Re: Dealing with GTK 3.3.18 scrolling handling changes for GNOME 3.4

[Matthias Clasen <matthias clasen gmail com>]

On Wed, Mar 14, 2012 at 2:17 PM, Sebastien Bacher <seb128 ubuntu com> wrote:
> Hi everyone,
>
> GTK 3.3.18 and smooth scrolling landing created quite some issues which
> seems to have been mostly unnoticed, unaddressed so far, since the hard
> freeze for GNOME 3.4 is next week I'm bringing the topic there.
>
> Some of the details there might be wrong and I'm happy to be corrected, it's
> just my understanding of the changes
>
> * widgets need to opt-in for scroll events (GDK_SCROLL_MASK), that makes
> scrolling stop working in applications using custom widgets
> (example:
> http://git.gnome.org/browse/nautilus/commit/?id=04116ab2876412445c788091be07d7f7321a4a94)
>
> * if you are on xserver 1.12 with xinput 2.2 your application stop receiving
> GDK_SCROLL_DOWN and GDK_SCROLL_UP events, but receive GDK_SCROLL_SMOOTH with
> an increment instead
>
> that change seems to create quite some issue, it breaks for example mouse
> wheel scrolling over sound sliders in the control center, or scrolling in
> nautilus compact view
>
> Grepping around in my work tree I see there are quite a lot of GNOME
> components using GDK_SCROLL_UP,DOWN, I guess those will stop working as they
> should.
> Nautilus fixed a such issue in
> http://git.gnome.org/browse/nautilus/commit/?id=1a76e044a2c9b834d00c4ea30f1e3af3321d8cdd
> It's likely that other applications will need to add extra cases to handle
> the new way
>
> I think that's an issue we should look at addressing before 3.4, either by
> doing some "compat" work in GTK (i.e keep emiting the scroll up down events
> as well as the smooth ones if possible) or by patching the applications, the
> rdepends list is likely not trivial though...
>
> Thoughts?

Thanks for bringing these up. I'm sure there will be some more fallout
from the xi2 changes. I don't know if we'll be able to have perfectly
seamless compatibility in the scroll event case, there are some
complications that make that hard. Unfortunately, I have no time at
all this week to dive into this; so any help in diagnosing and coming
up with fixes will be appreciated. You could also ask Carlos if he has
time to look.

Matthias