[HOpenGL] HOpenGL postRedisplay in Mac

[Balazs Komuves]

Hi,

It's not easy to answer these type of questions without looking at the code,

but I guess that you forgot "swapBuffers"; also "postRedisplay" is at the
wrong place.
Idle callback shouldn't be used in normal circumstances.

In double-buffering mode, by default OpenGL draws on the back plane, and you
see the
front page. After you finish the drawing, you swap the two using
"swapBuffers".

"postRedisplay Nothing" tells GLUT that the screen is needing a refresh
(normal
applications do not render continuously, just when something happens on the
screen).
If you want continuous animation, I recommend the following code structure,
where
swapBuffers and postRedisplay are at the end of the display callback:

-- This is the display callback. You do the drawing here.
> -- Idle callback shouldn't be used at all. Animation should be depend
>
   -- only on time, not on frames.

> display = do
>
>   matrixMode $= Projection
>   loadIdentity
>   -- set projection matrix here, for example:
>   ortho (-1) 1 (-1) 1 (-1) 1
>
>   matrixMode $= Modelview 0
>   loadIdentity
>
>      t1 <- get elapsedTime
     let t = fromIntegral t1 * 0.001 :: Double        -- elapsed time in
seconds

  -- do some drawing here, depending on "t"
>   renderPrimitive Lines $ do
>     vertex (Vertex2 ....)
>     -- etc
>
>   swapBuffers                  -- this is for correct double buffer
>   postRedisplay Nothing   -- this is to ensure that the next frame will be
> rendered, too
>


Hope this helps,
Balazs


On Tue, Mar 15, 2011 at 11:19 PM, Francisco Listas <
francisco.listas at gmail.com> wrote:

> Hello all,
>
> I am following the tutorial on
> http://www.haskell.org/haskellwiki/OpenGLTutorial2 everything works
> ok, but the moment I  add "postRedisplay Nothing" to the idle function
> nothing is displayed.
> I've tried passing the current window to postRedisplay, adding double
> buffering (it is supposed to be done internally on mac) but no image.
> If I comment out postRedisplay then I can see the image but no animation
>
> I am using Snow Leopard 10.6 and GHC from the 32bit Haskell Platform
> 2010.2.0.0
>
> Any clue to what's happening?
>
> Thx,
> Francisco
>
> _______________________________________________
> HOpenGL mailing list
> HOpenGL at haskell.org
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>
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