Allow changing fonts for EPUBs

[zhen-huan-hu]

I really appreciate that Komga now supports EPUB files. I'd like to see more customization options for EPUB files, particularly changing font types.

This would be particularly useful for reading books written in different languages. On my Kindle, I use Adobe Jenson Pro for English books and Adobe Source Han Serif for Chinese books.

Many EPUB readers allow changing a few fonts supplied by the application itself. Only a few supports loading external fonts (Kindle, Thorium Reader). Some of my favorite fonts are commercial fonts so able to load external fonts would be a really useful feature.

Here is how Adobe Jenson Pro looks like in Thorium Reader, and how the same texts look in Komga. Notice the ligature "fi" and "Th"? It is those small things of a professionally designed font that really makes the reading experience more pleasant in my opinion:

[gotson]

The current epub library used supports additional fonts. Would you know what kind of free fonts are usually available on readers that would make sense bundling with Komga ?

For non-free fonts i would need to find a way to expose them for the whole Komga server. What are the file format of those fonts you use ? Would you be able to share the fonts privately (via Discord DM) with me, for development purpose only ?

[zhen-huan-hu]

I prefer OTF fonts because they support some more advanced features (such as ligatures). The more traditional font format is TTF.

Can you expand a bit on that ? I am not very familiar with font formats. From what i saw of the epub library, it can load WOFF and WOFF2 fonts for sure.

WOFF seems to be a web font format and is a compression of TTF/OTF with metadata: https://en.wikipedia.org/wiki/Web_Open_Font_Format

Adobe Source fonts provide WOFF2 format as well: https://github.com/adobe-fonts/source-han-serif/releases

[gotson]

I'll some testing with adding some fonts in the Komga config folder and load them dynamically, see if that works

[gotson]

@zhen-huan-hu i've got a working prototype, the fonts have to be stored in a sub-directory of the Komga config directory.

The Epub reader then displays a dropdown list with the available fonts, and it can be changed on the fly.

[zhen-huan-hu]

@zhen-huan-hu i've got a working prototype, the fonts have to be stored in a sub-directory of the Komga config directory.

The Epub reader then displays a dropdown list with the available fonts, and it can be changed on the fly.

That's fantastic. Thank you.

[gotson]

Dev is done, i've also bundled Open Dyslexic so it's always available. Will be in the next release.

[zhen-huan-hu]

Fonts included by some other readers I used

• Marvin: Arvo, Charis, Gentium, Liberation Mono, Lora, Notica Text, Open Dyslexic, Open Sans (almost same as Noto Sans), Volkhov
• Kavita: EB Garamond, Fira Sans, Lato, Libre Baskerville, Merriweather, Nanum Gothic, Rocknroll One, Open Dyslexic

[gotson]

🎉 This issue has been resolved in 1.19.0 (Release Notes)