Vertical Metrics Confusion

AbrahamLee
AbrahamLee Posts: 262
in Font Technology
The other day I ran into an issue, brought to my attention by a friend. Is there any logic in having any of a font's ascent values the same as the cap-height? I'm asking because I've seen some from prominent foundries and it seemed odd to me especially since the overshoot of many glyphs, not just caps, but numerals as well as others, extend beyond all but the WinAscent value. In my community of users, this has caused some problems with the calculation of text bounding boxes in software they use. Any thoughts? Is this a historical choice that is only now causing "problems"? It's not really a design choice, but an underlying software library bug in the font-handling functions (Qt), at least I'm pretty sure it is.

For example, here are the ascending metrics for one of the fonts in question:
  • Cap height = 688
  • Ascent = 688
  • HHead Ascent = 688
  • Typo Ascent = 688
  • Win Ascent 936
And then, for the descending ones, also kind of odd to me:
  • Descent = -312
  • HHead Descent = -312
  • Typo Descent = -312
  • Win Descent = -220

I feel pretty comfortable in understanding what each of the metrics is meant for. So, am I just off my rocker or am I right in thinking this is a really poor strategy nowadays? Can you think of a reason they would be set up this way? I appreciate any insight.

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Comments

  • Kent Lew
    Kent Lew Posts: 937
    If you don’t want to call out the font in question, can you at least give some idea of the era from which it comes originally?

    I suspect this is a typeface that originated in early digital era, or possibly before, and then evolved through various font format conversions. These values look like a legacy from an early Postscript Type 1 font, with later values retrofitted, and only the Win Ascent/Descent accommodating contemporary considerations.
  • AbrahamLee
    AbrahamLee Posts: 262
    I’d say what font it is, just didn’t know how kosher that kind of disclosure is around here. If you don’t think it’s a big deal, let me know.

    Looks like the family was originally released in 1990 and possibly updated around 2001. So, maybe you’re right.
  • Thomas Phinney
    Thomas Phinney Posts: 2,883
    That is pretty ancient. 2001 was pretty early in the days of OpenType, and 1990 would have been at the dawn of TrueType.

    Best practices for vertical metrics have changed quite a bit in the past 17 years.
  • AbrahamLee
    AbrahamLee Posts: 262
    edited August 2018
    That’s what I thought, as well. Just thought I’d ask to make sure I wasn’t missing something obvious. Thanks!

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