Support for alternate row color in JTree

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

@@ -102,6 +102,7 @@
  * @uiDefault Tree.selectionForeground				Color
  * @uiDefault Tree.selectionInactiveBackground		Color
  * @uiDefault Tree.selectionInactiveForeground		Color
+ * @uiDefault Tree.alternateRowColor				Color
  * @uiDefault Tree.selectionInsets					Insets
  * @uiDefault Tree.selectionArc						int
  * @uiDefault Tree.wideSelection					boolean
@@ -141,6 +142,7 @@ public class FlatTreeUI
 	@Styleable protected Color selectionInactiveBackground;
 	@Styleable protected Color selectionInactiveForeground;
 	@Styleable protected Color selectionBorderColor;
+	/** @since 3.6 */ @Styleable protected Color alternateRowColor;
 	/** @since 3 */ @Styleable protected Insets selectionInsets;
 	/** @since 3 */ @Styleable protected int selectionArc;
 	@Styleable protected boolean wideSelection;
@@ -192,6 +194,7 @@ protected void installDefaults() {
 		selectionInactiveBackground = UIManager.getColor( "Tree.selectionInactiveBackground" );
 		selectionInactiveForeground = UIManager.getColor( "Tree.selectionInactiveForeground" );
 		selectionBorderColor = UIManager.getColor( "Tree.selectionBorderColor" );
+		alternateRowColor = UIManager.getColor( "Tree.alternateRowColor" );
 		selectionInsets = UIManager.getInsets( "Tree.selectionInsets" );
 		selectionArc = UIManager.getInt( "Tree.selectionArc" );
 		wideSelection = UIManager.getBoolean( "Tree.wideSelection" );
@@ -227,6 +230,7 @@ protected void uninstallDefaults() {
 		selectionInactiveBackground = null;
 		selectionInactiveForeground = null;
 		selectionBorderColor = null;
+		alternateRowColor = null;
 
 		defaultLeafIcon = null;
 		defaultClosedIcon = null;
@@ -570,6 +574,15 @@ protected void paintRow( Graphics g, Rectangle clipBounds, Insets insets, Rectan
 		boolean isSelected = tree.isRowSelected( row );
 		boolean isDropRow = isDropRow( row );
 		boolean needsSelectionPainting = (isSelected || isDropRow) && isPaintSelection();
+
+		if( alternateRowColor != null && row % 2 != 0 ) {
+			g.setColor( alternateRowColor );
+
+			// paint respecting selection arc
+			final float arc = UIScale.scale( selectionArc / 2f );			
+			FlatUIUtils.paintSelection( (Graphics2D) g, 0, bounds.y, tree.getWidth(), bounds.height,
+					UIScale.scale( selectionInsets ), arc, arc, arc, arc, 0 );
+		}
 
 		// do not paint row if editing
 		if( isEditing ) {

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

@@ -965,6 +965,7 @@ void tree() {
 			"selectionInactiveBackground", Color.class,
 			"selectionInactiveForeground", Color.class,
 			"selectionBorderColor", Color.class,
+			"alternateRowColor", Color.class,
 			"selectionInsets", Insets.class,
 			"selectionArc", int.class,
 			"wideSelection", boolean.class,

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

@@ -938,6 +938,7 @@ void tree() {
 		testColor( c, ui, "selectionInactiveBackground", 0x123456 );
 		testColor( c, ui, "selectionInactiveForeground", 0x123456 );
 		testColor( c, ui, "selectionBorderColor", 0x123456 );
+		testColor( c, ui, "alternateRowColor", 0x123456 );
 		testInsets( c, ui, "selectionInsets", 1,2,3,4 );
 		testInteger( c, ui, "selectionArc", 123 );
 		testBoolean( c, ui, "wideSelection", true );

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

@@ -1187,6 +1187,7 @@ void tree() {
 		ui.applyStyle( "selectionInactiveBackground: #fff" );
 		ui.applyStyle( "selectionInactiveForeground: #fff" );
 		ui.applyStyle( "selectionBorderColor: #fff" );
+		ui.applyStyle( "alternateRowColor: #fff" );
 		ui.applyStyle( "selectionInsets: 1,2,3,4" );
 		ui.applyStyle( "selectionArc: 8" );
 		ui.applyStyle( "wideSelection: true" );

flatlaf-theme-editor/src/main/resources/com/formdev/flatlaf/themeeditor/FlatLafUIKeys.txt

@@ -1182,6 +1182,7 @@ Tree.dropCellForeground
 Tree.dropLineColor
 Tree.editorBorder
 Tree.editorBorderSelectionColor
+Tree.alternateRowColor
 Tree.expandedIcon
 Tree.focusInputMap
 Tree.focusInputMap.RightToLeft