Description
Is your feature request related to a problem? Please describe.
As a laptop user, I use the trackpad (touchpad) 99% of the time as macOS makes it very easy to work with its many gestures. As a touch-input device, it feels very natural to pinch to zoom in and out of a photo, especially since we're so used to it by using smartphones for more than 15 years now. Weirdly, darktable does not support it, so its behaviour feels very mouse-only-oriented. With a mouse, scrolling over a photo is the best solution for zooming in and out but that should not carry over for touch pads, too.
New users should learn darktable's workflow and tools and not how basic behaviour is different for this software. For me, this is bad UX design and supporting this feature would be beneficial to new (and existing) users.
Describe the solution you'd like
Pinch to zoom in and out of a photo should work on a touchpad.