Styling: basic implementation of styling support using client property JComponent.style and CSS syntax

only for JSlider (at the moment)

e.g. `mySlider.putClientProperty( "JComponent.style", "trackValueColor: #00f; trackColor: #f00; thumbColor: #0f0; trackWidth: 6; thumbSize: 40,20; focusWidth: 20" );`

(issues #117 and #340)

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

@@ -126,6 +126,16 @@ public interface FlatClientProperties
 
 	//---- JComponent ---------------------------------------------------------
 
+	/**
+	 * Specifies the style of a component in CSS syntax ("key1: value1; key2: value2; ...").
+	 * <p>
+	 * <strong>Components</strong> {@link javax.swing.JComponent}<br>
+	 * <strong>Value type</strong> {@link java.lang.String}<br>
+	 *
+	 * @since TODO
+	 */
+	String COMPONENT_STYLE = "JComponent.style";
+
 	/**
 	 * Specifies minimum width of a component.
 	 * <p>

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

@@ -726,6 +726,21 @@ public abstract class FlatLaf
 		customDefaultsSources.remove( folder );
 	}
 
+	/**
+	 * Parses a UI defaults value string and converts it into a binary object.
+	 * <p>
+	 * See: <a href="https://www.formdev.com/flatlaf/properties-files/">https://www.formdev.com/flatlaf/properties-files/</a>
+	 *
+	 * @param key the key, which is used to determine the value type
+	 * @param value the value string
+	 * @return the binary value
+	 * @throws IllegalArgumentException on syntax errors
+	 * @since TODO
+	 */
+	public static Object parseDefaultsValue( String key, String value ) throws IllegalArgumentException {
+		return UIDefaultsLoader.parseValue( key, value );
+	}
+
 	private static void reSetLookAndFeel() {
 		EventQueue.invokeLater( () -> {
 			LookAndFeel lookAndFeel = UIManager.getLookAndFeel();

flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatSliderUI.java

@@ -27,6 +27,8 @@ import java.awt.event.MouseEvent;
 import java.awt.geom.Ellipse2D;
 import java.awt.geom.Path2D;
 import java.awt.geom.RoundRectangle2D;
+import java.beans.PropertyChangeListener;
+import java.util.Map;
 import javax.swing.JComponent;
 import javax.swing.JSlider;
 import javax.swing.LookAndFeel;
@@ -34,6 +36,8 @@ import javax.swing.SwingUtilities;
 import javax.swing.UIManager;
 import javax.swing.plaf.ComponentUI;
 import javax.swing.plaf.basic.BasicSliderUI;
+import com.formdev.flatlaf.FlatClientProperties;
+import com.formdev.flatlaf.util.Graphics2DProxy;
 import com.formdev.flatlaf.util.HiDPIUtils;
 import com.formdev.flatlaf.util.UIScale;
 
@@ -90,6 +94,7 @@ public class FlatSliderUI
 	protected Color disabledTrackColor;
 	protected Color disabledThumbColor;
 	protected Color disabledThumbBorderColor;
+	protected Color tickColor;
 
 	private Color defaultBackground;
 	private Color defaultForeground;
@@ -98,6 +103,7 @@ public class FlatSliderUI
 	protected boolean thumbPressed;
 
 	private Object[] oldRenderingHints;
+	private Map<String, Object> oldStyleValues;
 
 	public static ComponentUI createUI( JComponent c ) {
 		return new FlatSliderUI();
@@ -107,6 +113,13 @@ public class FlatSliderUI
 		super( null );
 	}
 
+	@Override
+	public void installUI( JComponent c ) {
+		super.installUI( c );
+
+		applyStyle( FlatStyleSupport.getStyle( slider ) );
+	}
+
 	@Override
 	protected void installDefaults( JSlider slider ) {
 		super.installDefaults( slider );
@@ -134,6 +147,7 @@ public class FlatSliderUI
 		disabledTrackColor = UIManager.getColor( "Slider.disabledTrackColor" );
 		disabledThumbColor = UIManager.getColor( "Slider.disabledThumbColor" );
 		disabledThumbBorderColor = FlatUIUtils.getUIColor( "Slider.disabledThumbBorderColor", "Component.disabledBorderColor" );
+		tickColor = FlatUIUtils.getUIColor( "Slider.tickColor", Color.BLACK ); // see BasicSliderUI.paintTicks()
 
 		defaultBackground = UIManager.getColor( "Slider.background" );
 		defaultForeground = UIManager.getColor( "Slider.foreground" );
@@ -155,9 +169,12 @@ public class FlatSliderUI
 		disabledTrackColor = null;
 		disabledThumbColor = null;
 		disabledThumbBorderColor = null;
+		tickColor = null;
 
 		defaultBackground = null;
 		defaultForeground = null;
+
+		oldStyleValues = null;
 	}
 
 	@Override
@@ -165,6 +182,57 @@ public class FlatSliderUI
 		return new FlatTrackListener();
 	}
 
+	@Override
+	protected PropertyChangeListener createPropertyChangeListener( JSlider slider ) {
+		PropertyChangeListener superListener = super.createPropertyChangeListener( slider );
+		return e -> {
+			superListener.propertyChange( e );
+
+			switch( e.getPropertyName() ) {
+				case FlatClientProperties.COMPONENT_STYLE:
+					applyStyle( FlatStyleSupport.toString( e.getNewValue() ) );
+					slider.revalidate();
+					slider.repaint();
+					break;
+			}
+		};
+	}
+
+	/**
+	 * @since TODO
+	 */
+	protected void applyStyle( String style ) {
+		oldStyleValues = FlatStyleSupport.parse( oldStyleValues, style, this::applyStyleProperty );
+	}
+
+	/**
+	 * @since TODO
+	 */
+	protected Object applyStyleProperty( String key, Object value ) {
+		Object oldValue;
+		switch( key ) {
+			case "trackWidth": oldValue = trackWidth; trackWidth = (int) value; break;
+			case "thumbSize": oldValue = thumbSize; thumbSize = (Dimension) value; break;
+			case "focusWidth": oldValue = focusWidth; focusWidth = (int) value; break;
+
+			case "trackValueColor": oldValue = trackValueColor; trackValueColor = (Color) value; break;
+			case "trackColor": oldValue = trackColor; trackColor = (Color) value; break;
+			case "thumbColor": oldValue = thumbColor; thumbColor = (Color) value; break;
+			case "thumbBorderColor": oldValue = thumbBorderColor; thumbBorderColor = (Color) value; break;
+			case "focusedColor": oldValue = focusedColor; focusedColor = (Color) value; break;
+			case "focusedThumbBorderColor": oldValue = focusedThumbBorderColor; focusedThumbBorderColor = (Color) value; break;
+			case "hoverThumbColor": oldValue = hoverThumbColor; hoverThumbColor = (Color) value; break;
+			case "pressedThumbColor": oldValue = pressedThumbColor; pressedThumbColor = (Color) value; break;
+			case "disabledTrackColor": oldValue = disabledTrackColor; disabledTrackColor = (Color) value; break;
+			case "disabledThumbColor": oldValue = disabledThumbColor; disabledThumbColor = (Color) value; break;
+			case "disabledThumbBorderColor": oldValue = disabledThumbBorderColor; disabledThumbBorderColor = (Color) value; break;
+			case "tickColor": oldValue = tickColor; tickColor = (Color) value; break;
+
+			default: throw new IllegalArgumentException( "unknown style '" + key + "'" );
+		}
+		return oldValue;
+	}
+
 	@Override
 	public int getBaseline( JComponent c, int width, int height ) {
 		if( c == null )
@@ -306,6 +374,19 @@ debug*/
 		((Graphics2D)g).fill( track );
 	}
 
+	@Override
+	public void paintTicks( Graphics g ) {
+		// because BasicSliderUI.paintTicks() always uses
+		//   g.setColor( UIManager.getColor("Slider.tickColor") )
+		// we override this method and use our tickColor field to allow styling
+		super.paintTicks( new Graphics2DProxy( (Graphics2D) g ) {
+			@Override
+			public void setColor( Color c ) {
+				super.setColor( tickColor );
+			}
+		} );
+	}
+
 	@Override
 	public void paintThumb( Graphics g ) {
 		Color thumbColor = getThumbColor();

flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatStyleSupport.java

@@ -0,0 +1,108 @@
+/*
+ * Copyright 2021 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.formdev.flatlaf.ui;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.function.BiFunction;
+import javax.swing.JComponent;
+import com.formdev.flatlaf.FlatClientProperties;
+import com.formdev.flatlaf.FlatLaf;
+import com.formdev.flatlaf.util.StringUtils;
+
+/**
+ * Support for styling components in CSS syntax.
+ *
+ * @author Karl Tauber
+ * @since TODO
+ */
+public class FlatStyleSupport
+{
+	/**
+	 * Parses styles in CSS syntax ("key1: value1; key2: value2; ..."),
+	 * converts the value strings into binary and invokes the given function
+	 * to apply the properties.
+	 *
+	 * @param oldStyleValues map of old values modified by the previous invocation, or {@code null}
+	 * @param style the style in CSS syntax
+	 * @param applyProperty function that is invoked to apply the properties;
+	 *                      first parameter is the key, second the binary value;
+	 *                      the function must return the old value
+	 * @return map of old values modified by the given style, or {@code null}
+	 * @throws IllegalArgumentException on syntax errors
+	 */
+	public static Map<String, Object> parse( Map<String, Object> oldStyleValues,
+		String style, BiFunction<String, Object, Object> applyProperty ) throws IllegalArgumentException
+	{
+		// restore previous values
+		if( oldStyleValues != null ) {
+			for( Entry<String, Object> e : oldStyleValues.entrySet() )
+				applyProperty.apply( e.getKey(), e.getValue() );
+		}
+
+		// ignore empty style
+		if( style == null || style.trim().isEmpty() )
+			return null;
+
+		Map<String, Object> oldValues = null;
+
+		// split style into parts and process them
+		for( String part : StringUtils.split( style, ';' ) ) {
+			// ignore empty parts
+			part = part.trim();
+			if( part.isEmpty() )
+				continue;
+
+			// find separator colon
+			int sepIndex = part.indexOf( ':' );
+			if( sepIndex < 0 )
+				throw new IllegalArgumentException( "missing colon in '" + part + "'" );
+
+			// split into key and value
+			String key = part.substring( 0, sepIndex ).trim();
+			String value = part.substring( sepIndex + 1 ).trim();
+			if( key.isEmpty() )
+				throw new IllegalArgumentException( "missing key in '" + part + "'" );
+			if( value.isEmpty() )
+				throw new IllegalArgumentException( "missing value in '" + part + "'" );
+
+			// parse value string and convert it into binary value
+			Object val = FlatLaf.parseDefaultsValue( key, value );
+			Object oldValue = applyProperty.apply( key, val );
+
+			// remember previous value
+			if( oldValues == null )
+				oldValues = new HashMap<>();
+			oldValues.put( key, oldValue );
+		}
+
+		return oldValues;
+	}
+
+	public static boolean hasStyle( JComponent c ) {
+		return getStyle( c ) != null;
+	}
+
+	public static String getStyle( JComponent c ) {
+		return toString( c.getClientProperty( FlatClientProperties.COMPONENT_STYLE ) );
+	}
+
+	static String toString( Object style ) {
+		return (style instanceof String) ? (String) style : null;
+	}
+}