source: josm/src/org/openstreetmap/josm/actions/AutoScaleAction.java@ 93

package org.openstreetmap.josm.actions;

import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.util.Collection;

import javax.swing.AbstractAction;

import org.openstreetmap.josm.Main;
import org.openstreetmap.josm.data.SelectionChangedListener;
import org.openstreetmap.josm.data.coor.EastNorth;
import org.openstreetmap.josm.data.coor.LatLon;
import org.openstreetmap.josm.data.osm.OsmPrimitive;
import org.openstreetmap.josm.data.osm.visitor.BoundingXYVisitor;
import org.openstreetmap.josm.gui.MapFrame;
import org.openstreetmap.josm.gui.layer.Layer;
import org.openstreetmap.josm.tools.ImageProvider;

/**
 * Toggles the autoScale feature of the mapView
 * @author imi
 */
public class AutoScaleAction extends GroupAction {

        private enum AutoScaleMode {data, selection, layer, conflict}
        private AutoScaleMode mode = AutoScaleMode.data;
        private final MapFrame mapFrame;

        private class Action extends AbstractAction {
                private final AutoScaleMode mode;
                public Action(AutoScaleMode mode) {
                        super("Auto Scale: "+mode, ImageProvider.get("dialogs/autoscale/"+mode));
                        putValue(SHORT_DESCRIPTION, "Auto zoom the view to "+mode+". Disabled if the view is moved.");
                        this.mode = mode;
                }
                public void actionPerformed(ActionEvent e) {
                        AutoScaleAction.this.mode = mode;
                        if (mapFrame.mapView.isAutoScale())
                mapFrame.mapView.recalculateCenterScale();
            else
                mapFrame.mapView.setAutoScale(true);
                        putValue("active", true);
                }
        }

        public AutoScaleAction(final MapFrame mapFrame) {
                super(KeyEvent.VK_A, 0);
                for (AutoScaleMode mode : AutoScaleMode.values())
                        actions.add(new Action(mode));
                setCurrent(0);
                this.mapFrame = mapFrame;
                Main.ds.addSelectionChangedListener(new SelectionChangedListener(){
                        public void selectionChanged(Collection<OsmPrimitive> newSelection) {
                                if (mode == AutoScaleMode.selection)
                                        mapFrame.mapView.recalculateCenterScale();
                        }
                });
        }

        public BoundingXYVisitor getBoundingBox() {
                BoundingXYVisitor v = new BoundingXYVisitor();
                switch (mode) {
                case data:
                        for (Layer l : mapFrame.mapView.getAllLayers())
                                l.visitBoundingBox(v);
                        break;
                case layer:
                        mapFrame.mapView.getActiveLayer().visitBoundingBox(v);
                        break;
                case selection:
                case conflict:
                        Collection<OsmPrimitive> sel = mode == AutoScaleMode.selection ? Main.ds.getSelected() : mapFrame.conflictDialog.conflicts.keySet();
                        for (OsmPrimitive osm : sel)
                                osm.visit(v);
                        // special case to zoom nicely to one single node
                        if (v.min != null && v.max != null && v.min.north() == v.max.north() && v.min.east() == v.max.east()) {
                                EastNorth en = Main.proj.latlon2eastNorth(new LatLon(0.02, 0.02));
                                v.min = new EastNorth(v.min.east()-en.east(), v.min.north()-en.north());
                                v.max = new EastNorth(v.max.east()+en.east(), v.max.north()+en.north());
                        }
                        break;
                }
                return v;
        }
}