使用日历控件MonthCalendar选择日期时，怎么知道鼠标点的是日期还是上边变换月份的小按钮？

var
  m: Cardinal = 0;
  b: Boolean = False;  // 如果为true表示月份改变了，相当点击了左右选择月份的按钮

// OnGetMonthInfo 事件
procedure TForm1.monthCalendar1GetMonthInfo(Sender: TObject; Month: Cardinal;
  var MonthBoldInfo: Cardinal);
begin
  b := m <> Month;
end;

//   returns FALSE if MCS_MULTISELECT
//   returns TRUE and sets *pst to the currently selected date otherwise
{$EXTERNALSYM MonthCal_GetCurSel}
function MonthCal_GetCurSel(hmc: HWND; var pst: TSystemTime): BOOL;

//   returns FALSE if MCS_MULTISELECT
//   returns TURE and sets the currently selected date to *pst otherwise
{$EXTERNALSYM MonthCal_SetCurSel}
function MonthCal_SetCurSel(hmc: HWND; const pst: TSystemTime): BOOL;

//   returns the maximum number of selectable days allowed
{$EXTERNALSYM MonthCal_GetMaxSelCount}
function MonthCal_GetMaxSelCount(hmc: HWND): DWORD;

//   sets the max number days that can be selected iff MCS_MULTISELECT
{$EXTERNALSYM MonthCal_SetMaxSelCount}
function MonthCal_SetMaxSelCount(hmc: HWND; n: UINT): BOOL;

//   sets rgst[0] to the first day of the selection range
//   sets rgst[1] to the last day of the selection range
{$EXTERNALSYM MonthCal_GetSelRange}
function MonthCal_GetSelRange(hmc: HWND; rgst: PSystemTime): BOOL;

//   selects the range of days from rgst[0] to rgst[1]
{$EXTERNALSYM MonthCal_SetSelRange}
function MonthCal_SetSelRange(hmc: HWND; rgst: PSystemTime): BOOL;

//   if rgst specified, sets rgst[0] to the starting date and
//      and rgst[1] to the ending date of the the selectable (non-grayed)
//      days if GMR_VISIBLE or all the displayed days (including grayed)
//      if GMR_DAYSTATE.
//   returns the number of months spanned by the above range.
{$EXTERNALSYM MonthCal_GetMonthRange}
function MonthCal_GetMonthRange(hmc: HWND; gmr: DWORD; rgst: PSystemTime): DWORD;

//   cbds is the count of DAYSTATE items in rgds and it must be equal
//   to the value returned from MonthCal_GetMonthRange(hmc, GMR_DAYSTATE, NULL)
//   This sets the DAYSTATE bits for each month (grayed and non-grayed
//   days) displayed in the calendar. The first bit in a month's DAYSTATE
//   corresponts to bolding day 1, the second bit affects day 2, etc.
{$EXTERNALSYM MonthCal_SetDayState}
function MonthCal_SetDayState(hmc: HWND; cbds: Integer; const rgds: TNMDayState): BOOL;

//   sets prc the minimal size needed to display one month
{$EXTERNALSYM MonthCal_GetMinReqRect}
function MonthCal_GetMinReqRect(hmc: HWND; var prc: TRect): BOOL;

// set what day is "today"   send NULL to revert back to real date
{$EXTERNALSYM MonthCal_SetToday}
function MonthCal_SetToday(hmc: HWND; const pst: TSystemTime): BOOL;

// get what day is "today"
// returns BOOL for success/failure
{$EXTERNALSYM MonthCal_GetToday}
function MonthCal_GetToday(hmc: HWND; var pst: TSystemTime): BOOL;

// determine what pinfo->pt is over
{$EXTERNALSYM MonthCal_HitTest}
function MonthCal_HitTest(hmc: HWND; var info: TMCHitTestInfo): DWORD;

// set colors to draw control with -- see MCSC_ bits below
{$EXTERNALSYM MonthCal_SetColor}
function MonthCal_SetColor(hmc: HWND; iColor: Integer; clr: TColorRef): TColorRef;

{$EXTERNALSYM MonthCal_GetColor}
function MonthCal_GetColor(hmc: HWND; iColor: Integer): TColorRef;

// set first day of week to iDay:
// 0 for Monday, 1 for Tuesday, ..., 6 for Sunday
// -1 for means use locale info
{$EXTERNALSYM MonthCal_SetFirstDayOfWeek}
function MonthCal_SetFirstDayOfWeek(hmc: HWND; iDay: Integer): Integer;

// DWORD result...  low word has the day.  high word is bool if this is app set
// or not (FALSE == using locale info)
{$EXTERNALSYM MonthCal_GetFirstDayOfWeek}
function MonthCal_GetFirstDayOfWeek(hmc: HWND): Integer;

//   modifies rgst[0] to be the minimum ALLOWABLE systemtime (or 0 if no minimum)
//   modifies rgst[1] to be the maximum ALLOWABLE systemtime (or 0 if no maximum)
//   returns GDTR_MIN|GDTR_MAX if there is a minimum|maximum limit
{$EXTERNALSYM MonthCal_GetRange}
function MonthCal_GetRange(hmc: HWND; rgst: PSystemTime): DWORD;

//   if GDTR_MIN, sets the minimum ALLOWABLE systemtime to rgst[0], otherwise removes minimum
//   if GDTR_MAX, sets the maximum ALLOWABLE systemtime to rgst[1], otherwise removes maximum
//   returns TRUE on success, FALSE on error (such as invalid parameters)
{$EXTERNALSYM Monthcal_SetRange}
function Monthcal_SetRange(hmc: HWND; gdtr: DWORD; rgst: PSystemTime): BOOL;

//   returns the number of months one click on a next/prev button moves by
{$EXTERNALSYM MonthCal_GetMonthDelta}
function MonthCal_GetMonthDelta(hmc: HWND): Integer;

//   sets the month delta to n. n = 0 reverts to moving by a page of months
//   returns the previous value of n.
{$EXTERNALSYM MonthCal_SetMonthDelta}
function MonthCal_SetMonthDelta(hmc: HWND; n: Integer): Integer;

//   sets *psz to the maximum width/height of the "Today" string displayed
//   at the bottom of the calendar (as long as MCS_NOTODAY is not specified)
{$EXTERNALSYM MonthCal_GetMaxTodayWidth}
function MonthCal_GetMaxTodayWidth(hmc: HWND): DWORD;

{$EXTERNALSYM MonthCal_SetUnicodeFormat}
function MonthCal_SetUnicodeFormat(hwnd: HWND; fUnicode: BOOL): BOOL;

{$EXTERNALSYM MonthCal_GetUnicodeFormat}
function MonthCal_GetUnicodeFormat(hwnd: HWND): BOOL;