bug#50178: 28.0.50; Size of echo area does not account for line-spacing

[Óscar Fuentes]

Gregory Heytings <gregory@heytings.org> writes:

> Try emacs -Q, C-h h to see why it is impossible to have "an API that
> returns how many lines fit on a given window".

Any graphics environment worth its salt has methods for measuring
whatever object without actually rendering it. It's also true that those
systems work on pixels (or some other suitable, fine-grained unit) all
the way, they do not reveal themselves as TTY-oriented systems when the
user says "ok, then put this right here." The impossibility you mention
is a limitation of Emacs.

So going back to Emacs, the doctstring of max-mini-window-height is

"...
If an integer, it specifies the maximum height in units of the
mini-window frame’s default font’s height.
"

Why that was implemented that way? (instead of using pixels, for
instance.) Maybe because the relevant use case was to support resizing
the mini window on a way that guarantees that certain number of lines
(rendered on the default font) will fit on it?