Re: Minutes of the GTK+ Team Meeting - 2009-11-27

[alex <acastro igalia com>]

On Tue, Nov 24, 2009 at 10:13:20PM +0000, Emmanuele Bassi wrote:
>
> [...]
>
> 4. Implement finger and kinetic scrolling [jjardon]
> - Midori has a finger/kinetic scrolled window implementation
> - Hildon has one as well
> - OpenMoko had one
> - would it make sense to port the feature to GtkScrolledWindow when
>   :gtk-touchscreen-mode is set to TRUE?
> - issue: event delivery to children requires subclassing to override
>   current default behaviour of gtk+ widgets
>

Hi,

some comments about the hildon kinetic scrolling widget
(HildonPannableArea [1]), it was implemented using moko finger
scroll, the solution was improved so basically we could consider
both options the same one, some of the changes:
   - added API (jump-to, scroll-to)
   - changed children detection
   - added gesture signals
   - changed the structure of the composition
   - overshooting
   - added more events handlers
   - added the auto-mode
   - reviewed kinetics (very adapted to the N900)
   - etc.

Basically it has a GdkWindow and it captures and later uses or
reinjects the events to the proper children. Before that we did the
test of implementing it as a modification of gtkscrolledwindow with
signals, it was restricted to direct children, not an option for
hildon. We decided to use the gdkwindow+reinjection solution but it
created a very different code so we decided to create a new widget
instead of adding the code. I agree with Kris about adding a new
widget if we do not implement a new support to the event handling that
removes all the gdkwindow/event hadler/signals.

The main issues now:
   - Selection/dragging vs scrolling (touchscreen mode?, more complex
   widgets or subclassing)
   - Animations with timeouts in gtk are not that good (check Owen posts about
   that), this is something to discuss about the library
   - Embedding finger scroll widgets inside each other?
   - Double events in the callbacks, original and reinjection if
   widgets do not deal with them.

I do not think this solution is a clean option, we should add clean
support for this event handling, maybe using top-down widget detection
in csw or adding new specific gdk event or something like that. We
could check how to do that.

Anyway, not sure if we should think about a touchscreen mode in
the library, not just in the widget if we want to add this kind of
features. Or if this should stay in a mobile/touchscreen specific fork
(hildon/gtk) at least if we do not find any good option to include the
code, was there any debate about this?

I hope it helps.

[1] http://maemo.gitorious.org/hildon/hildon/blobs/master/hildon/hildon-pannable-area.c