GhostImageFigure.java

/*******************************************************************************
 * Copyright (c) 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:
 *     Research Group Software Construction,
 *     RWTH Aachen University, Germany - initial API and implementation
 */
package org.eclipse.draw2d;

import org.eclipse.swt.graphics.GC;
import org.eclipse.swt.graphics.Image;
import org.eclipse.swt.graphics.ImageData;
import org.eclipse.swt.graphics.PaletteData;
import org.eclipse.swt.graphics.RGB;
import org.eclipse.swt.widgets.Display;

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

/**
 * A figure used to render a partly transparent copy of an original source
 * figure.
 * 
 * This class is pretty much based on a sample, posted within the GEF newsgroup
 * (http://dev.eclipse.org/newslists/news.eclipse.tools.gef/msg15158.html),
 * although we decided to not cache the ghost image itself (but only its image
 * data), so the figure does not have to be disposed (and may thus directly
 * extend {@link Figure} rather than {@link ImageFigure}).
 * 
 * @author Alexander Nyssen
 * @author Philip Ritzkopf
 * 
 * @since 3.6
 */
public class GhostImageFigure extends Figure {

	private int alpha = -1;
	private ImageData ghostImageData;

	/**
	 * The single constructor.
	 * 
	 * @param source
	 *            The original figure that will be used to render the ghost
	 *            image.
	 * @param alpha
	 *            The desired transparency value, to be forwarded to
	 *            {@link Graphics#setAlpha(int)}.
	 * @param transparency
	 *            The RBG value of the color that is to be regarded as
	 *            transparent. May be <code>null</code>.
	 */
	public GhostImageFigure(final IFigure source, int alpha, RGB transparency) {
		this.alpha = alpha;

		Rectangle sourceFigureRelativePrecisionBounds = new PrecisionRectangle(
				source.getBounds().getCopy());

		Image offscreenImage = new Image(Display.getCurrent(),
				sourceFigureRelativePrecisionBounds.width,
				sourceFigureRelativePrecisionBounds.height);

		GC gc = new GC(offscreenImage.getDevice());
		SWTGraphics swtGraphics = new SWTGraphics(gc);
		swtGraphics.translate(-sourceFigureRelativePrecisionBounds.x,
				-sourceFigureRelativePrecisionBounds.y);
		source.paint(swtGraphics);

		ghostImageData = offscreenImage.getImageData();
		if (transparency != null) {
			ghostImageData.transparentPixel = ghostImageData.palette
					.getPixel(transparency);
		}

		offscreenImage.dispose();
		swtGraphics.dispose();
		gc.dispose();
	}

	/**
	 * @see Figure#paintFigure(Graphics)
	 */
	protected void paintFigure(Graphics graphics) {
		Image feedbackImage = new Image(Display.getCurrent(), ghostImageData);
		graphics.setAlpha(alpha);
		graphics.setClip(getBounds().getCopy());
		graphics.drawImage(feedbackImage, 0, 0, ghostImageData.width,
				ghostImageData.height, getBounds().x, getBounds().y,
				getBounds().width, getBounds().height);
		feedbackImage.dispose();
	}
}