Check glyphs are not constructed from transformed components

[m4rc1e]

Some families have glyphs which have been constructed by using transformed components e.g in Comfortaa the 'u' is constructed from a flipped 'n'.

From a designers point of view, this sounds like a win (less work). However, such approaches can lead to rasterisation issues. In the above example, since the 'u' is just a flipped 'n', we cannot assign cvts to it. When I run the font through ttfautohint, the 'u' doesn't sit on the baseline at certain sizes.

[felipesanches]

I want to work on this. @m4rc1e, can you point me to the commit in which the trick is used? (I presume you already fixed that on more recent commits)

[felipesanches]

@m4rc1e is this meant to be a general ban on component transforms? Or is this specific to hacks like this one?

I have myself used component transforms in Beth Ellen in order to not include 2 copies of the outlines of the glyphs that make-up some ligatures.

I can perhaps detect only rotate transforms and emit a WARN so that the user is notified about the potential raster issues. In this cases should we suggest the designers prioritize rasterization-safety over reduction of file-sizes?

[kontur]

@m4rc1e Thanks for the context 👍

[felipesanches]

Today @vv-monsalve and @RosaWagner suggested Priority Level: 8 (1=lowest, 10=highest)

[felipesanches]

The rationale text for this check should mention this:

When building the font with fontmake, this problem can be fixed by using the "Decompose Transformed Components" filter.

[simoncozens]

For anyone (like me) getting the error and not knowing precisely how to fix it with fontmake, you add this to the command line: --filter DecomposeTransformedComponentsFilter.

[simoncozens]

@felipesanches What do you think about moving this check to universal? It is not strictly a GF-related check as it causes problems in various rendering environments.

[chrissimpkins]

What is the rationale for this fail if a font is not hinted with ttfa? It looks like this landed in universal and we are now failing on unhinted TT font builds.