ModernWPF.Internal.LegacyBorderManager.SetRegion C# (CSharp) Method

        static void SetRegion(IntPtr hwnd, int width, int height, bool force)
        {
            if (Dwmapi.IsCompositionEnabled)
            {
                //clear
                if (force)
                {
                    User32.SetWindowRgn(hwnd, IntPtr.Zero, User32.IsWindowVisible(hwnd));
                }
            }
            else
            {
                var wpl = default(WINDOWPLACEMENT);
                wpl.length = (uint)Marshal.SizeOf(typeof(WINDOWPLACEMENT));

                if (User32.GetWindowPlacement(hwnd, ref wpl))
                {
                    if (wpl.showCmd == ShowWindowOption.SW_MAXIMIZE)
                    {
                        //clear
                        User32.SetWindowRgn(hwnd, IntPtr.Zero, User32.IsWindowVisible(hwnd));
                    }
                    else
                    {
                        // always rectangle to prevent rounded corners for some themes
                        IntPtr rgn = IntPtr.Zero;
                        try
                        {
                            if (width == 0 || height == 0)
                            {
                                RECT r = default(RECT);
                                User32.GetWindowRect(hwnd, ref r);
                                width = r.Width;
                                height = r.Height;
                            }

                            rgn = Gdi32.CreateRectRgn(0, 0, width, height);
                            User32.SetWindowRgn(hwnd, rgn, User32.IsWindowVisible(hwnd));
                        }
                        finally
                        {
                            if (rgn != IntPtr.Zero)
                            {
                                Gdi32.DeleteObject(rgn);
                            }
                        }
                    }
                }
            }
        }