用C#窗体画一个可以指定角度的倾斜椭圆非旋转坐标系方法

最近遇到一个需要画一个倾斜的椭圆的问题，一般常见的解决办法都是旋转坐标系，这个方法是当时没有学过旋转坐标系时想出的解决办法，既然椭圆能旋转其他图形也不在话下，可以上传提供借鉴一下，希望能有所帮助。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Ellipse
{
    public partial class Form1 : Form
    {
        PointF xyPoint = new PointF（）;
        PointF centerPoint = new PointF（）;
        PointF movePoint = new PointF（）;
        PointF xiePointF=new PointF（）;
        PointF xiedPointF = new PointF（）;
        private double perAngle = 0;
        private double nowAngle;
        private double moveAngle;
        PointF[] pointFs=new PointF[201];
        PointF[] pointFs1=new PointF[201];
        PointF[] xiePointFs=new PointF[201];
        PointF[] xiePointFs1 = new PointF[201];
        private float a =200;
        private float b =100;
        private float stepLength = 2;
        private float xLength = 0;
        private float yLength = 0;
        private float dbYlength = 0;
        private float xiedLength = 0;
        private int angle = 0;
        public Form1（）
        {
            InitializeComponent（）;
        }

        private void panel1_Paint（object sender PaintEventArgs e）
        {
            
        }

        private void panel1_MouseClick（object sender MouseEventArgs e）
        {
            if （e.Button != MouseButtons.Left）
            {
                return;
            }
            if （this.textBox1.Text == ““）
            {
                this.errorProvider1.SetError（this.textBox1 “请输入倾斜的角度“）;
                return;
            }
            else
            {
                this.errorProvider1.SetError（this.textBox1 ““）;
            }
            xyPoint.X = this.panel1.Width/2-200;
            xyPoint.Y = this.panel1.Height/2-100;
            centerPoint.X = xyPoint.X + a;
            centerPoint.Y = xyPoint.Y + b;
            Graphics graphics = this.panel1.CreateGraphics（）;
            graphics.SmoothingMode = SmoothingMode.HighQuality;
            graphics.Clear（this.panel1.BackColor）;
            Pen pen = new Pen（Color.Red）;
            for （int index = 0; index < pointFs.Length; index++）
            {
                movePoint.X = index * stepLength + xyPoint.X;
                xLength = centerPoint.X - movePoint.X;
                yLength = （float）（Math.Sqrt（（1 - （xLength * xLength） / 40000） * 10000））;
                movePoint.Y = b - yLength + xyPoint.Y;
                pointFs[index] = movePoint;
            }
            graphics.DrawCurve（pen pointFs 1.5f）;
            for （int index = 0; index < pointFs1.Length; index++）
            {
                dbYlength = centerPoint.Y - pointFs[index].Y;
                pointFs1[index].Y = centerPoint.Y + dbYlength;
                pointFs1[index].X = pointFs[index].X;
            }
            graphics.DrawCurve（pen pointFs1 1.5f）;
            for （int index 

 属性            大小     日期    时间   名称
----------- ---------  ---------- -----  ----
     目录           0  2015-07-14 16:02  Ellipse\
     文件         990  2015-07-13 12:40  Ellipse.sln
     文件       34816  2015-08-01 23:23  Ellipse.v12.suo
     文件         187  2015-07-13 12:40  Ellipse\App.config
     目录           0  2015-07-13 12:40  Ellipse\bin\
     目录           0  2015-07-13 13:04  Ellipse\bin\Debug\
     文件       16896  2015-08-01 23:23  Ellipse\bin\Debug\Ellipse.exe
     文件         187  2015-07-13 12:40  Ellipse\bin\Debug\Ellipse.exe.config
     文件       30208  2015-08-01 23:23  Ellipse\bin\Debug\Ellipse.pdb
     文件       24224  2015-08-01 23:23  Ellipse\bin\Debug\Ellipse.vshost.exe
     文件         187  2015-07-13 12:40  Ellipse\bin\Debug\Ellipse.vshost.exe.config
     文件         490  2013-06-18 20:28  Ellipse\bin\Debug\Ellipse.vshost.exe.manifest
     文件        3794  2015-07-13 13:04  Ellipse\Ellipse.csproj
     文件       14790  2015-07-14 16:02  Ellipse\Form1.cs
     文件        5394  2015-07-14 15:55  Ellipse\Form1.Designer.cs
     文件        6019  2015-07-14 15:55  Ellipse\Form1.resx
     目录           0  2015-07-13 12:40  Ellipse\obj\
     目录           0  2015-08-01 23:23  Ellipse\obj\Debug\
     文件        1453  2015-07-13 20:50  Ellipse\obj\Debug\DesignTimeResolveAssemblyReferences.cache
     文件        6911  2015-07-13 12:40  Ellipse\obj\Debug\DesignTimeResolveAssemblyReferencesInput.cache
     文件         555  2015-08-01 23:23  Ellipse\obj\Debug\Ellipse.csproj.FileListAbsolute.txt
     文件         977  2015-07-14 15:55  Ellipse\obj\Debug\Ellipse.csproj.GenerateResource.Cache
     文件        2211  2015-07-13 13:04  Ellipse\obj\Debug\Ellipse.csprojResolveAssemblyReference.cache
     文件       16896  2015-08-01 23:23  Ellipse\obj\Debug\Ellipse.exe
     文件         180  2015-07-14 15:55  Ellipse\obj\Debug\Ellipse.Form1.resources
     文件       30208  2015-08-01 23:23  Ellipse\obj\Debug\Ellipse.pdb
     文件         180  2015-07-13 13:04  Ellipse\obj\Debug\Ellipse.Properties.Resources.resources
     文件           0  2015-07-13 12:40  Ellipse\obj\Debug\TemporaryGeneratedFile_036C0B5B-1481-4323-8D20-8F5ADCB23D92.cs
     文件           0  2015-07-13 12:40  Ellipse\obj\Debug\TemporaryGeneratedFile_5937a670-0e60-4077-877b-f7221da3dda1.cs
     文件           0  2015-07-13 12:40  Ellipse\obj\Debug\TemporaryGeneratedFile_E7A71F73-0F8D-4B9B-B56E-8E70B10BC5D3.cs
     目录           0  2015-07-13 12:40  Ellipse\obj\Debug\TempPE\
............此处省略7个文件信息