Re: Increase default `line-spacing' to 0.05, 0.10 or 0.15 [proposal]

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Tue, 4 May 2021 16:29:03 -0500
> Cc: emacs-devel@gnu.org
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> Emacs by default uses a leading of the font size + a few pixels (the
> >> `line-spacing' variable is 0).
> >
> > I don't understand this (or disagree): AFAIU, by default line-spacing
> > is strictly zero, and we don't add anything to the font size.  If you
> > see something else in the code, can you point me to the code which I'm
> > missing, and which implements that default line-spacing?
> 
> This is not based on any reading of the code, but merely a casual
> observation based on what I see when I look at my screen: there are a
> couple of pixels between characters (glyphs) on different rows.  If you
> say that there is nothing extra added in addition to the font size, then
> that is how it is.

We add nothing by default.  The height of each screen line is just the
maximum value of the sum of the glyph ascents and glyph descents on
that line.

If you move the cursor between two screen lines, you should see that
the cursor on line N ends exactly where the cursor on line N+1
begins.  Since the cursor's height is exactly the height of the screen
line, that confirms what I see in the code.