bundles/org.eclipse.draw2d/src/org/eclipse/draw2d/EllipseAnchor.java

/*******************************************************************************
 * Copyright (c) 2000, 2010 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.draw2d;

import org.eclipse.draw2d.geometry.Point;
import org.eclipse.draw2d.geometry.Rectangle;

/**
 * Similar to a {@link org.eclipse.draw2d.ChopboxAnchor}, except this anchor is
 * located on the ellipse defined by the owners bounding box.
 * 
 * @author Alex Selkov Created 31.08.2002 23:11:43
 */
public class EllipseAnchor extends AbstractConnectionAnchor {

	/**
	 * @see org.eclipse.draw2d.AbstractConnectionAnchor#AbstractConnectionAnchor()
	 */
	public EllipseAnchor() {
	}

	/**
	 * @see org.eclipse.draw2d.AbstractConnectionAnchor#AbstractConnectionAnchor(IFigure)
	 */
	public EllipseAnchor(IFigure owner) {
		super(owner);
	}

	/**
	 * Returns a point on the ellipse (defined by the owner's bounding box)
	 * where the connection should be anchored.
	 * 
	 * @see org.eclipse.draw2d.ConnectionAnchor#getLocation(Point)
	 */
	public Point getLocation(Point reference) {
		Rectangle r = Rectangle.SINGLETON;
		r.setBounds(getOwner().getBounds());
		r.translate(-1, -1);
		r.resize(1, 1);
		getOwner().translateToAbsolute(r);

		Point ref = r.getCenter().negate().translate(reference);

		if (ref.x == 0)
			return new Point(reference.x, (ref.y > 0) ? r.bottom() : r.y);
		if (ref.y == 0)
			return new Point((ref.x > 0) ? r.right() : r.x, reference.y);

		float dx = (ref.x > 0) ? 0.5f : -0.5f;
		float dy = (ref.y > 0) ? 0.5f : -0.5f;

		// ref.x, ref.y, r.width, r.height != 0 => safe to proceed

		float k = (float) (ref.y * r.width) / (ref.x * r.height);
		k = k * k;

		return r.getCenter().translate((int) (r.width * dx / Math.sqrt(1 + k)),
				(int) (r.height * dy / Math.sqrt(1 + 1 / k)));
	}
}