source: josm/src/org/openstreetmap/josm/gui/ImageProvider.java@ 22

package org.openstreetmap.josm.gui;

import java.awt.Graphics;
import java.awt.GraphicsConfiguration;
import java.awt.GraphicsEnvironment;
import java.awt.Transparency;
import java.awt.image.BufferedImage;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;

import javax.swing.Icon;
import javax.swing.ImageIcon;

import org.openstreetmap.josm.Main;

/**
 * Helperclass to support the application with images.
 * @author imi
 */
public class ImageProvider {

        /**
         * Position of an overlay icon
         * @author imi
         */
        public enum OverlayPosition {NORTHWEST, NORTHEAST, SOUTHWEST, SOUTHEAST}
        
        /**
         * The icon cache
         */
        private static Map<URL, Icon> cache = new HashMap<URL, Icon>();
        
        /**
         * Return an image from the specified location.
         *
         * @param subdir        The position of the directory, e.g. "layer"
         * @param name          The icons name (without the ending of ".png")
         * @return      The requested ImageIcon.
         */
        public static Icon get(String subdir, String name) {
                if (subdir != "")
                        subdir += "/";
                URL path = Main.class.getResource("/images/"+subdir+name+".png");
                Icon icon = cache.get(path);
                if (icon == null) {
                        icon = new ImageIcon(Main.class.getResource("/images/"+subdir+name+".png"));
                        cache.put(path, icon);
                }
                return icon;
        }

        /**
         * Shortcut for get("", name);
         */
        public static Icon get(String name) {
                return get("", name);
        }

        /**
         * Return an icon that represent the overlay of the two given icons. The
         * second icon is layed on the first relative to the given position.
         *
         * @param ground The ground icon (base)
         * @param overlay The icon to put on top of the ground (overlay)
         * @return The merged icon.
         */
        public static Icon overlay(Icon ground, Icon overlay, OverlayPosition pos) {
                GraphicsConfiguration conf = GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice().getDefaultConfiguration();
                int w = ground.getIconWidth();
                int h = ground.getIconHeight();
                int wo = overlay.getIconWidth();
                int ho = overlay.getIconHeight();
                BufferedImage img = conf.createCompatibleImage(w,h, Transparency.TRANSLUCENT);
                Graphics g = img.createGraphics();
                ground.paintIcon(null, g, 0, 0);
                int x = 0, y = 0;
                switch (pos) {
                case NORTHWEST: x = 0;          y = 0;          break;
                case NORTHEAST: x = w-wo;       y = 0;          break;
                case SOUTHWEST: x = 0;          y = h-ho;       break;
                case SOUTHEAST: x = w-wo;       y = h-ho;       break;
                }
                overlay.paintIcon(null, g, x, y);
                return new ImageIcon(img);
        }
}