UIDefaultsLoader: added over() color function to convert a translucent color into a solid color based on any background color

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

@@ -466,6 +466,10 @@ class UIDefaultsLoader
 				if( knownValueTypes == null ) {
 					// create lazy
 					knownValueTypes = new HashMap<>();
+					// system colors
+					knownValueTypes.put( "activeCaptionBorder", ValueType.COLOR );
+					knownValueTypes.put( "inactiveCaptionBorder", ValueType.COLOR );
+					knownValueTypes.put( "windowBorder", ValueType.COLOR );
 					// SplitPane
 					knownValueTypes.put( "SplitPane.dividerSize", ValueType.INTEGER );
 					knownValueTypes.put( "SplitPaneDivider.gripDotSize", ValueType.INTEGER );
@@ -780,6 +784,7 @@ class UIDefaultsLoader
 				case "tint":			return parseColorMix( "#fff", params, resolver, reportError );
 				case "shade":			return parseColorMix( "#000", params, resolver, reportError );
 				case "contrast":		return parseColorContrast( params, resolver, reportError );
+				case "over":			return parseColorOver( params, resolver, reportError );
 			}
 		} finally {
 			parseColorDepth--;
@@ -847,7 +852,7 @@ class UIDefaultsLoader
 		int lightness = parsePercentage( params.get( 2 ) );
 		int alpha = hasAlpha ? parsePercentage( params.get( 3 ) ) : 100;
 
-		float[] hsl = new float[] { hue, saturation, lightness };
+		float[] hsl = { hue, saturation, lightness };
 		return new ColorUIResource( HSLColor.toRGB( hsl, alpha / 100f ) );
 	}
 
@@ -1041,6 +1046,33 @@ class UIDefaultsLoader
 		return parseColorOrFunction( resolver.apply( darkOrLightColor ), resolver, reportError );
 	}
 
+	/**
+	 * Syntax: over(foreground,background)
+	 *   - foreground: a foreground color (e.g. #f00) or a color function;
+	 *                 the alpha of this color is used as weight to mix the two colors
+	 *   - background: a background color (e.g. #f00) or a color function
+	 */
+	private static Object parseColorOver( List<String> params, Function<String, String> resolver, boolean reportError ) {
+		String foregroundStr = params.get( 0 );
+		String backgroundStr = params.get( 1 );
+
+		// parse foreground color
+		ColorUIResource foreground = (ColorUIResource) parseColorOrFunction( resolver.apply( foregroundStr ), resolver, reportError );
+		if( foreground == null || foreground.getAlpha() == 255 )
+			return foreground;
+
+		Color foreground2 = new Color( foreground.getRGB() );
+
+		// parse background color
+		ColorUIResource background = (ColorUIResource) parseColorOrFunction( resolver.apply( backgroundStr ), resolver, reportError );
+		if( background == null )
+			return foreground2;
+
+		// create new color
+		float weight = foreground.getAlpha() / 255f;
+		return new ColorUIResource( ColorFunctions.mix( foreground2, background, weight ) );
+	}
+
 	private static Object parseFunctionBaseColor( String colorStr, ColorFunction function,
 		boolean derived, Function<String, String> resolver, boolean reportError )
 	{

flatlaf-theme-editor/src/main/java/com/formdev/flatlaf/themeeditor/FlatCompletionProvider.java

@@ -482,6 +482,10 @@ class FlatCompletionProvider
 				"dark", colorParamDesc,
 				"light", colorParamDesc,
 				"threshold", "(optional) 0-100%, default is 43%" );
+
+			addFunction( "over",
+				"foreground", colorParamDesc,
+				"background", colorParamDesc );
 		}
 
 		private void addFunction( String name, String... paramNamesAndDescs ) {

flatlaf-theme-editor/src/main/java/com/formdev/flatlaf/themeeditor/FlatThemeTokenMaker.java

@@ -76,6 +76,7 @@ public class FlatThemeTokenMaker
 		tokenMap.put( "tint", TOKEN_FUNCTION );
 		tokenMap.put( "shade", TOKEN_FUNCTION );
 		tokenMap.put( "contrast", TOKEN_FUNCTION );
+		tokenMap.put( "over", TOKEN_FUNCTION );
 
 		// function options
 		tokenMap.put( "relative", Token.RESERVED_WORD );

flatlaf-theme-editor/theme-editor-test.properties

@@ -118,6 +118,12 @@ Prop.6.selectionForeground = contrast($Prop.6.selectionBackground,#000,#fff)
 Prop.7.selectionBackground = #FF9500
 Prop.7.selectionForeground = contrast($Prop.7.selectionBackground,#000,#fff)
 
+Prop.colorFunc60 = over(#fff8,#f00)
+Prop.colorFunc61 = over(#fff8,#0f0)
+Prop.colorFunc62 = over(#f000,#0f0)
+Prop.colorFunc63 = over(#f00,#0f0)
+Prop.colorFunc64 = over(#f008,null)
+
 
 
 @varStyle1 = #f0f