[CTabFolder] Ask the renderer for the background of tab controls

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/CTabFolder.java

@@ -4096,7 +4096,8 @@ void updateBkImages(boolean colorChanged) {
 					int tabHeight = getTabHeight();
 					int height = this.getSize().y;
 					boolean wrapped = onBottom ? bounds.y + bounds.height < height - tabHeight : bounds.y > tabHeight;
-					if (wrapped || gradientColors == null) {
+					// only a custom renderer can paint something else here
+					if (useDefaultRenderer && (gradientColors == null || wrapped)) {
 						bkImageBounds[i]=null;
 						control.setBackgroundImage(null);
 						control.setBackground(getBackground());
@@ -4110,11 +4111,21 @@ void updateBkImages(boolean colorChanged) {
 							bounds.y = -1;
 						}
 						bounds.x = 0;
+						if (bounds.height <= 0) {
+							// drop the cache, so a skipped color change is not lost
+							bkImageBounds[i] = null;
+							continue;
+						}
 						// do not redraw when only translated:
 						if (colorChanged || !bounds.equals(bkImageBounds[i])) {
 							bkImageBounds[i] = bounds;
 							if (controlBkImages[i] != null) controlBkImages[i].dispose();
-							controlBkImages[i] = new Image(control.getDisplay(), (gc, imageWidth, imageHeight) -> renderer.draw(CTabFolderRenderer.PART_BACKGROUND, 0, bounds, gc), bounds.width, bounds.height);
+							controlBkImages[i] = new Image(control.getDisplay(), (gc, imageWidth, imageHeight) -> {
+								// pixels a renderer leaves untouched would stay blank in an image
+								gc.setBackground(getBackground());
+								gc.fillRectangle(0, 0, imageWidth, imageHeight);
+								renderer.draw(CTabFolderRenderer.PART_BACKGROUND, 0, bounds, gc);
+							}, bounds.width, bounds.height);
 							control.setBackground(null);
 							control.setBackgroundImage(controlBkImages[i]);
 						}

examples/org.eclipse.swt.snippets/Snippets.md

@@ -61,6 +61,7 @@ To contribute a new snippet, [create a snippet contribution as a pull request](h
 - [create a non-rectangular button](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet294.java) – [(preview)](https://github.com/eclipse-platform/eclipse.platform.swt/blob/master/examples/org.eclipse.swt.snippets/previews/Snippet294.png "Preview for Snippet 294")
 - [create buttons with wrapped titles](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet345.java) – [(preview)](https://github.com/eclipse-platform/eclipse.platform.swt/blob/master/examples/org.eclipse.swt.snippets/previews/Snippet345.png "Preview for Snippet 345")
 
+
 ### **Canvas**
 - [paint a circle in a canvas](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet245.java) – [(preview)](https://github.com/eclipse-platform/eclipse.platform.swt/blob/master/examples/org.eclipse.swt.snippets/previews/Snippet245.png "Preview for Snippet 245")
 - [scroll an image (flicker free, no double buffering)](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet48.java) – [(preview)](https://github.com/eclipse-platform/eclipse.platform.swt/blob/master/examples/org.eclipse.swt.snippets/previews/Snippet48.png "Preview for Snippet 48")
@@ -119,6 +120,7 @@ To contribute a new snippet, [create a snippet contribution as a pull request](h
 - [min and max buttons, close button and image only on selected tab](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet165.java) – [(preview)](https://github.com/eclipse-platform/eclipse.platform.swt/blob/master/examples/org.eclipse.swt.snippets/previews/Snippet165.png "Preview for Snippet 165")
 - [demonstration of a multi line CTabFolder](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet371.java) – [(preview)](https://github.com/eclipse-platform/eclipse.platform.swt/blob/master/examples/org.eclipse.swt.snippets/previews/Snippet371.png "Preview for Snippet 371")
 - [dirty indicator using bullet dot on close button with theme switching](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet394.java)
+- [background of a top right control that wraps below the tab row](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet396.java)
 
 ### **Cursor**
 - [set the hand cursor into a control](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet44.java) – [(preview)](https://github.com/eclipse-platform/eclipse.platform.swt/blob/master/examples/org.eclipse.swt.snippets/previews/Snippet44.png "Preview for Snippet 44")

examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet396.java

@@ -0,0 +1,91 @@
+/*******************************************************************************
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *******************************************************************************/
+package org.eclipse.swt.snippets;
+
+/*
+ * CTabFolder example: background of a top right control that wrapped below the
+ * tab row. Widen the shell until the tool bar fits next to the tabs.
+ *
+ * For a list of all SWT example snippets see
+ * http://www.eclipse.org/swt/snippets/
+ */
+import org.eclipse.swt.*;
+import org.eclipse.swt.custom.*;
+import org.eclipse.swt.graphics.*;
+import org.eclipse.swt.layout.*;
+import org.eclipse.swt.widgets.*;
+
+public class Snippet396 {
+	static final Color TAB_ROW = new Color(0x21, 0x22, 0x2C);
+	static final Color BODY = new Color(0x28, 0x2A, 0x36);
+
+	/** Paints tab row and body in two different colors. */
+	static class TwoToneRenderer extends CTabFolderRenderer {
+		TwoToneRenderer(CTabFolder parent) {
+			super(parent);
+		}
+
+		@Override
+		protected void draw(int part, int state, Rectangle bounds, GC gc) {
+			if (part == PART_BACKGROUND) {
+				int split = bounds.y + parent.getTabHeight();
+				gc.setBackground(TAB_ROW);
+				gc.fillRectangle(bounds.x, bounds.y, bounds.width, split - bounds.y);
+				gc.setBackground(BODY);
+				gc.fillRectangle(bounds.x, split, bounds.width, bounds.y + bounds.height - split);
+				return;
+			}
+			super.draw(part, state, bounds, gc);
+			if (part == PART_HEADER) {
+				int split = bounds.y + parent.getTabHeight() + 3;
+				gc.setBackground(BODY);
+				gc.fillRectangle(bounds.x, split, bounds.width, bounds.y + bounds.height - split);
+			}
+		}
+	}
+
+	public static void main(String[] args) {
+		Display display = new Display();
+		Shell shell = new Shell(display);
+		shell.setText("Wrapped top right control");
+		shell.setLayout(new FillLayout());
+
+		CTabFolder folder = new CTabFolder(shell, SWT.NONE);
+		folder.setRenderer(new TwoToneRenderer(folder));
+		folder.setBackground(TAB_ROW);
+		folder.setForeground(display.getSystemColor(SWT.COLOR_WHITE));
+
+		for (String name : new String[] { "Variables", "Breakpoints", "Expressions" }) {
+			CTabItem item = new CTabItem(folder, SWT.NONE);
+			item.setText(name);
+			Composite content = new Composite(folder, SWT.NONE);
+			content.setBackground(BODY);
+			item.setControl(content);
+		}
+		folder.setSelection(0);
+
+		Composite topRight = new Composite(folder, SWT.NONE);
+		topRight.setLayout(new FillLayout());
+		ToolBar toolBar = new ToolBar(topRight, SWT.FLAT);
+		for (String text : new String[] { "Collapse", "Expand", "Filter", "Menu" }) {
+			new ToolItem(toolBar, SWT.PUSH).setText(text);
+		}
+		folder.setTopRight(topRight, SWT.RIGHT | SWT.WRAP);
+
+		shell.setSize(360, 200);
+		shell.open();
+		while (!shell.isDisposed()) {
+			if (!display.readAndDispatch())
+				display.sleep();
+		}
+		display.dispose();
+	}
+}

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_custom_CTabFolder.java

@@ -39,13 +39,17 @@
 import org.eclipse.swt.custom.CTabFolder;
 import org.eclipse.swt.custom.CTabFolder2Listener;
 import org.eclipse.swt.custom.CTabFolderEvent;
+import org.eclipse.swt.custom.CTabFolderRenderer;
 import org.eclipse.swt.custom.CTabItem;
 import org.eclipse.swt.custom.SashForm;
 import org.eclipse.swt.graphics.Color;
 import org.eclipse.swt.graphics.Font;
 import org.eclipse.swt.graphics.FontData;
+import org.eclipse.swt.graphics.GC;
 import org.eclipse.swt.graphics.Image;
+import org.eclipse.swt.graphics.ImageData;
 import org.eclipse.swt.graphics.Point;
+import org.eclipse.swt.graphics.RGB;
 import org.eclipse.swt.graphics.Rectangle;
 import org.eclipse.swt.internal.DPIUtil;
 import org.eclipse.swt.layout.FillLayout;
@@ -1166,6 +1170,141 @@ public void test_moveItem_errorCases() {
 			"out-of-range to index must be rejected");
 }
 
+/* Paints tab row and body in two colors, neither of them the folder background. */
+private static final RGB TAB_ROW_COLOR = new RGB(255, 0, 0);
+private static final RGB BODY_COLOR = new RGB(0, 255, 0);
+private static final RGB FOLDER_BACKGROUND = new RGB(0, 0, 255);
+
+private static final class TwoToneRenderer extends CTabFolderRenderer {
+	TwoToneRenderer(CTabFolder parent) {
+		super(parent);
+	}
+
+	@Override
+	protected void draw(int part, int state, Rectangle bounds, GC gc) {
+		if (part == PART_BACKGROUND) {
+			int split = bounds.y + parent.getTabHeight();
+			gc.setBackground(new Color(TAB_ROW_COLOR));
+			gc.fillRectangle(bounds.x, bounds.y, bounds.width, split - bounds.y);
+			gc.setBackground(new Color(BODY_COLOR));
+			gc.fillRectangle(bounds.x, split, bounds.width, bounds.y + bounds.height - split);
+			return;
+		}
+		super.draw(part, state, bounds, gc);
+	}
+}
+
+/** A custom renderer that leaves PART_BACKGROUND to the built-in implementation. */
+private static final class PlainSubclassRenderer extends CTabFolderRenderer {
+	PlainSubclassRenderer(CTabFolder parent) {
+		super(parent);
+	}
+}
+
+/** The color a control shows: its background image if it has one, else its background. */
+private static RGB effectiveBackground(Control control) {
+	Image image = control.getBackgroundImage();
+	if (image != null) {
+		ImageData data = image.getImageData();
+		return data.palette.getRGB(data.getPixel(0, 0));
+	}
+	return control.getBackground().getRGB();
+}
+
+private Composite createFolderWithTopRightToolBar(int shellWidth, boolean withGradient) {
+	return createFolderWithTopRightToolBar(shellWidth, withGradient, true);
+}
+
+private Composite createFolderWithTopRightToolBar(int shellWidth, boolean withGradient, boolean twoTone) {
+	makeCleanEnvironment();
+	shell.setLayout(new FillLayout());
+	ctabFolder.setRenderer(twoTone ? new TwoToneRenderer(ctabFolder) : new PlainSubclassRenderer(ctabFolder));
+	ctabFolder.setBackground(new Color(FOLDER_BACKGROUND));
+	if (withGradient) {
+		ctabFolder.setBackground(new Color[] { new Color(FOLDER_BACKGROUND), new Color(FOLDER_BACKGROUND) },
+				new int[] { 100 });
+	}
+	for (int i = 0; i < 3; i++) {
+		CTabItem item = new CTabItem(ctabFolder, SWT.NONE);
+		item.setText("A rather long tab title " + i);
+		item.setControl(new Composite(ctabFolder, SWT.NONE));
+	}
+	ctabFolder.setSelection(0);
+
+	// the IDE wraps the tool bar in a Composite, which is what carries the background
+	Composite topRight = new Composite(ctabFolder, SWT.NONE);
+	topRight.setLayout(new FillLayout());
+	ToolBar toolBar = new ToolBar(topRight, SWT.FLAT);
+	for (int i = 0; i < 6; i++) {
+		new ToolItem(toolBar, SWT.PUSH).setText("Item " + i);
+	}
+	ctabFolder.setTopRight(topRight, SWT.RIGHT | SWT.WRAP);
+
+	shell.setSize(shellWidth, 300);
+	shell.open();
+	SwtTestUtil.processEvents();
+	ctabFolder.layout(true, true);
+	SwtTestUtil.processEvents();
+	return topRight;
+}
+
+@Test
+public void test_topRightControl_wrappedBelowTabRow_matchesBody() {
+	Composite toolBar = createFolderWithTopRightToolBar(240, false);
+	assertTrue(toolBar.getBounds().y > ctabFolder.getTabHeight(),
+			"tool bar did not wrap below the tab row, bounds " + toolBar.getBounds());
+	assertEquals(BODY_COLOR, effectiveBackground(toolBar),
+			"a wrapped control sits on the body and has to match what the renderer paints there");
+}
+
+@Test
+public void test_topRightControl_inTabRow_matchesTabRow() {
+	Composite toolBar = createFolderWithTopRightToolBar(900, false);
+	assertFalse(toolBar.getBounds().y > ctabFolder.getTabHeight(),
+			"tool bar unexpectedly wrapped, bounds " + toolBar.getBounds());
+	assertEquals(TAB_ROW_COLOR, effectiveBackground(toolBar),
+			"a control in the tab row has to match what the renderer paints there");
+}
+
+@Test
+public void test_topRightControl_rendererKeepingDefaultBackground_staysOnTheFolderBackground() {
+	Composite toolBar = createFolderWithTopRightToolBar(240, false, false);
+	assertEquals(FOLDER_BACKGROUND, effectiveBackground(toolBar),
+			"a renderer that does not paint PART_BACKGROUND has to leave the folder background");
+}
+
+@Test
+public void test_topRightControl_defaultRendererWithGradient_keepsFlatBackground() {
+	makeCleanEnvironment();
+	shell.setLayout(new FillLayout());
+	ctabFolder.setBackground(new Color(FOLDER_BACKGROUND));
+	ctabFolder.setBackground(new Color[] { new Color(TAB_ROW_COLOR), new Color(BODY_COLOR) },
+			new int[] { 100 });
+	for (int i = 0; i < 3; i++) {
+		CTabItem item = new CTabItem(ctabFolder, SWT.NONE);
+		item.setText("A rather long tab title " + i);
+		item.setControl(new Composite(ctabFolder, SWT.NONE));
+	}
+	ctabFolder.setSelection(0);
+	Composite topRight = new Composite(ctabFolder, SWT.NONE);
+	topRight.setLayout(new FillLayout());
+	ToolBar toolBar = new ToolBar(topRight, SWT.FLAT);
+	for (int i = 0; i < 6; i++) {
+		new ToolItem(toolBar, SWT.PUSH).setText("Item " + i);
+	}
+	ctabFolder.setTopRight(topRight, SWT.RIGHT | SWT.WRAP);
+	shell.setSize(240, 300);
+	shell.open();
+	SwtTestUtil.processEvents();
+	ctabFolder.layout(true, true);
+	SwtTestUtil.processEvents();
+
+	assertTrue(topRight.getBounds().y > ctabFolder.getTabHeight(),
+			"tool bar did not wrap below the tab row, bounds " + topRight.getBounds());
+	assertNull(topRight.getBackgroundImage(),
+			"the built-in renderer paints the body flat, a wrapped control needs no image");
+}
+
 /** Layout with a preferred size the test can change at will. */
 private static final class FixedSizeLayout extends Layout {
 	int width;