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

[Trevor Spiteri]

On 18/05/2020 19:31, Clément Pit-Claudel wrote:
> On 18/05/2020 12.08, Eli Zaretskii wrote:
>> On second thought, I think I misunderstood you.  If the font that is
>> used shows "ffi" as a _single_ glyph ffi, and LibreOffice indeed
>> highlights parts of this glyph, then I'd like to know how it does
>> that, and how far does this capability extend.  I mean, what does it
>> do with ligatures like ae, displayed as æ -- does it highlight the
>> common vertical stroke for both parts?  And what about "st", displayed
>> as st -- this has a curved "hand" connecting s and t -- to which of the
>> 2 does it belong for the purposes of highlighting?  There's also "hv"
>> displayed as ƕ, let alone "fs" displayed as ẞ and "fz" displayed as
>> ß.
> I've attached a screenshot with a few examples, though I couldn't find a font 
> that displays ae as æ.
>
> Firefox does the same as LibreOffice (try it here, for example: 
> https://developer.mozilla.org/en-US/docs/Web/CSS/font-variant-ligatures).  
> Since Firefox uses Harbuzz, I think there's a good chance we can support that 
> feature too :)

For what it's worth, LibreOffice does it differently. I think what it
does is place the cursor on the position it would be if any following
text was missing. So moving after the second f in ffi would move the
cursor to the same position as after ff if the i was missing. This is
evident from fraction ligatures; in the screenshot I'm attaching, "63"
is selected and the selection matches the 63 in the bottom line.

fraction.png
Description: PNG image