Design Work for Gesture-based Input from Touchscreens and Touchpads in Plasma / Applications

Touchscreen gestures in Wayland will need to be implemented to provide user experience on par with that of other DEs and OSs. Keeping with KDE's principles, the default setup should be simple and intuitive, but the customization level should be high. For this reason, touchscreen and touchpad gestures should be identical by default, but can and should be distinguishable if the user wants to.

Keep in mid that here we are talking about "simple" gestures (swipe, pinch, rotate...), not "drawn" gestures (symbols, letters) which anyway are partially already implemented (although they do not seem to work at the moment).

For inspiration, the currently working Linux implementations of custom gesture software are:

libinput-gestures (libinput only, https://github.com/bulletmark/libinput-gestures)
touchegg (synaptics only, https://github.com/JoseExposito/touchegg)

Libinput (https://wayland.freedesktop.org/libinput/doc/latest/gestures.html), which is going to be used by Wayland, currently supports pinch and swipe with 2<=fingers<=4 (swipes with 2 fingers are usually reserved for scrolling). Atop of these gestures, additional possible gestures could be (as implemented by other OSs):

5 finger gestures (?)
4 finger tap (1,2,3 finger taps are already implemented)
swipes from outside border (Sailfish OS - like, VERY useful!)
rotation
Multifinger tap
Single finger edge drag
Press and hold

Another possibility is to combine gestures, e.g.: three finger tap, followed by three finger hold, three finger hold + tap. These are implemented by others (Unity, Gnome)

These are the default actions in other systems:

MacOSX: http://www.danrodney.com/mac/multitouch.html
Windows: http://windows.microsoft.com/en-us/windows-10/touchpad-gestures-for-windows-10
Unity: https://wiki.ubuntu.com/Multitouch
Gnome: https://wiki.gnome.org/Design/OS/Gestures

By default, Plasma should be able to assign gestures to Plasma commands (change desktop, present windows, Krunner, close windows...) and custom commands/scripts. Shortcut customization based on application is also an important option (either based on the application under the mouse - better - or the active application).

Below are proposals for default Plasma gestures and application gestures, not considering:

5 finger gestures
4-5 finger taps
"from outside" gestures

Note left/right may need to be switched if one does not want natural scrolling-like behaviour.

Default Gestures for Plasma

Fingers	Direction	Gesture	Action	Screen/Pad/Both?
2	Pinch	Out		Both
2	Pinch	In		Both
3	Pinch	Out		Both
3	Pinch	In		Both
3	Swipe	Left		Both
3	Swipe	Down		Both
3	Swipe	Right		Both
3	Swipe	Up		Both
4	Pinch	Out	Desktop grid	Both
4	Pinch	In	Show desktop	Both
4	Swipe	Left	Next window (continuous window switcher, like keeping Alt pressed)	Both
4	Swipe	Down	Close window	Both
4	Swipe	Right	Previous window (continuous window switcher, like keeping Alt pressed)	Both
4	Swipe	Up	Present windows	Both

Default Gestures for (Kirigami) Desktop Applications

Fingers	Direction	Gesture	Action	Screen/Pad/Both?
2	Pinch	Out	Continuous zoom out	Both
2	Pinch	In	Continuous zoom in	Both
3	Pinch	Out		Both
3	Pinch	In		Both
3	Swipe	Left	Next tab/page/image	Both
3	Swipe	Down	Close tab	Both
3	Swipe	Right	Previous tab/page/image	Both
3	Swipe	Up	New tab	Both
4	Pinch	Out		Both
4	Pinch	In		Both
4	Swipe	Left		Both
4	Swipe	Down		Both
4	Swipe	Right		Both
4	Swipe	Up		Both