Is there a way to decompose components of a glyph in a TTF?

I am attempting to decompose components in glyphs within a TTF, but having trouble.

Is there a way to do this?

It seems that there is nothing direct, and that I may need to use pens. I am pretty new to pens, and not sure I understand them completely.

I think I would need to find a way to record points of each component to a pen object, and then draw those points into the ttGlyph with the .drawPoints() method. However, it doesn’t seem that the decomposingRecordingPen works with TTFont objects. I also can’t figure out whether I am using the ttGlyphPen correctly (can it even record points, or is it just a way to store points to later draw?).

def decomposeGlyph(font, glyphName):

    components = (font['glyf'][glyphName].getComponentNames(font['glyf']))

    ## BASIC IDEA (not yet working)
    # for component in glyph
        # record tt points of component base
        # draw points to glyph
    
    glyphset = font.getGlyphSet()

    for comp in components:
        glyph = glyphset[comp]
        pen = ttGlyphPen.TTGlyphPen(glyph)
        # font['glyf'][glyphName].drawPoints(pen, font['glyf'])
        font['glyf'][glyphName].draw(pen, font['glyf'])

It may or may not be a related goal, but I am also hoping to remove overlap in the glyphs in a TTF. If this is easy to point out, I would love to get a head start on it, but if it’s a totally separate thing, feel free to skip this part and I will look into it separately.

Thank you so much for any tips or insights!

[justvanrossum]

This snippet works:

from fontTools.ttLib import TTFont
from fontTools.pens.recordingPen import DecomposingRecordingPen
from fontTools.pens.ttGlyphPen import TTGlyphPen


src = "font.ttf"
dst = "font-decomposed.ttf"

f = TTFont(src)

glyfTable = f["glyf"]
gs = f.getGlyphSet()
for glyphName in gs.keys():
    if not glyfTable[glyphName].isComposite():
        continue
    dcPen = DecomposingRecordingPen(gs)
    gs[glyphName].draw(dcPen)
    ttPen = TTGlyphPen(None)
    dcPen.replay(ttPen)
    glyfTable[glyphName] = ttPen.glyph()

f.save(dst)

[anthrotype]

I will check out ufo2ft for a reference.

The way ufo2ft uses pathops.union() function will not work with a TTGlyph object as these don’t have getPen() method (unlike defcon or ufoLib2 Glyph). I have already updated Just’s script to remove overlaps using skia-pathops (via Path.simplify() which is the underlying method called upon by pathops.union). Just use that.