GC.setClipping(path) doesn't paint on Linux when transformed #3120

The fix for Bug 531667 (d7ce597)
introduced a regression when calling `setClipping(Path)` after
`setTransform(Transform)`. The rectangle used when resetting the clip
doesn't consider the previously done transformation, producing an empty
clip if this rectangle and the `Path` don't intersect.

Instead of using the local `clipping` variable (which contains the
initial clip when the GC was created), the `resetClipping()` method now
uses the rectangle returned by `getClipping()`, which internally applies
the transformation matrix.

To reproduce, execute the attached snippet. The rectangle in this
example should be green, as it is drawn over the red rectangle.

Closes #3120

Author: ptziegler

tests/org.eclipse.swt.tests.gtk/ManualTests/org/eclipse/swt/tests/gtk/snippets/Issue3120_GC_setClipping_is_wrong_after_transform.java

@@ -0,0 +1,75 @@
+/*******************************************************************************
+ * Copyright (c) 2026 Patrick Ziegler and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://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.SWT;
+import org.eclipse.swt.graphics.GC;
+import org.eclipse.swt.graphics.Path;
+import org.eclipse.swt.graphics.Transform;
+import org.eclipse.swt.layout.FillLayout;
+import org.eclipse.swt.widgets.Display;
+import org.eclipse.swt.widgets.Shell;
+
+/**
+ * Description: {@link GC#setClipping(Path)} doesn't respect a previous call to
+ * {@link GC#setTransform(Transform)}.
+ * <ol>
+ * <li>Run the snippet.</li>
+ * </ol>
+ * Expected results: The painted rectangle should be green.<br>
+ * Actual results: The painted rectangle is red.
+ *
+ * @see <a href="https://bugs.eclipse.org/bugs/show_bug.cgi?id=531667">Bug
+ *      531667 - [GTK3] Cannot draw Canvas with Control.print(GC) </a>
+ */
+public class Issue3120_GC_setClipping_is_wrong_after_transform {
+
+    public static void main(String[] args) {
+        Shell shell = new Shell();
+        shell.setLayout(new FillLayout());
+        shell.setSize(600, 300);
+
+        Display display = shell.getDisplay();
+
+        shell.addPaintListener(event -> {
+        	GC gc = event.gc;
+
+        	Path p = new Path(display);
+        	p.addRectangle(50, 350, 100, 100);
+
+        	Transform t = new Transform(display);
+        	t.translate(0, -300);
+
+        	gc.setTransform(t);
+
+        	gc.setBackground(display.getSystemColor(SWT.COLOR_RED));
+        	gc.fillPath(p);
+        	gc.setClipping(p);
+        	gc.setBackground(display.getSystemColor(SWT.COLOR_GREEN));
+        	gc.fillPath(p);
+
+        	p.dispose();
+
+        	gc.setTransform(null);
+        	t.dispose();
+        });
+
+        shell.open();
+
+        while(!shell.isDisposed()) {
+            if(!display.readAndDispatch()) {
+                display.sleep();
+            }
+        }
+    }
+}

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

@@ -16,6 +16,7 @@
 
 import static org.eclipse.swt.internal.DPIUtil.pointToPixel;
 import static org.eclipse.swt.tests.junit.SwtTestUtil.assertSWTProblem;
+import static org.junit.jupiter.api.Assertions.assertAll;
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
@@ -791,42 +792,60 @@ public void test_setBackgroundLorg_eclipse_swt_graphics_Color() {
 			"No exception thrown for color disposed");
 }
 
+@Test
+public void test_setClippingIIII_withTransform() {
+	Transform t = new Transform(gc.getDevice());
+	t.scale(1.5f,0.5f);
+	t.translate(-5,-25);
+
+	gc.setClipping(0,5,10,20);
+	gc.setTransform(t);
+
+	Rectangle rect = gc.getClipping();
+	assertAll(
+		() -> assertEquals(5,rect.x),
+		() -> assertEquals(35, rect.y),
+		() -> assertEquals(7,rect.width),
+		() -> assertEquals(40,rect.height));
+}
+
 @Test
 public void test_setClippingIIII() {
-	// intermittently fails on XP for reasons unknown, comment out the test case
-	// until the problem is figured out
-//	Canvas canvas = new Canvas(shell, SWT.BORDER);
-//	shell.setSize(110,110);
-//	canvas.setSize(100,100);
-//	shell.open();
-//	GC testGc = new GC(canvas);
-//	testGc.setClipping(0,5,10,20);
-//	Rectangle rect = testGc.getClipping();
-//	assertTrue(rect.x == 0);
-//	assertTrue(rect.y == 5);
-//	assertTrue(rect.width == 10);
-//	assertTrue(rect.height == 20);
-//	testGc.dispose();
-//	canvas.dispose();
+	gc.setClipping(0,5,10,20);
+	Rectangle rect = gc.getClipping();
+	assertAll(
+		() -> assertEquals(0,rect.x),
+		() -> assertEquals(5, rect.y),
+		() -> assertEquals(10,rect.width),
+		() -> assertEquals(20,rect.height));
+}
+
+@Test
+public void test_setClippingLorg_eclipse_swt_graphics_Rectangle_withTransform() {
+	Transform t = new Transform(gc.getDevice());
+	t.scale(1.5f,0.5f);
+	t.translate(-5,-25);
+
+	gc.setClipping(new Rectangle(0,5,10,20));
+	gc.setTransform(t);
+
+	Rectangle rect = gc.getClipping();
+	assertAll(
+		() -> assertEquals(5,rect.x),
+		() -> assertEquals(35, rect.y),
+		() -> assertEquals(7,rect.width),
+		() -> assertEquals(40,rect.height));
 }
 
 @Test
 public void test_setClippingLorg_eclipse_swt_graphics_Rectangle() {
-	// intermittently fails on XP for reasons unknown, comment out the test case
-	// until the problem is figured out
-//	Canvas canvas = new Canvas(shell, SWT.BORDER);
-//	shell.setSize(110,110);
-//	canvas.setSize(100,100);
-//	shell.open();
-//	GC testGc = new GC(canvas);
-//	testGc.setClipping(new Rectangle(0,5,10,20));
-//	Rectangle rect = testGc.getClipping();
-//	assertTrue(rect.x == 0);
-//	assertTrue(rect.y == 5);
-//	assertTrue(rect.width == 10);
-//	assertTrue(rect.height == 20);
-//	testGc.dispose();
-//	canvas.dispose();
+	gc.setClipping(new Rectangle(0,5,10,20));
+	Rectangle rect = gc.getClipping();
+	assertAll(
+		() -> assertEquals(0,rect.x),
+		() -> assertEquals(5, rect.y),
+		() -> assertEquals(10,rect.width),
+		() -> assertEquals(20,rect.height));
 }
 
 @Test