dlig features

Craig Eliason
Craig Eliason Posts: 1,436
edited October 2012 in Technique and Theory
In my version of Mac TextEdit (1.6), there is considerable though not complete access to OpenType features, and they can be controlled through the Typography panel from the Fonts panel.
I notice that Zapfino's many contextual alternates (e.g. changing /Z/a/p/f/i/n/o into the /Z_a_p_f_i_n_o glyph), which are programmed into the dlig feature, show up automatically, and can be turned off by deselecting "Special Ligatures."
Question one: How/why is "Special Ligatures" (e.g. dlig) turned on by default?--I would expect it to be off.
Question two: Why with the font I've designed with discretionary ligatures doesn't the "Special Ligatures" option appear in the Typography panel? I can't seem to access those ligatures.
(Zapfino is a .ttf, my font an .otf, if that matters.)
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Comments

  • Mark Simonson
    Mark Simonson Posts: 1,734
    edited October 2012
    Zapfino that ships with Macs isn't an OpenType font. It's an AAT (Apple Advanced Typography) font, a format that came out of QuickDraw GX a few years before OpenType. Like OpenType, it's an extension to TrueType (some extra tables). It has features similar to OpenType, but doesn't map one-to-one with OpenType. There are things you can do in one that you can't do in the other, and vice versa. It's quite a bit more difficult to program and Mac-only, hence not very common. What you're seeing with the "Special Ligatures" option probably has something to do with AAT.
  • Craig Eliason
    Craig Eliason Posts: 1,436
    That explains it, thanks Mark.
  • Ralf
    Ralf Posts: 170
    The Wikipedia article on AAT even uses that Zapfino ligature example:
    http://en.wikipedia.org/wiki/Apple_Advanced_Typography
  • Craig Eliason
    Craig Eliason Posts: 1,436
    Am I right in guessing that, when I open Zapfino with FontLab's "Open Installed Font" function, I am not seeing all of the programming in that font file due to FontLab's limitations? For example, TextEdit's Typography panel offers a cool "Avoid d-collisions" feature that (so far as I can tell) doesn't appear in the OT window in FLab.
  • Mark Simonson
    Mark Simonson Posts: 1,734
    edited October 2012
    Right, FontLab has no support for AAT. Font Forge does, but I don't know much about it.

    I wish that there was better support for AAT in my preferred font editors. As I understand it, it's quite possible for TrueType fonts to include AAT tables in addition to OpenType tables. A lot of Mac apps don't have very good support for OpenType, but full AAT support is built into the OS.

    Being able to add AAT features to my fonts would allow better results in apps like Final Cut Pro and Pages. TextEdit has pretty good OT support because it uses the latest font APIs, but other apps (like Final Cut Pro and Pages) still use older APIs, and whomever is in charge of those products doesn't seem to think better font support is a priority. If I could add AAT features in my fonts, they would work better even in older Mac apps that will never get better OT support, such as Final Cut Pro 7.

    (Sorry for hijacking the discussion.)
  • Craig Eliason
    Craig Eliason Posts: 1,436
    No apologies, you're answering my questions helpfully!
    Certainly the possibility of custom names (like "Avoid d-collisions") for features is a welcome possibility as far as user interaction goes.
  • Mark Simonson
    Mark Simonson Posts: 1,734
    edited October 2012
    One of the cool things about AAT is that you can define the names of features. So, if you want a feature called "Schoolbook Alternates" or "Unicase", you can do it, and you don't have to wait for the next version of the OT spec, and then wait for apps to add support for it. AAT can also detect things like the beginning or end of a line of text, something that's not possible in OT. It's too bad it only works on Macs. It's also notoriously difficult to write AAT features. It's based on something called a "state engine", which I've never been able to understand very well. Apple's font group released some new tools recently that are supposed to make things easier, but I haven't had much of a chance to look at them.
  • James Puckett
    James Puckett Posts: 1,992
    If I could add AAT features in my fonts, they would work better even in older Mac apps that will never get better OT support, such as Final Cut Pro 7.
    Sounds like a good topic for an ILT essay. You could lump it in with Apple’s other typographical incompetence, such as using Helvetica as a UI typeface.
  • Thomas Phinney
    Thomas Phinney Posts: 2,885
    > "Apple's font group released some new tools recently that are supposed to make things easier"

    It shows how disconnected Apple and AAT are from mainstream font development that this is the first I've heard of it. :(

    > "using Helvetica as a UI typeface"

    I still rag on this every chance I get. I once jailbroke my iPhone specifically to be able to change the UI font. No other reason. Too much hassle to stay jailbroken, though.

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