using System;
using System.Drawing;
using System.Windows.Forms;
using System.Drawing.Drawing2D;

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        Point center, oldCenter, dragStart;
        GraphicsPath path;
        int scale = 100;

        public Form1()
        {
            this.Size = new Size(600, 400);
            center = new Point(this.ClientSize.Width / 2, this.ClientSize.Height / 2);
            path = GeneratePath();
        }

        // 根据计算好的控制点绘制分形
        protected override void OnPaint(PaintEventArgs e)
        {
            using (Graphics g = e.Graphics)
            {
                g.DrawPath(Pens.Red, path);
            }
            this.Text = string.Format("center: {0,3},{1,3}  scale: {2}", center.X, center.Y, scale);
        }

        // 用滚轮控制放大缩小
        protected override void OnMouseWheel(MouseEventArgs e)
        {
            scale = scale + e.Delta / 4;
            scale = Math.Min(10000, scale);
            scale = Math.Max(10, scale);

            path = GeneratePath();
            Invalidate();
        }

        protected override void OnMouseDown(MouseEventArgs e)
        {
            dragStart = e.Location;
            oldCenter = center;
            this.Capture = true;
        }

        protected override void OnMouseUp(MouseEventArgs e)
        {
            this.Capture = false;
        }

        // 用鼠标移动图形
        protected override void OnMouseMove(MouseEventArgs e)
        {
            if (this.Capture)
            {
                center = Point.Add(oldCenter, new Size(e.X - dragStart.X, e.Y - dragStart.Y));
                path = GeneratePath();
                Invalidate();
            }
        }

        // 创建图形的控制点
        GraphicsPath GeneratePath()
        {
            byte[] types = new byte[this.ClientSize.Width];
            for (int i = 0; i < types.Length; i++) types[i] = (byte)PathPointType.Line;

            PointF[] samples = new PointF[types.Length];
            for (int x = 0; x < samples.Length; x++)
            {
                // 只画屏幕中看得到的x点。30.0f用来减缓频率以美观图形
                samples[x].X = x;
                samples[x].Y = Sinc((x - center.X) / (scale / 30.0f)) * scale + center.Y;
            }

            return new GraphicsPath(samples, types);
        }

        static float Sinc(float theta)
        {