改变右击SysMenu后弹出的菜单

// Add to WndProc
    case WM_CONTEXTMENU:
        if (lParam != -1 &&
            SendMessage(hwnd, WM_NCHITTEST,
                        0, lParam) == HTSYSMENU) {
            HMENU hmenu = CreatePopupMenu();
            if (hmenu) {
                AppendMenu(hmenu, MF_STRING, 1,
                           TEXT("Custom menu"));
                TrackPopupMenu(hmenu, TPM_LEFTALIGN | TPM_TOPALIGN |
                                      TPM_RIGHTBUTTON,
                               GET_X_LPARAM(lParam),
                               GET_Y_LPARAM(lParam), 0, hwnd, NULL);
                DestroyMenu(hmenu);
            }
            return 0;
        }
        break;