Re: Ligatures

[Stefan Monnier]

> 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:

Disregarding the theoretical question of whether a font can use
ligatures that involve the LF character (and hence affect the definition
of what is a line), I still see a chicken-and-egg problems:
How do you know where the current "screen line" ends if you don't know
how narrow/wide the font and its ligatures will render the text?

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?


        Stefan