change keyboard event handling

examples/example04.hs

@@ -35,7 +35,7 @@ data UserData = UserData
   , actors       :: M.Map String (Actor String)
   , foreground   :: G.GeglBuffer
   , updateActors :: [Actor String]
-  , keyDown      :: Maybe SDL.Keycode
+  , keysDown     :: [SDL.Keycode]
   , cameraX      :: Double
   }
 
@@ -126,7 +126,7 @@ load = do
     , actors       = actorMap
     , foreground   = buffer
     , updateActors = []
-    , keyDown      = Nothing
+    , keysDown      = []
     , cameraX      = 0
     }
 
@@ -157,8 +157,9 @@ update dt = do
   ud <- getAffection
 
   traceM $ show (1 / dt) ++ " FPS"
+  -- traceM $ show $ keysDown ud
 
-  maybe (return ()) (\code -> do
+  mapM_ (\code -> do
     let vel = 400 -- velocity in Pixels per second
         leg = vel * dt
     (G.PropertyDouble xpos) <-
@@ -195,7 +196,7 @@ update dt = do
       , updateActors = (nmap M.! "rect") : updateActors ud
       , cameraX = cameraX ud + offset
       }
-    ) (keyDown ud)
+    ) (keysDown ud)
 
 handle :: SDL.EventPayload -> Affection UserData ()
 handle (SDL.KeyboardEvent dat) =
@@ -204,11 +205,13 @@ handle (SDL.KeyboardEvent dat) =
     if (SDL.keyboardEventKeyMotion dat == SDL.Pressed)
     then
       putAffection ud
-        { keyDown = Just $ SDL.keysymKeycode $ SDL.keyboardEventKeysym dat
+        { keysDown =
+            SDL.keysymKeycode (SDL.keyboardEventKeysym dat) : keysDown ud
         }
     else
       putAffection ud
-        { keyDown = Nothing
+        { keysDown =
+            delete (SDL.keysymKeycode $ SDL.keyboardEventKeysym dat) (keysDown ud)
         }
 
 handle (SDL.WindowClosedEvent _) = do