Add opt-in method to propagate zoom changes

Contributes to eclipse-platform#62
and eclipse-platform#127

bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/internal/DPIUtil.java

@@ -44,6 +44,7 @@ public class DPIUtil {
 	private static enum AutoScaleMethod { AUTO, NEAREST, SMOOTH }
 	private static AutoScaleMethod autoScaleMethodSetting = AutoScaleMethod.AUTO;
 	private static AutoScaleMethod autoScaleMethod = AutoScaleMethod.NEAREST;
+	public static boolean autoScaleOnRuntime = false;
 
 	private static String autoScaleValue;
 	private static boolean useCairoAutoScale = false;
@@ -84,6 +85,16 @@ private static enum AutoScaleMethod { AUTO, NEAREST, SMOOTH }
 	 * <a href="https://bugs.eclipse.org/493455">bug 493455</a>.
 	 */
 	private static final String SWT_AUTOSCALE_METHOD = "swt.autoScale.method";
+
+	/**
+	 * System property to enable to scale the applicaiton on runtime
+	 * when a DPI change is detected.
+	 * <ul>
+	 * <li>"true": the application is scaled on DPI changes</li>
+	 * <li>"false": the application will remain in its initial scaling</li>
+	 * </ul>
+	 */
+	private static final String SWT_AUTOSCALE_UPDATE_ON_RUNTIME = "swt.autoScale.updateOnRuntime";
 	static {
 		autoScaleValue = System.getProperty (SWT_AUTOSCALE);
 
@@ -95,6 +106,9 @@ private static enum AutoScaleMethod { AUTO, NEAREST, SMOOTH }
 				autoScaleMethod = autoScaleMethodSetting = AutoScaleMethod.SMOOTH;
 			}
 		}
+
+		String updateOnRuntimeValue = System.getProperty (SWT_AUTOSCALE_UPDATE_ON_RUNTIME);
+		autoScaleOnRuntime = Boolean.parseBoolean(updateOnRuntimeValue);
 	}
 
 /**

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/internal/DPIZoomChangeHandler.java

@@ -0,0 +1,21 @@
+/*******************************************************************************
+ * Copyright (c) 2024 Yatta Solutions 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:
+ *     Yatta Solutions - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.swt.internal;
+
+import org.eclipse.swt.widgets.*;
+
+@FunctionalInterface
+public interface DPIZoomChangeHandler {
+	public void handleDPIChange(Widget widget, int newZoom, float scalingFactor);
+}

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/internal/DPIZoomChangeRegistry.java

@@ -0,0 +1,47 @@
+/*******************************************************************************
+ * Copyright (c) 2024 Yatta Solutions 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:
+ *     Yatta Solutions - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.swt.internal;
+
+import java.util.*;
+import java.util.Map.*;
+
+import org.eclipse.swt.widgets.*;
+
+public class DPIZoomChangeRegistry {
+
+	private static Map<Class<? extends Widget>, DPIZoomChangeHandler> dpiZoomChangeHandlers =  new TreeMap<>(
+			(o1, o2) -> {
+	            if(o1.isAssignableFrom(o2)) {
+	            	return -1;
+	            }
+	            if(o2.isAssignableFrom(o1)) {
+	            	return 1;
+	            }
+	            return o1.getName().compareTo(o2.getName());
+	        });
+
+	public static <E> void applyChange(Widget widget, int newZoom, float scalingFactor) {
+		for (Entry<Class<? extends Widget>, DPIZoomChangeHandler> entry : dpiZoomChangeHandlers.entrySet()) {
+			Class<? extends Widget> clazz = entry.getKey();
+			DPIZoomChangeHandler handler = entry.getValue();
+			if (clazz.isInstance(widget)) {
+				handler.handleDPIChange(widget, newZoom, scalingFactor);
+			}
+		}
+	}
+
+	public static <E> void registerHandler(DPIZoomChangeHandler zoomChangeVisitor, Class<? extends Widget> clazzToRegisterFor) {
+		dpiZoomChangeHandlers.put(clazzToRegisterFor, zoomChangeVisitor);
+	}
+}

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Widget.java

@@ -51,6 +51,8 @@
  * @see <a href="http://www.eclipse.org/swt/">Sample code and further information</a>
  */
 public abstract class Widget {
+
+	private int currentDeviceZoom;
 	int style, state;
 	Display display;
 	EventTable eventTable;
@@ -166,6 +168,7 @@ public Widget (Widget parent, int style) {
 	checkSubclass ();
 	checkParent (parent);
 	this.style = style;
+	this.currentDeviceZoom = parent != null ? parent.getCurrentDeviceZoom() : DPIUtil.getDeviceZoom();
 	display = parent.display;
 	reskinWidget ();
 	notifyCreationTracker();
@@ -2631,4 +2634,24 @@ void notifyDisposalTracker() {
 	}
 }
 
+
+/**
+ * The current DPI zoom level the widget is scaled for
+ * (Warning: This field is platform dependent)
+ * <p>
+ * <b>IMPORTANT:</b> This field is <em>not</em> part of the SWT
+ * public API. It is marked public only so that it can be shared
+ * within the packages provided by SWT. It is not available on all
+ * platforms and should never be accessed from application code.
+ * </p>
+ *
+ * @noreference This field is not intended to be referenced by clients.
+ */
+public int getCurrentDeviceZoom() {
+	return currentDeviceZoom;
+}
+
+void setCurrentDeviceZoom(int currentDeviceZoom) {
+	this.currentDeviceZoom = currentDeviceZoom;
+}
 }