30 FPS in Safari

Did not expect that! Thats interesting!

The Observable built-in "now" has no temporal spacing, it's just a generator that yields Dte.now(): https://github.com/observablehq/stdlib/blob/master/src/now.js What you're observing is the difference in requestAnimationFrame(), which is what drives Observable's evaluation of generator cells.

This FPS counter may also be of interest: https://observablehq.com/d/8bea3f94176f0330

Thanks for that Fabian. In my Safari, the frame rate starts at 30 fps, but if frameCap is changed and then reset to none, it jumps to 60 fps.

I've read that Safari throttles requestAnimationFrame to 30 fps in cross-origin iframes without user interaction. Changing frameCap will likely count as interaction and thus remove the throttling.

Ah, that matches the experience here. It doesn't just throttle requestAnimationFrame. The setInterval etc. versions also start at 30 fps.

Tom: If I add a html`<button>` cell in this notebook, and then click it, Safari also jumps to 60 FPS.

This is misleading you can't really slow down updates in a more general case

See https://talk.observablehq.com/t/refresh-cells-on-a-timer/4447/13