Yearly Archives: 2006

Ekiga

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I’ve been testing out Ekiga recently, and so far the experience has been a bit hit and miss.

  • Firewall traversal has been unreliable. Some numbers (like the SIPPhone echo test) work great. In some cases, no traffic has gotten through (where both parties were behind Linux firewalls). In other cases, voice gets through in one direction but not the other. Robert Collins has some instructions on setting up siproxd which might solve all this though, so I’ll have to try that.
  • The default display for the main window is a URI entry box and a dial pad. It would make much more sense to display the user’s list of contacts here instead (which are currently in a separate window). I rarely enter phone numbers on my mobile phone, instead using the address book. I expect that most VoIP users would be the same, provided that using the address book is convenient.
  • Related to the previous point: the Ekiga.net registration service seems to know who is online and who is not. It would be nice if this information could be displayed next to the contacts.
  • Ekiga supports multiple sound cards. It was a simple matter of selecting “Logitech USB Headset” as the input and output device on the audio devices page of the preferences to get it to use my headset. Now I hear the ring on my desktop’s speakers, but can use the headset for calls.
  • It is cool that Ekiga supports video calls, but I have no video camera on my computer. Even though I disabled video support in the preferences, there is still a lot of knobs and whistles in the UI related to video.

Even though there are still a few warts, Ekiga shows a lot of promise. As more organisations provide SIP gateways become available (such as the UWA gateway), this software will become more important as a way of avoiding expensive phone charges as well as a way of talking to friends/colleagues.

Firefox Ligature Bug Followup

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Thought I’d post a followup on my previous post since it generated a bit of interest. First a quick summary:

  • It is not an Ubuntu Dapper specific bug. With the appropriate combination of fonts and pango versions, it will exhibit itself on other Pango-enabled Firefox builds (it was verified on the Fedora build too).
  • It is not a DejaVu bug, although it is one of the few fonts to exhibit the problem. The simple fact is that not many fonts provide ligature glyphs and include the required OpenType tables for them to be used.
  • It isn’t a Pango bug. The ligatures are handled correctly in normal GTK applications on Dapper. The bug only occurs with Pango >= 1.12, but that is because older versions did not make use of the OpenType tables in the “basic” shaper (used for latin scripts like english).
  • The bug only occurs in the Pango backend, but then the non-Pango renderer doesn’t even support ligatures. Furthermore, there are a number of languages that can’t be displayed correctly with the non-Pango renderer so it is not very appealing.

The firefox bug is only triggered in the slow, manual glyph positioning code path of the text renderer. This only gets invoked if you have non-default letter or word spacing (such as justified text). In this mode, the width of the normal glyph of the first character in the ligature seems to be used for positioning which results in the overlapping text.

It seems that the bug may be fixed in the Firefox 1.6 series, but if that fix can’t be backported easily in time for Dapper, it might be easier to switch to a different default font that doesn’t contain the ligatures (such as Bitstream Vera). That would certainly reduce the chance of the bug occurring.

Annoying Firefox Bug

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Ran into an annoying Firefox bug after upgrading to Ubuntu Dapper. It seems to affect rendering of ligatures.

At this point, I am not sure if it is an Ubuntu specific bug. The current conditions I know of to trigger the bug are:

  • Firefox 1.5 (I am using the 1.5.dfsg+1.5.0.1-1ubuntu10 package).
  • Pango rendering enabled (the default for Ubuntu).
  • The web page must use a font that contains ligatures and use those ligatures. Since the “DejaVu Sans” includes ligatures and is the default “sans serif” font in Dapper, this is true for a lot of websites.
  • The text must be justified (e.g. use the “text-align: justify” CSS rule).

If you view a site where these conditions are met with an affected Firefox build, you will see the bug: ligature glyphs will be used to render character sequences like “ffi“, but only the advance of the first character’s normal glyph is used before drawing the next glyph. This results in overlapping glyphs

It also results in a weird effect when selecting text, since the ligatures get broken appart if the selection begins or ends in the middle of the ligature, causing the text to jump around.

I wonder if this bug affects the Firefox packages in any other distributions, or is an Ubuntu only problem?

Re: Lazy loading

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Emmanuel: if you are using a language like Python, you can let the language keep track of your state machine for something like that:

def load_items(treeview, liststore, items):
    for obj in items:
        liststore.append((obj.get_foo(),
                          obj.get_bar(),
                          obj.get_baz()))
        yield True
    treeview.set_model(liststore)
    yield False

def lazy_load_items(treeview, liststore, items):
    gobject.idle_add(load_items(treeview, liststore, item).next)

Here, load_items() is a generator that will iterate over a sequence like [True, True, ..., True, False]. The next() method is used to get the next value from the iterator. When used as an idle function with this particular generator, it results in one item being added to the list store per idle call til we get to the end of the generator body where the “yield False” statement results in the idle function being removed.

For a lot of algorithms, this removes the need to design and debug a state machine equivalent. Of course, it is possible to do similar things in C but that’s even more obscure 🙂.

pygpgme 0.1 released

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Back in January I started working on a new Python wrapper for the GPGME library. I recently put out the first release:

http://cheeseshop.python.org/pypi/pygpgme/0.1

This library allows you to encrypt, decrypt, sign and verify messages in the OpenPGP format, using gpg as the backend. In general, it stays fairly close to the C API with the following changes:

  • Represent C structures as Python classes where appropriate (e.g. contexts, keys, etc). Operations on those data types are converted to methods.
  • The gpgme_data_t type is not exposed directly. Instead, any Python object that looks like a file object can be passed (including StringIO objects).
  • In cases where there are gpgme_op_XXXX() and gpgme_op_XXXX_result() function pairs, these have been replaced by a single gpgme.Context.XXXX() method. Errors are returned in the exception where appropriate.
  • No explicit memory management. As expected for a Python module, memory management is automatic.

The module also releases the global interpreter lock over calls that fork gpg subprocesses. This should make the module multithread friendly.

This code is being used inside Launchpad to verify incoming email and help manage users’ PGP public keys.

In other news, gnome-gpg 0.4 made it into dapper, so users of the next Ubuntu release can see the improvements.