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instancer: document case when peak is < 1.0 but outer limit exceeds 2.0

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Cosimo Lupo 2019-11-15 18:35:37 +00:00
parent 7d136da836
commit 6142825d7b
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GPG Key ID: 20D4A261E4A0E642
1 changed files with 11 additions and 4 deletions
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15
Lib/fontTools/varLib/instancer.py
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@ -289,10 +289,14 @@ def limitTupleVariationAxisRange(var, axisTag, axisRange):
var.axes[axisTag] = (newLower, newPeak, newUpper) var.axes[axisTag] = (newLower, newPeak, newUpper)
return [var] return [var]
# case 4: new limit doesn't fit, we need to chop the tent into two triangles, # case 4: new limit doesn't fit; we need to chop the deltaset into two 'tents',
# with an additional tent with scaled-down deltas that peaks as the original # because the shape of a triangle with part of one side cut off cannot be
# one tapers down. NOTE: This increases the file size! # represented as a triangle itself. It can be represented as sum of two triangles.
# NOTE: This increases the file size!
else: else:
# duplicate the tent, then adjust lower/peak/upper so that the outermost limit
# of the original tent is +/-2.0, whereas the new tent's starts as the old
# one peaks and maxes out at +/-1.0.
newVar = TupleVariation(var.axes, var.coordinates) newVar = TupleVariation(var.axes, var.coordinates)
if negative: if negative:
var.axes[axisTag] = (-2.0, -1 * newPeak, -1 * newLower) var.axes[axisTag] = (-2.0, -1 * newPeak, -1 * newLower)
@ -300,8 +304,11 @@ def limitTupleVariationAxisRange(var, axisTag, axisRange):
else: else:
var.axes[axisTag] = (newLower, newPeak, MAX_F2DOT14) var.axes[axisTag] = (newLower, newPeak, MAX_F2DOT14)
newVar.axes[axisTag] = (newPeak, 1.0, 1.0) newVar.axes[axisTag] = (newPeak, 1.0, 1.0)
# TODO: document optimization # the new tent's deltas are scaled by the difference between the scalar value
# for the old tent at the desired limit...
scalar1 = supportScalar({axisTag: limit}, {axisTag: (lower, peak, upper)}) scalar1 = supportScalar({axisTag: limit}, {axisTag: (lower, peak, upper)})
# ... and the scalar value for the clamped tent (with outer limit +/-2.0),
# which can be simplified like this:
scalar2 = 1 / (2 - newPeak) scalar2 = 1 / (2 - newPeak)
newVar.scaleDeltas(scalar1 - scalar2) newVar.scaleDeltas(scalar1 - scalar2)