syntax highlighting of code blocks only works for default theme about foliate

[johnfactotum]

Yes, that would be possible in theory, but probably too localized and complicated to be ever implemented in Foliate itself.

Some alternatives, when the book already has syntax highlighting, which most of them do, are

• Allow disabling color overrides
• Use other methods such as filters to change the colors
• Bring back support for __ibooks_internal_theme, and then the book itself can use -webkit-text-fill-color to force the text color

[johnfactotum]

This is a feature to ensure that the text is legible. I think this is also the behavior in Apple Books and Readium/Thorium.

I suppose the easiest way out would be to just add an option to disable this.

[nylki]

This is a feature to ensure that the text is legible. I think this is also the behavior in Apple Books and Readium/Thorium.

I suppose the easiest way out would be to just add an option to disable this.

Thank you for your quick response! Just to avoid confusion: Is my assumption correct that the non-default themes don't have a code-block specific stylesheet that would fit their color scheme? (so they are colored as if they are plaintext).

[johnfactotum]

The syntax highlighting is part of the stylesheet of the EPUB file. Most EPUB files are designed to be displayed on a white background only and look broken when you apply a custom theme. So when using non-white background, Foliate overrides all foreground and background colors so that the theme would be applied consistently and the text would remain readable. See 29eed7e.

[nylki]

@johnfactotum Thanks for explaining, makes way more sense now 🙂 ! I did not know that the syntax coloring is baked into the EPUB itself.
I was hoping that code blocks were somehow defined in a more generic way in EPUB (like a <code></code>-block), so that applying a syntax theme would be relatively easy.

I wonder if it would be feasible to heuristically identify code blocks and then define a custom theme for those section.

Anyways, feel free to close the issue if you like.

[johnfactotum]

Yes, the code should be marked up with the <code> element. However, to quote the HTML Standard:

There is no formal way to indicate the language of computer code being marked up.

So automatically applying syntax highlighting would be problematic.

[nylki]

I see. So, just to entertain the idea: although there is no formal way, auto-detection of the language inside a block could be an option (perhaps as an option that is disabled by default, or more involved, via a button to change the detected language). For example highlight.js does supports auto-detection of languages.