Problem with Helzel Fraktur typefaces

[Fahneflycht]

Big fan of Affinity software suite here! As a fly in the ointment, however, I have now discovered an irksome problem with its handling of certain Fraktur fonts. In addition to being well designed and historically accurate, Gerhard Helzel's opentype fraktur fonts (www.fraktur.biz) automatically provide the correct setting of ligatures as well as the long s, where the typographical rules require it in German. Helzel's fonts may thus pretty much be considered the aesthetic standard in this genre. The Affinity suite accurately sets the long s as well as other ligatures like [long-]st, fi, ff, fl, etc. It also generally correctly does not set ligatures where these do not belong (e.g., in words like "ausstellen" or "auffinden". Unfortunately, with some of Helzel's fonts, the ligature fl is incorrectly replaced with an "fi" — instead of setting "auflösen" (correct would in this case be no ligature), Affinity converts the fl into fi, i.e., it sets "auffiösen". It seems this problem is confined to the ligature fl alone, and curiously enough only with some of the Helzel fonts, with most of them Affinity correctly sets [f+l] in such words. As MS Word as well as another Windows app of mine always function properly with the affected fonts, I conclude it must be Affinity that contains a bug here. Manually intervening with zero-width spaces is possible, but is a highly cumbersome method to use in longer texts. The problem only affects about 20% of the Helzel fonts and even with these, Word gets it right and the false ligature apparently only appears in Affinity (see attached screenshots for how both applications set the word "auflösen" in a few sample Helzel fonts).

Is there perhaps a quick fix to this problem (e.g., substituting "fl" for "fi" at the relevant place in the code, perhaps?) that could be included in the next upgrade?

[kenmcd]

In the OpenType era this kind of language-specific stuff is typically handled in the localization and ligatures features of the font.
Given that this happens with only two of the fonts points to the fonts as the issue.
And given the horrible disorganized 1990s mess of a website - I do not have a lot of faith in the quality of the fonts.

To troubleshoot this issue the fonts need to be examined.
It is not likely the solution would be some sort of special rule built into the Affinity text shaper.
It could be an error in the OpenType features coding, but again the fonts would be needed to evaluate the issue.

Note: Other applications may have auto-correct features which may also affect this.
In early Unicode fonts with no OpenType features the applications may have helped with auto-correct rules.
I make sure to turn-those off to see what the font is actually doing.

[Fahneflycht]

OK, thanks for your quick reply. The fonts I showed in my sample aren't the only ones affected by this problem. What I don't quite understand is why only some of his fonts (I'm guessing about 20%) would have this issue whereas most work flawlessly with Affinity and with other applications. I would have thought he'd use the same engine for all his fonts, as the typographical rules apply to all fraktur typefaces, regardless of their outward appearance. I also don't understand why this problem doesn't occur when using Word 2016, which was why I thought it might have something to do with Affinity. Still, I accept that the only way to find out would be to examine the code used in the affected fonts, but since none of these are freeware, this would require Mr. Helzel's permission. Bottom line this means that I will simply have to avoid using the affected fonts for any longer project, at least until further notice.  

[kenmcd]

One would assume all the fonts' OpenType feature code would be the same, but even the web page appears to show different levels of support in different fonts. Which is why I would want to see multiple fonts - both working and not working. Then they could be compared. There is more than one way to write the OpenType feature code and some ways work better than others.

The issue could be a problem in the Affinity text rendering, but there is no way to know without the actual fonts.