Game is unplayable on HiDPI devices

[MarSoft]

I have a 15" laptop with 3840x2160 resolution. When I run asciiportal without any additional arguments, it shows me a tiny window with tiny letters. If I resize that window then everything stays in its top left corner.
If I pass -r 1280x1800 or other resolution, number of characters in window increases but characters themselves are still tiny and nearly unreadable.
If I use fullscreen mode (-f) then interface occupies the whole screen - but still with the same tiny characters, regardless of -r setting.

How do I change font size used by the game?