GTK+2 vs. GTK+3 signal "expose/draw/render" events

Question

I recently asked some questions here and here concerning a program I am working on and that offers a visualization interface for molecules, atomic systems ... as mentioned in these previous messages I do have 3 different versions of my program:

• (a) GTK2 + GtkGlext : works great !
• (b) GTK3 + X11 : works just fine !
• (c) GTK3 + GtkGLArea : does not work :-(

While I am still working on (c), some things came up while I was trying to find out the origin of some behavior differences between (a) and (b). The OpenGL rendering is significantly slower in (b) than in (a), or I thought that was the case. If you check this link you will see that I got some help and manage to find out that GTK+ signals were not handled in the same way between GTK+2 (a) and GTK+3 (b), and (c) even if I only got a black screen in that case (but that is another issue), here is how I prepare(d) the GtkWidget(s) and the corresponding signals, note that I only present hereafter the GTK+ related commands:

• (a)

  GtkWidget * drawing_area = gtk_drawing_area_new ();
  g_signal_connect (G_OBJECT (drawing_area), "expose-event", G_CALLBACK (on_expose), data);
  

• (b)

  GtkWidget * drawing_area = gtk_drawing_area_new ();
  g_signal_connect (G_OBJECT (drawing_area), "draw", G_CALLBACK(on_expose), data);
  

• (c)

  GtkWidget * drawing_area = gtk_gl_area_new ();
  g_signal_connect (G_OBJECT (drawing_area), "render", G_CALLBACK(on_expose), data);
  

Using the tool Apitrace I noticed in case (a) that each OpenGL frame was drawn once, while it was drawn 5 times in cases (b) and (c). Then just adding a basic counter in the callback I confirmed that for each "expose/draw/render" the signal was emitted (and thus the "drawing-area" was rendered that many times, for the same frame):

• (a) : once
• (b) : 5 times
• (c) : 5 times

(a) is GTK+2, (b) and (c) are GTK+3 ... now my question will be rather obvious, but how can I changed or maybe should I say correct the GTK+3 version of my program to make it as smooth, on an OpenGL rendering point of view, as the GTK+2 version, or if you prefer to have signal emitted only once with GTK+3 instead of 5 times ?

Thanks in advance !

Answer 1

Answering my own question, hopefully to help someone to avoid the same mistake I did.

To re-draw my OpenGL window I was using:

void update (GtkWidget * plot)
{
  gtk_widget_hide (plot);
  gtw_widget_show (plot);
}

Instead I should have been using:

gtk_widget_queue_draw (plot);

All problems solved !