ColorFunctions: added lighten(), darken(), saturate(), desaturate() and spin()

CHANGELOG.md

@@ -16,6 +16,9 @@ FlatLaf Change Log
 - ToolBar: Toolbars are no longer floatable by default (dots on left side of
   toolbar that allows dragging toolbar). Use `UIManager.put(
   "ToolBar.floatable", true )` if you want the old behavior.
+- Added more color functions to class `ColorFunctions` for easy use in
+  applications: `lighten()`, `darken()`, `saturate()`, `desaturate()`, `spin()`,
+  `tint()`, `shade()` and `luma()`.
 
 #### Fixed bugs
 

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

@@ -25,6 +25,86 @@ import java.awt.Color;
  */
 public class ColorFunctions
 {
+	/**
+	 * Increase the lightness of a color in HSL color space by an absolute amount.
+	 * <p>
+	 * Consider using {@link #tint(Color, float)} as alternative.
+	 *
+	 * @param color base color
+	 * @param amount the amount (in range 0-1) that is added to the lightness
+	 * @return new color
+	 * @since 2
+	 */
+	public static Color lighten( Color color, float amount ) {
+		return hslIncreaseDecrease( color, amount, 2, true );
+	}
+
+	/**
+	 * Decrease the lightness of a color in HSL color space by an absolute amount.
+	 * <p>
+	 * Consider using {@link #shade(Color, float)} as alternative.
+	 *
+	 * @param color base color
+	 * @param amount the amount (in range 0-1) that is subtracted from the lightness
+	 * @return new color
+	 * @since 2
+	 */
+	public static Color darken( Color color, float amount ) {
+		return hslIncreaseDecrease( color, amount, 2, false );
+	}
+
+	/**
+	 * Increase the saturation of a color in HSL color space by an absolute amount.
+	 *
+	 * @param color base color
+	 * @param amount the amount (in range 0-1) that is added to the saturation
+	 * @return new color
+	 * @since 2
+	 */
+	public static Color saturate( Color color, float amount ) {
+		return hslIncreaseDecrease( color, amount, 1, true );
+	}
+
+	/**
+	 * Decrease the saturation of a color in HSL color space by an absolute amount.
+	 *
+	 * @param color base color
+	 * @param amount the amount (in range 0-1) that is subtracted from the saturation
+	 * @return new color
+	 * @since 2
+	 */
+	public static Color desaturate( Color color, float amount ) {
+		return hslIncreaseDecrease( color, amount, 1, false );
+	}
+
+	/**
+	 * Rotate the hue angle (0-360) of a color in HSL color space in either direction.
+	 *
+	 * @param color base color
+	 * @param angle the number of degrees to rotate (in range -360 - 360)
+	 * @return new color
+	 * @since 2
+	 */
+	public static Color spin( Color color, float angle ) {
+		return hslIncreaseDecrease( color, angle, 0, true );
+	}
+
+	private static Color hslIncreaseDecrease( Color color, float amount, int hslIndex, boolean increase ) {
+		// convert RGB to HSL
+		float[] hsl = HSLColor.fromRGB( color );
+		float alpha = color.getAlpha() / 255f;
+
+		// apply HSL color change
+		float amount2 = increase ? amount : -amount;
+		if( hslIndex == 0 )
+			hsl[0] = (hsl[0] + amount2) % 360;
+		else
+			hsl[hslIndex] = clamp( hsl[hslIndex] + (amount2 * 100) );
+
+		// convert HSL to RGB
+		return HSLColor.toRGB( hsl[0], hsl[1], hsl[2], alpha );
+	}
+
 	/**
 	 * Returns a color that is a mixture of two colors.
 	 * <p>

flatlaf-core/src/test/java/com/formdev/flatlaf/util/TestColorFunctions.java

@@ -25,6 +25,37 @@ import org.junit.jupiter.api.Test;
  */
 public class TestColorFunctions
 {
+	@Test
+	void colorFunctions() {
+		assertEquals( new Color( 0xff6666 ), ColorFunctions.lighten( Color.red, 0.2f ) );
+		assertEquals( new Color( 0x990000 ), ColorFunctions.darken( Color.red, 0.2f ) );
+
+		// saturate, desaturate
+		assertEquals( new Color( 0x9c3030 ), ColorFunctions.saturate( new Color( 0x884444 ), 0.2f ) );
+		assertEquals( new Color( 0x745858 ), ColorFunctions.desaturate( new Color( 0x884444 ), 0.2f ) );
+
+		// spin
+		assertEquals( new Color( 0xffaa00 ), ColorFunctions.spin( Color.red,40 ) );
+		assertEquals( new Color( 0xff00aa ), ColorFunctions.spin( Color.red,-40 ) );
+
+		// mix
+		assertEquals( new Color( 0x1ae600 ), ColorFunctions.mix( Color.red, Color.green, 0.1f ) );
+		assertEquals( new Color( 0x40bf00 ), ColorFunctions.mix( Color.red, Color.green, 0.25f ) );
+		assertEquals( new Color( 0x808000 ), ColorFunctions.mix( Color.red, Color.green, 0.5f ) );
+		assertEquals( new Color( 0xbf4000 ), ColorFunctions.mix( Color.red, Color.green, 0.75f ) );
+		assertEquals( new Color( 0xe61a00 ), ColorFunctions.mix( Color.red, Color.green, 0.9f ) );
+
+		// tint
+		assertEquals( new Color( 0xff40ff ), ColorFunctions.tint( Color.magenta, 0.25f ) );
+		assertEquals( new Color( 0xff80ff ), ColorFunctions.tint( Color.magenta, 0.5f ) );
+		assertEquals( new Color( 0xffbfff ), ColorFunctions.tint( Color.magenta, 0.75f ) );
+
+		// shade
+		assertEquals( new Color( 0xbf00bf ), ColorFunctions.shade( Color.magenta, 0.25f ) );
+		assertEquals( new Color( 0x800080 ), ColorFunctions.shade( Color.magenta, 0.5f ) );
+		assertEquals( new Color( 0x400040 ), ColorFunctions.shade( Color.magenta, 0.75f ) );
+	}
+
 	@Test
 	void luma() {
 		assertEquals( 0, ColorFunctions.luma( Color.black ) );