[Haskell-cafe] How to variables
yin at atom.sk
Mon Jul 18 16:39:24 EDT 2005
robert dockins wrote:
> yin wrote:
>> Hello all!
>> I'm doing a 3D simulation. Now I need something like variables in
>> imperative languages. My mainLoop check for new events and renders
> Then you want IORef.
> Consider, however, that this kind of construct can be done without
> mutable variables. (warning, made-up code ahead)
> main = loop 0 0 0 -- initial values
> where loop loop_num xpos ypos =
> do e <- pollEvent
> let xpos' = <calculate new xpos>
> ypos' = <calculate new ypos>
> someActionInvolvingPosition xpos' ypos'
> when breakCondition (return ())
> loop (loop_num+1) xpos' ypos'
I saw it. The problem is, I need an amount of 100*X of mutable variables
to implement the system (camera position, rotation, aceleration, ...,
position and deformetion infomations for every object, ..., renderer
situations [like temprary fading and other efects], ... and more)
I tried something like this:
main = withInit [InitVideo] $
do progname <- getProgName
mainLoop :: Int -> IO ()
mainLoop ll = do
event <- pollEvent
quit <- case event of
VideoResize w h -> resizeGLScene w h >> return False
KeyDown (Keysym SDLK_q _ _) -> return True
Quit -> return True
_ -> drawGLScreen ((fromIntegral ll) / 10) >> return False
when (not quit) (mainLoop (ll + 1))
drawGLScreen :: Double -> IO ()
drawGLScreen = do
translate $ (\(x,y,z) -> Vector3 x y z) getCameraPos
rotate blah, blah, ...
renderPrimitive Polygon $ mapM_ (\(x,y,z) -> vertex$Vertex3 x y z)
getCameraPos :: (GLfloat, GLfloat, GLfloat)
getCameraPos = readIORef refCameraPos
setCameraPos :: (GLfloat, GLfloat, GLfloat) -> IO ()
setCameraPos (a, b, c) = writeIORef refCameraPos (a, b, c)
And there si the problem - how to initialize refCameraPos with newIORef,
and then using it.
If I write "refCameraPos = newIORef (0, 0, 0)" it will initialize new
IORef every time. I need Just persistent, mutualy variable. I was
covered on this list , but I've deleted the messages.
Matej 'Yin' Gagyi
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