[varLib.avar] New module to compile avar from .designspace file

Fixes https://github.com/fonttools/fonttools/issues/3275

Lib/fontTools/varLib/avar.py

@@ -0,0 +1,70 @@
+from fontTools.varLib import _add_avar, load_designspace
+from fontTools.misc.cliTools import makeOutputFileName
+import logging
+
+log = logging.getLogger("fontTools.varLib.avar")
+
+
+def main(args=None):
+    """Add `avar` table from designspace file to variable font."""
+
+    if args is None:
+        import sys
+
+        args = sys.argv[1:]
+
+    from fontTools import configLogger
+    from fontTools.ttLib import TTFont
+    from fontTools.designspaceLib import DesignSpaceDocument
+    import argparse
+
+    parser = argparse.ArgumentParser(
+        "fonttools varLib.avar",
+        description="Add `avar` table from designspace file to variable font.",
+    )
+    parser.add_argument("font", metavar="varfont.ttf", help="Variable-font file.")
+    parser.add_argument(
+        "designspace", metavar="family.designspace", help="Designspace file."
+    )
+    parser.add_argument(
+        "-o",
+        "--output-file",
+        type=str,
+        help="Output font file name.",
+    )
+    parser.add_argument(
+        "-v", "--verbose", action="store_true", help="Run more verbosely."
+    )
+
+    options = parser.parse_args(args)
+
+    configLogger(level=("INFO" if options.verbose else "WARNING"))
+
+    font = TTFont(options.font)
+    if not "fvar" in font:
+        log.error("Not a variable font.")
+        return 1
+
+    axisTags = [a.axisTag for a in font["fvar"].axes]
+
+    ds = load_designspace(options.designspace)
+
+    if "avar" in font:
+        log.warning("avar table already present, overwriting.")
+        del font["avar"]
+
+    _add_avar(font, ds.axes, ds.axisMappings, axisTags)
+
+    if options.output_file is None:
+        outfile = makeOutputFileName(options.font, overWrite=True, suffix=".avar")
+    else:
+        outfile = options.output_file
+    if outfile:
+        log.info("Saving %s", outfile)
+        font.save(outfile)
+
+
+if __name__ == "__main__":
+    import sys
+
+    sys.exit(main())