[Haskell-cafe] Inconsistent window updates with SDL library

[Michael Serra]

Oh, in case the code would be helpful.. ;)

import Data.Set (toList, fromList, intersection, size)
import Data.List ((\\))
import System.Random (randomRIO)
import Data.Word (Word32)
import Graphics.UI.SDL as SDL

main = do
  SDL.init [InitVideo, InitTimer, InitEventthread]
  w <- setVideoMode 1440 900 32 []
  setCaption "LIFE" "life"
  eventLoop w cells
  quit

eventLoop w cs = do
  drawCells w cs
  e <- waitEventBlocking
  checkEvent e
    where
      checkEvent (KeyUp (Keysym SDLK_ESCAPE _ _)) = return ()
      checkEvent (KeyUp (Keysym SDLK_n _ _))      = eventLoop w $ nextgen cs
      checkEvent _                                = eventLoop w cs

drawCells w cs = do
  clearScreen
  s <- createRGBSurface [SWSurface] size size 32 0 0 0 0
  sequence $ map (draw s) $ scale cs
  SDL.flip w
    where
      clearScreen  = fillRect w (Just $ Rect 0 0 1440 900) $ Pixel 0x0
      rect x y     = Just $ Rect x y size size
      scale        = map (\(x,y) -> (x * size, y * size))
      size         = 16
      draw s (x,y) =
        do
          r <- randomRIO (0::Int, 0xFFFFFF)
          fillRect s (rect 0 0) $ Pixel (fromIntegral r :: Word32)
          blitSurface s (rect 0 0) w $ rect x y

--------------------------------------------------------------------------------
cells      = [(25,14),(26,14),(25,15),(24,15),(25,16)]

nextgen cs = (filter (live cs) cs) ++ births cs

live cs c  = size neighbors > 1  &&  size neighbors < 4
               where neighbors = adj c `intersection` fromList cs

births cs  = (filter neighbors3 allAdjacent) \\ cs
               where allAdjacent  = nub $ concatMap (toList . adj) cs
                     neighbors3 c = size (neighbors c) == 3
                     neighbors c  = adj c `intersection` fromList cs
                     nub          = toList . fromList

adj (x,y)  = fromList $ tail [(a,b) | a <- [x,x+1,x-1], b <- [y,y+1,y-1]]
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20110516/367e6a01/attachment.htm>