bug#26445: 26.0.50; Scroll margin and cursor movement working incorrectly when scrolling over different height lines

[Eli Zaretskii <eliz@gnu.org>]

> Cc: npostavs@users.sourceforge.net, 26445@debbugs.gnu.org
> From: Alexander Miller <alexanderm@web.de>
> Date: Fri, 14 Apr 2017 12:56:30 +0200
> 
> On 14/04/17 09:06, Eli Zaretskii wrote:
> > That depends on what font you have installed that's used to display
> > those characters.  It is best to have fonts of approximately the same
> > height.
> How would I go about finding out which fonts have which height

I don't know any way except by trying, sorry.  Perhaps some font
expert could offer a more useful method.

> and how to make emacs use them?

You do that by customizing the default fontset.  There are examples in
the Emacs manual, and you can see more examples in fontset.el which
comes with Emacs.

> For emacs I found I could do something like
> (set-fontset-font "fontset-default" nil (font-spec :size 1 :name "Symbola"))
> but that doesn't seem to do anything.

If you have Symbola installed, Emacs will already use it by default.
You can see which font is used for a character by invoking "C-u C-x ="
at that character's position.  If Symbola is not used for some
characters, you could customize your default fontset so that it is.

> > There's no need to get rid of margins, as I think the problem you
> > describe is purely aesthetic, and quite expected when you have lines
> > of different height.  Why does it bother you so much?
> I just don't like the inconsistency. The scroll stutter happens when I'm 
> quickly scrolling through a buffer and suddenly see my cursor change
> position for seemingly no reason.

There's no way around that when screen lines have different height.
The most you can do is make sure (most of) your fonts are of the same
height.  FWIW, the characters you mentioned in your email are
displayed on my system using Symbola, and the height of the line is
the same as for the surrounding text.  So perhaps you should just make
sure your Emacs uses Symbola for them?

> > Btw, , , and  are private-use area (PUA) characters, so I'm not
> > sure what you expected from Emacs to do with them.
> I've picked those up from Font Awesome, which brings us back to my 
> previous question.

I tried to answer it above.

> Is it possible to tell emacs that Font Awesome Icons should have the
> same size as my default text font, and if yes how do I do it?

Once you tell Emacs to use that font for some range of characters, it
should choose the best size automatically.