source: josm/src/org/openstreetmap/josm/actions/mapmode/ZoomAction.java@ 15

package org.openstreetmap.josm.actions.mapmode;

import java.awt.Rectangle;
import java.awt.event.KeyEvent;

import org.openstreetmap.josm.data.GeoPoint;
import org.openstreetmap.josm.gui.MapFrame;
import org.openstreetmap.josm.gui.Layer;
import org.openstreetmap.josm.gui.SelectionManager;
import org.openstreetmap.josm.gui.SelectionManager.SelectionEnded;

/**
 * Enable the zoom mode within the MapFrame. 
 * 
 * Holding down the left mouse button select a rectangle with the same aspect 
 * ratio than the current layer.
 * Holding down left and right let the user move the former selected rectangle.
 * Releasing the left button zoom to the selection.
 * 
 * Rectangle selections with either height or width smaller than 3 pixels 
 * are ignored.
 * 
 * @author imi
 */
public class ZoomAction extends MapMode implements SelectionEnded {

        /**
         * Shortcut to the mapview.
         */
        private final Layer mv;
        /**
         * Manager that manages the selection rectangle with the aspect ratio of the
         * Layer.
         */
        private final SelectionManager selectionManager;


        /**
         * Construct a ZoomAction without a label.
         * @param mapFrame The MapFrame, whose zoom mode should be enabled.
         */
        public ZoomAction(MapFrame mapFrame) {
                super("Zoom", "zoom", "Zoom in by dragging", KeyEvent.VK_Z, mapFrame);
                mv = mapFrame.layer;
                selectionManager = new SelectionManager(this, true, mv);
        }

        /**
         * Zoom to the rectangle on the map.
         */
        public void selectionEnded(Rectangle r, boolean alt, boolean shift, boolean ctrl) {
                if (r.width >= 3 && r.height >= 3) {
                        double scale = mv.getScale() * r.getWidth()/mv.getWidth();
                        GeoPoint newCenter = mv.getPoint(r.x+r.width/2, r.y+r.height/2, false);
                        mv.zoomTo(newCenter, scale);
                }
        }

        @Override
        public void registerListener() {
                super.registerListener();
                selectionManager.register(mv);
        }

        @Override
        public void unregisterListener() {
                super.unregisterListener();
                selectionManager.unregister(mv);
        }
}