[interpolatable] WIP use uharfbuzz if available

[behdad]

For faster drawing. However, I'm hitting a lot of
node-count-differs errors. I have not tracked the cause down yet.

I thought this line might be:

https://github.com/harfbuzz/harfbuzz/blob/df635ab78ae1d397396e3a0fe688b8a4674b2e8a/src/hb-draw.hh#L148

But disabling it in uharfbuzz didn't help.

[behdad]

@khaledhosny Any help here is appreciated.

[behdad]

Reopening to investigate so at least we know who's stealing a point from the outline!

[anthrotype]

you need to explicitly emit the implied closing line otherwise a duplicate line segment at the end of a contour can get eaten up, see

fonttools/Lib/fontTools/pens/pointPen.py

Lines 231 to 247 in 9c154e8

	# For closed contours, a 'lineTo' is always implied from the last oncurve
	# point to the starting point, thus we can omit it when the last and
	# starting point don't overlap.
	# However, when the last oncurve point is a "line" segment and has same
	# coordinates as the starting point of a closed contour, we need to output
	# the closing 'lineTo' explicitly (regardless of the value of the
	# 'outputImpliedClosingLine' option) in order to disambiguate this case from
	# the implied closing 'lineTo', otherwise the duplicate point would be lost.
	# See https://github.com/googlefonts/fontmake/issues/572.
	if (
	i + 1 != nSegments
	or outputImpliedClosingLine
	or not closed
	or pt == lastPt
	):
	pen.lineTo(pt)
	lastPt = pt

[anthrotype]

and that's because SegmentToPointPen always pops the last node when path is closed and last == first

fonttools/Lib/fontTools/pens/pointPen.py

Lines 321 to 323 in 9c154e8

	if len(self.contour) > 1 and self.contour[0][0] == self.contour[-1][0]:
	self.contour[0] = self.contour[-1]
	del self.contour[-1]

so to compensate and make sure points are roundtripped when going points => segments => points you need to make sure the segment representation has explicit closing lineTos

[behdad]

Yeah but doing that in HB didn't seem to help my problem. I'll investigate more.

[behdad]

The fonttools RecordingPen and draw() work fine for me. HB is doing something different.