用Winform绘制不规则矩形

1.新建DownLayerForm的窗体。

2.定义不规则窗体的点，并在构造函数里面加载这些不规则的点。

3.效果如图所示。

private int layerWidth = 320;

      /// <summary>
      /// 消息框的宽度
      /// </summary>
      public int LayerWidth
      {
          get { return layerWidth; }
          set { layerWidth = value; }
      }

      public DownLayerForm()
      {
          InitializeComponent();
          //创建不规则窗体 
          POINTAPI[] poin;
          poin = new POINTAPI[7];
          poin[0].x = 0;
          poin[0].y = 10;

          poin[1].x = layerWidth / 2 - 10;
          poin[1].y = 10;

          poin[2].x = layerWidth / 2;
          poin[2].y = 0;

          poin[3].x = layerWidth / 2 + 10;
          poin[3].y = 10;

          poin[4].x = layerWidth;
          poin[4].y = 10;

          poin[5].x = layerWidth;
          poin[5].y = 130;

          poin[6].x = 0;
          poin[6].y = 130;
          Boolean flag = true;
          IntPtr hRgn = CreatePolygonRgn(ref poin[0], 8, 1);
          SetWindowRgn(this.Handle, hRgn, ref flag);
          this.BackColor = Color.White;
      }
      [StructLayout(LayoutKind.Sequential)]
      private struct POINTAPI
      {
          internal int x;
          internal int y;
      }
      [DllImport("gdi32.dll")]
      private static extern IntPtr CreatePolygonRgn(ref POINTAPI lpPoint, int nCount, int nPolyFillMode);
      [DllImport("user32.dll")]
      private static extern IntPtr SetWindowRgn(IntPtr hWnd, IntPtr hRgn, ref Boolean bRedraw);
      //设置窗体显示状态 
      [DllImport("user32.dll")]
      private static extern int SetWindowPos(IntPtr hwnd, int hWndInsertAfter, int x, int y, int cx, int cy, int wFlags);