Java: Retrieve current Windows Display Scale during runtime, e.g. 1.0 = 100%, 1.25 = 125%, 1.5 = 150%, 1.75 = 175%, 2.0 = 200%

WindowsDisplayScale.java

import com.sun.jna.platform.win32.GDI32;
import com.sun.jna.platform.win32.WinDef;

import java.awt.Toolkit;
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

/**
 * This <code>WindowsDisplayScale</code> class retrieves the current <code>Windows Display
 * Scale</code> throughout a <code>Java</code> applications' runtime, e.g.
 * <code>1.0  = 100%, 1.25 = 125%, 1.5  = 150%, 1.75 = 175%, 2.0  = 200%</code>.
 *
 * <p>It uses <code>Java AWT</code> and the <code>Java Native Access (JNA) platform</code>
 * to access the <code>Display Device Context (DC)</code> from <code>Microsoft
 * Windows graphics device interface (GDI)</code></p>
 *
 * @implNote Requires <code>net.java.dev.jna.platform (Maven)</code>
 * <p>Full support for <code>Java 8</code> on <code>Windows 11</code>: Value updates throughout runtime</p>
 * <p>Partial support for <code>Java 11</code> on <code>Windows 11</code>: Value from application startup</p>
 *
 * @author     <a href="https://gist.github.com/jcoester/52817d1fd7b8018e8127b57c56079804">jcoester</a>
 * @author     built on previous version from <a href="https://gist.github.com/tresf/00a8ed7c9860e3bd73cebf764a49789f">tresf</a>
 * @version    1.0 (2024 Feb. 17)
 */
public class WindowsDisplayScale {

    public static void main(String[] args) {

        // For demonstration: Check Windows Display Scale every 5 seconds
        ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
        scheduler.scheduleAtFixedRate(WindowsDisplayScale::update, 0, 5, TimeUnit.SECONDS);
    }

    private static void update() {

        // Retrieval of the Windows Display Scale
        double scaleDecimal = detectWindowsDisplayScale();
        int scalePercentage = (int) (scaleDecimal * 100);

        // Usage of the Windows Display Scale
        System.out.println("Windows Display Scale (double): " + scaleDecimal); // e.g. 1.0, 1.25, 1.5, 1.75, 2.0
        System.out.println("Windows Display Scale ( int% ): " + scalePercentage); // e.g. 100, 125, 150, 175, 200
        System.out.println(); // Easier readability during demonstration
    }

    public static double detectWindowsDisplayScale() {

        /* Retrieve AWT scale
         * (Detects the Windows Display Scale once during application startup) */
        double awtScale = Toolkit.getDefaultToolkit().getScreenResolution() / 96.0f;

        // Retrieve HDC (Handle to Device Context (DC))
        WinDef.HDC hdc = GDI32.INSTANCE.CreateCompatibleDC(null);
        if (hdc == null)
            return 0;

        /* Retrieve HDC Display info
         * (Detects changes to the Windows Display Scale during the application runtime) */
        double a = GDI32.INSTANCE.GetDeviceCaps(hdc, 10); // 10=VERTRES
        double b = GDI32.INSTANCE.GetDeviceCaps(hdc, 117); // 117=DESKTOPVERTRES
        GDI32.INSTANCE.DeleteDC(hdc);
        if (a == 0 || b == 0)
            return 0;

        // Offset HDC Vertical pixels with the initial AWT scale
        b = b * awtScale;

        // Calculate Windows Display Scale
        double windowsDisplayScale = a > b ? a / b : b / a;

        // Round to two decimals and return
        return BigDecimal.valueOf(windowsDisplayScale).setScale(2, RoundingMode.HALF_UP).doubleValue();
    }
}