最近在用C#進行程式設計，重寫CheckBox，需要繪畫圓角矩形，在網上查找了許多資料，用C#FillPath的方式繪畫總感覺太麻煩，需要算座標，不如直接呼叫C++的方法繪畫圓角矩形。
宣告：本程式碼借鑑網上程式碼，在此僅做整理出來供大家參考使用

        [DllImport("user32.dll")]
        public static extern int SetWindowRgn(IntPtr hWnd,
            IntPtr hRgn, bool bRedraw);
        [DllImport("gdi32.dll")]
        public
 
 static extern IntPtr CreateRoundRectRgn(int x1, int y1,
            int x2, int y2, int cx, int cy);
        [DllImport("gdi32.dll")]
        public static extern bool RoundRect(IntPtr hDC, int x1,
            int y1, int x2, int y2,
            int x3, int y3);
        [DllImport("user32")]
        public
 
 static extern IntPtr GetDC(IntPtr hwnd);
        [DllImport("gdi32.dll")]
        public static extern IntPtr CreatePen(
            int fnPenStyle,    // pen style
            int nWidth,        // pen width
            int crColor        // pen color
            );
        [DllImport("gdi32.dll")]
        public
 
 static extern IntPtr CreateSolidBrush(int crColor);
        [DllImport("gdi32.dll")]
        public static extern IntPtr SelectObject(IntPtr hdc, IntPtr hgdiobj);
        [DllImport("gdi32.dll")]
        public static extern bool DeleteObject(IntPtr hObject);
        [DllImport("gdi32.dll")]
        public static extern IntPtr GetStockObject(int fnObject);
        [DllImport("gdi32.dll")]
        public static extern IntPtr CreateCompatibleDC(IntPtr hDC);
        [DllImport("gdi32.dll")]
        public static extern IntPtr CreateCompatibleBitmap(IntPtr hdc,
            int nWidth, int nHeight);
        [DllImport("gdi32.dll")]
        public static extern int BitBlt(IntPtr hdcDest, int nXDest, int nYDest,
            int nWidth, int nHeight, IntPtr hdcSrc, int nXSrc, int nYSrc,
            UInt32 dwRop);
        /// <summary>
        /// 繪畫矩形(利用C++API繪畫圓角矩形)
        /// </summary>
        public static bool DrawRoundRectC(Graphics e,
            Pen pen, SolidBrush Br,
            int X1, int Y1, int X2,
            int Y2, int X3, int Y3)
        {
            IntPtr hPen, oldpen;
            IntPtr hBr, oldBr;
            IntPtr hMemDc;
            IntPtr hBitmap, hOldBitmap;

            hPen = CreatePen((int)pen.DashStyle,
                (int)pen.Width,
                ColorTranslator.ToWin32(pen.Color)
                );
            //hPen = GetStockObject(8);//空畫筆
            hBr = CreateSolidBrush(ColorTranslator.ToWin32(Br.Color));
            //hbrush = GetStockObject(5);//空畫刷
            IntPtr hDC = e.GetHdc();
            //建立相容DC
            ///////////////////////////////////////////////////////////////
            int iWidth = X2 - X1;
            int iHeight = Y2 - Y1;
            hMemDc = CreateCompatibleDC(hDC);
            hBitmap = CreateCompatibleBitmap(hDC, iWidth, iHeight);
            hOldBitmap = SelectObject(hMemDc, hBitmap);
            BitBlt(hMemDc, 0, 0, iWidth, iHeight, hDC, 0, 0, (UInt32)0xcc0020);

            /////////////////////////////////////////////////////////////
            //選入畫刷和畫筆
            oldBr = SelectObject(hMemDc, hBr);
            oldpen = SelectObject(hMemDc, hPen);
            bool bRet = RoundRect(hMemDc, X1, Y1, X2, Y2, X3, Y3);

            BitBlt(hDC, 0, 0, iWidth, iHeight, hMemDc, 0, 0, (UInt32)0xcc0020);

            //資源釋放
            SelectObject(hMemDc, oldpen);
            SelectObject(hMemDc, oldBr);
            SelectObject(hMemDc, hOldBitmap);

            DeleteObject(hBitmap);
            DeleteObject(hMemDc);
            DeleteObject(hBr);
            DeleteObject(hPen);
            e.ReleaseHdc(hDC);

            return bRet;

        }

還有一種方法是網上利用C#的另一種方法

        /// <summary>
        /// 填充圓角矩形
        /// </summary>
        private void FillRound(Rectangle rectangle,
            Graphics g, Brush br, int _radius)
        {
            g.FillPath(br, DrawRoundRect(rectangle.X,
                rectangle.Y, rectangle.Width - 2,
                rectangle.Height - 1, _radius));
        }
        /// <summary>
        /// 生成圓角矩形路徑
        /// </summary>
        public static GraphicsPath DrawRoundRect(int x, int y, int width, int height, int radius)
        {
            GraphicsPath gp = new GraphicsPath();
            gp.AddArc(x, y, radius, radius, 180, 90);
            gp.AddArc(width - radius, y, radius, radius, 270, 90);
            gp.AddArc(width - radius, height - radius, radius, radius, 0, 90);
            gp.AddArc(x, height - radius, radius, radius, 90, 90);
            gp.CloseAllFigures();
            return gp;
        }

在編寫過程中，若擔心pen，brush資源釋放問題，可以使用

using(Pen p = new Pen(Color.Red))
{
}

這種方式資源會自動釋放。

本人編寫了重繪了CheckBox，使其為一種可滑動的安妞形狀，類似手機的滑動按鈕方式