Alignment Zones in exported fonts

[JeremyTankard]

I’ve set the Family Alignment Zones to match the Regular weight Alignment Zones.
On export and looking at the font file in OTMA both the BlueValues/OtherBlues and FamilyBlues/FamilyOtherBlues are different. Notably the values in the OtherBlues and FamilyOtherBlues. I was expeting them to be identical in the Regular font.

This is exported from Glyphs 2. A quick test from Glyphs 3 had the same result.

[JeremyTankard]

I remain confused as to how Glyphs handles the Alignment Zones and Family Alignment Zones.

How does Glyphs (2 and 3) differentiate between BlueValues and OtherBlues?
If I have a Bottom Zone (OtherBlue) that is above the Baseline (such as bottom alignment zone of superiors) – how is this specified so Glyphs knows it is a bottom zone? Is it dependent on specifiying the top or bottom of the zone and a pos or neg range?

In the Glyphs Manual you state that only 5 top zones and 6 bottom zones can be specified. Whereas the spec says up to 7 top pairs and up to 5 bottom pairs.

I guess I could just ignore Glyphs and edit in OTMA but this seems a bit painful (perhaps).

[JeremyTankard]

same font exported from FontLab 7 - and its results in OTMA

[mekkablue (Rainer Erich Scheichelbauer)]

@JeremyTankard

In the Glyphs Manual you state that only 5 top zones and 6 bottom zones can be specified. Whereas the spec says up to 7 top pairs and up to 5 bottom pairs.

Thank you for the nudge. I had another look at the spec. I refer to ‘Type1 Font Format’ published by Adobe. Chapter 5.3 BlueValues, page 36 and 37, my emphasis:

The value associated with BlueValues is an array containing an even number of integers taken in pairs, and which follow a small number of rules:

• The first integer in each pair is less than or equal to the second integer in that pair.
• The first pair is the baseline overshoot position and the baseline. This is a bottom-zone.
• All subsequent pairs describe top-zones, that is, alignment zones for the tops of character features, for example, x-height and x-height overshoot position, ascender-height and ascender-height overshoot position, cap-height and cap-height overshoot position, figure-height and figure-height overshoot position.
• Up to seven pairs may be given in the BlueValues array; the first pair must be the baseline pair.
• Different pairs must be at least 3 units apart from each other and from pairs in OtherBlues, as described in the following section. (This minimum distance can be modified by the optional BlueFuzz entry in the Private dictionary; see the definition of BlueFuzz, that follows.)
• The maximum difference between values in one pair is constrained as described under the description of BlueScale, that follows.

And then there is chapter 5.4 OtherBlues, page 38, again my emphasis:

The optional OtherBlues entry in the Private dictionary is associated with an array of pairs of integers similar to the BlueValues array. However, the OtherBlues array describes bottom-zones only. For example, these may include: descender-depth overshoot position and descender-depth, superior baseline overshoot position and superior baseline, and ordinal baseline overshoot position and ordinal baseline. Up to five pairs (10 integers) may be specified in the OtherBlues array. Numbers in a pair must be in ascending order, with the same restriction on the maximum difference in a pair. Pairs must be at least 3 units apart from all other pairs, including those in the BlueValues array. (This minimum distance can be modified by the optional BlueFuzz entry in the Private dictionary.)

So, in the wording of the spec, it is one ‘baseline overshoot’, six ‘top-zones’ and five bottom-zones. So, if you count the baseline overshoot as a bottom zone (which is how it is treated in the Glyphs UI), it is six and six. This is how I described it in the tutorial:

You can have up to 6 top zones (positive sizes), and 6 bottom zones including the baseline zone (negative sizes). As soon as you have any zones, one of them must be the baseline zone.

And: It does not matter whether OtherBlues are above or below the baseline, the spec specifically lists the superior baseline overshoot in the examples for OtherBlues. I remember a misleading blogpost on Adobe’s blog stating that OtherBlues were meant for metrics below the baseline. But that makes no sense.

The new PDF manual is in the works, but will still take a while. Tutorials currently take precedence. I hope to find more time in the Xmas holidays.

[JeremyTankard]

Thanks!
and for the link – I couldn’t find that as I was searching for ‘Alignment Zones’

I was beginning to guess that Baseline was treated as a Bottom Zone . . .
All sorted now