Establishing GTK3 port "rules" (and some q.s)

[Andrzej]

On 20/02/15 15:10, ikey wrote:
> So, that thread hit reddit. Time to make rules clear on how I'll
> approach this port.. Or rather to clarify my position :)
>
> This will be a *like-for-like* port. This does not mean taking a
> look at GTK3 and saying "oo shiny" and using things *just because*.
> So that means no patch introduced by this initiative will seek to
> introduce CSDs or redesigns to apps. That's the domain of the XFCE
> project only.

That is a good direction. Big questions are:

1. Do we support Gtk2 in the same codebase? Currently some libraries 
allow that (e.g. libxfce4-panel) but this is rather limiting and 
difficult to maintain.

2. Do we want to be able to distribute&install Xfce4 and Xfce5 
simultaneously? IMHO this should be possible so that we don't force 
users down the "Gnome2->Mate" path, in case if users ended up being 
dissatisfied with the port.
I would recommend bumping major revisions, SONAMEs, and renaming at 
least core components (xfce4-panel->xfce5-panel). If someone wants to 
maintain and distribute Xfce4 that should be possible without massive a 
renaming effort (like the Gnome2->Mate one).

> 2) One whacking great deprecation I can't mentally avoid, so will now
> mention.. GtkImageMenuItem. That fella is gone. What do we want to do
> about this? (Alternatives include just dropping images in menu items
> or forking it into libxfce4ui)

Talking about my own experience with porting the panel 
(andrzejr/wrapper3 branch[1]), there were some performance issues with 
GtkImageMenuItem's (CPU use, flicker), but that could have been due to 
issues in our code. Otherwise, GtkImageMenuItem may be deprecated but 
Gtk devs promise not to remove any APIs during Gtk3 development cycle so 
I have no problem with using it.

> 3) Ok more than a couple. :) GTK_STOCK* usage is also deprecated some
> time now, so I may have to harass you all on IRC about which icon names
> to use. Basically named icons are used everywhere now. :)

This seems OK with me, assuming we can make this change transparent to 
users (i.e. icons are still working).

I found that the difficult and/or annoying bits fall into following 
categories:
- switch to Cairo drawing and associated change in coordinates 
calculation (some changes were non-trivial)
- different treatment of widget backgrounds, especially with 
GtkPlug/GtkSocket
- dropped support for some X11 specific Gdk functions - parts of systray 
had to be ported to plain Xlib.
- theming stuff, it is just different and occasionally new mechanism 
does not provide functionality available before.
- countless minor API changes ("because we can") - this may look like 
just an annoyance but it makes writing and maintaining Gtk2&3 compatible 
code difficult.

Overall, porting was fairly easy but there were many little changes and 
occasional roadblocks. Some of the problems (performance, background, 
context menu positioning) were not solved, which was the main reason we 
postponed gtk3 port of the panel until the next release.

[1] http://git.xfce.org/xfce/xfce4-panel/log/?h=andrzejr/wrapper3
Unfortunately, it is not up to date with the current master branch.

Thanks,
Andrzej