Indeed, the original was in Flash, it was only ported to canvas much later.

I can't even notice the load on the system - Chrome's task manager tells me it's using 10% CPU, and I'm running on a 4k monitor.

EDIT: just tested with Firefox on MacOS and it's incredibly choppy and CPU-hungry. the `drawImage` call always goes over budget for RAF, there are a ton of open issues about it: https://bugzilla.mozilla.org/show_bug.cgi?id=1602299

Drawing at half scale gets it back to 60ms with time to spare:

    window_w = w * dpr / 2;
    window_h = h * dpr / 2;