[autofit] Prevent overlapping blue zones.
Problem reported as
https://github.com/google/fonts/issues/632
The font in question (Nunito) has values 705 and 713 for the
reference and overshoot values, respectively, of the first blue
zone. Blue zone 2, however, has value 710 for both the reference
and overshoot. At 12ppem, reference and overshoot of blue zone 0
becomes 8px, while blue zone 2 becomes 9px.
A peculiarity of this font is that the tops of isolated vertical
stems like `N' have a slight overshoot also. The auto-hinter tries
to find the nearest blue zone using the *original* coordinates. For
vertical stems, this is value 713. For normal horizontal tops like
in character `E', this is value 710. Since value 713 is mapped to
8px but value 710 to 9px, `N' and similar characters are one pixel
higher than `E', which looks very bad.
This commit sanitizes blue zones to avoid such a behaviour.
* src/autofit/aflatin.c (af_latin_sort_blue): New function.
(af_latin_metrics_init_blues): Sort blue values and remove overlaps.
2 files changed
