[CTabFolder] Give top right controls the color painted behind them

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

@@ -175,6 +175,7 @@ public class CTabFolder extends Composite {
 	Listener tabControlZoomListener;
 	boolean ignoreTraverse;
 	boolean useDefaultRenderer;
+	boolean paintedBackgroundsPending;
 
 	/* External Listener management */
 	CTabFolder2Listener[] folderListeners = new CTabFolder2Listener[0];
@@ -2147,6 +2148,18 @@ void onPaint(Event event) {
 	gc.setFont(gcFont);
 	gc.setForeground(gcForeground);
 	gc.setBackground(gcBackground);
+
+	if (!useDefaultRenderer && !paintedBackgroundsPending && controls != null) {
+		Rectangle damage = event.getBounds();
+		for (Control control : controls) {
+			// a custom renderer can change its colors with only a redraw
+			if (!control.isDisposed() && damage.intersects(control.getBounds())) {
+				paintedBackgroundsPending = true;
+				getDisplay().asyncExec(this::updatePaintedBackgrounds);
+				break;
+			}
+		}
+	}
 }
 
 void onResize(Event event) {
@@ -3268,6 +3281,8 @@ public void setRenderer(CTabFolderRenderer renderer) {
 	if (useDefaultRenderer) renderer = new CTabFolderRenderer(this);
 	this.renderer = renderer;
 	updateFolder(REDRAW);
+	// the renderer decides what the top right controls get as background
+	updateBkImages(true);
 }
 /**
  * Set the selection to the tab at the specified item.
@@ -4107,7 +4122,8 @@ void updateBkImages(boolean colorChanged) {
 					if (wrapped || gradientColors == null) {
 						bkImageBounds[i]=null;
 						control.setBackgroundImage(null);
-						control.setBackground(getBackground());
+						// a custom renderer may paint anything behind the control
+						control.setBackground(useDefaultRenderer ? getBackground() : getPaintedColor(bounds.x + bounds.width / 2, bounds.y + bounds.height / 2));
 					} else {
 						bounds.width = 10;
 						if (!onBottom) {
@@ -4118,11 +4134,21 @@ 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]);
 						}
@@ -4133,6 +4159,52 @@ void updateBkImages(boolean colorChanged) {
 
 	}
 }
+/** Gives the controls with a flat background the color the renderer now paints behind them. */
+void updatePaintedBackgrounds() {
+	paintedBackgroundsPending = false;
+	if (isDisposed() || useDefaultRenderer || hovering || controls == null) return;
+	for (Control control : controls) {
+		if (control.isDisposed() || control.getBackgroundImage() != null) continue;
+		Rectangle bounds = control.getBounds();
+		Color color = getPaintedColor(bounds.x + bounds.width / 2, bounds.y + bounds.height / 2);
+		if (!color.equals(control.getBackground())) control.setBackground(color);
+	}
+}
+/** Returns the color the folder paints at the given point, as onPaint draws body and header. */
+Color getPaintedColor(int x, int y) {
+	Point size = getSize();
+	if (x < 0 || y < 0 || x >= size.x || y >= size.y) return getBackground();
+	Rectangle bodyRect = new Rectangle(0, 0, size.x, size.y);
+	// a few pixels around the point, translated, so the renderer still gets the full folder bounds
+	Image image = new Image(getDisplay(), (gc, imageWidth, imageHeight) -> {
+		Transform transform = new Transform(gc.getDevice());
+		try {
+			transform.translate(1 - x, 1 - y);
+			gc.setTransform(transform);
+			// in user space, so that a renderer saving and restoring the clipping keeps it
+			gc.setClipping(x - 1, y - 1, imageWidth, imageHeight);
+			gc.setFont(getFont());
+			gc.setForeground(getForeground());
+			// pixels a renderer leaves untouched show the widget background on screen
+			gc.setBackground(getBackground());
+			gc.fillRectangle(x - 1, y - 1, imageWidth, imageHeight);
+			renderer.draw(CTabFolderRenderer.PART_BODY, SWT.BACKGROUND | SWT.FOREGROUND, bodyRect, gc);
+			gc.setFont(getFont());
+			gc.setForeground(getForeground());
+			gc.setBackground(getBackground());
+			renderer.draw(CTabFolderRenderer.PART_HEADER, SWT.BACKGROUND | SWT.FOREGROUND, bodyRect, gc);
+		} finally {
+			transform.dispose();
+		}
+	}, 3, 3);
+	try {
+		// the zoom the folder is shown at, so that the renderer is invoked as on screen
+		ImageData data = image.getImageData(DPIUtil.getZoomForAutoscaleProperty(getShell().getZoom()));
+		return new Color(data.palette.getRGB(data.getPixel(data.width / 2, data.height / 2)));
+	} finally {
+		image.dispose();
+	}
+}
 String _getToolTip(int x, int y) {
 	CTabItem item = getItem(new Point (x, y));
 	if (item == null) return null;

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

@@ -119,6 +119,7 @@ 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/Snippet392.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/Snippet394.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/Snippet394.java

@@ -0,0 +1,83 @@
+/*******************************************************************************
+ * 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 Snippet394 {
+	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) {
+			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();
+	}
+}