bundles/org.eclipse.jface/src/org/eclipse/jface/resource/ImageDescriptor.java

/*******************************************************************************
 * Copyright (c) 2000, 2003 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials 
 * are made available under the terms of the Common Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/cpl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.jface.resource;

import java.net.URL;

import org.eclipse.swt.SWTException;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.widgets.Display;

/**
 * An image descriptor is an object that knows how to create
 * an SWT image.  It does not hold onto images or cache them,
 * but rather just creates them on demand.  An image descriptor
 * is intended to be a lightweight representation of an image
 * that can be manipulated even when no SWT display exists.
 * <p>
 * This package defines a concrete image descriptor implementation
 * which reads an image from a file (<code>FileImageDescriptor</code>).
 * It also provides abstract framework classes (this one and
 * <code>CompositeImageDescriptor</code>) which may be subclassed to define
 * news kinds of image descriptors.
 * </p>
 * <p>
 * Using this abstract class involves defining a concrete subclass
 * and providing an implementation for the <code>getImageData</code>
 * method.
 * </p>
 *
 * @see org.eclipse.swt.graphics.Image
 */
public abstract class ImageDescriptor {
	
	/** 
	 * A small red square used to warn that an image cannot be created.
	 * <p>
	 */
	protected static final ImageData DEFAULT_IMAGE_DATA= new ImageData(6, 6, 1, new PaletteData(new RGB[] { new RGB(255, 0, 0) }));
/**
 * Constructs an image descriptor.
 */
protected ImageDescriptor() {
}
/**
 * Creates and returns a new image descriptor from a file.
 * Convenience method for
 * <code>new FileImageDescriptor(location,filename)</code>.
 *
 * @param location the class whose resource directory contain the file
 * @param filename the file name
 * @return a new image descriptor
 */
public static ImageDescriptor createFromFile(Class location, String filename) {
	return new FileImageDescriptor(location, filename);
}
/**
 * Creates and returns a new image descriptor from a URL.
 *
 * @param url The URL of the image file.
 * @return a new image descriptor
 */
public static ImageDescriptor createFromURL(URL url) {
	if (url == null) {
		return getMissingImageDescriptor();
	}
	return new URLImageDescriptor(url);
}
/**
 * Creates and returns a new SWT image for this image descriptor.
 * Note that each call returns a new SWT image object.
 *
 * @return a new image
 */
public Image createImage() {
	return createImage(true);
}
/**
 * Creates and returns a new SWT image for this image descriptor.
 * Note that if returnMissingImageOnError is true a default image
 * is returned
 *
 * @param returnMissingImageOnError The flag that determines if a default image is returned on error
 * @return a new image or null if the image could not be created
 */
public Image createImage(boolean returnMissingImageOnError) {
	return createImage(returnMissingImageOnError, Display.getCurrent());	
}
/**
 * Creates and returns a new SWT image for this image descriptor.
 *
 * @param device the device on which to create the image
 * @return a new image or null if the image could not be created
 * @since 2.0
 */
public Image createImage(Device device) {
	return createImage(true, device);
}
/**
 * Creates and returns a new SWT image for this image descriptor.
 * Note that if returnMissingImageOnError is true a default image
 * is returned
 *
 * @param returnMissingImageOnError The flag that determines if a default image is returned on error
 * @param device the device on which to create the image
 * @return a new image or null if the image could not be created
 * @since 2.0
 */
public Image createImage(boolean returnMissingImageOnError, Device device) {

	ImageData data = getImageData();
	if (data == null) {
		if (!returnMissingImageOnError) {
			return null;
		} else {
			data = DEFAULT_IMAGE_DATA;
		}
	}

	/*
	* Try to create the supplied image. If there is an SWT Exception try and create
	* the default image if that was requested. Return null if this fails.
	*/
	
	try {
		if (data.transparentPixel >= 0) {
			ImageData maskData = data.getTransparencyMask();
			return new Image(device, data, maskData);
		}
		return new Image(device, data);
	} catch (SWTException exception) {
		if (returnMissingImageOnError) {
			try {
				return new Image(device, DEFAULT_IMAGE_DATA);
			} catch (SWTException nextException) {
				return null;
			}
		} else
			return null;
	}
}
/**
 * Creates and returns a new SWT <code>ImageData</code> object
 * for this image descriptor.
 * Note that each call returns a new SWT image data object.
 * <p>
 * This framework method is declared public so that it is
 * possible to request an image descriptor's image data without
 * creating an SWT image object.
 * </p>
 *
 * @return a new image data
 */
public abstract ImageData getImageData();
/**
 * Returns the shared image descriptor for a missing image.
 *
 * @return the missing image descriptor
 */
public static ImageDescriptor getMissingImageDescriptor() {
	return MissingImageDescriptor.getInstance();
}
}