UIDefaultsLoader: added systemColor() color function that can be used to change accent color (preparation for getting accent color from operating system)

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

@@ -98,6 +98,7 @@ public abstract class FlatLaf
 	private static List<Object> customDefaultsSources;
 	private static Map<String, String> globalExtraDefaults;
 	private Map<String, String> extraDefaults;
+	private static Function<String, Color> systemColorGetter;
 
 	private String desktopPropertyName;
 	private String desktopPropertyName2;
@@ -897,14 +898,14 @@ public abstract class FlatLaf
 	 * E.g. using {@link UIManager#setLookAndFeel(LookAndFeel)} or {@link #setup(LookAndFeel)}.
 	 * <p>
 	 * The global extra defaults are useful for smaller additional defaults that may change.
-	 * E.g. accent color. Otherwise, FlatLaf properties files should be used.
+	 * Otherwise, FlatLaf properties files should be used.
 	 * See {@link #registerCustomDefaultsSource(String)}.
 	 * <p>
 	 * The keys and values are strings in same format as in FlatLaf properties files.
 	 * <p>
-	 * Sample that setups "FlatLaf Light" theme with red accent color:
+	 * Sample that setups "FlatLaf Light" theme with white background color:
 	 * <pre>{@code
-	 * FlatLaf.setGlobalExtraDefaults( Collections.singletonMap( "@accentColor", "#f00" ) );
+	 * FlatLaf.setGlobalExtraDefaults( Collections.singletonMap( "@background", "#fff" ) );
 	 * FlatLightLaf.setup();
 	 * }</pre>
 	 *
@@ -929,15 +930,15 @@ public abstract class FlatLaf
 	 * E.g. using {@link UIManager#setLookAndFeel(LookAndFeel)} or {@link #setup(LookAndFeel)}.
 	 * <p>
 	 * The extra defaults are useful for smaller additional defaults that may change.
-	 * E.g. accent color. Otherwise, FlatLaf properties files should be used.
+	 * Otherwise, FlatLaf properties files should be used.
 	 * See {@link #registerCustomDefaultsSource(String)}.
 	 * <p>
 	 * The keys and values are strings in same format as in FlatLaf properties files.
 	 * <p>
-	 * Sample that setups "FlatLaf Light" theme with red accent color:
+	 * Sample that setups "FlatLaf Light" theme with white background color:
 	 * <pre>{@code
 	 * FlatLaf laf = new FlatLightLaf();
-	 * laf.setExtraDefaults( Collections.singletonMap( "@accentColor", "#f00" ) );
+	 * laf.setExtraDefaults( Collections.singletonMap( "@background", "#fff" ) );
 	 * FlatLaf.setup( laf );
 	 * }</pre>
 	 *
@@ -979,6 +980,36 @@ public abstract class FlatLaf
 		return val;
 	}
 
+	/**
+	 * Returns the system color getter function, or {@code null}.
+	 *
+	 * @since 3
+	 */
+	public static Function<String, Color> getSystemColorGetter() {
+		return systemColorGetter;
+	}
+
+	/**
+	 * Sets a system color getter function that is invoked when function
+	 * {@code systemColor()} is used in FlatLaf properties files.
+	 * <p>
+	 * The name of the system color is passed as parameter to the function.
+	 * The function should return {@code null} for unknown system colors.
+	 * <p>
+	 * Can be used to change the accent color:
+	 * <pre>{@code
+	 * FlatLaf.setSystemColorGetter( name -> {
+	 *     return name.equals( "accent" ) ? Color.red : null;
+	 * } );
+	 * FlatLightLaf.setup();
+	 * }</pre>
+	 *
+	 * @since 3
+	 */
+	public static void setSystemColorGetter( Function<String, Color> systemColorGetter ) {
+		FlatLaf.systemColorGetter = systemColorGetter;
+	}
+
 	private static void reSetLookAndFeel() {
 		EventQueue.invokeLater( () -> {
 			LookAndFeel lookAndFeel = UIManager.getLookAndFeel();

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

@@ -84,6 +84,7 @@ class UIDefaultsLoader
 
 	private static int parseColorDepth;
 
+	private static Map<String, ColorUIResource> systemColorCache;
 	private static final SoftCache<String, Object> fontCache = new SoftCache<>();
 
 	static void loadDefaultsFromProperties( Class<?> lookAndFeelClass, List<FlatDefaultsAddon> addons,
@@ -105,6 +106,10 @@ class UIDefaultsLoader
 		Properties additionalDefaults, boolean dark, UIDefaults defaults )
 	{
 		try {
+			// temporary cache system colors while loading defaults,
+			// which avoids that system color getter is invoked multiple times
+			systemColorCache = (FlatLaf.getSystemColorGetter() != null) ? new HashMap<>() : null;
+
 			// load core properties files
 			Properties properties = new Properties();
 			for( Class<?> lafClass : lafClasses ) {
@@ -276,6 +281,9 @@ class UIDefaultsLoader
 
 			// remember variables in defaults to allow using them in styles
 			defaults.put( KEY_VARIABLES, variables );
+
+			// clear/disable system color cache
+			systemColorCache = null;
 		} catch( IOException ex ) {
 			LoggingFacade.INSTANCE.logSevere( "FlatLaf: Failed to load properties files.", ex );
 		}
@@ -769,6 +777,7 @@ class UIDefaultsLoader
 		try {
 			switch( function ) {
 				case "if":			return parseColorIf( value, params, resolver );
+				case "systemColor":	return parseColorSystemColor( value, params, resolver );
 				case "rgb":			return parseColorRgbOrRgba( false, params, resolver );
 				case "rgba":		return parseColorRgbOrRgba( true, params, resolver );
 				case "hsl":			return parseColorHslOrHsla( false, params );
@@ -813,6 +822,44 @@ class UIDefaultsLoader
 		return parseColorOrFunction( resolver.apply( ifValue ), resolver );
 	}
 
+	/**
+	 * Syntax: systemColor(name[,defaultValue])
+	 *   - name: system color name
+	 *   - defaultValue: default color value used if system color is not available
+	 */
+	private static Object parseColorSystemColor( String value, List<String> params, Function<String, String> resolver ) {
+		if( params.size() < 1 )
+			throwMissingParametersException( value );
+
+		ColorUIResource systemColor = getSystemColor( params.get( 0 ) );
+		if( systemColor != null )
+			return systemColor;
+
+		String defaultValue = (params.size() > 1) ? params.get( 1 ) : "";
+		if( defaultValue.equals( "null" ) || defaultValue.isEmpty() )
+			return null;
+
+		return parseColorOrFunction( resolver.apply( defaultValue ), resolver );
+	}
+
+	private static ColorUIResource getSystemColor( String name ) {
+		Function<String, Color> systemColorGetter = FlatLaf.getSystemColorGetter();
+		if( systemColorGetter == null )
+			return null;
+
+		// use containsKey() because value may be null
+		if( systemColorCache != null && systemColorCache.containsKey( name ) )
+			return systemColorCache.get( name );
+
+		Color color = systemColorGetter.apply( name );
+		ColorUIResource uiColor = (color != null) ? new ColorUIResource( color ) : null;
+
+		if( systemColorCache != null )
+			systemColorCache.put( name, uiColor );
+
+		return uiColor;
+	}
+
 	/**
 	 * Syntax: rgb(red,green,blue) or rgba(red,green,blue,alpha)
 	 *   - red:   an integer 0-255 or a percentage 0-100%

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatDarkLaf.properties

@@ -63,7 +63,7 @@
 # accent colors (blueish)
 #   set @accentColor to use single accent color or
 #   modify @accentBaseColor to use variations of accent base color
-@accentColor = null
+@accentColor = systemColor(accent,null)
 @accentBaseColor = #4B6EAF
 @accentBase2Color = lighten(saturate(spin(@accentBaseColor,-8),13%),5%)
 #   accent color variations

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatLightLaf.properties

@@ -63,7 +63,7 @@
 # accent colors (blueish)
 #   set @accentColor to use single accent color or
 #   modify @accentBaseColor to use variations of accent base color
-@accentColor = null
+@accentColor = systemColor(accent,null)
 @accentBaseColor = #2675BF
 @accentBase2Color = lighten(saturate(@accentBaseColor,10%),6%)
 #   accent color variations