Windows: update fonts (and scaling) when user changes Windows text size

CHANGELOG.md

@@ -7,6 +7,8 @@ FlatLaf Change Log
 - Added `Flat*Laf.install()` methods.
 - macOS: Use native screen menu bar if system property
   `apple.laf.useScreenMenuBar` is `true`.
+- Windows: Update fonts (and scaling) when user changes Windows text size
+  (Settings > Ease of Access > Display > Make text bigger).
 
 
 ## 0.11

flatlaf-core/src/main/java/com/formdev/flatlaf/FlatLaf.java

@@ -21,6 +21,7 @@ import java.awt.Color;
 import java.awt.Component;
 import java.awt.Container;
 import java.awt.Dimension;
+import java.awt.EventQueue;
 import java.awt.Font;
 import java.awt.Insets;
 import java.awt.KeyboardFocusManager;
@@ -28,6 +29,8 @@ import java.awt.Toolkit;
 import java.awt.Window;
 import java.awt.event.AWTEventListener;
 import java.awt.event.KeyEvent;
+import java.beans.PropertyChangeEvent;
+import java.beans.PropertyChangeListener;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.ArrayList;
@@ -43,6 +46,7 @@ import javax.swing.LookAndFeel;
 import javax.swing.SwingUtilities;
 import javax.swing.UIDefaults;
 import javax.swing.UIManager;
+import javax.swing.UnsupportedLookAndFeelException;
 import javax.swing.UIDefaults.LazyValue;
 import javax.swing.plaf.ColorUIResource;
 import javax.swing.plaf.DimensionUIResource;
@@ -71,6 +75,9 @@ public abstract class FlatLaf
 
 	private BasicLookAndFeel base;
 
+	private String desktopPropertyName;
+	private PropertyChangeListener desktopPropertyListener;
+
 	private AWTEventListener mnemonicListener;
 	private static boolean altKeyPressed;
 
@@ -111,10 +118,30 @@ public abstract class FlatLaf
 				altKeyChanged( e.getID() == KeyEvent.KEY_PRESSED );
 		};
 		Toolkit.getDefaultToolkit().addAWTEventListener( mnemonicListener, AWTEvent.KEY_EVENT_MASK );
+
+		// listen to desktop property changes to update UI if system font or scaling changes
+		if( SystemInfo.IS_WINDOWS ) {
+			// Windows 10 allows increasing font size independent of scaling:
+			//   Settings > Ease of Access > Display > Make text bigger (100% - 225%)
+			desktopPropertyName = "win.messagebox.font";
+		}
+		if( desktopPropertyName != null ) {
+			desktopPropertyListener = e -> {
+				reSetLookAndFeel();
+			};
+			Toolkit.getDefaultToolkit().addPropertyChangeListener( desktopPropertyName, desktopPropertyListener );
+		}
 	}
 
 	@Override
 	public void uninitialize() {
+		// remove desktop property listener
+		if( desktopPropertyListener != null ) {
+			Toolkit.getDefaultToolkit().removePropertyChangeListener( desktopPropertyName, desktopPropertyListener );
+			desktopPropertyName = null;
+			desktopPropertyListener = null;
+		}
+
 		// remove mnemonic listener
 		if( mnemonicListener != null ) {
 			Toolkit.getDefaultToolkit().removeAWTEventListener( mnemonicListener );
@@ -478,6 +505,35 @@ public abstract class FlatLaf
 		return strs;
 	}
 
+	private static void reSetLookAndFeel() {
+		EventQueue.invokeLater( () -> {
+			try {
+				// re-set current LaF
+				LookAndFeel lookAndFeel = UIManager.getLookAndFeel();
+				UIManager.setLookAndFeel( lookAndFeel );
+
+				// must fire property change events ourself because old and new LaF are the same
+				PropertyChangeEvent e = new PropertyChangeEvent( UIManager.class, "lookAndFeel", lookAndFeel, lookAndFeel );
+				for( PropertyChangeListener l : UIManager.getPropertyChangeListeners() )
+					l.propertyChange( e );
+
+				// update UI
+				updateUI();
+			} catch( UnsupportedLookAndFeelException ex ) {
+				ex.printStackTrace();
+			}
+		} );
+	}
+
+	/**
+	 * Update UI of all application windows.
+	 * Invoke after changing LaF.
+	 */
+	public static void updateUI() {
+		for( Window w : Window.getWindows() )
+			SwingUtilities.updateComponentTreeUI( w );
+	}
+
 	public static boolean isShowMnemonics() {
 		return altKeyPressed || !UIManager.getBoolean( "Component.hideMnemonics" );
 	}

flatlaf-core/src/test/java/com/formdev/flatlaf/FlatTestFrame.java

@@ -22,6 +22,8 @@ import java.awt.event.ComponentEvent;
 import java.awt.event.KeyEvent;
 import java.awt.event.WindowAdapter;
 import java.awt.event.WindowEvent;
+import java.beans.PropertyChangeEvent;
+import java.beans.PropertyChangeListener;
 import java.util.prefs.Preferences;
 import javax.swing.*;
 import javax.swing.plaf.ColorUIResource;
@@ -167,6 +169,18 @@ public class FlatTestFrame
 				updateTitle();
 			}
 		} );
+
+		UIManager.addPropertyChangeListener( e -> {
+			if( "lookAndFeel".equals( e.getPropertyName() ) ) {
+				EventQueue.invokeLater( () -> {
+					// update title because user scale factor may change
+					updateTitle();
+
+					// enable/disable scale factor combobox
+					updateScaleFactorComboBox();
+				} );
+			}
+		} );
 	}
 
 	private void updateTitle() {
@@ -233,14 +247,8 @@ public class FlatTestFrame
 				// change look and feel
 				UIManager.setLookAndFeel( lafClassName );
 
-				// update title because user scale factor may change
-				updateTitle();
-
-				// enable/disable scale factor combobox
-				updateScaleFactorComboBox();
-
 				// update all components
-				SwingUtilities.updateComponentTreeUI( this );
+				FlatLaf.updateUI();
 
 				// increase size of frame if necessary
 				if( pack )

flatlaf-demo/src/main/java/com/formdev/flatlaf/demo/ControlBar.java

@@ -79,6 +79,15 @@ class ControlBar
 		lafModel.setSelectedItem( lafModel.getElementAt( sel ) );
 
 		lookAndFeelComboBox.setModel( lafModel );
+
+		UIManager.addPropertyChangeListener( e -> {
+			if( "lookAndFeel".equals( e.getPropertyName() ) ) {
+				EventQueue.invokeLater( () -> {
+					// update info label because user scale factor may change
+					updateInfoLabel();
+				} );
+			}
+		} );
 	}
 
 	void initialize( JFrame frame, JTabbedPane tabbedPane ) {
@@ -173,11 +182,8 @@ class ControlBar
 				// change look and feel
 				UIManager.setLookAndFeel( newLaf.className );
 
-				// update info label because user scale factor may change
-				updateInfoLabel();
-
 				// update all components
-				SwingUtilities.updateComponentTreeUI( frame );
+				FlatLaf.updateUI();
 
 				// increase size of frame if necessary
 				int width = frame.getWidth();