Add dummy DSIG table

[m4rc1e]

I'm wondering whether it's worthwhile to include a dummy dsig table?

http://typedrawers.com/discussion/1147/are-empty-dsig-tables-in-a-font-useless

Glyphsapp still exports fonts with a dummy DSIG table.

I don't exactly know all the apps which still require it so I started a thread on FB as well, fonttools/fontbakery#1845

[anthrotype]

I'm -1 on this. I think one can always run a post-compile script to merge that in. Oh actually, you can already do that: just put your dummy DSIG as a ttx file inside the UFO/data directory, and ufo2ft will merge it for you.

[khaledhosny]

It is a so common task (since many versions of MS Office will not enable OpenType features for TrueType fonts without it), that I think an option to do (or a link key) is warranted. Every one having to do it separately and figure out how to create a dummy DSIG is not the best way to handle it IMO.

[anthrotype]

Well, ok. I don't particularly need it, but you're welcome to send a PR.

[anthrotype]

The main problem I have with the whole dummy DISG approach is the "dummy" part. I'd rather see it either completely deprecated from the spec (since the spec is lacking and the only public MS implementation doesn't even follow it -- see OT mailing list for the issue with checksum calculation), or implemented it properly using python cryptography libraries. But there is less and less incentive in spending time to do that, given that MS folks themselves seems to not care any more.

[khaledhosny]

It is just a workaround for broken but widely used application(s), otherwise I can’t care less about DSIG table.

[chrissimpkins]

For those who come across this thread and need a workaround, there is a script available in the Font Bakery repository (perhaps moved to the Google font scripts repo with the recent transition in much of the source?) and a derivative of it in the Hack repository that was created for our post-compile workflow ---> https://github.com/source-foundry/Hack/blob/master/postbuild_processing/fixes/fix-dsig.py

[graphicore]

perhaps moved to the Google font scripts repo

it's here: https://github.com/googlefonts/tools/blob/master/bin/gftools-fix-dsig.py

[chrissimpkins]

@khaledhosny Do you happen to know what era of MS applications are affected by this issue?

[madig]

MS Office Word to this day I think. No DSIG, no OTL like kerning.

[chrissimpkins]

MS Office Word to this day I think. No DSIG, no OTL like kerning.

Jens indicated that this is not the case in fonttools/fontbakery#1845 (comment)

[khaledhosny]

I don’t have up to date information on this.

[chrissimpkins]

Thanks Khaled. I reached out to the MS team today. I will let you know what I hear back.

[chrissimpkins]

The MS team confirmed the findings here through the developer who changed the behavior in MS Word back in 2014. The absence of a DSIG table has not blocked the enumeration of OpenType features in MS Word since.