While most of my Emacs workflows are typically keyboard-driven, I'm fairly pragmatic about mouse usage. My MacBook's trackpad is great for just kicking back to read and scroll through text.
There are brief times, however, when that keyboard-driven muscle memory overlaps my mouse usage, resulting in a buffer catastrophe. I joke of course. What I'm actually referring to is nothing more than a slight annoyance. There are times when I inadvertently trigger <C-wheel-up> or <C-wheel-down> events (because I happen to hold Ctrl down while triggering scrolling events). This results in buffer font size quickly changing to either really large or super small, depending on whether I was scrolling up or down at the time. The snafu is further exacerbated by inertial scrolling on trackpads. Go ahead and press the Ctrl key while your buffer is carrying some of that inertia. The font size is affected just the same, even though there was no explicit physical/touching activity on the trackpad at the time.
While this behaviour was a little annoying, I would typically just reopen the file via C-x C-v RET (aka find-alternate-file), which would reset the font size as a convenient side-effect. Now, you may wonder if reopening the file would also forget the point/cursor position, but that's not an issue if you've got the handy built-in save-place-mode turned on (highly recommended).
Ok and all, but this is a second-class workaround at best. What I really wanted is for the mouse/trackpad to stop messing with my font size.
Lucky for me, I bumped into a simple solution shared by Shane Celis and Thanga Ayyanar. It worked a treat, and it's only a few lines of elisp.
(global-set-key (kbd "<pinch>") 'ignore)
(global-set-key (kbd "<C-wheel-up>") 'ignore)
(global-set-key (kbd "<C-wheel-down>") 'ignore)
Thank you folks. Balance restored.
While I was using C-x C-v RET (aka find-alternate-file) to reset font size, Luke T. Shumaker and Matthew G. shared a better reset alternative:
C-u 0 M-x text-scale-adjust