8287912: GTK L&F : Background of tree icons are red

src/java.desktop/share/classes/com/sun/java/swing/plaf/gtk/GTKPainter.java

@@ -1275,8 +1275,10 @@ public void paintTreeCellBackground(SynthContext context, Graphics g,
                 ENGINE.startPainting(g, x, y, w, h, id, state);
                 // the string arg should alternate based on row being painted,
                 // but we currently don't pass that in.
-                ENGINE.paintFlatBox(g, context, id, gtkState, ShadowType.NONE,
-                        "cell_odd", x, y, w, h, ColorType.TEXT_BACKGROUND);
+                if (context.getComponent().isOpaque()) {
+                    ENGINE.paintFlatBox(g, context, id, gtkState, ShadowType.NONE,
+                            "cell_odd", x, y, w, h, ColorType.TEXT_BACKGROUND);
+                }
                 ENGINE.finishPainting();
             }
         }

test/jdk/javax/swing/JTree/TestTreeBackgroundColor.java

@@ -0,0 +1,112 @@
+
+/*
+ * Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8287912
+ * @key headful
+ * @requires (os.family == "linux")
+ * @summary Verifies if tree background color is red when
+ * setOpaque(false) method is called for tree component
+ * @run main TestTreeBackgroundColor
+ */
+
+import java.awt.Color;
+import java.awt.GridLayout;
+import java.awt.Point;
+import java.awt.Rectangle;
+import java.awt.Robot;
+import java.awt.image.BufferedImage;
+import java.io.File;
+import javax.imageio.ImageIO;
+import javax.swing.JFrame;
+import javax.swing.JPanel;
+import javax.swing.JTree;
+import javax.swing.SwingUtilities;
+import javax.swing.UIManager;
+
+public class TestTreeBackgroundColor {
+
+    private static JFrame frame;
+    private static JPanel panel;
+    private static JTree tree;
+
+    public static void main(String[] args) throws Exception {
+        UIManager.setLookAndFeel("com.sun.java.swing.plaf.gtk.GTKLookAndFeel");
+        Robot robot = new Robot();
+        robot.setAutoDelay(100);
+        try {
+            SwingUtilities.invokeAndWait(new Runnable() {
+                public void run() {
+                    createAndShowUI();
+                }
+            });
+
+            robot.waitForIdle();
+            robot.delay(1000);
+            Point pt = tree.getLocationOnScreen();
+            BufferedImage img =
+                    robot.createScreenCapture(new Rectangle(pt.x, pt.y,
+                            tree.getWidth(),
+                            tree.getHeight()));
+
+            boolean passed = false;
+            for (int x = 0; x < img.getWidth() - 1; ++x) {
+                for (int y = 0; y < img.getHeight() - 1; ++y) {
+                    Color c = new Color(img.getRGB(x, y));
+
+                    if (c.equals(Color.RED)) {
+                        passed = true;
+                    }
+                }
+            }
+            if (!passed) {
+                ImageIO.write(img, "png", new File("TreeBackgroundColorTestFail.png"));
+                throw new RuntimeException("Test Case Failed : Tree Background Color is Not Red");
+            }
+        } finally {
+            SwingUtilities.invokeAndWait(() -> {
+                if (frame != null) {
+                    frame.dispose();
+                }
+            });
+        }
+    }
+
+    private static void createAndShowUI() {
+        frame = new JFrame();
+        panel = new JPanel();
+        tree = new JTree();
+        panel.setBackground(Color.red);
+        panel.setLayout(new GridLayout(1, 1));
+        tree.setOpaque(false);
+        panel.add(tree);
+        frame.getContentPane().add(panel);
+        frame.pack();
+        frame.setSize(250, 200);
+        frame.setLocationRelativeTo(null);
+        frame.setVisible(true);
+    }
+}
+