Hammer.js is for use on touch screens, not trackpads. I found the demo on the page to be a bit vague, too, but a much better demo in the following Codepen convinced me to use it. Plus, it has a much lighter footprint than Interact.js.

http://codepen.io/klawdyo/full/azmapQ/

On a non-touch screen, hold shift while dragging the green box to emulate pinch and rotate gestures.