[wasmperson]

You appear to be making assumptions about immediate mode UI limitations based on some implementations you've worked with and not based on what's actually dictated by the interface itself. You touch on this somewhat by claiming that it's possible to be fast as long as the UI is merely a "thin veneer" over something more stateful, but that isn't a distinction I care about.

I'm not a good advocate for IMGUI; there are resources available online which explain it better than I can. I'm just trying to point out that the claim that immediate mode GUIs are some sort of CPU hog isn't really true. That's what I meant by "doesn't necessarily sacrifice performance," not that there is literally zero overhead (although I wouldn't be surprised if that were the case!).

> ...The browser's task manager shows this tab never goes idle...

As far as I can tell, the demo you linked appears to be bugged. You can see from poking around in a profiler (and from the frame timer under the "backend" popout) that the UI code does in fact go idle, but the requestAnimationFrame loop is never disabled for some reason. Regardless, even if this particular GUI library has problems going idle, that's not an inherent problem with the paradigm. I get the impression you understand this already, so I'm not sure why you've brought it up.