Get outline coordinates of a font glyph in Python

Question

I need to extract regular spaced boundary coordinates of glyphs from an OTF file in order to draw them (approximated) as a shape consisting of straight segments. That is, for a given string 'draft' I want to read the corresponding glyphs from the OTF file (if possible, using ligatures when appropriate) and calculate their outline coordinates (say with a font size of 100 units and a coordinate spacing of about 1 unit) in order to draw them in a context where I can only draw shapes consisting of straight lines. I need to do all of this using Python (though calling external command line tools would certainly be okay).

After searching around a bit online, my impression is that I should be able to get there (or almost there) using fontTools, but I'm having trouble finding what I need in the documentation. It is quite long and does not contain a lot of examples, which makes it difficult for me to determine if it has what I need.

• Is fontTools the tool for me? If not, is there a Python library I can use instead?
• How can I read the correct glyphs from the OTF file?
• How can I interpolate between the control points of the glyphs?

Answer 1

yes fontTools is perfect for you!

If you have an OTF file you find find the drawing in CFF or CFF2 table. I recommend running ttx font.otf and inspect outputted xml file to understand the structure.

You cff table will probably be subroutinized. This means that parts of the contour are saved as "elements" and used across the fonts to save some weight. This replaces components known from TrueType fonts. Just run subroutinize method on the CFF table and you should be able to read everything you need.

A snippet replacing every glyph in list named keep_g_names

    def process_cff(self) -> None:
        cff = self.font["CFF "]
        cmap_reversed = {v: k for k, v in self.font.getBestCmap().items()}

        if hasattr(cff, "desubroutinize"):
            cff.desubroutinize()

        content = cff.cff[cff.cff.keys()[0]]  # can it have more fonts?

        for key in content.CharStrings.keys():
            if key in self.keep_g_names:
                continue
            content.CharStrings[key] = content.CharStrings["n"]

Does this help you?

What do you mean by How can I interpolate between the control points of the glyphs?