How do "Supplemental" fonts work on the Kobo

[trekky0623]

I have a Kobo Clara BW running software version 4.45.23697. I have noticed many unicode characters not rendering correctly with some fonts, specifically characters like thin space (U+2009), em space (U+2003), and in one book the "leftwards arrow with hook" (U+21A9) that was being used for backlinks from citations.

I figured the font being used must not have these, so I downloaded Code2000 and verified that all three of these characters are in that font. If I set the book to use this font, characters display fine. However, the trouble comes when I try to use a different font with Code2000 as a supplemental font.

The info icon next to the Supplemental font selection says that "If a character cannot be rendered by the main font selected for the book, we try to render it using the supplemental font." However, selecting Code2000 as the supplemental font does nothing. The characters show as � or as an empty box regardless of the supplemental font chosen.

This seems like a bug to me, and not the expected behavior. Wondering if there is a fix or if anyone else has noticed this.

The book in question is a Kepub book converted with Calibre.

[icallaci]

I have this exact problem. I have been busy with other things, so it's on my list of things to look into some day, but as far as I know it's just supposed to work without jumping through hoops, although for me it doesn't. At least I know I'm not the only one. My books are epubs that are converted to kepub when I sideload them using Calibre.

[fogice]

I contacted Kobo about the thin space issue (only some of their built-in fonts contain this character). They talked to their engineers, and for some reason, space characters aren't handled the same way as regular characters with regard to supplemental fonts. Which is totally lame.

As a workaround, consider using Nico's modified fonts for ereading (free). His 4.0 release incorporates the special space characters that are causing us issues, and he has a specific version of his fonts tweaked for Kobo/kepub rendering.

[trekky0623]

Originally Posted by fogice

I contacted Kobo about the thin space issue (only some of their built-in fonts contain this character). They talked to their engineers, and for some reason, space characters aren't handled the same way as regular characters with regard to supplemental fonts. Which is totally lame.

As a workaround, consider using Nico's modified fonts for ereading (free). His 4.0 release incorporates the special space characters that are causing us issues, and he has a specific version of his fonts tweaked for Kobo/kepub rendering.

I also contacted Kobo support this week, and they told me my ticket had been escalated after sending video of the issue to them. I think I had seen a post about the spaces, but it seems to be affecting more than just whitespace.

And thank you for that repo! I have my own folder of fonts I've been tweaking for my e-reader for years now, lol, but these look really nice. I might try those out and see about adding some of the missing characters to my own.

[icallaci]

Thank you! This explains what I'm seeing. And thanks for the link to Nico's modified fonts. Will they work as a fallback?

Originally Posted by fogice

I contacted Kobo about the thin space issue (only some of their built-in fonts contain this character). They talked to their engineers, and for some reason, space characters aren't handled the same way as regular characters with regard to supplemental fonts. Which is totally lame.

As a workaround, consider using Nico's modified fonts for ereading (free). His 4.0 release incorporates the special space characters that are causing us issues, and he has a specific version of his fonts tweaked for Kobo/kepub rendering.

[fogice]

Originally Posted by trekky0623

And thank you for that repo! I have my own folder of fonts I've been tweaking for my e-reader for years now, lol, but these look really nice. I might try those out and see about adding some of the missing characters to my own.

One of his other repos is the script he uses to prepare the fonts for Kobo. You might try running that on the fonts that your already use.

[fogice]

Originally Posted by icallaci

Thank you! This explains what I'm seeing. And thanks for the link to Nico's modified fonts. Will they work as a fallback?

I don't think anything works properly as a fallback, but feel free to try and report back.