ASP.NET使用递归算法实现画树程序

实现效果如下：（随机生成）

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication5
{
    public partial class Form1 : Form
{
    public Form1()
    {
        this.AutoScaleBaseSize = new Size(6, 14);
        this.ClientSize = new Size(600, 400);
        this.Paint += new PaintEventHandler(this.Form1_Paint);//注册paint事件
        this.Click+=new EventHandler(this.Redraw);//注册单击事件
    }

    private void Redraw(object sender, EventArgs e)
    {
        this.Invalidate();//使窗口重绘
    }

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        graphics = e.Graphics ;
        drawTree( 10, 200, 310, 100, -PI/2 );
    }

    private Graphics graphics;
    const double PI = Math.PI;
    double th1 = 40 * Math.PI / 180;
    double th2 = 30 * Math.PI / 180;
    double per1 = 0.6;
    double per2 = 0.7;
    Random rnd = new Random();
    double rand()
    {
        return rnd.NextDouble();
    }
    void drawTree(int n,
            double x0, double y0, double leng, double th)
    {
        if( n==0 ) return;

        double x1 = x0 + leng * Math.Cos(th);
        double y1 = y0 + leng * Math.Sin(th);

        drawLine(x0, y0, x1, y1, n/2);

        drawTree( n - 1, x1, y1, per1 * leng*(0.5+rand()), th + th1*(0.5+rand()) );//使用递归算法反复执行drawTree方法，直到n=0，跳出
        drawTree( n - 1, x1, y1, per2 * leng*(0.4+rand()), th - th2*(0.5+rand()) );
        if (rand() > 0.6)
            drawTree(n - 1, x1, y1, per2 * leng * (0.4 + rand()), th - th2 * (0.5 + rand()));
    }
    void drawLine( double x0, double y0, double x1, double y1, int width ){
        graphics.DrawLine(
            new Pen(Color.Blue, width ),
            (int)x0, (int)y0, (int)x1, (int)y1 );
    }
}
}