/**
 * This class draws H-trees on a SimpleCanvas
 * 
 * @author Lyndon While 2018
 */
public class Htree
{
    SimpleCanvas sc;

    public Htree()
    {
        sc = new SimpleCanvas();
    }
    
    public void draw(int n)
    {
        draw(n, 200, 200, 180);
    }

    // draw an H-tree of order n and size s centred at x,y
    public void draw(int n, int x, int y, int s) 
    {
        if (n == 0) return;
        drawH(x, y, s);

        // compute the coordinates of the four half-size H-trees
        int x0 = x - s / 2;
        int x1 = x + s / 2;
        int y0 = y - s / 2;
        int y1 = y + s / 2;
        
        // recursively draw four half-size H-trees of order n-1
        draw(n-1, x0, y0, s / 2); // lower left  H-tree
        draw(n-1, x0, y1, s / 2); // upper left  H-tree
        draw(n-1, x1, y0, s / 2); // lower right H-tree
        draw(n-1, x1, y1, s / 2); // upper right H-tree
    }

    // draw an H of size s centred at x,y
    public void drawH(int x, int y, int s) {

        // compute the coordinates of the four tips of the H
        int x0 = x - s / 2;
        int x1 = x + s / 2;
        int y0 = y - s / 2;
        int y1 = y + s / 2;

        // draw the three line segments of the H
        sc.drawLine(x0, y0, x0, y1); // left  vertical segment of the H
        sc.drawLine(x1, y0, x1, y1); // right vertical segment of the H
        sc.drawLine(x0,  y, x1,  y); // connect the two vertical segments of the H
    }
}