https://bugzilla.redhat.com/show_bug.cgi?id=1496466

--- Comment #15 from Nicolas Mailhot nicolas.mailhot@laposte.net --- (In reply to David Kaspar [Dee'Kej] from comment #13)

Looking at the sizes of the OTF and TTF, the OTF seems to be "compressed", therefore in order to save users' space, I would again vote for using this format.

TTF uses quadratic splines whereas OTF uses cubic splines. Type1 uses cubic splines. That's why you can get lossless glyph shape conversion between Type1 and OTF but not between Type1 and TTF, and why upstream wrote they absolutely needed a CFF format to make sure there was no deviation in metrics from the standard.

(One can approximate a cubic spline with a series of quadratic splines, that's how font tools convert Type1/OTF to TTF, the result is good enough for the human eye, but technically it's not lossless. In your case absolutely no deviation is better than minimal deviations given the glyph sizes are standardised).

That's why generally speaking it's better to use OTF when evolving a Type1 font, except for legacy windows-oriented apps that understand TTF but not OTF. Linux systems do not care they have good support both for OTF and for TTF. Hardware has passed the point where computing cubics was significantly more expensive than computing quadratics a long time ago.

The spline part of OTF files is more compact than Type1. One is CFF2 the other is CFF1 — they are mathematically equivalent but the state of the art had improved between both specs (both written essentially by Adobe).