Archive for the ‘gtk+’ Category

Statuses

Improvements for visually impaired people

In Bluefish,Gnome,gtk+,open source,Programming on April 29, 2012 by oli4444

Last week I received an email if Bluefish could be improved for people with a visual impairment. I never occurred to me that there would be people with limited vision wanting to use Bluefish. The most requested features in the email were:

  1. Zoom in/out with ctrl+ / ctrl-
  2. Maximum screen estate
  3. Better cursor visibility

The first feature was easy. Bluefish  already has zoom with ctrl-mousewheel, so I added the accelerators (it turned out that the requester was not aware of this feature).

For the second feature I created an option that automatically hides all menu bars, status bars and toolbars on fullscreen (F11). It displays them again if you hit F11 again. This way basically every bit of the screen is used by the editor itself. The only issue I found is when LXDE is used. LXDE has bound F11 to the window-manager fullscreen, so the application fullscreen never gets called. I moved my code to the configure event handler, where I can detect both the internal fullscreen as well as a window manager fullscreen.

The third feature was the hardest bit. With some help from IRC I managed to make the cursor-aspect-ratio user defined.

In gtk2 it looks like this:

style "bluefish-cursor" {GtkWidget::cursor-aspect-ratio = %f }
class "GtkTextView" style "bluefish-cursor"

which is loaded with gtk_rc_parse_string()

In gtk3it is slightly nicer:

GtkTextView {-GtkWidget-cursor-aspect-ratio: %f;}

which is loaded with gtk_css_provider_load_from_data() and gtk_style_context_add_provider()

Next to a bigger cursor I made a setting to highlight the cursor position: it paints a differently coloured background on the character left and right of the cursor. I connected that to the mark-set insert-text and delete-range signals, the last two with g_signal_connect_after() to get the new location of the cursor and not the old location.

This code does have quite a performance impact: scrolling with the arrow keys is significantly slower with this option enabled. I used this code:

     gtk_text_buffer_get_bounds(btv->buffer, &it1, &it2);
     gtk_text_buffer_remove_tag(btv->buffer, btv->cursortag, &it1, &it2);
     it1 = *location;
     it2 = it1;
     gtk_text_iter_backward_char(&it1);
     gtk_text_iter_forward_char(&it2);
     gtk_text_buffer_apply_tag(btv->buffer, btv->cursortag, &it1, &it2);

What this code causes is an update the internal structure of the GtkTextBuffer (probably something like a balanced tree) that keeps track where each tag starts and stops – for every cursor move. After rethinking this I remembered this is much easier done in the expose event!

get the coordinates with gtk_text_view_get_iter_location(), convert them with gtk_text_view_buffer_to_window_coords() and paint with cairo_rectangle() and cairo_fill():

   gtk_text_buffer_get_iter_at_mark(buffer, &it, gtk_text_buffer_get_insert(buffer));
   gtk_text_view_get_iter_location(view,&it,&itrect);
   gtk_text_view_buffer_to_window_coords(view, GTK_TEXT_WINDOW_TEXT
            , itrect.x, itrect.y, &x2, &y2);
   cairo_rectangle(cr, (gfloat)x2-width, (gfloat)y2, (gfloat)(width*2 )
            , (gfloat)itrect.height);
   cairo_fill(cr);

The result is visible below. So now it is test time!

Statuses

Debugging a reference count bug

In Bluefish,gtk+,open source,Programming,Ubuntu on February 5, 2012 by oli4444 Tagged:

Last days I have been debugging some weird reports. They all show the same characteristics:

  • the users are on Ubuntu 11.10
  • they use bluefish compiled against gtk 3.2 (so not the bluefish package that is provided by Ubuntu, but a newer one)
  • in the Bluefish run the sort function of a GtkTreeModelSort is called after the GtkTreeModelSort should have been finalized and free’ed.

First I used gobject-list.c from http://people.gnome.org/~mortenw/gobject-list.c to see all refs and unrefs on all GtkTreeModelSort objects in Bluefish (luckily there is only 1 used in Bluefish).This showed that there was indeed a GtkTreeModelSort with lots of references left after it should have been finalized. I tried the same thing on Fedora 16 (also gtk-3.2), but it can only be reproduced on Ubuntu 11.10.I tried to get backtraces with gobject-list (which uses libunwind for that) but those backtraces turned out to be useless.

Luckily I received some help on IRC #gtk+ from Company and alex. The first idea was to use systemtap, but since there is no useful kernel for systemtap available for Ubuntu I had to use something more low tech suggested by Company:  I set a breakpoint on gtk_tree_model_sort_new to retrieve the pointer of the GtkTreeModelSort. Once I got that pointer I could set a breakpoint on g_object_ref and g_object_unref with a condition on this pointer. Then I created an automatic backtrace on each breakpoint:

break g_object_ref if object == 0x123123123
commands
bt
c
end

I configured gdb to log everrything to a file, and did a bluefish run. This resulted in a 2.1 Mb logfile with backtraces. This log also showed there were more refs than unrefs.

In this logfile there were a lot of similar backtraces, with an identical function doing a ref and an unref. I wrote a short python script to parse the backtraces and skip all ‘valid pairs’

After this step I had only 15 backtraces left. And from these backtraces the leaking references were easily identified.

Because I was unsure if this is a Ubuntu specific bug or a generic gtk bug the resulting bugreport can be found both at https://bugzilla.gnome.org/show_bug.cgi?id=669376 and at https://bugs.launchpad.net/bugs/926889

Now I am wondering if this approach would work for any reference count leaking problem. I guess the most difficult issue is to find the value of the pointer that is leaking if you have many objects of the same type.. Any suggestions how to do this?