Method build_subset

src/__init__.py:7545–7607

Build font subset using fontTools. Args: buffer: (bytes) the font given as a binary buffer. unc_set: (set) required glyph ids. Returns: Either None if subsetting is unsuccessful or the subset font buffer.

(buffer, unc_set, gid_set)

            doc.update_object(new_xref, font_str)

        def build_subset(buffer, unc_set, gid_set):
            """Build font subset using fontTools.

            Args:
                buffer: (bytes) the font given as a binary buffer.
                unc_set: (set) required glyph ids.
            Returns:
                Either None if subsetting is unsuccessful or the subset font buffer.
            """
            try:
                import fontTools.subset as fts
            except ImportError:
                if g_exceptions_verbose:    exception_info()
                message("This method requires fontTools to be installed.")
                raise
            import tempfile
            with tempfile.TemporaryDirectory() as tmp_dir:
                oldfont_path = f"{tmp_dir}/oldfont.ttf"
                newfont_path = f"{tmp_dir}/newfont.ttf"
                uncfile_path = f"{tmp_dir}/uncfile.txt"
                args = [
                    oldfont_path,
                    "--retain-gids",
                    f"--output-file={newfont_path}",
                    "--layout-features=*",
                    "--passthrough-tables",
                    "--ignore-missing-glyphs",
                    "--ignore-missing-unicodes",
                    "--symbol-cmap",
                ]

                # store glyph ids or unicodes as file
                with io.open(f"{tmp_dir}/uncfile.txt", "w", encoding='utf8') as unc_file:
                    if 0xFFFD in unc_set:  # error unicode exists -> use glyphs
                        args.append(f"--gids-file={uncfile_path}")
                        gid_set.add(189)
                        unc_list = list(gid_set)
                        for unc in unc_list:
                            unc_file.write(f"{unc}\n")
                    else:
                        args.append(f"--unicodes-file={uncfile_path}")
                        unc_set.add(255)
                        unc_list = list(unc_set)
                        for unc in unc_list:
                            unc_file.write(f"{unc:04x}\n")

                # store fontbuffer as a file
                with io.open(oldfont_path, "wb") as fontfile:
                    fontfile.write(buffer)
                try:
                    os.remove(newfont_path)  # remove old file
                except Exception:
                    pass
                try:  # invoke fontTools subsetter
                    fts.main(args)
                    font = Font(fontfile=newfont_path)
                    new_buffer = font.buffer  # subset font binary
                    if font.glyph_count == 0:  # intercept empty font