using System;

using System.Drawing;

using System.Drawing.Imaging;

using System.Windows.Forms;

using System.Collections.Generic;

namespace Faraday {

    public class MainWindow : Form {

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

		double tangentLength = 1000.0;

		double normalLength = 50.0;

		double pointRadius = 4.0;

		double targetX = 0.0;

		double targetY = 0.0;

		double aaRadius = 25.0;

		double radiusX = 400.0;

		double radiusY = 100.0;

		public MainWindow() {

            Paint += OnPaint;

			MouseMove += OnMouseMove;

            WindowState = FormWindowState.Maximized;

        }

        public void OnPaint(Object sender, PaintEventArgs e) {

            Draw(e.Graphics);

        }

        public void OnMouseMove(Object sender, MouseEventArgs e) {

			targetX = e.X - 0.5*ClientSize.Width;

			targetY = e.Y - 0.5*ClientSize.Height;

			Invalidate();

        }

        public void Draw(Graphics g) {

            g.Clear(Color.White);

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

			double centerX = 0.5*ClientSize.Width;

			double centerY = 0.5*ClientSize.Height;

			g.DrawEllipse(

				Pens.Gray,

				(float)(centerX - radiusX),

				(float)(centerY - radiusY),

				(float)(2.0*radiusX),

				(float)(2.0*radiusY));

			g.FillEllipse(

				Brushes.Blue,

				(float)(centerX + targetX - pointRadius),

				(float)(centerY + targetY - pointRadius),

				(float)(2.0*pointRadius),

				(float)(2.0*pointRadius));

			if (Math.Abs(targetX) > 0.0 || Math.Abs(targetY) > 0.0) {

				double targetL = Math.Sqrt(

					targetY*targetY +

					targetX*targetX);

				double targetNormX = targetX/targetL;

				double targetNormY = targetY/targetL;

				g.DrawLine(

					Pens.Black,

					(float)centerX,

					(float)centerY,

					(float)(centerX + tangentLength*targetNormX),

					(float)(centerY + tangentLength*targetNormY));

				double crossL = Math.Sqrt(

					targetY*targetY*radiusX*radiusX +

					targetX*targetX*radiusY*radiusY);

				double crossX = targetX*radiusX*radiusY/crossL;

				double crossY = targetY*radiusX*radiusY/crossL;

				g.FillEllipse(

					Brushes.Blue,

					(float)(centerX + crossX - pointRadius),

					(float)(centerY + crossY - pointRadius),

					(float)(2.0*pointRadius),

					(float)(2.0*pointRadius));

				double tangentL = Math.Sqrt(

					targetY*targetY*radiusX*radiusX*radiusX*radiusX +

					targetX*targetX*radiusY*radiusY*radiusY*radiusY);

				double tangentX = targetY*radiusX*radiusX/tangentL;

				double tangentY = -targetX*radiusY*radiusY/tangentL;

				g.DrawLine(

					Pens.Blue,

					(float)(centerX + crossX - tangentX*tangentLength),

					(float)(centerY + crossY - tangentY*tangentLength),

					(float)(centerX + crossX + tangentX*tangentLength),

					(float)(centerY + crossY + tangentY*tangentLength));

				double normalX = -tangentY;

				double normalY = tangentX;

				g.DrawLine(

					Pens.Blue,

					(float)(centerX + crossX),

					(float)(centerY + crossY),

					(float)(centerX + crossX + normalX*normalLength),

					(float)(centerY + crossY + normalY*normalLength));

				double dot = normalX*targetNormX + normalY*targetNormY;

				double aa = aaRadius/dot;

				//double aaX = aa*targetNormX;

				//double aaY = aa*targetNormY;

				double dotInv =

					tangentL/(targetX*targetX*radiusY*radiusY + targetY*targetY*radiusX*radiusX);

				double aaX = aaRadius*targetX*dotInv;

				double aaY = aaRadius*targetY*dotInv;

				g.DrawLine(

					Pens.Red,

					(float)(centerX + targetX - aaX),

					(float)(centerY + targetY - aaY),

					(float)(centerX + targetX + aaX),

					(float)(centerY + targetY + aaY));

				g.FillEllipse(

					Brushes.Red,

					(float)(centerX + targetX - aaX - pointRadius),

					(float)(centerY + targetY - aaY - pointRadius),

					(float)(2.0*pointRadius),

					(float)(2.0*pointRadius));

				g.FillEllipse(

					Brushes.Red,

					(float)(centerX + targetX + aaX - pointRadius),

					(float)(centerY + targetY + aaY - pointRadius),

					(float)(2.0*pointRadius),

					(float)(2.0*pointRadius));

			}

        }

    }

}