> immediate mode may actually be more performant compared to retained mode. Go to any web page and resize the browser window, and you'll notice that the browser is very slow to do the layout and eats a lot of CPU doing it. Resize a window in egui by contrast, and you'll get smooth 60 FPS at no extra CPU cost.
The key part there is no EXTRA cost. Most immediate mode GUI libraries redraw 60 frames everytime, so there is a constant somewhat high cost, especially compared with a retained mode program.
To clarify, egui has a mode where it only redraws while you're interacting with the app (e.g hovering, clicking). It doesn't do anything while idle (e.g. In between keystrokes)
Krita, SailfishOS, Calibre, Audacious, AsteroidOS, OBS, VLC, KDE (though I prefer a tiling WM, I have to admit Okular is superb). Qt is cross-platform too, and its FOSS and proprietary friendly.