Re: Verticality and future of display engine and lines (bis) [Was: Re: RTL lines]

[Alexandre Garreau]

Le jeudi 28 octobre 2021, 08:53:21 CEST Eli Zaretskii a écrit :
> > From: Alexandre Garreau <galex-713@galex-713.eu>
> > Date: Wed, 27 Oct 2021 21:54:11 +0200
> > 
> > > So you are not only talking about a revolution in the display
> > > engine,
> > > you are also talking about a revolution in scrolling commands.
> > 
> > That’s less than half a dozen of commands and the change is trivial,
> > it’s just level of abstraction.
> 
> I guess you are unaware, or perhaps forgot, that the display engine
> itself scrolls the window when it finds that necessary.

oh… but still that’s a few functions right…? I hope… like “scroll down” 
and “scroll up” calls that should be conditionally changed to “scroll 
forward” and “scroll backward”

> > > I don't see any excess height of the lines, I think if you see that
> > > in
> > > Emacs, you have a faulty font or something.
> > 
> > Did you really look at the screenshots? don’t you see all the blank
> > between the lines?
> 
> I'm talking about what I see in my Emacs session where I read your
> email.  If any Emacs session displays that as you describe, that's
> either a font configuration problem or some rendering bug that isn't
> present in my build of Emacs.

But did you look at the screenshots? doesn’t your gnus support simple and 
direct display of mime attachments?

> > > Showing just one diacritic is TRT in this case.  Anything else is a
> > > display bug.
> > 
> > So how do you display languages which *need* several diacritics?
> 
> Not every arbitrary combination of the diacritics on the same base
> character is valid.  Lumping the same diacritic several times on the
> same base character certainly isn't.  For valid combination of the
> diacritics, we will display them the way the font and the shaping
> engine (HarfBuzz) tell us to do.

oh ok

> IOW, find a real-life case with several diacritics on the same
> character, and then let's talk.  The example you provided makes no
> sense in real life, and the correct reaction of the Emacs display
> engine to that nonsensical example is to show just one diacritic.
>
> > > > Btw it would be nice if emacs supported such tweaking of
> > > > directionality
> > > > (although my friend wouldn’t benefit from it since he’s a user of
> > > > vim,
> > > > but I’m pretty sure that would be a point in advertising emacs to
> > > > him).
> > > 
> > > You can have this with special bidirectional formatting control
> > > characters, like LRO and RLO.  Emacs supports them.
> > 
> > Yes I know but I mean to have that systematically without having to
> > manually enter them at each script change (and avoiding to put them in
> > a possibly shared file with people with different opinions regarding
> > directionality)
> 
> Using those formatting controls _is_ the systematic way of changing
> the text directionality.  Emacs is not a playground for arbitrarily
> messing with the text layout, it follows relevant standards of
> layout.  And in those standards, the _only_ way of controlling the
> text directionality is by using directionality controls and
> overrides.
> 
> You could, of course, go overboard and modify the basic properties of
> the characters, which Emacs holds in char-tables.

Ohhhhh thank you! I should then look into that

> But that is not
> recommended,

well as you said that’s non-standard

> and I'm not even sure I understand why would you like to
> do something like that.

I already said it was to make reading more comfortable without having to 
lump from one part of the text to another, read, and yet again go there to 
resume reading, so the direction of reading is always consistent (and 
ideally to have even less jumping, one would need to use boustrophedon as 
a script direction, but afaik no existing software supports that)