[varLib.featureVars] Buggy

From Just:

from pprint import pprint
from fontTools.varLib.featureVars import overlayFeatureVariations

rules = [
    ([{'abcd': (4, 9)}], {0: 0}),
    ([{'abcd': (5, 10)}], {1: 1}),
    ([{'abcd': (0, 8)}], {2: 2}),
    ([{'abcd': (3, 7)}], {3: 3}),
]

pprint(overlayFeatureVariations(rules))

-->

[({'abcd': (5, 7)}, [{0: 0}, {1: 1}, {2: 2}, {3: 3}]),
 ({'abcd': (7, 8)}, [{0: 0}, {1: 1}, {2: 2}]),
 ({'abcd': (4, 5)}, [{0: 0}, {2: 2}, {3: 3}]),
 ({'abcd': (3, 7)}, [{2: 2}, {3: 3}]),
 ({'abcd': (8, 9)}, [{0: 0}, {1: 1}]),
 ({'abcd': (8, 10)}, [{1: 1}])]

There is no rule vor (0, 3) in the overlayed ruleset.

Here’s another one:

rules = [
    ([{'abcd': (1, 9)}], {0: 0}),
    ([{'abcd': (8, 10)}], {1: 1}),
    ([{'abcd': (3, 4)}], {2: 2}),
    ([{'abcd': (1, 10)}], {3: 3}),
]

pprint(overlayFeatureVariations(rules))

-->

[({'abcd': (3, 4)}, [{0: 0}, {2: 2}, {3: 3}]),
 ({'abcd': (8, 9)}, [{0: 0}, {1: 1}, {3: 3}]),
 ({'abcd': (8, 10)}, [{1: 1}, {3: 3}]),
 ({'abcd': (4, 8)}, [{0: 0}, {3: 3}]),
 ({'abcd': (1, 10)}, [{3: 3}])]

For an axis value of 2, both {0: 0} and {3: 3} should trigger, but only {3: 3} ends up in the overlayed list.

[behdad]

I see the difference. What you are doing is to create one lookup per changeset. Whereas in the code, Just originally decided, to generate one lookup per input changeset and reference multiple lookups from each region. This is typically beneficial by not duplicating the lookup content multiple times. But in your case, combining is more compact. Let me think, we can probably find out what the optimal combination is and produce that…

[behdad]

What I am doing is rather primitive. Instead of using lookups, I define the substitutions directly inside the feature variations.

I’m guessing that that just doesn’t do anything. Does it work?!