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title: private use
idx: 30
metadesc: understanding the private use area in fonts
codelang: python
this isn't an essay, it's more like a journal. i'm putting things in here that i find interesting and i try to string them together. i will probably update this over time, it will change as i learn more but i will try to keep the learning-spirit of it present.
> the Private Use Areas are three ranges of code points (U+E000–U+F8FF in the BMP, and planes 15 and 16)
-- <a href="">Private Use Area (unicode)</a>
I did the math and realized that's 137,469 possible glyphs. That's a lot of glyph.
Here [at work](, I'd been trying to rationalize our use of various icons and so forth. But how? It's challenging because we have icons that are ka-specific but we also like having things like [fontawesome]( around.
A while back, I made the decision to fork fontawesome so we could add in a few superfluous glyphs. [Lots of peolpe do this actually]( but, maybe i'm missing something because I don't hear very much about it or their experiences forking an open source icon font.
## what's the big deal?
The main challenges, as far as i'm concerned, at least as far as this all goes, is that when you're forking a stable project, you're creating some cognitive dissonance for your team who are already used to using the upstream version. Second, you're making a conscious decision to ignore or absorb upstream changes. Third, you may be trying to find a way to keep your project merging safely with the upstream project's.
Iconfonts are a strange beast because (unlike most text faces) they have the capacity to be [incredibly modular](, but the tooling around them does not encourage it. And you basically have four options: fontlab, fontforge, glyphs, and robofont (to say nothing of fontographer and type tool), all of which natively use a different file format.
## and why, again?
At the time i had two goals: add extra glyphs to the font and change fontawesome's `[class="icon-*"]` selector so that it cost us less per-page-load. It turns out the selector change landed in 4.0, so at least i didn't spend too much time on that. But the issue of adding new glyphs remained legitimate.
The secondary benefit, which i hadn't considered at first, but which now seems quite legitimate, is reducing the glyph count. Of my earliest experiments when beginning this process, was seeing how many font-awesome glyphs we used. Here's some handy shell incantation you can use to figure this out for yourself
ack -ho "(?:[\" ])(icon-[a-z\-]+)" --html | \
sed 's/.\(.*\)/\1/' | \
sort | \
if you have looked at fontawesome recently, you will find upwards of 350 glyphs in use. do you need all those? clearly services like the (mostly) disemvoweled [icnfnt]( are aware of this disconnect, but naturally a question is how to generate a version of the font with the above information without having to bother with clickity clicking a website.
## generating a font
by far the easiest way of going about this is by running the Generate Font action that every font editor has available. but... are there other ways? yes! there are.
for example, if you're using a .ufo-based workflow, then you have at your disposal the afdko which now (natively) generates opentype fonts. If you're building one in release mode, the incantation goes something, for font awesome, like this:
$ makeotf -f FontAwesome.ufo \
-o FontAwesome.otf
-ff fdk/features \
-gf fdk/glyphOrder \
-mf fdk/menuname \
which assumes you have a folder sitting around called fdk which contains opentype-specific features/glyphorder/etc. for reference, adobe publishes a [reference implementation]( for Minion. Miguel Sousa wrote a small thing about how to generate this in a [typophile GlyphOrderAndAliasDB thread](
Robofont generates this folder when you run the Generate Font command
if you are using robofont, then the app adds an entry to the font's `lib` called `public.glyphOrder` so you could, for example, do something like this:
def glyphorder(font_path='/path/to/font.ufo', dest='glyphOrder'):
MAX_POINTS = 1114113
font =
if font.lib.get('public.glyphOrder', None):
# for a robofont font, you can get
order = font.lib.get('public.glyphOrder')
# otherwise, you can do
order = font.keys()
sorted(order, key=lambda g: font[g].unicode or MAX_POINTS)
with open(dest, 'w') as out:
for g in order:
outstr = "%s %s" % (g, g)
if font[g].unicode:
outstr += " uni%04X" % font[g].unicode
Removing glyphs from the glyphOrder file doesn't *really* change anything and won't remove any of the glyphs from the font. to do that you need the `tx` tool or you would need to build a new version of the font from the source ufo.
## fixing the font version string
For whatever reason, `makeotf` will generate an obtuse version string. It would be nice to be able to include things like "the git commit that yielded this font" rather than just a version number which may be stale.
To do this, you need `ttx` from the fonttools package. you can `pip install fonttools` for that. Having it, you can then run:
$ ttx myfont.otf
this will generate a file called myfont.ttx which is, semi-conveniently, an xml file.
You can then modify it by running a python script like this
""" - call like `python font.ttx vcs_hash'
it will make a file called font-vcs_hash.ttx
import sys
import os
import xml.etree.ElementTree as ET
def versionit(ttx_file, vcs_hash):
ttx_root = ET.parse(ttx_file)
version = ttx_root.find('CFF/CFFFont/version').get('value')
for name in ttx_root.findall('name/namerecord[@nameID="5"]'):
name.text = "Version %s; %s" % (version, vcs_hash)
filename, extension = os.path.splitext(ttx_file)
ttx_root.write('%s-%s%s' % (filename, vcs_hash, extension),
xml_declaration=True, encoding='utf-8')
if __name__ == '__main__':
filename = sys.argv[1]
vcs_hash = sys.argv[2]
versionit(filename, vcs_hash)
this is super-basic, but you could extend this however you like, presumably by having it call ttx again on the resultant file and the
## the pua
in case it's not obvious, it's quite common to work with the pua, the good folks at [SIL]( document their use of it (mostly so others can understand how they've assigned ideographs and symbols).