Werner, I completely misdiagnosed the problem. It is indeed the autohinter that produces unpredictable advance and height in variable fonts.
Unhinted variable font, which falls back on the autohinter is https://github.com/adobe-fonts/source-sans/tree/release/VF A hinted VF is Roboto. Make sure to get the hinted version. https://github.com/googlefonts/roboto-3-classic/releases Alexei On Tue, Aug 26, 2025 at 12:49 PM Werner LEMBERG <w...@gnu.org> wrote: > > > >> Playing with ftmulti I noticed that almost all variable fonts > >> exhibit jumpy heights and advances when varying individual axes, > >> instead of monotonous changes. I could associate this weird > >> behavior with the bytecode hinting. Without it or with autohining, > >> the heights and advances are changing smoothly. > > > > The best way to see this behaviour is > > > > % ftgrid.exe -f6 ~/Fonts/Adobe/SourceSans3VF-Roman.ttf > > I couldn't find this font. Link, please! However, the font > `SourceSans3-VariableFont_wght.ttf` (as downloaded from Google Fonts) > doesn't contain any hints – or rather, it contains a pseudo-prep table > with a few instructions while `maxSizeOfInstructions` in the `maxp` > table is incorrectly set to zero... > > > When you start increasing the weight [F4] the advance line wiggles. > > It would be interesting to see the behaviour with a font that contains > real bytecode instructions... > > > Werner -- Alexei A. Podtelezhnikov, PhD
