draw_glyphs_with_pen.py

from glyphsLib import GSFont


# 'offcurve' GSNode.type is equivalent to 'None' in UFO PointPen API
_UFO_NODE_TYPES = {"line", "curve", "qcurve"}


def drawGSLayerWithPointPen(layer, pointPen):
    """ Draw a Glyphs layer with a FontTools PointPen.

    Args:
        layer: a glyphsLib.classes.GSLayer object
        pointPen: a UFO point pen (cf. fontTools AbstractPointPen).

    Source:
    https://github.com/googlefonts/glyphsLib/blob/master/Lib/glyphsLib/builder/paths.py
    https://github.com/googlefonts/glyphsLib/blob/master/Lib/glyphsLib/builder/components.py
    """
    for path in layer.paths:
        nodes = list(path.nodes)

        pointPen.beginPath()

        if not nodes:
            pointPen.endPath()
            continue

        if not path.closed:
            node = nodes.pop(0)
            assert node.type == "line", "Open path starts with off-curve points"
            pointPen.addPoint(tuple(node.position), segmentType="move")
        else:
            # In Glyphs.app, the starting node of a closed contour is always
            # stored at the end of the nodes list.
            nodes.insert(0, nodes.pop())

        for node in nodes:
            node_type = node.type if node.type in _UFO_NODE_TYPES else None
            node_data = dict(node.userData)
            node_name = node_data.pop("name", None)
            pointPen.addPoint(
                tuple(node.position),
                segmentType=node_type,
                smooth=node.smooth,
                name=node_name,
                userData=node_data,
            )
        pointPen.endPath()

    for component in layer.components:
        pointPen.addComponent(component.name, component.transform)


if __name__ == "__main__":
    import sys
    from pprint import pprint
    from functools import partial

    filename = sys.argv[1]
    font = GSFont(filename)

    # for master in font.masters...
    master = next(iter(font.masters))

    # for glyph in font.glyphs...
    try:
        glyph_name = sys.argv[2]
    except IndexError:
        glyph_name = "a"

    glyph = font.glyphs[glyph_name]
    if glyph is None:
        sys.exit(f"glyph {glyph_name!r} is missing")

    # get each glyph's master layer
    layer = font.glyphs[glyph_name].layers[master.id]

    # draw the layer with a point pen
    drawPointsFunc = partial(drawGSLayerWithPointPen, layer)

    # E.g. dump it to GLIF format
    from fontTools.ufoLib.glifLib import writeGlyphToString

    glif = writeGlyphToString(glyph_name, drawPointsFunc=drawPointsFunc)
    print(glif)

    # Or record it with a RecordingPointPen
    from fontTools.pens.recordingPen import RecordingPointPen

    rec = RecordingPointPen()
    drawPointsFunc(rec)
    pprint(rec.value)

    # if you need segments, use PointToSegmentPen adapter pen
    from fontTools.pens.recordingPen import RecordingPen
    from fontTools.pens.pointPen import PointToSegmentPen

    rec = RecordingPen()
    pointPen = PointToSegmentPen(rec)
    drawPointsFunc(pointPen)
    pprint(rec.value)