[MPEG-OTSPEC] Some research on TT instructions and cubics

Hin-Tak Leung htl10 at users.sourceforge.net
Sat Sep 23 00:40:52 CEST 2023

 Yes, besides being slightly storage-efficient, the implicit on-curve points in quadratic also makes for smooth joins between curve segments. I think there are fonts / glyphs built entirely / mostly of off-curve points for that reason.
We still have the ambiguity of 1, 3, 4 (and more) off-curve cubic to deal with. I suppose the 1 case is easy - you just go back to quadratic and ignore the cubic bit. 3,4 or above is ambiguous: is 3 = 1 + 2 or 2 + 1 (with an implied on-curve point in the middle), and is 4 = 2 + 2 (two cubic) or 4 = 1 + 2 + 1 (two quadratics on either side of a cubic)? etc.
I think assuming people will start with existing fonts (and do conversions) is dangerous - people will find interesting ways of using the "corners" (rightly or maliciously) and then argue that their newly hacked up fonts should be interpreted / rasterized in such and such way.
    On Friday, 22 September 2023 at 23:05:32 BST, Georg Seifert <typogeorg at gmail.com> wrote:  

> Am 23.09.2023 um 00:03 schrieb Laurence Penney <lorp at lorp.org>:
>> Quadratic curve have some disadvantage over cubic as they are less versatile on what curves they can represent and often need more segments. But the trick with the implicit oncurve point between consecutive offcurves allow certain things. E.g. there are no kinks. So limiting the designer to only two offcurve points it a really bad idea. 
> You may well be correct but I don’t think that affects the proposed experiment (using fonts with public sources that already exist).
Yes. My comment has nothing to do with the cubic proposal.


> - Laurence

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