+ -f <num>
+ Generate a distance field texture. The argument controls the amount of
+ oversampling when calculating distances. Larger values may produce more
+ accurate results but take longer to process. Distance fields are always
+ stored without alpha and with large/positive values indicating the inside
+ of glyphs; the -t and -i options are ignored.
+
+ -b <pixels>
+ Set the border zone width for distance field. The default is the square
+ root of the font size.
+