Styling: support Tree icons

flatlaf-core/src/main/java/com/formdev/flatlaf/icons/FlatTreeClosedIcon.java

@@ -37,6 +37,8 @@ public class FlatTreeClosedIcon
 
 	@Override
 	protected void paintIcon( Component c, Graphics2D g ) {
+		FlatTreeCollapsedIcon.setStyleColorFromTreeUI( c, g, ui -> ui.iconClosedColor );
+
 		/*
 			<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16">
 			  <polygon fill="#6E6E6E" fill-rule="evenodd" points="1 2 6 2 8 4 15 4 15 13 1 13"/>

flatlaf-core/src/main/java/com/formdev/flatlaf/icons/FlatTreeCollapsedIcon.java

@@ -19,7 +19,12 @@ package com.formdev.flatlaf.icons;
 import java.awt.Color;
 import java.awt.Component;
 import java.awt.Graphics2D;
+import java.util.function.Function;
+import javax.swing.JTree;
+import javax.swing.SwingUtilities;
 import javax.swing.UIManager;
+import javax.swing.plaf.TreeUI;
+import com.formdev.flatlaf.ui.FlatTreeUI;
 import com.formdev.flatlaf.ui.FlatUIUtils;
 
 /**
@@ -46,8 +51,12 @@ public class FlatTreeCollapsedIcon
 
 	@Override
 	protected void paintIcon( Component c, Graphics2D g ) {
+		setStyleColorFromTreeUI( c, g );
 		rotate( c, g );
 
+		String arrowType = getStyleFromTreeUI( c, ui -> ui.iconArrowType );
+		boolean chevron = (arrowType != null) ? FlatUIUtils.isChevron( arrowType ) : this.chevron;
+
 		if( chevron ) {
 			// chevron arrow
 			g.fill( FlatUIUtils.createPath( 3,1, 3,2.5, 6,5.5, 3,8.5, 3,10, 4.5,10, 9,5.5, 4.5,1 ) );
@@ -57,8 +66,34 @@ public class FlatTreeCollapsedIcon
 		}
 	}
 
+	void setStyleColorFromTreeUI( Component c, Graphics2D g ) {
+		setStyleColorFromTreeUI( c, g, ui -> ui.iconCollapsedColor );
+	}
+
 	void rotate( Component c, Graphics2D g ) {
 		if( !c.getComponentOrientation().isLeftToRight() )
 			g.rotate( Math.toRadians( 180 ), width / 2., height / 2. );
 	}
+
+	/**
+	 * Because this icons are always shared for all trees,
+	 * get icon specific style from FlatTreeUI.
+	 */
+	static <T> T getStyleFromTreeUI( Component c, Function<FlatTreeUI, T> f ) {
+		JTree tree = (c instanceof JTree)
+			? (JTree) c
+			: (JTree) SwingUtilities.getAncestorOfClass( JTree.class, c );
+		if( tree != null ) {
+			TreeUI ui = tree.getUI();
+			if( ui instanceof FlatTreeUI )
+				return f.apply( (FlatTreeUI) ui );
+		}
+		return null;
+	}
+
+	static void setStyleColorFromTreeUI( Component c, Graphics2D g, Function<FlatTreeUI, Color> f ) {
+		Color color = getStyleFromTreeUI( c, f );
+		if( color != null )
+			g.setColor( color );
+	}
 }

flatlaf-core/src/main/java/com/formdev/flatlaf/icons/FlatTreeExpandedIcon.java

@@ -34,6 +34,11 @@ public class FlatTreeExpandedIcon
 		super( UIManager.getColor( "Tree.icon.expandedColor" ) );
 	}
 
+	@Override
+	void setStyleColorFromTreeUI( Component c, Graphics2D g ) {
+		setStyleColorFromTreeUI( c, g, ui -> ui.iconExpandedColor );
+	}
+
 	@Override
 	void rotate( Component c, Graphics2D g ) {
 		g.rotate( Math.toRadians( 90 ), width / 2., height / 2. );

flatlaf-core/src/main/java/com/formdev/flatlaf/icons/FlatTreeLeafIcon.java

@@ -37,6 +37,8 @@ public class FlatTreeLeafIcon
 
 	@Override
 	protected void paintIcon( Component c, Graphics2D g ) {
+		FlatTreeCollapsedIcon.setStyleColorFromTreeUI( c, g, ui -> ui.iconLeafColor );
+
 		/*
 			<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16">
 			  <g fill="none" fill-rule="evenodd">

flatlaf-core/src/main/java/com/formdev/flatlaf/icons/FlatTreeOpenIcon.java

@@ -37,6 +37,8 @@ public class FlatTreeOpenIcon
 
 	@Override
 	protected void paintIcon( Component c, Graphics2D g ) {
+		FlatTreeCollapsedIcon.setStyleColorFromTreeUI( c, g, ui -> ui.iconOpenColor );
+
 		/*
 			<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16">
 			  <g fill="none" fill-rule="evenodd">

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

@@ -96,6 +96,28 @@ import com.formdev.flatlaf.util.UIScale;
  * @uiDefault Tree.wideSelection					boolean
  * @uiDefault Tree.showCellFocusIndicator			boolean
  *
+ * <!-- FlatTreeExpandedIcon -->
+ *
+ * @uiDefault Component.arrowType					String	chevron (default) or triangle
+ * @uiDefault Tree.icon.expandedColor				Color
+ *
+ * <!-- FlatTreeCollapsedIcon -->
+ *
+ * @uiDefault Component.arrowType					String	chevron (default) or triangle
+ * @uiDefault Tree.icon.collapsedColor				Color
+ *
+ * <!-- FlatTreeLeafIcon -->
+ *
+ * @uiDefault Tree.icon.leafColor					Color
+ *
+ * <!-- FlatTreeClosedIcon -->
+ *
+ * @uiDefault Tree.icon.closedColor					Color
+ *
+ * <!-- FlatTreeOpenIcon -->
+ *
+ * @uiDefault Tree.icon.openColor					Color
+ *
  * @author Karl Tauber
  */
 public class FlatTreeUI
@@ -109,6 +131,15 @@ public class FlatTreeUI
 	@Styleable protected boolean wideSelection;
 	@Styleable protected boolean showCellFocusIndicator;
 
+	// for icons
+	// (needs to be public because icon classes are in another package)
+	@Styleable(dot=true) public String iconArrowType;
+	@Styleable(dot=true) public Color iconExpandedColor;
+	@Styleable(dot=true) public Color iconCollapsedColor;
+	@Styleable(dot=true) public Color iconLeafColor;
+	@Styleable(dot=true) public Color iconClosedColor;
+	@Styleable(dot=true) public Color iconOpenColor;
+
 	private Color defaultCellNonSelectionBackground;
 	private Color defaultSelectionBackground;
 	private Color defaultSelectionForeground;

flatlaf-core/src/test/java/com/formdev/flatlaf/ui/FlatStylingTests.java

@@ -573,6 +573,14 @@ public class FlatStylingTests
 		ui.applyStyle( "selectionBorderColor: #fff" );
 		ui.applyStyle( "wideSelection: true" );
 		ui.applyStyle( "showCellFocusIndicator: true" );
+
+		// icons
+		ui.applyStyle( "icon.arrowType: chevron" );
+		ui.applyStyle( "icon.expandedColor: #fff" );
+		ui.applyStyle( "icon.collapsedColor: #fff" );
+		ui.applyStyle( "icon.leafColor: #fff" );
+		ui.applyStyle( "icon.closedColor: #fff" );
+		ui.applyStyle( "icon.openColor: #fff" );
 	}
 
 	//---- component borders --------------------------------------------------