import java.awt.*;
import javax.swing.*;

public class RecursiveTriangles				// the book calls this a Sierpinski Triangle (see pages 755-756 for their implementation, mine is shorter and hopefully a little easier to understand)
{
	public static void main(String[] args)
	{
		JFrame frame=new JFrame();
		frame.setSize(500,500);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		GP p = new GP();
		frame.add(p);
		frame.setVisible(true);
	}
	
	public static class GP extends JPanel
	{
		public void paintComponent(Graphics g)
		{
			draw(g,250,100,400,400,100,400,6);		// start drawing the outermost triangle, 6 is the depth of recursion
		}
		
		public void draw(Graphics g, int x1, int y1, int x2, int y2, int x3, int y3, int n)	// 3 end points x1,y1, x2,y2, x3,y3
		{
			if(n>0)									// if we haven't recursed 6 times yet, draw the new triangle at these 3 endpoints
			{
				g.drawLine(x1,y1,x2,y2);
				g.drawLine(x2,y2,x3,y3);
				g.drawLine(x3,y3,x1,y1);
				draw(g,x1,y1,(x1+x2)/2,(y1+y2)/2,(x1+x3)/2,(y1+y3)/2,n-1);  // and recurse using one of the three points as a base and the other two endpoints to compute midpoints
				draw(g,(x1+x2)/2,(y1+y2)/2,x2,y2,(x2+x3)/2,(y2+y3)/2,n-1);	//     our recursive triangle will share one end point and the two new midpoints
				draw(g,(x1+x3)/2,(y1+y3)/2,(x2+x3)/2,(y2+y3)/2,x3,y3,n-1);
			}
		}
	}
}