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[interpolatable] Make the kink-detector a lot more conservative

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Most kinks are not visible at regular outline sizes. We
don't want to pollute the report with them.

One can still use the --kinkiness parameter to get more
kinky.
This commit is contained in:
Behdad Esfahbod 2023-11-26 14:45:06 -07:00
parent 79522fcd31
commit 758b16fdf0
1 changed files with 18 additions and 5 deletions
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23
Lib/fontTools/varLib/interpolatable.py
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@ -26,7 +26,7 @@ log = logging.getLogger("fontTools.varLib.interpolatable")
DEFAULT_TOLERANCE = 0.95 DEFAULT_TOLERANCE = 0.95
DEFAULT_KINKINESS = 0.5 DEFAULT_KINKINESS = 0.5
DEFAULT_KINKINESS_LENGTH = 0.001 # ratio of UPEM DEFAULT_KINKINESS_LENGTH = 0.003 # ratio of UPEM
DEFAULT_UPEM = 1000 DEFAULT_UPEM = 1000
@ -340,7 +340,6 @@ def test_gen(
if kinkiness >= 10: if kinkiness >= 10:
kinkiness *= 0.01 kinkiness *= 0.01
assert 0 <= kinkiness assert 0 <= kinkiness
r_diff_threshold = upem * DEFAULT_KINKINESS_LENGTH / kinkiness
if names is None: if names is None:
names = glyphsets names = glyphsets
@ -878,10 +877,11 @@ def test_gen(
# Sharp corner. # Sharp corner.
continue continue
r0 = sqrt(abs(d0_prev) * abs(d1_next)) # Fine, if handle ratios are similar...
r1 = sqrt(abs(d1_prev) * abs(d0_next)) r0 = abs(d0_prev) / (abs(d0_prev) + abs(d0_next))
r1 = abs(d1_prev) / (abs(d1_prev) + abs(d1_next))
r_diff = abs(r0 - r1) r_diff = abs(r0 - r1)
if r_diff < r_diff_threshold: if abs(r_diff) < t:
# Smooth enough. # Smooth enough.
continue continue
@ -898,12 +898,25 @@ def test_gen(
except ZeroDivisionError: except ZeroDivisionError:
continue continue
# ...or if the angles are similar.
if abs(sin_mid) * (tolerance * kinkiness) <= t: if abs(sin_mid) * (tolerance * kinkiness) <= t:
# Smooth enough. # Smooth enough.
continue continue
# How visible is the kink?
cross = sin_mid * abs(mid_d0) * abs(mid_d1)
arc_len = abs(mid_d0 + mid_d1)
deviation = abs(cross / arc_len)
if deviation < upem * DEFAULT_KINKINESS_LENGTH:
continue
deviation_ratio = deviation / arc_len
if deviation_ratio > t:
continue
this_tolerance = t / (abs(sin_mid) * kinkiness) this_tolerance = t / (abs(sin_mid) * kinkiness)
#print(deviation, deviation_ratio, sin_mid, r_diff, this_tolerance)
yield ( yield (
glyph_name, glyph_name,
{ {