Added EllipseDropShadowBorder

To evaluate the usability of the AbstractDropShadowBorder a shadow
border for ellipses and circles is added.

Author: azoitl

org.eclipse.draw2d/src/org/eclipse/draw2d/shadows/EllipseDropShadowBorder.java

@@ -0,0 +1,54 @@
+/*******************************************************************************
+ * Copyright (c) 2026 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
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     IBM Corporation - initial API and implementation
+ *******************************************************************************/
+
+package org.eclipse.draw2d.shadows;
+
+import org.eclipse.draw2d.Graphics;
+import org.eclipse.draw2d.geometry.Rectangle;
+
+/**
+ * A versatile border that provides a CSS-style drop shadow effect for circular
+ * and elliptical figures.
+ *
+ * This border simulates visual depth by layering semi-transparent shapes using
+ * multi-pass exponential decay. It is designed to work "out of the box" for
+ * standard diagramming nodes while remaining highly tunable for other use
+ * cases.
+ *
+ * @since 3.2
+ */
+public class EllipseDropShadowBorder extends AbstractDropShadowBorder {
+
+	@Override
+	protected void paintDropShadow(Graphics graphics, Rectangle shadowRect, int size) {
+		final Rectangle r = shadowRect.getCopy();
+		for (int i = 0; i < size; i++) {
+			final double progress = (double) i / size;
+			graphics.setAlpha(calcAlphaValue(progress));
+			graphics.drawArc(r, 270 + i, 90 - i);
+			r.translate(1, 1);
+		}
+	}
+
+	@Override
+	protected void paintHalo(Graphics graphics, Rectangle shadowRect, int size) {
+		final Rectangle r = shadowRect.getCopy();
+		for (int i = 0; i < size; i++) {
+			final double progress = (double) i / size;
+			graphics.setAlpha(calcAlphaValue(progress));
+			graphics.drawOval(r);
+			r.expand(1, 1);
+		}
+	}
+
+}