How to add a session type button to lightdm-webkit-greeter theme?

Question

I'm experimenting with the webkit greeter for lightdm. Ubuntu 13.10 64 bits. I want to learn to create my own themes. I noticed that the default theme does not show a language select button or a session type select button. With the unity-greeter I can choose to start Unity or Gnome 3. Recently I started to prefer Gnome 3, that means that the webkit greeter is unusable to me right now as I'm forced to start with Unity when I want Gnome 3.

Is It possible to add a session type button to a webkit-greeter theme? How? Must I edit the default theme files to show the button?

Answer 1

If you look at lightdm-webkit-greeter.c in the source code, there are all sorts of interesting values we can get at from webkit. For a quick and dirty method to add a session selection dropdown to the default theme I did the following (this could definitely be expanded and improved upon):

In the default index.html, right above the line that writes the user list to the greeter:

document.write('<table id="user_table" style="margin: auto;">');

I added some code to write out the session selector:

document.write('<select id="session_list">');
for (i in lightdm.sessions)
{
  session = lightdm.sessions[i];
  if (session.key == lightdm.default_session)
    document.write('<option selected="selected" value="' + session.key + '">' + session.name + '</option>');
  else
    document.write('<option value="' + session.key + '">' + session.name + '</option>');
}
document.write('</select>');

The value attributes aren't really necessary in this code, I was going to use them to select the session, but decided to use the index instead. The other change is to the authentication_complete() function. In the default code we have:

if (lightdm.is_authenticated)
  lightdm.login (lightdm.authentication_user, lightdm.default_session);

So it always uses the default_session key. We want to instead use the selected session, so we can do something like:

if (lightdm.is_authenticated)
{
  session_list = document.getElementById('session_list');
  session = lightdm.sessions[session_list.selectedIndex];
  lightdm.login (lightdm.authentication_user, session.key);
}