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GC.setClipping(Path) doesn't paint on Linux when transformed #3120
The fix for Bug 531667 (d7ce597) is incomplete and doesn't properly update the clipping of a `Path` when a `Transform` is set. This is because the clipping is calculated by intersecting the clipping rectangle when the GC instance was created with the `Path`. The region described by the `Path` is affected by the transformation, while the region of the rectangle is not. To fix this problem, the transformation needs to be cleared and re-applied when resetting the clipping, so that the region of the clipping rectangle is properly updated. Closes #3120
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‎bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/graphics/GC.java‎

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@@ -3094,7 +3094,19 @@ public void setClipping(int x, int y, int width, int height) {
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public void setClipping(Path path) {
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if (handle == 0) SWT.error(SWT.ERROR_GRAPHIC_DISPOSED);
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if (path != null && path.isDisposed()) SWT.error(SWT.ERROR_GRAPHIC_DISPOSED);
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Transform t = null;
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if (currentTransform != null) {
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t = new Transform(getDevice());
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getTransform(t);
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setTransform(null);
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}
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resetClipping();
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if (t != null) {
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setTransform(t);
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t.dispose();
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}
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if (path != null) {
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initCairo();
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long cairo = data.cairo;

‎tests/org.eclipse.swt.tests.gtk/ManualTests/org/eclipse/swt/tests/gtk/snippets/Issue3120_GC_setClipping_with_Transform.java‎

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/*******************************************************************************
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* Copyright (c) 2026 Patrick Ziegler and others.
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*
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* This program and the accompanying materials are made available under the
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* terms of the Eclipse Public License 2.0 which is available at
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* http://www.eclipse.org/legal/epl-2.0.
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*
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* SPDX-License-Identifier: EPL-2.0
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*
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* Contributors:
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* Patrick Ziegler - initial API and implementation
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*******************************************************************************/
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package org.eclipse.swt.tests.gtk.snippets;
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import java.util.function.Consumer;
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import org.eclipse.swt.SWT;
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import org.eclipse.swt.graphics.Color;
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import org.eclipse.swt.graphics.GC;
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import org.eclipse.swt.graphics.Path;
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import org.eclipse.swt.graphics.Transform;
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import org.eclipse.swt.layout.FillLayout;
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import org.eclipse.swt.widgets.Composite;
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import org.eclipse.swt.widgets.Display;
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import org.eclipse.swt.widgets.Shell;
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/**
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* Description: {@link GC#setClipping(Path)} doesn't respect a previous call to
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* {@link GC#setTransform(Transform)}.
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* <ol>
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* <li>Run the snippet.</li>
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* </ol>
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* Expected results: All painted rectangle should be green.<br>
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* Actual results: The rectangles are at least partially painted red.
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*
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* @see <a href="https://bugs.eclipse.org/bugs/show_bug.cgi?id=531667">Bug
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* 531667 - [GTK3] Cannot draw Canvas with Control.print(GC) </a>
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*/
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public class Issue3120_GC_setClipping_with_Transform {
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private static Display DISPLAY = Display.getDefault();
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private static Color COLOR_RED = DISPLAY.getSystemColor(SWT.COLOR_RED);
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private static Color COLOR_GREEN = DISPLAY.getSystemColor(SWT.COLOR_GREEN);
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public static void main(String[] args) {
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Shell shell = new Shell();
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shell.setLayout(new FillLayout());
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shell.setSize(800, 300);
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Composite composite1 = new Composite(shell, SWT.BORDER);
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composite1.addPaintListener(
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event -> paint(event.gc, p -> p.addRectangle(310, 310, 100, 100), t -> t.translate(-300, -300)));
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Composite composite2 = new Composite(shell, SWT.BORDER);
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composite2.addPaintListener(
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event -> paint(event.gc, p -> p.addRectangle(20, 5, 200, 50), t -> t.scale(0.5f, 2.0f)));
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Composite composite3 = new Composite(shell, SWT.BORDER);
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composite3.addPaintListener(
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event -> paint(event.gc, p -> p.addRectangle(10, 10, 100, 100), t -> t.shear(1.0f, 0.0f)));
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Composite composite4 = new Composite(shell, SWT.BORDER);
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composite4.addPaintListener(event -> paint(event.gc, p -> p.addRectangle(10, 605, 100, 50), t -> {
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t.scale(1.0f, 2.0f);
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t.translate(0, -600);
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}));
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Composite composite5 = new Composite(shell, SWT.BORDER);
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composite5.addPaintListener(event -> paint(event.gc, p -> p.addRectangle(10, 10, 100, 100), t -> {}, gc -> {
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Path p = new Path(DISPLAY);
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p.addRectangle(55, 55, 10, 10);
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gc.setClipping(p);
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p.dispose();
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}));
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Composite composite6 = new Composite(shell, SWT.BORDER);
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composite6.addPaintListener(event -> paint(event.gc, p -> p.addRectangle(10, 275, 100, 50), t -> {
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t.scale(1.0f, 2.0f);
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t.translate(0, -270);
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}, gc -> {
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gc.setClipping(10, 10, 100, 100);
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}));
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shell.open();
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while(!shell.isDisposed()) {
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if (!DISPLAY.readAndDispatch()) {
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DISPLAY.sleep();
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}
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}
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}
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private static void paint(GC gc, Consumer<Path> c1, Consumer<Transform> c2) {
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paint(gc, c1, c2, ignore -> {
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});
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}
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private static void paint(GC gc, Consumer<Path> c1, Consumer<Transform> c2, Consumer<GC> c3) {
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Path p = new Path(DISPLAY);
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c1.accept(p);
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Transform t = new Transform(DISPLAY);
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c2.accept(t);
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gc.setTransform(t);
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t.dispose();
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gc.setBackground(COLOR_RED);
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gc.fillPath(p);
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c3.accept(gc);
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gc.setClipping(p);
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gc.setBackground(COLOR_GREEN);
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gc.fillPath(p);
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p.dispose();
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}
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}

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