Pinch to zoom

[alterae]

When using a trackpad, it would be nice to have the ability to zoom in and out with a pinch gesture, like in many other programs.
No clue how easy or hard this would be to implement, though.

[foxnne]

I believe what this comes down to is support built into GLFW and currently GLFW doesn't have any support for pinch gestures.

@slimsag would know more I'm sure, but as mach will be moving away from GLFW there's a chance that at least on macOS or certain platforms that pinch gestures could be supported in the future, but I think it will be a while before we end up getting to something like that.