Re: [gtk-list] Re: Using Mesa (openGL) with GTK

[Ivo Clarysse <soggie riv be>]

On Sun, 19 Oct 1997, Bj|rn Augustsson wrote:

> Juergen A. Erhard (jae@laden.ilk.de) wrote:
> >It works for me after changing dbuf in gui_init to start with GL_RGBA
> >and put the GLX_DOUBLEBUFFER at the end. Took me a couple minutes, and
> >comparing with glxdemo.c in Mesa 2.3...
> 
> I also inserted GLX_RGBA, but doing just that that doesn't work well at
> all, since the toplevel widget gets the default visual (In my case 
> PseudoColor 8), and then the program tries to attach the TrueColor 24
> visualled glarea widget to it.
> 
> The results are some pretty nasty kernel messages about failed asserts
> and the GL rendering seems to be in black&white. (not grayscale, B&W)
> 
> This should really be possible to do, as it seems there is an OpenGL
> widget for motif that can do it. (As seen in Mark Kilgards excellent
> article from the X Journal, which can be found at
> http://www.sgi.com/Technology/openGL/mjk.motif/  )
> I don't know how though.
> 
> The fix I've found is to force the entire app to use the best visual it
> can find. That works on my system (Sparc Solaris 2.5.1, OpenGL 1.0) at 
> least. What I did to the posted code was:
> 
> 1: Add GLX_RGBA to the dbuf[] array.
> 
> 2: Add
> 
>   gtk_widget_set_default_visual (gtk_preview_get_visual ());
>   gtk_widget_set_default_colormap (gtk_preview_get_cmap ());
> 
> just after the call to gtk_init().

This still doesn't work on SGI boxes with SGI's OpenGL and 24-bit gfx
cards.  ("**ERROR** : BadMatch") 

The Mark Kilgard OpenGL articles mention a problem with having windows
with just one contained widget in a different visual than the rest of 
the window, due to the fact that libXt has limited facilities for
this.  

http://www.sgi.com/Technology/openGL/mjk.motif/section3_2.html :

"The Motif drawing area widget would seem a natural widget for OpenGL 
rendering. Unfortunately, the X Toolkit's design (upon which Motif relies) 
allows programmers to specify a widget's visual only if its class
is derived from the shell widget class. Shell widgets are often called 
``top level'' widgets because they are designed to communicate with the 
window manager and act as containers for other widgets. Non-shell
widgets inherit the depth and visual of their parent widget. [...]"

Does GTK+ suffer from this Xt limitation as well ?


Soggie.

-----------------------------------------------------------------------
 Ivo Clarysse <soggie@riv.be>,                Riverland Research Group
 Research Assistant                        http://www.riv.be/research/
                                                      Excelsiorlaan 42
 http://www.riv.be/~soggie/me/                B-1930 Zaventem, Belgium