Woooow that zooooom (MacBook Trackpad)

[Martin-Pitt]

The zoom is super fast on the trackpad.

I'd recommend borrowing the work from @jakearchibald's implementation of pan-zoom from SVGOMG:
https://github.com/jakearchibald/svgomg/blob/master/src/js/page/ui/pan-zoom.js

Another useful source is: https://www.npmjs.com/package/normalize-wheel

[jakearchibald]

I started building a web component that does this, and also supports native panning. https://github.com/jakearchibald/pinch-zoomer/blob/master/index.js - haven't quite finished it yet, but the hard parts (the maths) are all there.