SDL.Surface
-- ^ The main surface (i.e. the window)
-> Wire s () IO () SDL.Surface
gameWire w = proc _ -> do
ev <- wGameInput -< ()
x <- wGameLogic -< ev
finalSurf <- wGameOutput w -< x
returnA -< finalSurf
main :: IO ()
main = do
SDL.init [SDL.InitEverything]
w <- SDL.setVideoMode 800 600 32 [SDL.SWSurface]
s <- SDL.createRGBSurfaceEndian [SDL.SWSurface] 800 600 32
run w (countSession_ 1) $ gameWire w
SDL.quit
run ::SDL.Surface -> Session IO s -> Wire s () IO () SDL.Surface -> IO ()
run mainSurf s w = do
(ds, s') <- stepSession s
(eSrcSurf, w') <- stepWire w ds (Right ())
case eSrcSurf of
Right srcSurf -> do
SDL.blitSurface srcSurf (Nothing) mainSurf (Nothing)
SDL.flip mainSurf
SDL.delay 30
run mainSurf s' w'
_ -> return ()