using System;

using System.Drawing;

using System.Drawing.Imaging;

using System.Windows.Forms;

using System.Collections.Generic;

namespace Autospline {

	public struct Segment {

		public double previous;

		public double current;

		public double next;

		public double nextnext;

		public static double get(double s, double p0, double pm, double p1) {

			return p0*(1.0-s)*(1.0-s) + 2.0*pm*(1.0-s)*s + p1*s*s;

		}

		public static double get(double s, double p0, double p1, double t0, double t1) {

			double h0 =  2.0*s*s*s - 3.0*s*s + 1.0;

			double h1 = -2.0*s*s*s + 3.0*s*s;

			double h2 =      s*s*s - 2.0*s*s + s;

			double h3 =      s*s*s -     s*s;

			double p = h0*p0 + h1*p1 + h2*t0 + h3*t1;

			return p;

		}

		public double get(double s) {

			return get(s, current, next, current - previous, next - current);

		}

		public double getCool(double s) {

			return get(s, current, next, 0.5*(next - previous), 0.5*(nextnext - current));

		}

		public double getCool2(double s) {

			return get(s, 0.5*(previous + current), current, 0.5*(current + next));

		}

	}

	public struct Segment2d {

		public Segment x;

		public Segment y;

	}

	public class MainWindow : Form {

        static public void Main() { Application.Run(new MainWindow()); }

		bool pressed = false;

		List<segment2d> segments = new List<segment2d>();</segment2d></segment2d>

		Bitmap buffer;

		void newCurve(double x, double y) {

			Segment2d segment;

			segment.x.previous = segment.x.current = segment.x.next = segment.x.nextnext = x;

			segment.y.previous = segment.y.current = segment.y.next = segment.y.nextnext = y;

			segments.Add(segment);

		}

		void addPoint(double x, double y) {

			Segment2d previous = segments[segments.Count - 1];

			previous.x.nextnext = x;

			previous.y.nextnext = y;

			segments[segments.Count - 1] = previous;

			Segment2d segment;

			segment.y.nextnext = y;

			segment.x.next = segment.x.nextnext = x;

			segment.y.next = segment.y.nextnext = y;

			segment.x.current = previous.x.next;

			segment.y.current = previous.y.next;

			segment.x.previous = previous.x.current;

			segment.y.previous = previous.y.current;

			segments.Add(segment);

		}

		public MainWindow() {

			OnResize(this, new EventArgs());

            Paint += OnPaint;

			MouseMove += OnMouseMove;

			MouseDown += OnMouseDown;

			MouseUp += OnMouseUp;

			Resize += OnResize;

            WindowState = FormWindowState.Maximized;

        }

		public void OnResize(Object sender, EventArgs e) {

			buffer = new Bitmap(ClientSize.Width, ClientSize.Height);

		}

        public void OnPaint(Object sender, PaintEventArgs e) {

			Graphics g = Graphics.FromImage(buffer);

            Draw(g);

			g.Flush();

			e.Graphics.DrawImageUnscaled(buffer, 0, 0);

        }

		public void OnMouseDown(Object sender, MouseEventArgs e) {

			if (e.Button == MouseButtons.Left) {

				newCurve(e.X, e.Y);

				pressed = true;

				Invalidate();

			} else

			if (e.Button == MouseButtons.Right) {

				segments.Clear();

				if (pressed) newCurve(e.X, e.Y);

				Invalidate();

			}

		}

		public void OnMouseUp(Object sender, MouseEventArgs e) {

			if (e.Button == MouseButtons.Left && pressed) {

				addPoint(e.X, e.Y);

				pressed = false;

				Invalidate();

			}

		}

		public void OnMouseMove(Object sender, MouseEventArgs e) {

			if (pressed) {

				addPoint(e.X, e.Y);

				Invalidate();

			}

        }

        public void Draw(Graphics g) {

            g.Clear(Color.White);

			g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

			int count = 100;

			double r = 2.0;

			double l = 2.0;

			Pen pen = new Pen(Color.FromArgb(128, 128, 128, 128));

			Pen cool = new Pen(Color.FromArgb(128, 0, 0, 255));

			foreach(Segment2d segment in segments) {

				double x0 = segment.x.get(0.0);

				double y0 = segment.y.get(0.0);

				for(int i = 1; i <= count; ++i) {

					double x1 = segment.x.get((double)i/(double)count);

					double y1 = segment.y.get((double)i/(double)count);

					if (i == count || (x1 - x0)*(x1 - x0) + (y1 - y0)*(y1 - y0) > l*l) {

						g.DrawLine(pen, (float)x0, (float)y0, (float)x1, (float)y1);

						x0 = x1;

						y0 = y1;

					}

				}

				x0 = segment.x.getCool2(0.0);

				y0 = segment.y.getCool2(0.0);

				for(int i = 1; i <= count; ++i) {

					double x1 = segment.x.getCool2((double)i/(double)count);

					double y1 = segment.y.getCool2((double)i/(double)count);

					if (i == count || (x1 - x0)*(x1 - x0) + (y1 - y0)*(y1 - y0) > l*l) {

						g.DrawLine(cool, (float)x0, (float)y0, (float)x1, (float)y1);

						x0 = x1;

						y0 = y1;

					}

				}

				g.FillEllipse(

					Brushes.Black,

					(float)(segment.x.current - r), (float)(segment.y.current - r),

					(float)(2.0*r), (float)(2.0*r) );

				g.FillEllipse(

					Brushes.Black,

					(float)(segment.x.next - r), (float)(segment.y.next - r),

					(float)(2.0*r), (float)(2.0*r) );

			}

        }

    }

}