[Haskell-cafe] HopenGL

Ruben Zilibowitz r.zilibowitz at student.unsw.edu.au
Fri Jun 8 05:05:38 EDT 2007


Thanks. I eventually figured it out by doing pretty much what you  
suggested with Lines.hs. I discovered that the thing that made lines  
come out only in black was:
lighting $= Enabled
So disabling lighting before drawing lines and re-enabling it  
afterwards allows me to draw colored lines now. Thanks for the  


On 08/06/2007, at 10:19 AM, Jason Dagit wrote:

> On 6/7/07, Ruben Zilibowitz <r.zilibowitz at student.unsw.edu.au> wrote:
>> Hi,
>> Thanks for the reply. The Lines.hs example program seems to work just
>> right. Unfortunately I still can't get colored lines to work in my 3d
>> program.
>> Maybe it has something to do with the fact my one is 3d and
>> the example program is in 2d.
> This is unlikely because of the way OpenGL does 3d vs. 2d.  In OpenGL,
> 2d is just a special case of 3d where 0 is used for the z coordinate.
> More likely than 3d vs. 2d is that you're not drawing in the correct
> part of coordinate space, the view volume is incorrect or something
> like that.
> I would try to work Lines.hs into your current example or start
> borrowing code from it and putting them into your example until you
> either break Lines.hs in the same way or your example starts to work.
> Does Lines.hs still work when you switch it over to 3d?  It should,
> but that could be a nice test to help you debug things.
> Did you remember to do all the double buffering operations?  Did you
> setup the clear color first?  One thing that you have to be careful
> about with OpenGL is that you correctly manage the state of the opengl
> machine.  Haskell should have a purely functional scene graph built on
> top of HOpenGL -- it's something I would like to work on -- but no one
> seems to be doing it.  For me at least, it's a matter of time and
> priority.  Maybe in a few months to a year I'll get some time for it,
> but don't hold your breath :)
> Jason

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