[varLib / ttLib] pen/GlyphSet API would be very handy for variable fonts

I would love the TTFont().getGlyphSet() API to be extended with variable font support. This is how I imagine this to work:

f = TTFont("myvarfont.ttf")
gs = f.getGlyphSet()
gs.setLocation({'wght': 120, 'wdth': 300})
g = gs['a']
g.draw(somePen)
print(g.width)
print(g.height)

To do this properly, varLib will have to grow a cleaner API to work with coordinates and deltas.

I have attached a very rough and sketchy implementation that uses some hacked up bits from varLib.mutator. I think this shows which parts of varLib need to be redesigned for easier reuse.

ttVarGlyphSet.py.zip

See also #1020

[behdad]

Sounds about right. I’ll give it a shot.

[behdad]

To do it on the fly is a great, but I wouldn’t want to burden the glyf module with it. Can the implementation be separate, near the TTGlyphSet code?

Okay I’ll see if that can be done. Good idea. It’s possible if we pass the location to getGlyphSet. I think that’s a fine idea. Then we can reuse your implementation.

Maybe factor out drawing to a pen from a list of coordinates + flags array, so it can be more reusable.

Sure that can be done.