C# 区域填充

        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);
            switch (m.Msg)
            {
                case WinUser.WM_CREATE:
                    break;
                case WinUser.WM_PAINT:
                    break;
                case WinUser.WM_LBUTTONDOWN:
                        POINT point;
                        point.x = WinUser.LOWORD((int)m.LParam);
                        point.y = WinUser.HIWORD((int)m.LParam);
                        ElliRgns(this.Handle, point);
                    break;
            }
        }

        /// <summary>
        /// 创建椭圆区域, 并进行填充
        /// </summary>
        /// <param name="hwnd"></param>
        /// <param name="point"></param>
        unsafe void ElliRgns(IntPtr hwnd, POINT point)
        {
            RECT rect, rectClient;
            IntPtr hrgn;
            IntPtr hBrush, hBrushOld;

            //DC
            IntPtr hdc = Win32Native.GetDC(hwnd);
            Win32Native.GetClientRect(hwnd, &rectClient);

            //点周围一块区域
            rect.left = point.x - 40;
            rect.right = point.x + 40;
            rect.top = point.y - 30;
            rect.bottom = point.y + 30;

            //创建区域
            hrgn = Win32Native.CreateEllipticRgnIndirect(&rect);

            //创建画刷
            hBrush = Win32Native.CreateSolidBrush(WinUser.RGB(0, 255, 0));
            hBrushOld = Win32Native.SelectObject(hdc, hBrush);

            //为 DC 选择画刷
            Win32Native.SelectObject(hdc, hBrush);

            //绘制区域
            Win32Native.PaintRgn(hdc, hrgn);

            //稀放资源
            hBrush = Win32Native.SelectObject(hdc, hBrushOld);
            Win32Native.DeleteObject(hBrush);
            Win32Native.DeleteObject(hrgn);
            Win32Native.DeleteDC(hdc);
        }