Allow disabling tap-and-drag

[alexdavid]

Similar to #1088, this adds a new touchpad drag configuration option that configures tap-and-drag behavior.

Currently tap-and-drag is always enabled when the tap setting is enabled, but other compositors allow setting this separately.

[YaLTeR]

Hm, so does this mean that when this PR is merged, everyone will suddenly have tap-and-drag disabled? That's not good.

If tap-and-drag is on by default, then I guess it makes more sense to have an inverse no-drag flag? Or an explicit drag false where unset fetches and uses the default libinput value?

[alexdavid]

Yeah good point. Would you prefer to go with a drag option that is an Option<bool> and only make the call to config_tap_set_drag_enabled if set?

[YaLTeR]

It needs to reset to default value if you comment it out while running niri.

[alexdavid]

Ah right, I suppose we could go with

device.config_tap_set_drag_enabled(c.drag.unwrap_or(true))

But let me know if you prefer a no-drag option, or fetching the default value from libinput (is this default configurable somewhere in libinput?)

[YaLTeR]

As far as I can tell from libinput code, tap-and-drag is always enabled by default. So I guess we could go with no-drag. Though, that reads a bit weird, so maybe it's better to go with drag: Option<bool>, at which point we might as well fetch the default from libinput when it's unset.

[alexdavid]

That makes sense, I'll look into fetching the default from libinput this weekend. 🙂