[glyf-1 cubic curves] Last cubic segment becomes quadratic

[justvanrossum]

This is happening when drawing a variable composite glyph from a TTGlyphSet onto a TTGlyphPointPen. All outlines are cubic in the source. The bug is either in the TTGlyphSet code or in TTGlyphPointPen. Or somewhere else. (I will dig deeper, and fix if I can.)

[behdad]

Thanks. Pretty sure it's in Glyph.draw().

[behdad]

Is this an on-curve-less outline?

[justvanrossum]

Is this an on-curve-less outline?

No, it's an ordinary mix of on-curve and off-curve points.

[behdad]

Is this an on-curve-less outline?

No, it's an ordinary mix of on-curve and off-curve points.

I can take a look if you send me a font.

[justvanrossum]

The bug is in TTGlyphPen and TTGlyphPointPen:

from fontTools.pens.ttGlyphPen import TTGlyphPen, TTGlyphPointPen
from fontTools.pens.recordingPen import RecordingPointPen

points = [
    ((0, 0), "curve"),
    ((0, 0), None),
    ((0, 0), None),
    ((0, 0), "curve"),
    ((0, 0), None),
    ((0, 0), None),
]

if True:
    pen = TTGlyphPointPen(None)
    pen.beginPath()
    for (x, y), segmentType in points:
        pen.addPoint((x, y), segmentType=segmentType)
    pen.endPath()
else:
    pen = TTGlyphPen(None)
    pen.moveTo((0, 0))
    pen.curveTo((0, 0), (0, 0), (0, 0))
    pen.curveTo((0, 0), (0, 0), (0, 0))
    pen.closePath()

glyph = pen.glyph()

rpen = RecordingPointPen()
glyph.drawPoints(rpen, None)

for m, args, kwargs in rpen.value:
    if args:
        pt, tp, *_ = args
        print(m, pt, tp)
    else:
        print(m)

In both cases, the output is:

beginPath
addPoint (0, 0) qcurve
addPoint (0, 0) None
addPoint (0, 0) None
addPoint (0, 0) curve
addPoint (0, 0) None
addPoint (0, 0) None
endPath

Where the first segmentType should be "curve" instead of "qcurve".

[justvanrossum]

Hm, maybe the bug is with glyph.drawPoints(): if I use glyph.draw() with RecordingPen the output seems fine.

[behdad]

Indeed:

            # Start with the appropriate segment type based on the final segment 
            segmentType = "line" if cFlags[-1] == 1 else "qcurve" 

[behdad]

Can you check with #3190

[justvanrossum]

Can you check with #3190

Yup, that fixes it, thanks!