kepub font oddity

[seanos]

I noticed an odd problem after recently installing the KoboTouchExtended driver in Calibre and sending a book to the Aura H2O in kepub format.

The embedded font looks like its kerning is really messed up for punctuation.

Epub format:


Kepub format:


The font is EB Garamond and I only see this with kepub. The font is also loaded on the device, but with a kepub it can’t be selected - well you can select it as much as you like, but the font does not change.

Any ideas why this is so? I can’t see anything obviously different about the font.

[GeoffR]

I think what you are seeing might be because the ePub reader uses GPOS kerning, but the KePub reader uses old-style 'kern' tables for kerning.

Most fonts seem to come only with GPOS kerning tables. If you want the kerning to work with the KePub reader then you need to add old-style 'kern' tables to the font. You can use fontforge to add the missing tables. (i.e. so the font will have both GPOS and 'kern' tables, and it will then work with both ePub and KePub readers.)

Edit: Actually, on looking closer, the letters seem to be kerned okay in the KePub version, so I guess the 'kern' tables must be present. I have EB Garamond on my Glo (in ttf format with 'kern' tables added) and it doesn't have this problem though.

Edit2: I think if the font is embedded in the book then you won't be able to select a sideloaded font with the same name. Do you have a link to the actual version of the font you have embedded? It looks a little different to the EB Garamond I have. (EBGaramond-0.016.zip from https://bitbucket.org/georgd/eb-garamond/downloads.)

[GeoffR]

What is interesting about the font you are using is that the KePub reader is displaying ligatures. With all the fonts I have seen, only the ePub reader displays ligatures.

The EBGaramond font I am using has the s_t and c_t ligatures in the font, but they are in the historical ligature set ('hlig' feature), not in the standard ligature set ('liga' feature), so they don't display automatically.

I wonder how your font's GSUB lookup tables are set out. Perhaps there is a way to make the KePub reader display ligatures for other fonts too, by editing the GSUB tables?

[344a]

I just wonder how can you capture the screen?

[Dr. Drib]

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seanos:
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[seanos]

Originally Posted by Dr. Drib

seanos:
Please take a few moments to read our Posting Guidelines, in particular the part about the maximum image size allowed (600x600 pixels). Images that violate those guidelines will be deleted.

It is every member's responsibility to read our Posting Guidelines and follow them.

Thanks.

It would be nice if you didn’t delete text as well as the images. Since this is easily fixed a small grace period would’ve been nice as we don’t all live in the same hemisphere.

[seanos]

Originally Posted by 344a

I just wonder how can you capture the screen?

There is a setting you can change that makes the power button take a screenshot. While the setting is activated you can’t switch off using the power button though.

See this thread.

[seanos]

Originally Posted by GeoffR

What is interesting about the font you are using is that the KePub reader is displaying ligatures. With all the fonts I have seen, only the ePub reader displays ligatures.

The EBGaramond font I am using has the s_t and c_t ligatures in the font, but they are in the historical ligature set ('hlig' feature), not in the standard ligature set ('liga' feature), so they don't display automatically.

I wonder how your font's GSUB lookup tables are set out. Perhaps there is a way to make the KePub reader display ligatures for other fonts too, by editing the GSUB tables?

I have run the font through FontSquirrel’s Webfont Generator which can fold OpenType features into the font (hlig in this case), so it’s possible that had done something strange along the way. It is odd that the problem only shows up in kepub though.

Although I have FontForge I’ve barely used it. Is it simply a matter of checking Old Style ‘kern’ in the font generation options? I notice there’s also a Windows-compatible ‘kern’ option — is that required as well? I had been using the OTF version.

I should probably go back and do some more testing.

[GeoffR]

Originally Posted by seanos

I have run the font through FontSquirrel’s Webfont Generator which can fold OpenType features into the font (hlig in this case), so it’s possible that had done something strange along the way. It is odd that the problem only shows up in kepub though.

The ePub reader uses code in Adobe's RMSDK to render the fonts, but the KePub reader uses WebKit. They are very different, but in general the ePub reader handles fonts better than the KePub reader does. Things like kerning and ligatures work out-of-the-box with the ePub reader, but either don't work at all or take a lot of tweaking of the fonts to get them to work in the KePub reader. The KePub reader also has some problems with uneven word spacing and irregular line justification which might be related to its handling of fonts.

Possibly the Webfont generator has folded in some feature that the KePub reader can't handle properly, perhaps the opbd/lfbd/rtbd features? It is interesting though, it might still be possible to fold in the ligatures without the other features and get a font where ligatures work in the KePub reader.

Although I have FontForge I’ve barely used it. Is it simply a matter of checking Old Style ‘kern’ in the font generation options? I notice there’s also a Windows-compatible ‘kern’ option — is that required as well? I had been using the OTF version.

Yes, to get the normal kerning working in the KePub reader just tick the Old Style 'kern' option. I haven't seen a WIndows-compatible option, but i am using an older version of FontForge. The Webfont generator might be doing something else with the kerning though, so maybe there are other ways to get the KePub kerning working.

[GeoffR]

One thing I just remembered about EB Garamond -- the KePub reader doesn't like the name for some reason, I had to use fontforge to change the family name from "EB Garamond 08" to "EB Garamond08" to make it work as a sideloaded font in the KePub reader.

Edit: Changing the font name to EBGaramondEight and the family name to EB Garamond Eight also works, so it seems to be the isolated numeral at the end of the name that it doesn't like.

[drjd]

Originally Posted by GeoffR

One thing I just remembered about EB Garamond -- the KePub reader doesn't like the name for some reason, I had to use fontforge to change the family name from "EB Garamond 08" to "EB Garamond08" to make it work as a sideloaded font in the KePub reader.

Edit: Changing the font name to EBGaramondEight and the family name to EB Garamond Eight also works, so it seems to be the isolated numeral at the end of the name that it doesn't like.

Ah.. I have been struggling with this for quite some time. Thanks GeoffR, for the proper solution. Should I just rename the font files or to go through procedure using FontForge?

[GeoffR]

Originally Posted by drjd

Ah.. I have been struggling with this for quite some time. Thanks GeoffR, for the proper solution. Should I just rename the font files or to go through procedure using FontForge?

You need to change the font's internal Family name (see attachment.)

If you just make the minimal change to remove the space before the final number in the Family Name, then you don't need to change the filename.

If you change the Fontname to EBGaramondTwelve-Regular and the Family Name to EB Garamond Twelve then the filename will need to change to match, but in that case FontForge should use the correct filename when it generates the new font.

(I also change the Name for Humans to match, but I'm not sure if that matters or not.)

[drjd]

Got it clear! Thanks.

[JSWolf]

How does one add to the ligatures that RMDSK uses?

[GeoffR]

Originally Posted by JSWolf

How does one add to the ligatures that RMDSK uses?

This is just what I have found by experimenting, there might be a better way:

The ePub reader seems to enable the 'liga' feature by default, so if you look in the GSUB lookup tables for a suitable 'liga' Standard Ligatures lookup subtable you can use "Edit Data" to add the ligatures you want.

If there are ligatures already present in 'hlig' or 'dlig' tables, then you can just edit the metadata for the table and change its feature to 'liga' to enable all the ligatures in the table; or else move individual ligatures from 'hlig' and 'dlig'' into a suitable 'liga' table.