Multi-touch gestures for zoom/scroll/rotate

[brentyi]

Hi!

Not sure if this project is still being maintained, but here's a basic+noninvasive implementation of gesture-based zoom/scroll/rotate operations that I've been using. Currently only enabled for the Freehand mode.

#427

[ChengduLittleA]

hummm interesting... will it break anything?

[brentyi]

I haven't had any issues; the main caveat is that the current gesture implementation isn't compatible with modes that inherit from DragMode. There's probably a simple fix for that, but I don't know Gtk or the mypaint code well enough to say for sure. 🤷

[odysseywestra]

Okay Appveyor is rebuilding the windows builds so you should be able to test it on windows too. Had a dependency issue that needed to be resolved.

[brentyi]

Thanks @odysseywestra!

Not sure if/when I'll have time to revisit this, but some notes/updates for posterity:

• I tested this in Windows, and the gesture itself works. But there's a minor issue where a click event (and thus a "dot" of paint) can be triggered at the end of the gesture.
• I'd like to get gestures working for the "drag" modes, but there seems to be a fundamental incompatibility with the pointer grabs. I can get things working perfectly by commenting out the pointer_grab() and pointer_ungrab() calls, but it's not clear to me what that might break. Pointer grabs have been deprecated for a long time anyways, so maybe if this code is updated with current practices getting gestures working robustly will be much easier.
• The current way my changes are set up, where the gesture events are attached/detached in the interaction mode enter/leave methods, doesn't make much sense when multiple interaction modes are stacked. But keeping things this way because pointer grabs from any of the DragMode subclasses break gesture events even after the pointer is ungrabbed; if the pointer grabs can be removed the gesture event handling can likely follow the same pattern as the scroll events.