You used to be able to change font, but now you can't?

[cgregurich]

Just want to make sure I'm understanding this page correctly. You used to be able to change the font being used, but then a new rendering engine was implemented, and that new engine... doesn't allow you to change the font? It's stuck with the one font?

I'm curious about why that's a thing. That seems like a pretty important feature to have in an ebook viewer. Why is the new rendering engine limited in that way?

[GitHubRulesOK]

Technically not a current issue as the historic change is clearly documented.
And there is/are open issue(s) for the future.
#2980
#476
#1406
#121
#2752
#3472
#3382
etc etc

The eBook engines were several (possibly 3 or more at one time) and thus 2 primary User interface streams needed constant maintaining in sync.

Those were combined into the same core MuPDF rendering which meant less problems with differences per engine but the same fixed screen rendering methods, as one common User Interface.

MuPDF does have some limited means to substitute fonts for SOME formats but not all.

[BH2WFR]

It's necessary for font changing feature to correctly read Chinese epub books. Default Chinese font is serif, and it is DIFFICULT for reading.

If I use a Non-serif font (Microsoft YaHei UI) to display Chinese Characters, it will ease my eyes while reading.