I thought I would add my two cents. I've been working on a side project for a 
few months and found out that there are some weird things with Fl_Gl_Window 
that you might not know. Maybe some documentation could be updated with this, 
unless I just missed it.

Fl_Gl_Window does not initialize OpenGL until the app is running via Fl::run(). 
I'm still not sure it it is holding off until the first draw call or what. It 
relates to textures in a way because you can't generate textures until OpenGL 
has been initialized. You can see this in glut as well if you try to use 
glGenTextures before your glutInit* calls.

I found this out because I use texture managers and I had it set to load all 
the textures before Fl::run() and it just didn't work. I would get white 
squares to show me OpenGL was rendering but no textures. And I tracked it back 
to glGenTextures not returning expected values. To get around this I had to add 
to my draw function to check if it was the first loop and load my textures 
there.

I hope this helps you and anyone who might be having similar problems.

> Patrick McCarthy wrote:
> >     Dear Loic, have a look at:
> >     http://fltk.org/doc-1.0/basics.html#basics
> >     it is a frequent problem!
>
>       Hmm, does that page cover texture mapping problems?
>
>       Also, looks like the 'hello world' image on that page
>       is pretty wacked out:
>       http://fltk.org/doc-1.0/hello.C.gif
>
>       Fortunately those are docs for a really ancient release of FLTK;
>       the 1.0.x series was put to pasture many years ago.
>       1.1.x has been the current stable release for the last 5 or 6
>       years at least; so the equivalent page would be here:
>       http://fltk.org/doc-1.1/basics.html#basics
>
>       Though I don't think that mentions textures either..

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