[GTK] Don't invalidate style context when setting background color #2702

When setting the background color while inside an SWT.Activate event,
pending events are not processed.

The gtk_style_context_invalidate() method is deprecated in GTK3 and
doesn't have a GTK4 counterpart, as GTK invalidates the style context
automatically.

With b7dee8a, this method call was
already removed, but later reverted due to test failures in the Eclipse
Platform. Rather than removing all references, this change only does so
for the call to setBackground().

To reproduce, execute the Snippet388. When clicking on a tree/table
item, the item should be selected. This is the current behavior on
Windows and MacOS, but not on Linux.

Closes #2702

Author: ptziegler

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Control.java

@@ -5258,7 +5258,6 @@ void setBackgroundGdkRGBA (long handle, GdkRGBA rgba) {
 
 	long context = GTK.gtk_widget_get_style_context(handle);
 	setBackgroundGdkRGBA(context, handle, rgba);
-	if (!GTK.GTK4) GTK3.gtk_style_context_invalidate(context);
 }
 /**
  * Sets the receiver's background image to the image specified

tests/org.eclipse.swt.tests.gtk/ManualTests/org/eclipse/swt/tests/gtk/snippets/Issue2702_DoubleClickBehavior.java

@@ -0,0 +1,65 @@
+/*******************************************************************************
+ * Copyright (c) 2025 Patrick Ziegler and others.
+ *
+ * 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
+ *
+ * Contributors:
+ *     Patrick Ziegler - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.swt.tests.gtk.snippets;
+
+import org.eclipse.swt.*;
+import org.eclipse.swt.graphics.*;
+import org.eclipse.swt.layout.*;
+import org.eclipse.swt.widgets.*;
+
+/**
+ * This snippet demonstrates a missed selection event when updating the
+ * background color within an SWT.Activate event. To reproduce, alternative
+ * between the table and the tree. On each click, the clicked tree/table item
+ * should be selected.
+ *
+ * @see <a href="https://github.com/eclipse-platform/eclipse.platform.swt/issues/2702">Issue 2702</a>
+ */
+public class Issue2702_DoubleClickBehavior {
+	private static Color ACTIVE = new Color(255, 255, 255);
+	private static Color INACTIVE = new Color(248, 248, 248);
+
+	public static void main(String[] args) {
+		Shell shell = new Shell();
+		shell.setLayout(new GridLayout(2, true));
+		shell.setSize(400, 200);
+
+		Tree tree = new Tree(shell,  SWT.FULL_SELECTION);
+		tree.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true));
+		TreeItem treeItem1 = new TreeItem(tree, SWT.NONE);
+		treeItem1.setText("Tree Item 1");
+		TreeItem treeItem2 = new TreeItem(tree, SWT.NONE);
+		treeItem2.setText("Tree Item 2");
+		tree.addListener(SWT.Activate, event -> tree.setBackground(ACTIVE));
+		tree.addListener(SWT.Deactivate, event -> tree.setBackground(INACTIVE));
+
+		Table table = new Table(shell, SWT.FULL_SELECTION);
+		table.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true));
+		TableItem tableItem1 = new TableItem(table, SWT.NONE);
+		tableItem1.setText("Table Item 1");
+		TableItem tableItem2 = new TableItem(table, SWT.NONE);
+		tableItem2.setText("Table Item 2");
+		table.addListener(SWT.Activate, event -> table.setBackground(ACTIVE));
+		table.addListener(SWT.Deactivate, event -> table.setBackground(INACTIVE));
+
+		shell.open();
+
+		Display display = shell.getDisplay();
+		while (!shell.isDisposed()) {
+		 	if (!display.readAndDispatch()) {
+		 		display.sleep();
+	 		}
+		}
+	}
+}