Re: Ligatures

[Pip Cet]

On Sat, May 23, 2020 at 12:48 PM Stefan Monnier
<address@hidden> wrote:
> > The crucial problem is that we currently perform layout decisions one
> > grapheme cluster at a time, whereas what HarfBuzz people say is that
> > we should basically do that one screen line at a time.
>
> I wonder how it is supposed to work and it works in other applications:

That's why I'd like us to use a more advanced internal API rather than
the limited HarfBuzz API, one that asynchronously requests information
about preceding/following codepoints, incrementally informing us of
the minimum width already reached, until it can reach a decision. It
should be easy enough to put in some heuristics that work in practice
until a better shaper comes along...

> Do current applications use a heuristic like "ligatures won't reduce the
> size by more than a factor 2, so estimate the lower bound on the final
> size to be at most half of what the font metrics say", so they will send
> up to twice as much text to be shaped as needed, and then they throw
> away the left overs?

I don't know.