Is there a way to reuse a master in a variable font to extend an axis where only the sidebearings change?

[alexcordy]

I am not sure how best to address a design goal I have within a variable font. I currently have an optical size axis that ranges from 14 to 32, with two masters, one for the smallest size and one for the largest.

The glyphs are drawn differently at both sizes, and their sidebearings also have different values at both sizes (tighter for larger optical sizes).

The issue I’m having is that I’d like to extend the optical size range to (for instance) 100, where the only thing that changes between 32 and 100 is the spacing between glyphs to make it progressively tighter until this new upper limit of 100, but the glyph designs themselves have no variation after 32.

I’m aware that I could duplicate the master at 32 and introduce a new master for 100, and then globally reduce the sidebearings for all glyphs within that master. But it seems inelegant to increase the file size by 50% (going from 2 to 3 masters) and to create two masters with identical designs just to adjust the spacing in one.

Perhaps there’s no other way, but that’s my question: is there a way to have the glyph designs interpolate between 14 and 32, but have the spacing interpolate between 14 and 100, with the shapes frozen at and after 32?

I’ve only been using Glyphs for a short while, so I apologize if this is a dumb question either because the answer is clearly no or clearly yes in some obvious way. I’d appreciate any insight into this!

[GeorgSeifert]

Maybe don’t do the master altogether and do the spacing with manually written variable GPOS?

[SCarewe (Sebastian Carewe)]

Have a look at this thread:

Side bearing deltas / intermediate sidebearings

Hi! Here’s an interesting problem with linear interpolation: narrow styles require letter spacing to be equal to the counter space, but only until some point, when a tighter spacing is preferred (wide, normal and slightly narrow styles). Thus, if you interpolate between ultra condensed and normal widths, everything in-between is spaced too tightly, as you can see on the example below. In static instances that can be solved with a filter, cool. Is there a solution for variable fonts? Perhaps, a …

Specifically, you want to add a virtual master. See further down:

Side bearing deltas / intermediate sidebearings

Hello, I am trying to achieve something similar. I have a project with only a weight and an italic axis. I would now like to add an opsz axis that controls only the spacing. Ideally, in my working file, I would like to add as little as possible in order to keep everything easily editable. My thought process is the following: I add an opsz axis and set the same value for all masters (20, let’s say) I add a “Virtual Master” custom parameter and set opsz to 8. I add variable GPOS code like in t…

Summary:

• add a “Virtual master” custom parameter in Font Info > Font. Set its opsz location to 100. Don’t change the other values.
• in Font Info > Features, add a feature “kern”, and write:

pos @All <0 0 0 0 (opsz:100) -20 0 -20 0>;

where -20 is the amount by which you want to change the spacing (or, technically, half).

[alexcordy]

Thank you @GeorgSeifert and @SCarewe for your suggestions. I’m unfamiliar with what GPOS or virtual masters are, so I’ll have to read a bit more about them, but I’ll see if those approaches yield a solution. I may return to ask some more questions but I’d like to figure out as much as I can without imposing on your time first. Thank you for the quick responses!