Java Swing app looks tiny on high-DPI screen when it should be scaled to normal size

Question

How can I make my Java Swing app GUI scale properly to users on high-DPI screens?

See the screenshot below. At the top you can see how tiny the app looks compared to Ubuntu's file explorer icons and gedit. In the bottom left you can see roughly what size the app should look like (and does look on regular DPI monitors). So I'm looking for a way to scale the GUI of the app properly when a high DPI monitor is in use. For example, gedit looks the same on both regular DPI and high DPI monitors. I want my app to behave like this.

Here is source code for the app: https://github.com/baobabKoodaa/baopass

This is an extremely common problem affecting many apps. Roughly half of the apps I run on Ubuntu are scaled properly without any actions from the user, the other half are not scaled and look really tiny. Note that I'm mainly looking for a solution that doesn't require actions from the user (although any help is appreciated at this point - I haven't found any ways to scale it at all).

According to this scaling should already work out of the box. It doesn't. I'm not sure if this is a bug or if there is some additional step I'm supposed to do besides running the app on Java 9?

Answer 1

You have to tell the drawing libraries to scale the app up.

GDK_SCALE=2 ./application

Will have the appropriate information set in the environment and the widgets will render scaled up such that each pixel effectively takes four pixels of footprint.

Note that the splash screen (if you use Java's splash screen support) isn't presented after the entire Swing libraries are loaded, so it won't scale regardless of the settings you attempt.

In some platforms, like the Linux distribution of Fedora, partial scaling is also possible, such that you can set GDK_SCALE=1.5. Just keep in mind that it's not universally available, and it is not settable to any scaling ratio you might want.

Finally, the older JVMs ignore this setting completely, so if you aren't launching with Java 9 or higher, odds are it won't work. And, of course, the way that things are tweaked for older JVMs and different operating systems tend to vary (if they work at all).