search

harfbuzz / boring-expansion-spec

Better-Engineered Font Formats; Part 1. Boring Expansion
80 stars 9 forks source link

avar3: Multi layered virtual masters #161

Open davelab6 opened 5 days ago

davelab6 commented 5 days ago

It is useful to be able to develop 'atomic' parametric axes (like XOPQ, XTRA) and then mid level 'molecule' virtual axes (that combine them in specific proportions) that are then used to blend top level 'user' axes (weight, width, opsz).

I request this based on discussions with @dberlow and @lorp

justvanrossum commented 5 days ago

Is this about:

  1. expressing things that are impossible to express with avar2
  2. expressing things that are hard to express with avar2

?

behdad commented 5 days ago

We should first rule out that this is not just a compiler distilling to avar2. I'll think about that.

Lorp commented 5 days ago

Here is a simple example of "multi-layer avar" (hmm, how many layers is this? fences or fenceposts?), using subscript digits to indicate the axis layer number:

xxUC, xxLC, xxFI mean uppercase, lowercase, figures respectively.

(I prefer the 'control' metaphor to the 'blend' metaphor, since that’s the direction inputs turn into outputs when the font is in use.)

During the avar2 design process, @behdad wondered if to allow more than 1 mapping layer. I confess I resisted it because of complexity, and I don’t think a spec concept emerged. However I think if we allow axisIndexMap to contain n axisCount records, where n* is the number of layers, we’re good :) Discussing with @behdad.

behdad commented 4 days ago

However I think if we allow axisIndexMap to contain n * axisCount records, where n is the number of layers, we’re good :) Discussing with @behdad.

The number of entries in axisIndexMap isn't part of the API of that structure. Let's not jump to a design yet, before we settle on the need and scope.

behdad commented 4 days ago

We should first rule out that this is not just a compiler distilling to avar2. I'll think about that.

I'm convinced myself that distilling it to avar2 will explode the number of tents. So, I'm happy to work on a avar3 to address that. It looks like we just need to add a numLayers item, and the rest can be deduced.

Lorp commented 4 days ago

SGTM

justvanrossum commented 4 days ago

I'm convinced myself that distilling it to avar2 will explode the number of tents.

How is a high number of tents an actual problem?