added system property flatlaf.updateUIOnSystemFontChange to allow disabling automatic UI update when system font changes (issue #580)

CHANGELOG.md

@@ -10,6 +10,8 @@ FlatLaf Change Log
 - Native window decorations (Windows 10/11 only): Added client property to mark
   components in embedded menu bar as "caption" (allow moving window). (issue
   #569)
+- Added system property `flatlaf.updateUIOnSystemFontChange` to allow disabling
+  automatic UI update when system font changes. (issue #580)
 
 #### Fixed bugs
 

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

@@ -276,6 +276,9 @@ public abstract class FlatLaf
 		}
 		if( desktopPropertyName != null ) {
 			desktopPropertyListener = e -> {
+				if( !FlatSystemProperties.getBoolean( FlatSystemProperties.UPDATE_UI_ON_SYSTEM_FONT_CHANGE, true ) )
+					return;
+
 				String propertyName = e.getPropertyName();
 				if( desktopPropertyName.equals( propertyName ) || propertyName.equals( desktopPropertyName2 ) )
 					reSetLookAndFeel();

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

@@ -16,6 +16,7 @@
 
 package com.formdev.flatlaf;
 
+import javax.swing.SwingUtilities;
 import com.formdev.flatlaf.util.UIScale;
 
 /**
@@ -139,6 +140,20 @@ public interface FlatSystemProperties
 	 */
 	String USE_TEXT_Y_CORRECTION = "flatlaf.useTextYCorrection";
 
+	/**
+	 * Specifies whether FlatLaf updates the UI when the system font changes.
+	 * If {@code true}, {@link SwingUtilities#updateComponentTreeUI(java.awt.Component)}
+	 * gets invoked for all windows if the system font has changed.
+	 * This is the similar to when switching to another look and feel (theme).
+	 * Applications that do not work correctly when switching look and feel,
+	 * should disable this option to avoid corrupted UI.
+	 * <p>
+	 * <strong>Allowed Values</strong> {@code false} and {@code true}<br>
+	 * <strong>Default</strong> {@code true}
+	 * @since 2.5
+	 */
+	String UPDATE_UI_ON_SYSTEM_FONT_CHANGE = "flatlaf.updateUIOnSystemFontChange";
+
 	/**
 	 * Specifies a directory in which the native FlatLaf library have been extracted.
 	 * The path can be absolute or relative to current application working directory.