I've been searching for a little while to investigate whether or not our Gtk+ 3 application (Gtk#, actually, but bound to Gtk+ 3) will be easily convertible to receive touch events rather than mouse clicks. This is pure investigation at the moment since I don't actually have a touch screen yet (that's also the reason why I can't easily test my theories).
As far as I can tell, the Gnome 3 can indeed do this and the documentation that seems relevant is the gesture stuff, found here.
I've not been able to find any sample Gtk+ code so I'm hoping it's a simple matter of instantiating one of the gesture classes and simply setting it up to deliver events to the main event loop.
Is there anyone with experience with Gtk gestures that can guide me in a simple example? Let's say I have a DrawableArea and I want to receive a very simple, single-touch event that gives me an event with the point within the area that was touched.
Once I have that, I should be able to build on it to handle swipes, pinches and so on.
You cannot inject pointer events as touch events: they are fundamentally different, and they interact with the gesture recognition state machine that lives inside GTK.
GTK has the ability (for debugging purposes) to emulate touch events via pointer, though obviously it cannot emulate multi-touch events because a pointing device only has one event sequence. If you have a recent version of GTK 3.x, you can use the GTK_TEST_TOUCHSCREEN environment variable set to a non-zero value.
If you want to know how to use GtkGesture implementations in your own widgets, then I suggest you look at the GtkGesture API reference, and look at the various types of gestures available, like GtkGestureSwipe or GtkGestureZoom. You're supposed to add GtkGesture instances to your widget when constructing it, and then catch the signals on the specific gesture when they are recognised.