Letters overlap each other on specific font and combination of letters

[antmelnyk]

Hey @RazrFalcon, I hope you're doing OK.

There is a weird issue with text resolving that was caught for one particular font and a combination of letters. Not sure exactly on which level that happens - either usvg-text-layout or rustybuzz. Maybe you have an idea?

SVG:

<svg width='100' height='100' viewBox='0 -201.7578125 100 251.3671875'
    xml:space='preserve'
    xmlns='http://www.w3.org/2000/svg'
    xmlns:xlink='http://www.w3.org/1999/xlink'>
    <text x='0' y='0' font-size='200' font-family='Fjalla One' fill='#000000'>fit</text>
</svg>

Font Fjalla One (https://fonts.google.com/specimen/Fjalla+One?noto.query=Roboto&preview.text=fit&preview.text_type=custom&query=fjalla)

Result of running minimal.rs example with added fontdb.load_font_file("./examples/Fjalla One-regular.ttf").unwrap();

Expected (rsvg-convert):

Actual (ReSVG):

[RazrFalcon]

This is a ligature handling bug. Similar to #614, but this time it doesn't fail immediately.
Seems like usvg-text-layout bug. rustybuzz produces the same output as harfbuzz.

It basically thinks that fi is a single character, which is not. Kinda...

[antmelnyk]

Yeah, that makes sense. I thought that it was about ligature handling.

For this font, the ligatures are classic ff, fi, fl, ffi, ffl.
And it fails to render fi and fl if there are more characters after these.

I checked 350 other Google Fonts, and quite a lot of them have these 2 ligatures (fi and fl). It fails to render only for this particular font, Fjalla One. Maybe that can help you to understand the difference and core of the issue.