Check wish: validate contour directions

[madig]

Expected behaviour

A check that validates all contour directions. We recently had a font-building oops that caused the cubic design outline's path direction to be preserved inside TTFs and no one noticed until it was time to check the hinting work. D'oh.

Resources and exact process needed to replicate

Maybe FontVal knows how to do this. Might even be non-trivial/impossible to do reliably? Needs research.

[HinTak]

FontVal does indeed. See
https://github.com/HinTak/Font-Validator/blob/master/NewHelp/E1110.htm

[madig]

The help file says that the detection might not work fully reliably. Maybe another approach would be to check only the outermost contours, since direction errors within are actually visible to the designer but invisible when everything is reversed. 🤔

[HinTak]

As far as I read that error message, it says if you have BOTH this and intersecting contours, you should correct the latter first, and see if this disappears also. I don't think it says it work unreliability for unknown / mystical reasons. It just says it is unreliable if you also have intersecting contour (which is another error, and you should deal with that FIRST). That's my understanding of that paragraph.

[HinTak]

Intersecting contour is E1111 . https://github.com/HinTak/Font-Validator/blob/master/NewHelp/E1111.htm

[madig]

Well, that's deal breaker for sources and e.g. variable or compatibly converted fonts.

[HinTak]

Yes, I see intersecting contours might be common with variable fonts.

[HinTak]

Had another thought. The glyf test tests rather the default instance in a variable font. It is still best practice not to have overlapping contours.

In fact I am not quite sure what is tested - it is most likely the default instance; but ideally it would be nice to do all the masters also.

[HinTak]

@madig : I think if you switch off the overlap contour test the rest of code, will do what you want.

The rest of code checks the individual contour directions. And the overall contour direction is the union of all.