[90] Fix cursor initialization when using fractional scaling

Recent Eclipse version support fractional zoom level as opposed to 100%
or 200% zoom. Because no icons exist for those levels, an
IllegalArgumentException is thrown when trying to create the
corresponding cursors.

In order to solve this, one has to consider the following cases:

1) Newer SWT versions provide a Cursor constructor that accepts an
ImageDataProvider. This constructor always creates image data matching
the device zoom. However, this constructor crashes when PNGs are used
and the automatic UI scaling is disabled.

2) Older SWT versions automatically upscales the image data to
match the device zoom. On Windows, the image data should always be at
100% because SWT internally scales the image to match the device zoom.
Sadly, this doesn't work either. So on both Windows and Non-Windows
systems, the image must be pre-scaled to the device zoom. This means
that on Windows, the cursor is always scaled twice.

Author: ptziegler

bundles/org.eclipse.gmf.runtime.gef.ui/src/org/eclipse/gmf/runtime/gef/ui/internal/l10n/Cursors.java

@@ -1,5 +1,5 @@
 /******************************************************************************
- * Copyright (c) 2002, 2003 IBM Corporation and others.
+ * Copyright (c) 2002, 2025 IBM Corporation 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 https://www.eclipse.org/legal/epl-2.0/
@@ -12,7 +12,14 @@
 
 package org.eclipse.gmf.runtime.gef.ui.internal.l10n;
 
+import java.lang.reflect.Constructor;
+
+import org.eclipse.jface.resource.ImageDescriptor;
 import org.eclipse.swt.graphics.Cursor;
+import org.eclipse.swt.graphics.Device;
+import org.eclipse.swt.graphics.Image;
+import org.eclipse.swt.graphics.ImageData;
+import org.eclipse.swt.graphics.ImageDataProvider;
 
 
 /**
@@ -37,11 +44,37 @@ public class Cursors {
     private static int deviceZoom = -1;
 
     static {
-		CURSOR_SEG_ADD = new Cursor(null, GefUIPluginImages.DESC_SEG_ADD.getImageData(getDeviceZoom()), 0, 0);
-		CURSOR_SEG_MOVE = new Cursor(null, GefUIPluginImages.DESC_SEG_MOVE.getImageData(getDeviceZoom()), 0, 0);
+		CURSOR_SEG_ADD = createCursor(GefUIPluginImages.DESC_SEG_ADD, 0, 0);
+		CURSOR_SEG_MOVE = createCursor(GefUIPluginImages.DESC_SEG_MOVE, 0, 0);
 	}
 
-    // Taken from org.eclipse.gef.SharedCursors.java
+    // Taken from org.eclipse.gef.internal.InternalGEFPlugin.java
+	private static Cursor createCursor(ImageDescriptor source, int hotspotX, int hotspotY) {
+		ImageDataProvider imageDataProvider = zoom -> getScaledImageData(source, zoom);
+		try {
+			// If this system property is disabled, SWT will crash trying to load e.g. the non-existent @1.5.png variant at 150% zoom.
+			if (isMonitorSpecificScalingActive()) {
+				Constructor<Cursor> ctor = Cursor.class.getConstructor(Device.class, ImageDataProvider.class, int.class,
+						int.class);
+				return ctor.newInstance(null, imageDataProvider, hotspotX, hotspotY);
+			}
+		} catch (NoSuchMethodException e) {
+			// SWT version < 3.131.0
+		} catch (ReflectiveOperationException e) {
+			throw new RuntimeException("Failed to instantiate Cursor", e); //$NON-NLS-1$
+		}
+		// Note: On Windows, the image data would always need to be created at 100% zoom. Sadly, that doesn't work...
+		// See https://github.com/eclipse-platform/eclipse.platform.swt/issues/2309
+		return new Cursor(null, imageDataProvider.getImageData(getDeviceZoom()), hotspotX, hotspotY);
+	}
+	
+	// Taken from org.eclipse.swt.internal.DPIUtil
+	public static boolean isMonitorSpecificScalingActive() {
+		boolean updateOnRuntimeValue = Boolean.getBoolean ("swt.autoScale.updateOnRuntime"); //$NON-NLS-1$
+		return updateOnRuntimeValue;
+	}
+
+	// Taken from org.eclipse.gef.SharedCursors.java
 	private static int getDeviceZoom() {
 		if (deviceZoom == -1) {
 			deviceZoom = 100; // default value
@@ -56,4 +89,19 @@ private static int getDeviceZoom() {
 		}
 		return deviceZoom;
 	}
+
+	private static ImageData getScaledImageData(ImageDescriptor descriptor, int zoom) {
+	    // Default case: Image in matching resolution has been found
+	    ImageData data = descriptor.getImageData(zoom);
+	    if (data != null) {
+	        return data;
+	    }
+	    // Otherwise artifically scale the image
+	    Image image = descriptor.createImage();
+	    try {
+	        return image.getImageData(zoom);
+	    } finally {
+	        image.dispose();
+	    }
+	}
 }