Re: OpenGL, GtkGlArea, GtkGLExt

[Emmanuele Bassi <ebassi gmail com>]

On Tue, 2008-03-04 at 19:37 +0000, Jon Harrop 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.

it may have many users, but it's unmaintained, so it is ipso facto
"dead".

> > 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.

on the bug linked in the thread, and in many gtk+ developers team
meetings it was reached a consensus for an integration towards a
cairo-style approach: inside the ::expose-event handlers you can
retrieve a GL context, draw on it using the GL API and the result will
be rendered on the widget's window.

that's what "we" means.

> 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.

you can't really get much simpler than a:

  GLXContext gl_context;

  gl_context = gdk_glx_create_context (GDK_DRAWABLE (widget->window));

or, since it should be portable across various backends:

static gboolean
widget_expose (GtkWidget      *widget,
               GdkExposeEvent *event)
{
  GdkGLContext *gl_context;

  /* creates or returns the (backend-dependent) GL context, which is
   * made current to the widget's GdkWindow - for instance, on GLX it
   * will create a context if not already present, and will call
   * glXMakeCurrent() for the display and window.
   */
  gl_context = gdk_gl_create_context (GDK_DRAWABLE (widget->window));

  /* ... draw using GL API ... */

  /* retrieve the platform-dependent implementation for mad crack */
  GLXContext glx_context = GDK_GLX_CONTEXT (gl_context);

  /* waits for vblank, calls glXSwapBuffers(), and unrefs the
   * GdkGLContext - but it does not destroy it.
   */
  g_object_unref (gl_context);
}

ciao,
 Emmanuele.

-- 
Emmanuele Bassi,
W: http://www.emmanuelebassi.net
B: http://log.emmanuelebassi.net