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determine direction to nudge pre-loop

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Cosimo Lupo 2021-01-15 19:11:10 +00:00
parent c9055871d6
commit c13b1cef84
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GPG Key ID: 179A8F0895A02F4F
1 changed files with 19 additions and 14 deletions
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33
Lib/fontTools/colorLib/geometry.py
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@ -96,9 +96,21 @@ def round_start_circle_stable_containment(c0, r0, c1, r1):
round_start = start.round()
round_end = end.round()
inside_after_round = round_start.inside(round_end)
# At most 3 iterations ought to be enough to converge. In the first, we
# check if the start circle keeps containment after normal rounding; then
if inside_before_round == inside_after_round:
return round_start
elif inside_after_round:
# start was outside before rounding: we need to push start away from end
direction = _vector_between(round_end.centre, round_start.centre)
radius_delta = +1.0
else:
# start was inside before rounding: we need to push start towards end
direction = _vector_between(round_start.centre, round_end.centre)
radius_delta = -1.0
# At most 2 iterations ought to be enough to converge. Before the loop, we
# know the start circle didn't keep containment after normal rounding; thus
# we continue adjusting by -/+ 1.0 until containment is restored.
# Normal rounding can at most move each coordinates -/+0.5; in the worst case
# both the start and end circle's centres and radii will be rounded in opposite
@ -112,23 +124,16 @@ def round_start_circle_stable_containment(c0, r0, c1, r1):
# -1.82842 after rounding (c0 is now outside c1). Nudging c0 by -1.0 on both
# x and y axes moves it towards c1 by hypot(-1.0, -1.0) = 1.41421. Two of these
# moves cover twice that distance, which is enough to restore containment.
max_attempts = 3
max_attempts = 2
for _ in range(max_attempts):
inside_after_round = round_start.inside(round_end)
if inside_before_round == inside_after_round:
break
if round_start.concentric(round_end):
# can't move c0 towards c1 (they are the same), so we change the radius
if inside_after_round:
round_start.radius += 1.0
round_start.radius += radius_delta
assert round_start.radius >= 0
else:
round_start.radius -= 1.0
else:
if inside_after_round:
direction = _vector_between(round_end.centre, round_start.centre)
else:
direction = _vector_between(round_start.centre, round_end.centre)
round_start.nudge_towards(direction)
if inside_before_round == round_start.inside(round_end):
break
else: # likely a bug
raise AssertionError(
f"Rounding circle {start} "