Re: Ligatures (was: Unify the Platforms: Cairo+FreeType+Harfbuzz Everywhere (except TTY))

[Pip Cet]

On Tue, May 19, 2020 at 2:39 PM Clément Pit-Claudel
<address@hidden> wrote:
> On 19/05/2020 09.56, Eli Zaretskii wrote:
> > I don't see anything on or after "a", I see a thin vertical line on
> > the "Z".  is that what is actually displayed?  If so, how do people
> > know the cursor is after "a"??
>
> They don't: "the seven equal slices that Firefox treats it as for 
> selection/editing purposes don't match up to the visual shapes of the 
> sub-glyphs at all well"

And I'm afraid the difference is much more obvious with box cursors
than it is with carets. I'm attaching a screenshot of a patched Emacs
displaying "ffi", with point on the second f, in the "Linux Libertine
Display O" font (using approximately equal slices).

I think this is a bit of a worst-case scenario, a three-letter
ligature in a font using ligatures and overhangs very
enthusiastically. It might be okay for other fonts.

My remaining idea is to stretch characters so we can break up a
ligature without changing its total width. I'm not sure how to do
that, though.

(I'm also attaching the patch, for the morbidly curious; it isn't
clean, readable, or finished in any way, and contains at least one
obvious bug. It's just good enough to produce the screenshot, and
maybe it can serve as a hint as to which files need changing for
ligatures to work; but such changes would have to be done very
differently from the patch.).

ffi-box-cursor.png
Description: PNG image

0001-Ligatures.diff
Description: Text Data