TL;DR

If you can't change font size and see only a few font choices in Emacs, you probably need to activate the xft USE flag for app-editors/emacs.

Now, while it recompiles, you may read my story :)

Gentoo, HDPI and the microscopic Emacs fonts

We Gentoo Linux users love to tweak our system to the extreme, often down to package compilation options. One purpose of this can be to trim down unused features we to create the perfect blend for us, but it's sometime a great way to shoot ourselves in the foot with some missing feature. To use Gentoo you really have to enjoy hurting yourself now and then, and happily learn from it. I do, at least.

While installing Gentoo on my brand new laptop - a Razer Blade 2016, I was confronted with my first HDPI ("retina") display. As I expected, the default KDE installation was lilliputian. I suppose KDE could query pixel density from the screen to automatically fix this, but plasma is still quite young. Anyway, I was able to configure everything smoothly: just had to increase my KDE font DPI to double it and everything was readable again. There may be a few old icons here and there that did not scale, but nothing too bad, almost everything seems vectorized.

Everything but Emacs, who still had dwarf-sized fonts. I couldn't blame it too harshly for not getting DPI from the screen or KDE though, so I decided to just double font size on this computer. To my surprise, C-x C-+ didn't work to increase font size. The font size modifier in the modeset would go up and down, but the rendering wouldn't change at all. I tweaked my lisp configuration, dug into it, asked google up to the third page, no way. Everyone just kept answering the default shortcuts and functions to change font size, which did not work for me, and I couldn't believe no one else ever encountered this problem. The fact I was typing LISP bent over my screen to decipher microscopic hieroglyphs did not help with the frustration. I quickly noticed emacs had only three font available, while fc-list listed quite a lot. Nobody else ever had this problem. Again, I could not believe I was the only human being on earth with this issue.

Then it hit me: maybe I actually was one of the rare person to hit this problem with my smart-ass distribution and my custom Emacs compilation. A quick eix emacs gave me the USE flags for my installation. The disabled xft flag caught my eye, and checking with ufed confirmed my suspicion: "Build with support for XFT font renderer". With the flag enabled and a quick recompilation, I fired up emacs: the font was nicely sized without any configuration modification, since KDE had set the default X font to the double-DPI when I changed it there.

I guess I learned something valuable today. Most of the time, Gentoo does a good job of providing a good default configuration despite being entirely configurable, but it slightly failed me there. I would say this use flag should be enabled by default on desktop profile - I use default/linux/amd64/13.0/desktop/plasma. No hard feeling though, I still love you, Gentoo.