Re: OpenGL, GtkGlArea, GtkGLExt

[Carlos Pereira <jose carlos pereira ist utl pt>]

Jon Harrop wrote:
> On Tuesday 04 March 2008 18:14:39 Behdad Esfahbod wrote:
>   
> > On Tue, 2008-03-04 at 17:04 +0000, Carlos Pereira wrote:
> >     
> > > 2) change the name, for example to Gtkglarea 2.0*, the legitimate
> > > sucessor to Gtkglarea 1 (the last version of Gtkglarea that I downloaded
> > > last week is 1.99 and still comes with gtk_signal_connect and other Gtk
> > > 1.2* functions deprecated long ago)
> > >       
> > No, gtkglarea is dead.
> >     
>
> GlArea still has many users and is the defacto standard for some languages.
>
>   
> > We don't want a new widget.  We want being able 
> > to render to widgets using OpenGL as an alternative to using cairo.
> > That is, the GtkGlExt approach.
> >     
>
> I'm not sure who you are referring to as "we" but many people need little 
> beyond GlArea. I have no desire to create Gtk-compatible widgets. I only want 
> to render general graphics quickly and easily using OpenGL.
>
>   
> > > I believe this would make Gtk more appealing, particularly for
> > > scientific/engineering/architecture applications.
> > > Carlos
> > >       
>
> I am a scientist writing software for scientists and engineers using Gtk from 
> OCaml via the LablGTK2 bindings. There are OCaml bindings for GlArea but not 
> GlExt because GlExt is considered too complicated to be worth binding.
>
> If anyone is interested in improving the situation for scientists and 
> engineers then I would recommend taking this into account: keep it simple to 
> bind.
>
>   
Hi,
I just ported my app (more than 200,000 lines, totally independent and 
unlimited number of OpenGL areas, sharing pre-compiled OpenGL lists, 
etc.) last night from Gtkglarea to Gtkglext, so I am in a good position 
to highlight the differences, from the user's point of view. What 
follows is a manual of everything I had to change (I assume GTK 2.0 is 
used, for example g_signal_connect instead of gtk_signal_connect):

1) in headers, replace this:
#include <gtkgl/gtkglarea.h>

by this:
#include <gtk/gtkgl.h>

2) in makefiles, replace this:
-lgtkgl

by this:
-lgtkglext-x11-1.0

3) in makefiles, replace this (distribution-dependent, Fedora 8 here):
-I/usr/include/gtkgl-2.0
by this:
-I/usr/include/gtkglext-1.0 -I/usr/lib64/gtkglext-1.0/include

4) in drawing code, replace this:
if (gtk_gl_area_make_current (GTK_GL_AREA (area)))
 {
 /* OpenGL here */
 }
by these:
GdkGLDrawable *gldrawable = gtk_widget_get_gl_drawable (area);
GdkGLContext *glcontext = gtk_widget_get_gl_context (area);
if (gdk_gl_drawable_gl_begin (gldrawable, glcontext))
 {
 /* OpenGL here */
 gdk_gl_drawable_gl_end (gldrawable);
 }

5) in starting code, replace this:
gdk_gl_query();

by this:
gtk_gl_init (&argc, &argv);
GdkGLContext *glcontext = NULL;
GdkGLDrawable *gldrawable = NULL;

6) in creating area code, replace this:
GtkWidget *area;
int attribute[] = { GDK_GL_RGBA, GDK_GL_DOUBLEBUFFER, GDK_GL_DEPTH_SIZE, 
1, GDK_GL_NONE };
area = gtk_gl_area_share_new (attribute, (GtkGLArea *) area);

by this:
GtkWidget *area;
if (glconfig == NULL)
 {
 glconfig = gdk_gl_config_new_by_mode (GDK_GL_MODE_RGB | 
GDK_GL_MODE_DEPTH | GDK_GL_MODE_DOUBLE);
 if (glconfig == NULL)
   {
   glconfig = gdk_gl_config_new_by_mode (GDK_GL_MODE_RGB | 
GDK_GL_MODE_DEPTH);
   if (glconfig == NULL) exit (1);
   }
 }
area = gtk_drawing_area_new ();
gtk_widget_set_gl_capability (area, glconfig, glcontext, TRUE, 
GDK_GL_RGBA_TYPE);

7) Initially, both glconfig and glcontext point to NULL. BEFORE the 
first drawing area is created, glconfig is obtained, with a double- or 
single-buffer, and used for all drawing areas. AFTER the first drawing 
area is realized (shown), glcontext must be obtained, and reused for all 
the other drawing areas, with this command (when creating the first 
area, glcontext is NULL):

glcontext = gtk_widget_get_gl_context (area);

Usually, throughout the application, there is ONE glconfig and ONE 
glcontext, even if there are unlimited, independent, OpenGL areas. 
OpenGL pre-compiled lists are shared only if glcontext is the same. 
Conceivably, users could have some areas sharing some lists (with one 
glcontext) and other areas sharing other lists, (with a different 
glcontext), but this not usual. Conceivably, users could also create 
areas with different capabilities, for example with or without depth 
buffer, using different glconfigs, but this is not usual.

This is ALL that is needed, to port applications from Gtkglarea to Gtkglext!

Gtkglext looks slightly more lower level and flexible than Gtkglarea, 
closer to the (X) metal as they say, but for users differences are small 
indeed...
Carlos