[Haskell-beginners] HOpenGL questions

Thomas Davie tom.davie at gmail.com
Wed May 19 02:43:38 EDT 2010

> - First of all, all tutorials are using GLUT. Is that really the way to
>  go with HOpenGL?

Probably not, but this is pretty typical of OpenGL tutorials – they use GLUT because it's simple to get going, and avoids having to demonstrate lots of things that are irrelevant to OpenGL.

> They define (among other things) a onIdle and a
>  onDraw function. That seems to me (at least for a game) not the way
>  to go. onIdle updates the game logic, and onDraw draws the screen. As
>  far as I can see, it does not make sense to update the game logic
>  more than once between consecutive calls to onDraw. Same thing is
>  true for class to onDraw between consecutive class to onIdle. Is this
>  accounted for in the approach?

Actually, at least the onIdle running many times between onDraw is completely reasonable for a game... To keep your physics simulation accurate, you want nice, short, time steps, you don't necessarily want to be rendering each and every one of them though.

> - In addition there is the onInput function. The onInput, onIdle and
>  onDraw functions communicate (in the tutorials) using variables
>  declared with newIORef. I come from the OO language C++ and almost no
>  experience with functional languages. But this puzzles me. Basically
>  they define global variables for  the exchange between the callback
>  functions, correct?!? So, for every piece of information I want to
>  pass between these functions, I have to declare a newIORef variable?

Yeh, that's horribly horribly ugly.  I would personally be spawning two threads, one to repeatedly update the game's state, and one to render.  The functions for each thread would accept a channel as input.  The game state updater would push game states into the channel, the renderer would pull all of them out and render the last one it finds.

> In C/C++ I find GLUT not a very good approach and prefer plain OpenGL.
> Does it make sense to go with plain OpenGL in Haskell too? Are there
> any resources on how to do that?

I don't get how you use "plain OpenGL".  There are no calls in OpenGL to set up graphics contexts, or accept user input etc.

Personally, I would be using your own system's functions for doing this though – i.e. on Mac OS I would be using Cocoa to do it; on Linux GTK/Qt; on Windows .Net; etc.


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