How to set the DPI of Java Swing apps on Windows/Linux?

Question

I'm currently investigating this issue on Windows. Here's what I found:

Most Swing Look & Feels don't support high DPI at all, not even Nimbus even though it's supposed to be scalable. I found some old blog posts saying that Nimbus might eventually offer high DPI scaling, but apparently that never happened.

The one exception is System LAF but its default font is ~10% smaller than the actual system font size, at all DPI settings. Moreover, System must be selected explicitly as described here: http://docs.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html

There's no single scaling factor that you could set in Swing, either. The specific LAF has to provide code to handle scaling. So the best you can do is select System and hope it's good enough.

However, JavaFX does correctly and automatically scale all the way up to 150% on my system. If at all possible, I suggest you use JavaFX to build your GUI.

edit: I made a couple small test programs and took comparison screenshots for various GUI frameworks, Swing themes, and DPI settings. This might be informative for people reading this question: http://kynosarges.org/GuiDpiScaling.html

Short answer: You need to run it on JRE 9+.

Long answer:
This is because the Java runtime declared itself to be "DPI-aware" but didn't really supported it for AWT and Swing. Java applications were sized and rendered based on pixels rather than being properly scaled, this included HiDPI displays. Anyways, this has been recently solved. See the issue JEP 263: HiDPI Graphics on Windows and Linux and the upgrade.

So, increasing the font size does not work (because it does not increase the rest of the things); the jvm argument -Dsun.java2d.dpiaware=false does not work (because it is not really supported); and the manifest file + registry edit (for Windows) just does not work.

Solution: You need to run it on JRE 9+ because it really supports this feature.

This answer solved the issue on my 4K-screen Ubuntu laptop.

In the application's config file, I added the -Dsun.java2d.uiScale=2.5 Java parameter and now, upon executing, the application is scaled well and is usable.

On Linux, it doesn't seem possible to do scaling with any Swing look and feel, according to my experiments. However, it is possible to do it using a hack involving VNC, vncdesk. Here is my configuration for running gradle --gui under vncdesk:

.vncdesk/1/settings.ini:

[desktop]
width = 1050
height = 650

[window]
title = gradle
name = gradle in vncdesk
class = GradleInVncdesk
scale_factor = 2

.vncdesk/1/startup:

#!/bin/sh
cd "$INVOCATION_DIR"
matchbox-window-manager&
exec gradle --gui "$@"

I managed to solve it following these instructions: Link.

It's in German, but I will translate the important stuff.

Create this registry-key:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\SideBySide]
"PreferExternalManifest"=dword:00000001

Create a manifest file with this content:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>

<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0" xmlns:asmv3="urn:schemas-microsoft-com:asm.v3">

<dependency>
  <dependentAssembly>
    <assemblyIdentity type="win32" name="Microsoft.Windows.Common-Controls" version="6.0.0.0" processorArchitecture="*" publicKeyToken="6595b64144ccf1df" language="*">
    </assemblyIdentity>
  </dependentAssembly>
</dependency>

<dependency>
  <dependentAssembly>
    <assemblyIdentity type="win32" name="Microsoft.VC90.CRT" version="9.0.21022.8" processorArchitecture="amd64" publicKeyToken="1fc8b3b9a1e18e3b">
    </assemblyIdentity>
  </dependentAssembly>
</dependency>

<trustInfo xmlns="urn:schemas-microsoft-com:asm.v3">
  <security>
    <requestedPrivileges>
      <requestedExecutionLevel level="asInvoker" uiAccess="false"/>
    </requestedPrivileges>
  </security>
</trustInfo>

<asmv3:application>
  <asmv3:windowsSettings xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">
    <ms_windowsSettings:dpiAware xmlns:ms_windowsSettings="http://schemas.microsoft.com/SMI/2005/WindowsSettings">false</ms_windowsSettings:dpiAware>
  </asmv3:windowsSettings>
</asmv3:application>

</assembly>

Copy it into the bin directory where the java.exe and javaw.exe is inside and named it java.exe.manifest and javaw.exe.manifest (You will have two files with the same content but different names).

HTH.

Bernd