Actually immediate mode came first, retained came later for perf reasons (redrawing the entire screen from scratch every frame is slow, even though immediate mode is easier). The original context was however graphics (OpenGL retained vs immediate modes) rather than UI (widget toolkits started out as retained, like OGL retained scene graphs, likewise canvases have always been immediate).

Of course I didn't? I filled a wall with the books I bought and didn't come across the term. What did I do wrong, what books could I have bought but didn't?

How many of those books weren't about the mainstream GUI toolkits (Qt, GTK, MFC, Cocoa, Swing…)? Has even one of those books described something that resemble "let's redraw everything every frame"? If so, how that technique was called?

> what books could I have bought but didn't?

Possibly none at all. Immediate mode anything is mostly a game dev thing, and what happens in game dev tends to stay in game dev. They don't seem to document their practices as much as other fields do.

Hence my suspicion that the authors of your books didn't even know about IMGUI. They just knew about "the" way to do GUI, which happens to involved retained state.

You're letting the tail wag the dog. You're assuming that people know terms that are used in "possibly none [no books] at all", or put differently, that the set of terms used in books for software developers is uncorrelated with the set of terms software developers may be assumed to know.

BTW, the code in Qt that draws rotated/sheared text/pixmaps was influenced in part by a book or chapter by Michael Abrash, as well as by articles in either Graphics Gems or conference papers (memory's fallible I'm afraid).