/*-------------------------
  ex11_2.java
  色々描く：1.ジュリア集合
 --------------------------*/
import java.applet.*;
import java.awt.*;

/*
<applet code="ex11_2" width="640" height="400">
</applet>
*/

public class ex11_2 extends Applet {
	static final int WIDTH = 640, HEIGHT = 400;
	static final double C = 4.0 / WIDTH;
	static final double YA = Math.sqrt(3) / 2;
	static final double THRESHOLD = 0.05 * 0.05;
	
	public void paint(Graphics g) {
		int i, j, k;
		double x, y, x2, y2, d, t;
		
		for (i = -WIDTH/2; i <= WIDTH/2; i++) {
			for (j = 0; j <= HEIGHT/2; j++) {
				x = C * i;
				y = C * j;
				for (k = 0; k <= 15; k++) {
					x2 = x * x;
					y2 = y * y;
					d = x2 + y2;
					
					if (d < 1E-10) break;
					
					d *= d;
					t = (1.0/3.0) * (2*x + (x2 - y2) / d);
					y = (2.0/3.0) * y * (1 - x/d);
					x = t;
					
					if (dist2(x-1, y) < THRESHOLD) {
						dot(g, i, +j, Color.cyan);
						dot(g, i, -j, Color.cyan);
						break;
					}
					if (dist2(x+0.5, y+YA) < THRESHOLD) {
						dot(g, i, +j, Color.yellow);
						dot(g, i, -j, Color.magenta);
						break;
					}
					if (dist2(x+0.5, y-YA) < THRESHOLD) {
						dot(g, i, +j, Color.magenta);
						dot(g, i, -j, Color.yellow);
						break;
					}
				}
			}
		}
	}
	
	private double dist2(double x, double y) {
		return x * x + y * y;
	}
	
	private void dot(Graphics g, int x, int y, Color c) {
		g.setColor(c);
		g.fillRect(WIDTH / 2 + x, HEIGHT / 2 - y, 1, 1);	// 画面中心を原点として，(x,y)に点を打つ
	}
}