Re: OpenGL support in GTK+

[Naofumi Yasufuku <naofumi yasufuku net>]

At Mon, 22 Sep 2003 08:27:55 -0400,
Tristan Van Berkom wrote:
> 
> Naofumi Yasufuku wrote:
> 
[snip]
> >
> >Basically, GdkGLExt API follows GLX 1.3 API (however, current internal
> >code uses GLX 1.2 for portability).
> >
> > X11
> > ----------------------------------------------------------------
> >  Display *display;
> >  Window window;
> >  GLXFBConfig fbconfig;
> >  GLXWindow glxwindow;
> >
> >  window = XCreateWindow (display, parent, ...);
> >  glxwindow = glXCreateWindow (display, fbconfig, window, NULL);
> > ----------------------------------------------------------------
> > GDK
> > ----------------------------------------------------------------
> >  GdkWindow *window;
> >  GdkGLConfig *glconfig;
> >  GdkGLWindow *glwindow;
> >
> >  window = gdk_window_new (parent, ...);
> >  glwindow = gdk_gl_window_new (glconfig, window, NULL);
> > ----------------------------------------------------------------
> >
> >Programmer have to take care to keep a pair of window and glwindow, so
> >GdkGLExt library provides gdk_window_*() extension functions which
> >add OpenGL support to GdkWindow.
> >
> > ----------------------------------------------------------------
> >  GdkWindow *window;
> >  GdkGLConfig *glconfig;
> >  GdkGLWindow *glwindow;
> >
> >  window = gdk_window_new (parent, ...);
> >  glwindow = gdk_window_set_gl_capability (window, glconfig, NULL);
> >
> >  ....
> >
> >  void a_func (GdkWindow *window)
> >  {
> >    GdkGLWindow *glwindow = gdk_window_get_gl_window (window);
> >  }
> > ----------------------------------------------------------------
> >
> >gdk_window_set_gl_capability() creates new GdkGLWindow, then set it to
> >GdkWindow's qdata. GdkWindow supports OpenGL, and programmer can add
> >OpenGL-capability using set_gl_capability(). If GdkWindow is
> >OpenGL-capable, get_gl_window() returns GdkGLWindow. The same thing is
> >also provided for GdkPixmap and GdkGLPixmap.
> >
[snip]

Hi, Tristan. Thank you for your comments.

> 
>  > Programmer have to take care to keep a pair of window and glwindow, so
>  > GdkGLExt library provides gdk_window_*() extension functions which
>  > add OpenGL support to GdkWindow.
> 
> I dont understand why the application programmer should have to manage 2 
> GdkWindow's.
> Why not have a GdkGLWindow that derives from the GdkWindow and 
> implements the
> GdkWindow in an OpenGL fashion ?

1. I developed GdkGL* objects to be able to use with *EXISTING* code.
   If GdkGLWindow is a subclass of GdkWindow, we have to override
   realize method of existing widget classes. It means that OpenGL can
   be used only with widgets specialized for OpenGL.

2. I think it is hard to derive from GdkWindow. GdkWindow is not
   simple new(type, properties...) style GObject in contrast with
   GTK+ widgets. GdkWindow is not intended to be a base class. At
   least, deriving from GdkWindow is impossible in external library
   without duplicating gdkwindow-x11.c code - it will be a nightmare.
   (Owen, is it right? correct me if I'm wrong.)

So GdkGLWindow is not GdkWindow (but another GdkDrawable for
convenience. In current GdkGLWindow implementation, GdkWindow is a
delegate object for GDK drawing.), and simply follows GLX 1.3 API.

> 
> Could the same be done for a GdkGLGC ? (and a GdkGLConfig could be a 
> delagate
> of the derived GdkGLGC ?)

I don't understand. We cannot set colormap, foreground/background
color, fill style, and so on, to the OpenGL rendering context.
GdkGLContext is not GdkGC.

Regards,
--Naofumi

> 
> This way GdkGL could be integrated into Gdk without any extra mucking 
> around with
> numerous drawables and extention functions, There would be little or no 
> need for
> Gtk+ widgets to have a dependancy (if theese objects were implemented as 
> a seperate
> library which extends gdk), And an already existant gtk+ application 
> could become
> OpenGL driven after a little mucking around in the theeme engines 
> (styles and gtkrc's
> etc..).
> 
> basicly, if you want to know if your widget has OpenGL capability:
> 
> if (GDK_IS_GLWINDOW(widget->window)) {
>     /* I have a gl window */
> }
> 
> I have to admit, I only sifted through this code a little (just the 
> headers and a few examples)
> so maybe I missed something that makes this approach impossible but it 
> seems to me to be
> the most intuitive way.
> 
> Cheers,
>                                  -Tristan
> 
> PS.
>    I must of overshot the subject scope, maybe this mail should be
>                 "OpenGL in Gtk+ implementation RFC" ?
> 
> 
> 
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