I am creating a Variable Font with Bracket Layers for several characters (e.g. a, e, s). Interpolation of Instances seems to work for all characters. The VariableFonts needs a Light Master between Thin and Black. After generating a Light Instance and creating a Light Master, the Bracket Layers are missing in the Light Master. When I create a Bracket Layer in the Light Master, it shows the unchanged character. I expected that ‘re-interpolate’ would eventually interpolate between the alternate characters in Thin and Black. It does not … What do I do wrong?
Can you show your exact setup? A screenshot of the layer panel maybe?
I just sent a file to Rainer 
The short answer is that you need an alternate layer for each master.
Or an alternate glyph I sent you a sample as a reply to the email.
The point is that we are talking about a fairly large number of Bracket Layers, and Masters to be interpolated in a family of several Variable Fonts. That is why I’d rather opt for smoothless generation of intermediate Masters instead of repairing things with scripts. I’ll send you an email with more details.
Seems to be working in Glyphs 3 latest update Thanks for adding this functionality so quickly!
Do you mean the interpolation of the bracket layers when generating instances?
Yes, at least that is what I got from Antonia. On last Tuesday both the Bracket Layers and the interpolated outlines appeared in the Masters generated form the instances in her version of Glyphs 3. After reading your message I installed the latest Beta (3.0.3 build 3065). I deleted two intermediate Masters and generated two new Masters from two existing Instances. In the first case, Bracket Layers did not appear in the Menu. Then I generated the other intermediate Master and Glyphs 3 crashed. In a second attempt I first deleted the instances, generated new instances and from these I generated two new intermediate Masters. Again, no Bracket Layers …
also, in »Ebenen«, the new Masters do not show their names (leer) and existing Masters are messing up. Thin appears under 18. Feb. … and under Thin I found Thin Condensed. Every now and then, in »Exportieren« some or all instances lose their icon letters and an OpenType logo is shown instead …
Just installed 3.0.3 (3066). Started from Glyphs File with Thin, Black, Thin Condensed and Black Condensed, created a new Instance for Light and derived a new Master from the Light Instance. Unfortunately the Bracket Layers as well as the interpolated characters in those Bracket Layers are still missing …
You did that with the Master from instance command in Font Info > Exports?
Yes.
The PDF I sent you tells you that on page 3.
I understand the problem but the solution is more complicated then I hoped.
Thanks! Let’s hope for the best
Glyphs 3: Unfortunately I am running into the same issue again. Several revised characters in Bracket Layers in Thin and Black Master need to be interpolated into the existing Bracket Layers in the intermediate Light Master. I selected a character, activated its Bracket Layer and used re-interpolate in the layers menu. The result is that Glyphs interpolates the outlines from the Masters and not from the outlines which are in the Bracket Layer. Tried the same with a copy of the Glyphs file: I deleted all instances except for the Light instance and created a Master from the light instance. The new Light master did not contain any bracket layers 
What I can think of is to make a copy of the Glyphs file, copy the outlines in the Thin and Black masters from the bracket layers to the normal layer, re-interpolate the normal layers and copy the new interpolated outlines to Bracket layers in the original Glyphs file. Sounds like a lot of clicks per character.
In some cases, characters have 3 bracket layers. Which means extra book keeping when copying
between two glyphs files …
Looked for a possibility to select all characters involved in that Glyphs file and copy them directly into the Bracket Layers in the original file by using paste-special (ignoring those characters that have more than one bracket layer). Even though I selected the glyphs and choose “contents of the active layer” in the paste-special menu, the characters were copied to the normal layer and not into the bracket layer. Did not work for single characters either, although the Layers menu shows the Bracket Layer(s) of a selected character. Did I miss something?
Perhaps it makes more sense to switch from alternate layers (=bracket layers) to alternate glyphs? Then you won’t have that nasty problem with reinterpolating.
I’ll see if I can come up with a script for circumventing the issue.
Thanks for your offer to write a script, but I am afraid that in this case it is too late to change the set up of the family for these cases. We would then have different solutions for identical features in the family. We are very close to produce the final fonts.
I see. I’ll try to fix this.
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