Check for nested components

[RosaWagner]

Observed behaviour

Component referring to another component (nested) are not exported correctly for ttf variable format. They take back the coordinates of the original glyph.

Expected behaviour

There should be a check to find any nested components.

Resources and exact process needed to replicate

I used Public Sans at commit uswds/public-sans@0a09945

But you can reproduce it with any font which have nested components (typically ohorn/uhorn with another accent)

[arrowtype]

This may be a more severe issue than just something messing up Samsa.

At arrowtype/recursive#412, I have described issues that occur when printing static TTFs with many printers. In summary: PostScript-based printers really mess up nested components in TTF fonts. This includes even high-end setups used for offset printing. One example of where things go wrong in current Recursive TTFs:

(There are more examples in the issue.)

There are two possible culprits:

• A problem in ttfautohint, or in how PostScript handles the hints from it
• A fundamental problem with PostScript’s handling of TTF nested components

Worse, printers that have PostScript installed apparently never update that software.

So, this check plus a script that un-nests components are probably relatively high-priority, if Google Fonts wants to give people any confidence in using the library for more than just web design. Not all of the alignment problems with TTFs & PostScript would be solved by this – it also messes up the positioning of glyph substituted via stylistic sets – but it seems that it would solve the majority of them.

[madig]

There's a ufo2ft filter to unnest composites automatically. Insert the following into your UFO's lib.plist:

    <key>com.github.googlei18n.ufo2ft.filters</key>
    <array>
      <dict>
        <key>name</key>
        <string>flattenComponents</string>
        <key>pre</key>
        <integer>1</integer>
      </dict>
    </array>

[arrowtype]

@madig THANK YOU, this is amazing news!

[madig]

It's actually been in there for decades, but we don't have time to write docs so all the filters are secret.

[anthrotype]

quite depressing that in 2020 we can't still have nested glyf components

[graphicore]

It's actually been in there for decades, but we don't have time to write docs so all the filters are secret.

I could be a good start to just drop some general lines about the existence of this mechanism and where to find the available filters and how to generally access and configure them.

[madig]

I started something at googlefonts/ufo2ft#286 last century but died before I could finish the job.

The stems of all .py files in https://github.com/googlefonts/ufo2ft/tree/master/Lib/ufo2ft/filters can be used as filters.

[simoncozens]

@madig: Would it be worth making FlattenComponents the default instead of DecomposeComponents?