/* hilbert.java -- hilbert curve
 *
 * Author: Eric Laroche
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * The Hilbert Curve is based on the simple recursive pattern:
 * ____ _ _ _ _
 * | | | |_| | | | | |
 * | | --> |_ _| ~ _ _ 
 * | | _| |_ _| |_
 */
import java.applet.*;
import java.awt.*;
/** hilbert -- hilbert curve.
 * The Hilbert Curve is based on a simple recursive pattern.
 * The turtle class is used to draw the curve.
 *
 * @author Eric Laroche
 * @version @(#) $Id: hilbert.java,v 1.2 1997年04月02日 22:08:38 laroche Exp $
 */
public class hilbert extends Applet implements Runnable
{
	/** version string */
	private static final String version =
		"@(#) $Id: hilbert.java,v 1.2 1997年04月02日 22:08:38 laroche Exp $";
	/** applet usage strings */
	private static final String[][] usage = {
		{ "depth", "int", "(maximal) recursion depth" },
		{ "delay", "long", "delay in milliseconds" } };
	/** maximal recursion depth and default value */
	private int maxdepth = 4;
	/** current recursion depth */
	private int depth = 0;
	/** paint delay in milliseconds and default value */
	private long delay = 2000;
	/** applet thread */
	private Thread t = null;
	/** main -- entry point for standalone application
	 */
	public static void main( String[] args )
	{
		System.err.println(
			"Sorry, you must run the thing as applet." );
	}
	/** init -- called after the constructor and before start().
	 * init sets the background color and reads in the applet parameters.
	 */
	public void init( )
	{
		setBackground( Color.white );
		String parm = null;
		parm = getParameter( "depth" );
		if ( parm != null )
		{
			maxdepth = Integer.valueOf( parm ).intValue( );
			if ( maxdepth < 0 ) throw new IllegalArgumentException( ); depth = maxdepth; /* we don't cycle if depth is given and delay isn't */ delay = 0; } parm = getParameter( "delay" ); if ( parm != null ) { delay = Long.valueOf( parm ).longValue( ); if ( delay < 0 ) throw new IllegalArgumentException( ); depth = 0; } } /** start -- called by the browser */ public void start( ) { if ( delay == 0 ) return; if ( t == null ) { t = new Thread( this ); t.start( ); } } /** stop -- called by the browser */ public void stop( ) { if ( t != null ) { t.stop( ); t = null; } } /** getAppletInfo -- called by the browser. * getAppletInfo returns info on this applet. */ public String getAppletInfo( ) { return version; } /** getParameterInfo -- called by the browser * getParameterInfo returns info on the parameters of this applet. */ public String[][] getParameterInfo( ) { return usage; } /** run -- thread action, called by start() */ public void run( ) { while ( t != null ) { repaint( ); try Thread.sleep( delay ); catch ( InterruptedException e ) break; depth++; if ( depth> maxdepth )
				depth = 0;
		}
	}
	/** paint -- paint the applet component.
	 * A new turtle is created and positioned so that the hilbert curve
	 * gets centered.
	 */
	public void paint( Graphics g )
	{
		Dimension d = size( );
		turtle t = new turtle( g, d );
		int len = Math.min( d.width, d.height ) - 1;
		/* need 1 part for depth 0, 3 (==1*2+1) for 1, 7 for 2, etc. */
		int partsneeded = ( 1 << depth + 1 ) - 1; int step = len / partsneeded; if ( step == 0 ) return; /* center the curve */ Point offset = new Point( Math.max( ( d.width - 1 - step * partsneeded ) / 2, 0 ), Math.max( ( d.height - 1 - step * partsneeded ) / 2, 0 ) ); t.setlocation( offset ); curve( t, depth, step, false ); } /** curve -- recursive algorithm to draw a hilbert curve. * No pattern is used to produce the recursion. */ private static void curve( turtle t, int depth, int step, boolean left ) { depth--; t.turnleft( ! left ); if ( depth>= 0 )
			curve( t, depth, step, ! left );
		t.advance( step );
		t.turnleft( left );
		if ( depth>= 0 )
			curve( t, depth, step, left );
		t.advance( step );
		if ( depth>= 0 )
			curve( t, depth, step, left );
		t.turnleft( left );
		t.advance( step );
		if ( depth>= 0 )
			curve( t, depth, step, ! left );
		t.turnleft( ! left );
	}
}
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