GDI+绘制五星红旗

五星红旗是由红色背景，加5个黄色五角星组成。绘制一个五星红旗的思路，就是先定义一个五角星的自定义控件，然后通过设置五角星的大小、位置、旋转角度等属性，组合成一个五星红旗。

五角星自定义控件代码：

public partial class MyStar : Control
{
    public MyStar()
    {
        InitializeComponent();
    }

    protected override void OnPaint(PaintEventArgs pe)
    {
        base.OnPaint(pe);

        Graphics g = pe.Graphics;
        PointF[] points = new PointF[]
        {
            new PointF(Center.X, Center.Y - Radius),
            new PointF((float)(Center.X + Radius * Math.Sin(72 * Math.PI / 180)), (float)(Center.Y - Radius * Math.Cos(72 * Math.PI / 180))),
            new PointF((float)(Center.X + Radius * Math.Sin(36 * Math.PI / 180)), (float)(Center.Y + Radius * Math.Cos(36* Math.PI / 180))),
            new PointF((float)(Center.X - Radius * Math.Sin(36 * Math.PI / 180)),(float)( Center.Y + Radius * Math.Cos(36 * Math.PI / 180))),
            

new PointF((float)(Center.X - Radius * Math.Sin(72 * Math.PI / 180)), (float)(Center.Y - Radius * Math.Cos(72 * Math.PI / 180))),
        };

        GraphicsPath path = new GraphicsPath(FillMode.Winding);
        path.AddLine(points[0], points[2]);
        path.AddLine(points[2], points[4]);
        path.AddLine(points[4], points[1]);
        path.AddLine(points[1], points[3]);
        path.AddLine(points[3], points[0]);
        path.CloseFigure();

        g.SmoothingMode = SmoothingMode.AntiAlias;
        g.RotateTransform(Angle);
        g.FillPath(new SolidBrush(ColorTranslator.FromHtml("#FFDF00")), path);
    }

    /// <summary>
    /// 中心点
    /// </summary>
    public Point Center { get; set; }

    /// <summary>
    /// 半径
    /// </summary>
    public int Radius { get; set; }

    /// <summary>
    /// 旋转角度
    /// </summary>
    public float Angle { get; set; }
}

如上的Center、Radius、Angle都是public类型暴露出来的公共属性，以便在初始化时动态的设置MyStar相关属性。

然后创建一个窗体(450*300)，并拖动一个Panel容器。

在VS中编译后会在工具栏生成MyStar控件，我们在窗体的Load事件中动态的添加MyStar控件即可。

private void Form1_Load(object sender, EventArgs e)
{
    this.panel1.BackColor = Color.Red;

    MyStar c1 = new MyStar();
    c1.Angle = 0F;
    c1.Location = new System.Drawing.Point(4, 10);
    c1.Size = new System.Drawing.Size(75, 75);
    c1.Center = new Point(50, 50);
    c1.Radius = 30;

    MyStar c2 = new MyStar();
    c2.Angle = 20F;
    c2.Location = new System.Drawing.Point(80, -10);
    c2.Size = new System.Drawing.Size(40, 40);
    c2.Center = new Point(25, 25);
    c2.Radius = 10;

    MyStar c3 = new MyStar();
    c3.Angle = -20F;
    c3.Location = new System.Drawing.Point(90, 30);
    c3.Size = new System.Drawing.Size(40, 40);
    c3.Center = new Point(25, 25);
    c3.Radius = 10;

    MyStar c4 = new MyStar();
    c4.Angle = 0F;
    c4.Location = new System.Drawing.Point(98, 55);
    c4.Size = new System.Drawing.Size(40, 40);
    c4.Center = new Point(25, 25);
    c4.Radius = 10;

    MyStar c5 = new MyStar();
    c5.Angle = 20F;
    c5.Location = new System.Drawing.Point(80, 70);
    c5.Size = new System.Drawing.Size(40, 40);
    c5.Center = new Point(25, 25);
    c5.Radius = 10;

    this.panel1.Controls.Add(c1);
    this.panel1.Controls.Add(c2);
    this.panel1.Controls.Add(c3);
    this.panel1.Controls.Add(c4);
    this.panel1.Controls.Add(c5);

    this.panel1.Click += (ss, ee) => { this.Close(); };
}

效果图：