Any thoughts?

Fine with the setting position (it makes the last panel have 5 items, but only when nightmode is enabled, and it's the same for ReaderRolling).
@NiLuJe will have to validate the BlitBuffer magic (right methods, in the right order, etc...)

The blitbuffer stuff is fine in principle, but note that k2pdfopt has a -neg option. It might be more efficient to use that instead.

Fine with the setting position (it makes the last panel have 5 items, but only when nightmode is enabled, and it's the same for ReaderRolling).

You said last panel, but this is currently on the contrast panel. Should it be moved to the last one to match "Invert Images"?

k2pdfopt has a -neg option. It might be more efficient to use that instead.

That's interesting. The part of k2pdfopt responsible for that seems to bek2settings->dst_negative. I don't think there is direct control over that with KOPTContext currently because k2pdfopt_settings_init_from_koptcontext(k2settings, kctx)doesn't set that option from the context.

I don't think there is direct control over that with KOPTContext currently because k2pdfopt_settings_init_from_koptcontext(k2settings, kctx)doesn't set that option from the context.

KOPTContext controls what we want it to control. ;-) But since it'll ultimately do something very similar it'd probably mostly be keeping things a touch more legible over here.

On the flip side, this way you can also apply the same thing to PicDocument.

You said last panel, but this is currently on the contrast panel. Should it be moved to the last one to match "Invert Images"?

Oh, right.
I wouldn't really mind in what panel it is: my point was that I don't like more than 4 items per panel - so we can see more of the page, but going from 4 to 5 in one panel only when in night mode can be ok (only nightmode users will suffer :))
But it feels it would not be out of place in the last panel (with other document related thingies like Document Language, Writing Directions, Document colons - it's about the document that it has/is real images, and we want them non-inverted in nightmode (+ the symetry with ReaderRolling/creopt).
The Contrast pannel might be considered more about the text/pages than the document ? (but I'm not really a Pdf reader).

But since it'll ultimately do something very similar it'd probably mostly be keeping things a touch more legible over here.

Yeah, that might be better than messing around with blitters. Although, one benefit of inverting it after is not having to update the cache.

But it feels it would not be out of place in the last panel (with other document related thingies like Document Language, Writing Directions, Document colons - it's about the document that it has/is real images, and we want them non-inverted in nightmode (+ the symetry with ReaderRolling/creopt).

That's definitely a good point. Although it might be more similar to the dewatermark and contrast option in practice, conceptually it is definitely a document option especially since it is dependent on night mode. And ultimately the consistency/symmetry with creopt is probably preferable.