Carlos Garcia Campos

The initial plan for this week was continue working on kinetic scrolling support for GtkScrolledWindow, however I decided to take a look at the other bugs to give some more time to get review/feedback of the kinetic scrolling work in progress patch.

GtkWidget::press-and-hold signal

This looked easier, since it already had a working patch attached to to the bug. I started porting the patch to GTK+ 3 to make it work with current git master. The signal is quite simple, it’s emitted when the mouse button is pressed for a given amount of time. If the mouse pointer is moved (beyond the drag threshold) during the long-press, the operation is cancelled. The tricky part is the animation that should be shown during the long-press to provide visual feedback to the user that something is going to happen when the mouse button is released. The patch, based on hildon code, implemented the animation by changing the current mouse cursor to an animated one. I didn’t like this approach. Talking with Carlos, he suggested to use a transparent popup window with a custom animation similar to the one implemented in the locate pointer plugin of gnome-settings-daemon. I thought we could even leave the animation to the theme engine and implement a popup window that simply calls gtk_render_activity(). So I wrote a new patch that uses the spinner style class to render the animation just to show how it would work. If we agree on this approach we’ll add a new style class and implement a custom animation in the theme engine so that it could be override by themes.

GtkLiveSearch

This is a widget already used by empathy, based on hildon code too, to show a search entry when typing on a given widget. It provides both, the UI to show the search entry, and a match function that implements the search algorithm. I think they are actually two different things. The widget that connects to key-press signal on a hook-widget to show an entry is implemented in other places like GtkTreeView, and even for other purposes than searching like the goto window used by evince to jump to a random page in presentation mode. The search algorithm might be used by other applications that use another UI like a find bar or a dialog.

GtkScrolledWindow

When kinetic scrolling mode is enabled, the scrollbars don’t make sense anymore as a control since the whole view is a scrolling control, however they still make sense as an indicator. HildonPannableArea has its own scrollbars, smaller and without stepper buttons, that are shown when scrolling starts and dissapear (with a fade animation) after a while when the scrolling operation has finished. Playing with the GTK+ theme I realized that we don’t need to implement our own scrollbars, we can just use a custom css to get something similar to the HildonPannableArea scrollbars. The only thing we would need is a way to show/hide the scrollbars that might be just a GtkScrolledWindow style property so that everything depends on the theme.

First of all, thank you very much to all the people who gave me so useful feedback after my previous post.

The idea for this week was to start integrating the HildonPanneableArea code into GtkScrolledWindow, however both Chris and Karl emailed me suggesting to use a time based approach rather than the one used by hildon. Chris pointed me to MxKineticScrollView, which is the evolution of HildonPanneableArea. The code is much easier and cleaner than the hildon one, so I decided to use it instead.

One of the things that caught my attention was that MxKineticScrollView doesn’t need to synthesize events. This is because clutter implements capture and bubble event handling. GTK+ does always bubble so that events are propagated from child to parent. Having support for capture event handling makes the kinetic scrolling implementation easier and simpler, so following the same approach than clutter, I wrote an initial patch to add GtkWidget::captured-event signal.

Using the new captured-event signal, integrate the MxKineticScrollView code into GtkScrolledWindow was a bit easier. I still had to use an input-only event window, and grab the device on button press to make sure that motion and button release events were received on the scrolled window. It’s still far from finished but I have already published a work in progress patch and a new test to try it out.

During the next week I plan to continue working on kinetic scrolling, fixing issues and completing the implementation with the missing features.

One of the main goals of the project is to improve the mobile experience in GTK+ by contribution upstream rather than creating another library. The Hildon library contains several widgets and features that could be ported or integrated into GTK+: HildonLiveSearch, HildonPannableArea, GtkEntry:hint-text property, GtkWidget::tap-and-hold signal.

HildonPannableArea

This is a scrollable widget, similar to GtkScrolledWindow, that allows the user to tap on any part of the widget and drag it. It also implements kinetic scrolling which is a feature currently present in most of the mobile platforms.

During this week I have focused on HildonPannableArea, trying to understand the code (there are several tricky parts) and thinking about how it could be integrated into GtkScrolledWindow. My initial idea was to port HildonPannableArea as a standalone widget deriving from GtkScrolledWindow, but there are use cases where switching between normal and touch mode makes sense, like with laptops that can work as tablets as Bastien pointed out. So, the idea is to integrate HildonPannableArea code into GtkScrolledWindow to add a kinetic mode. I started porting HildonPannableArea to GTK+3 and cleaning up the code a bit to make the integration easier. Next week I’ll focus on the real integration.