Although the question asks about Windows scaling, the accepted solution(s), do not work properly with Linux running JDK11.
The below technique uses JNA to detect the screen scale factor on Linux, which is compatible with Linux desktops exposing the Gtk (Gimp Toolkit) libraries.
The snippet contains several Gtk version-dependent workarounds as the Gtk API exposing scaling information has changed several times. Furthermore, information may be inaccurate for specific use-cases (mixed standard and HiDPI monitors on the same desktop) as scaling is monitor-specific.
Warning: If Java fixes this behavior -- or equally if Gtk changes their API -- in a future version, this solution will need to be updated. Furthermore, this solution requires Linux-only components: reflection is required (included) for cross-compilation to succeed.
Usage: GtkUtilities.getScaleFactor()
import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.Pointer;
import java.lang.reflect.Method;
public class GtkUtilities {
/**
* Initializes Gtk2/3 and returns the desktop scaling factor, usually 1.0 or 2.0
*/
public static double getScaleFactor() {
GTK gtkHandle = getGtkInstance();
if (gtkHandle != null && gtkHandle.gtk_init_check(0, null)) {
System.out.println("Initialized Gtk");
if (gtkHandle instanceof GTK2) {
return getGtk2ScaleFactor((GTK2)gtkHandle);
} else {
return getGtk3ScaleFactor((GTK3)gtkHandle);
}
} else {
System.err.println("An error occurred initializing the Gtk library");
}
return 0;
}
private static GTK getGtkInstance() {
System.out.println("Finding preferred Gtk version...");
switch(getGtkMajorVersion()) {
case 2:
return GTK2.INSTANCE;
case 3:
return GTK3.INSTANCE;
default:
System.err.println("Not a compatible Gtk version");
}
return null;
}
/**
* Get the major version of Gtk (e.g. 2, 3)
* UNIXToolkit is unavailable on Windows or Mac; reflection is required.
* @return Major version if found, zero if not.
*/
private static int getGtkMajorVersion() {
try {
Class toolkitClass = Class.forName("sun.awt.UNIXToolkit");
Method versionMethod = toolkitClass.getDeclaredMethod("getGtkVersion");
Enum versionInfo = (Enum)versionMethod.invoke(toolkitClass);
Method numberMethod = versionInfo.getClass().getDeclaredMethod("getNumber");
int version = ((Integer)numberMethod.invoke(versionInfo)).intValue();
System.out.println("Found Gtk " + version);
return version;
} catch(Throwable t) {
System.err.println("Could not obtain GtkVersion information from UNIXToolkit: {}", t.getMessage());
}
return 0;
}
private static double getGtk2ScaleFactor(GTK2 gtk2) {
Pointer display = gtk2.gdk_display_get_default();
System.out.println("Gtk 2.10+ detected, calling \"gdk_screen_get_resolution\"");
Pointer screen = gtk2.gdk_display_get_default_screen(display);
return gtk2.gdk_screen_get_resolution(screen) / 96.0d;
}
private static double getGtk3ScaleFactor(GTK3 gtk3) {
Pointer display = gtk3.gdk_display_get_default();
int gtkMinorVersion = gtk3.gtk_get_minor_version();
if (gtkMinorVersion < 10) {
System.err.println("Gtk 3.10+ is required to detect scaling factor, skipping.");
} else if (gtkMinorVersion >= 22) {
System.out.println("Gtk 3.22+ detected, calling \"gdk_monitor_get_scale_factor\"");
Pointer monitor = gtk3.gdk_display_get_primary_monitor(display);
return gtk3.gdk_monitor_get_scale_factor(monitor);
} else if (gtkMinorVersion >= 10) {
System.out.println("Gtk 3.10+ detected, calling \"gdk_screen_get_monitor_scale_factor\"");
Pointer screen = gtk3.gdk_display_get_default_screen(display);
return gtk3.gdk_screen_get_monitor_scale_factor(screen, 0);
}
return 0;
}
/**
* Gtk2/Gtk3 wrapper
*/
private interface GTK extends Library {
// Gtk2.0+
boolean gtk_init_check(int argc, String[] argv);
Pointer gdk_display_get_default();
Pointer gdk_display_get_default_screen (Pointer display);
}
private interface GTK3 extends GTK {
GTK3 INSTANCE = Native.loadLibrary("gtk-3", GTK3.class);
// Gtk 3.0+
int gtk_get_minor_version ();
// Gtk 3.10-3.21
int gdk_screen_get_monitor_scale_factor (Pointer screen, int monitor_num);
// Gtk 3.22+
Pointer gdk_display_get_primary_monitor (Pointer display);
int gdk_monitor_get_scale_factor (Pointer monitor);
}
private interface GTK2 extends GTK {
GTK2 INSTANCE = Native.loadLibrary("gtk-x11-2.0", GTK2.class);
// Gtk 2.1-3.0
double gdk_screen_get_resolution(Pointer screen);
}
}
