[Fieldtrip] Re: [HOpenGL] noticing freeglut vs not

[Claus Reinke]

Is this still an open issue in FieldTrip? If you look at the online versions 
of the files Sven mentioned

    http://darcs.haskell.org/packages/GLUT/include/HsGLUTExt.h
    http://darcs.haskell.org/packages/GLUT/Graphics/UI/GLUT/Extensions.hs

you can see how the dynamic lookup of functions that are only 
available in some extensions is handled. Looking at

    http://darcs.haskell.org/packages/GLUT/Graphics/UI/GLUT/Begin.hs

it does seem as if constants and StateVars are not directly protected like 
this, but 'actionOnWindowClose' calls 'glutSetOption', which you can see in 

    http://darcs.haskell.org/packages/GLUT/Graphics/UI/GLUT/QueryUtils.hs

as just such a dynamic lookup. In case this isn't clear: your code can
simply catch the exception thrown when that dynamic lookup fails,
letting the exception handler pursue an alternative path (since your ticket
recommends commenting out that line, the handler could perhaps just do 
nothing in your case, or issue a warning about missing freeglut?).

No change to the GLUT package should be needed, I think.
Claus

> Thanks for the pointers.
> 
> I'm looking for some way to program my library so that a graceful exit is
> made where possible and still runs, though exits less gracefully with
> non-free glut.  I'd be happy with either a new API entry for that case or a
> change to the meaning of MainLoopReturns.
> 
>  - Conal
> 
> On Thu, Nov 20, 2008 at 5:33 AM, Sven Panne <sven.panne at aedion.de> wrote:
> 
>> On Thursday 13 November 2008 03:24:29 Conal Elliott wrote:
>> > I'm looking for a way to use MainLoopReturns when freeglut is present and
>> > not when it isn't.  I could use some help.  I figure that the
>> > implementation has some way to generate that error message, and maybe we
>> > could similarly just do a standard ungraceful exit if freeglut is
>> missing.
>> >
>> > The great thing about MainLoopReturns is that it plays nicely with ghci.
>> > Closing a window returns to ghci for more fun.
>> >
>> > Some more info at http://trac.haskell.org/FieldTrip/ticket/8 .
>> >
>> > Any ideas?
>>
>> Currently the GLUT binding uses dynamic lookup to get freeglut-only API
>> entries (see /GLUT/Graphics/UI/GLUT/Extensions.hs, cbits/HsGLUT.c,
>> include/HsGLUTExt.h) and uses throwIfNull to test for non-existent API
>> entries. Therefore, e.g. actionOnWindowClose should throw an exception when
>> "classic" GLUT is used. I am not sure if I understand your request: Do you
>> want a new API entry for the GLUT binding or a different behavior of the
>> current entries?
>>
>> Cheers,
>>    S.
>>
>>
>


--------------------------------------------------------------------------------


> _______________________________________________
> HOpenGL mailing list
> HOpenGL at haskell.org
> http://www.haskell.org/mailman/listinfo/hopengl
>