Support for pinch events

[almarklein]

Experimental PR to look into pinch events. See #509

Status

Seems it can be made to work for Qt. Likely also for jupyter. Not (for now) on glfw. Also quite some work to do in pygfx. Looked into it, and made this PR to save what I found.

Tasks

• Implement for Qt.
• Implement for wx?
• Implement for glfw. Looks like we can't. Need a way to do pinch-to-zoom glfw/glfw#90
  • This is sad, because it makes code that uses pinch less portable.
• Implement for jupyter_rfb.
• Add modifiers and buttons to the event?
• Add x and y to the event so it can be scoped to a viewport in pygfx?
• In pygfx add support for pinch events.
• Support pinch events in pygfx controllers.

[Korijn]

In my experience, at least on the web, instead of working with these high level gesture events and abstractions, you just work with pointer events and use the pointer IDs to discern the fingers.

[almarklein]

Yes, that moves some of the complexity to the application level, but it is more flexible. So an alternative approach would be to make Qt work for multi-touch events. The event spec already supports multi-touch events btw.