UIDefaultsLoader: added mix() color function (inspired by Less CSS)

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

@@ -608,6 +608,7 @@ class UIDefaultsLoader
 				case "changeSaturation":return parseColorChange( 1, params, resolver, reportError );
 				case "changeLightness":	return parseColorChange( 2, params, resolver, reportError );
 				case "changeAlpha":		return parseColorChange( 3, params, resolver, reportError );
+				case "mix":				return parseColorMix( params, resolver, reportError );
 			}
 		} finally {
 			parseColorDepth--;
@@ -787,6 +788,34 @@ class UIDefaultsLoader
 		return parseFunctionBaseColor( colorStr, function, derived, resolver, reportError );
 	}
 
+	/**
+	 * Syntax: mix(color1,color2[,weight])
+	 *   - color1: a color (e.g. #f00) or a color function
+	 *   - color2: a color (e.g. #f00) or a color function
+	 *   - weight: the weight (in range 0-100%) to mix the two colors
+	 *             larger weight uses more of first color, smaller weight more of second color
+	 */
+	private static Object parseColorMix( List<String> params, Function<String, String> resolver, boolean reportError ) {
+		String color1Str = params.get( 0 );
+		String color2Str = params.get( 1 );
+		int weight = 50;
+
+		if( params.size() > 2 )
+			weight = parsePercentage( params.get( 2 ) );
+
+		// parse second color
+		String resolvedColor2Str = resolver.apply( color2Str );
+		ColorUIResource color2 = (ColorUIResource) parseColorOrFunction( resolvedColor2Str, resolver, reportError );
+		if( color2 == null )
+			return null;
+
+		// create function
+		ColorFunction function = new ColorFunctions.Mix( color2, weight );
+
+		// parse first color, apply function and create mixed color
+		return parseFunctionBaseColor( color1Str, function, false, resolver, reportError );
+	}
+
 	private static Object parseFunctionBaseColor( String colorStr, ColorFunction function,
 		boolean derived, Function<String, String> resolver, boolean reportError )
 	{

flatlaf-core/src/main/java/com/formdev/flatlaf/util/ColorFunctions.java

@@ -26,13 +26,16 @@ import java.awt.Color;
 public class ColorFunctions
 {
 	public static Color applyFunctions( Color color, ColorFunction... functions ) {
+		// convert RGB to HSL
 		float[] hsl = HSLColor.fromRGB( color );
 		float alpha = color.getAlpha() / 255f;
 		float[] hsla = { hsl[0], hsl[1], hsl[2], alpha * 100 };
 
+		// apply color functions
 		for( ColorFunction function : functions )
 			function.apply( hsla );
 
+		// convert HSL to RGB
 		return HSLColor.toRGB( hsla[0], hsla[1], hsla[2], hsla[3] / 100 );
 	}
 
@@ -208,4 +211,42 @@ public class ColorFunctions
 			return String.format( "fade(%.0f%%)", amount );
 		}
 	}
+
+	//---- class Mix ----------------------------------------------------------
+
+	/**
+	 * Mix two colors.
+	 *
+	 * @since 1.6
+	 */
+	public static class Mix
+		implements ColorFunction
+	{
+		public final Color color2;
+		public final float weight;
+
+		public Mix( Color color2, float weight ) {
+			this.color2 = color2;
+			this.weight = weight;
+		}
+
+		@Override
+		public void apply( float[] hsla ) {
+			// convert from HSL to RGB because color mixing is done on RGB values
+			Color color1 = HSLColor.toRGB( hsla[0], hsla[1], hsla[2], hsla[3] / 100 );
+
+			// mix
+			Color color = mix( color1, color2, weight / 100 );
+
+			// convert RGB to HSL
+			float[] hsl = HSLColor.fromRGB( color );
+			System.arraycopy( hsl, 0, hsla, 0, hsl.length );
+			hsla[3] = (color.getAlpha() / 255f) * 100;
+		}
+
+		@Override
+		public String toString() {
+			return String.format( "mix(#%08x,%.0f%%)", color2.getRGB(), weight );
+		}
+	}
 }

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

@@ -370,6 +370,11 @@ class FlatCompletionProvider
 			addFunction( "changeSaturation", hslChangeParams );
 			addFunction( "changeLightness", hslChangeParams );
 			addFunction( "changeAlpha", hslChangeParams );
+
+			addFunction( "mix",
+				"color1", colorParamDesc,
+				"color2", colorParamDesc,
+				"weight", "(optional) 0-100%, default is 50%" );
 		}
 
 		private void addFunction( String name, String... paramNamesAndDescs ) {

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

@@ -68,6 +68,7 @@ public class FlatThemeTokenMaker
 		tokenMap.put( "changeSaturation", TOKEN_FUNCTION );
 		tokenMap.put( "changeLightness", TOKEN_FUNCTION );
 		tokenMap.put( "changeAlpha", TOKEN_FUNCTION );
+		tokenMap.put( "mix", TOKEN_FUNCTION );
 		tokenMap.put( "lazy", TOKEN_FUNCTION );
 
 		// function options

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

@@ -54,3 +54,11 @@ Prop.colorFunc20 = changeHue(#f00,180)
 Prop.colorFunc21 = changeSaturation(#f00,50%)
 Prop.colorFunc22 = changeLightness(#f00,80%)
 Prop.colorFunc23 = changeAlpha(#f00,50%)
+
+Prop.colorFunc30 = mix(#f00,#0f0,10%)
+Prop.colorFunc31 = mix(#f00,#0f0,25%)
+Prop.colorFunc32 = mix(#f00,#0f0)
+Prop.colorFunc33 = mix(#f00,#0f0,75%)
+Prop.colorFunc34 = mix(#f00,#0f0,90%)
+Prop.colorFunc35 = mix($Prop.color1,$Prop.color2)
+Prop.colorFunc36 = mix($Prop.colorFunc20,$Prop.colorFunc30)