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MFC Classes for Multiple Monitors

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4.93 (40 votes)
27 Aug 2003CPOL
Class wrappers around the Win32 multi-monitor API

Sample Image - multimon.jpg


A while ago, I decided to write a screensaver application as a way to pick up MFC. After I got my first implementation up and running, I shipped it off to a friend. Well, the first thing he noted was a glaring bug: he uses multiple monitors and my screen saver only showed up on one.

After some scouring of the internet and research into MSDN, I was able to get the screensaver running on multiple monitors by using some API calls that were introduced with Windows 98/2000. This project is a couple of small MFC classes that wrap the multi-monitor API.

These classes can be safely used on Windows 95/NT4 as well. On those platforms, they just provide the properties of the one and only monitor.


Everything you ever wanted to know about the API for multiple monitors is described in a very well written article by David Campbell in the June 1997 issue of MSJ.

The API itself is simple and straightforward. It has some new constants to pass to GetSystemMetrics and a couple methods to enumerate all of the monitors currently attached to the system and get the properties of a given monitor.

All of the types and functions are defined by the platform SDK in the file multimon.h. If you #define WINVER to be greater than 0x400, you don't need to link to multimon.h, as the API gets defined in windef.h for Windows 98 and later targeted builds. Multimon.h also provides some stub functions that allow calls to be safely made on Windows 95/NT4 machines. These wrappers interrogate the runtime OS and either make fall-through calls into the actual API or return the properties of the one (and only) monitor on those older platforms.

The multi monitor classes take care of including multimon.h correctly depending on the value of WINVER.

Using the Code

CMointor is a basic MFC class that allows you to safely use the multi-monitor API on any Win32 platform.

There are three classes in this library:

CMonitors represents the collection of monitors currently attached to the system and wraps the EnumDisplayMonitors API function.

//CMonitors' interface
CMonitor GetMonitor( const int index ) const;
int GetCount() const; 

//returns the monitor closest to the specified item
static CMonitor GetNearestMonitor( const LPRECT lprc );
static CMonitor GetNearestMonitor( const POINT pt );
static CMonitor GetNearestMonitor( const CWnd* pWnd );

//is the specified item visible on any monitor
static BOOL IsOnScreen( const POINT pt );
static BOOL IsOnScreen( const CWnd* pWnd );
static BOOL IsOnScreen( const LPRECT lprc );

//returns the rectangle encompassing all monitors
static void GetVirtualDesktopRect( LPRECT lprc );

//determines whether the given handle is a valid monitor handle
static BOOL IsMonitor( const HMONITOR hMonitor );
static CMonitor GetPrimaryMonitor();
static BOOL AllMonitorsShareDisplayFormat();

static int GetMonitorCount();

CMonitor is a wrapper around an HMONITOR handle (returned from EnumDisplayMonitors) and the GetMonitorInfo function. With CMonitor, you can get at the characteristics of a given monitor.

//The interface of CMonitor            
void Attach( const HMONITOR hMonitor );
HMONITOR Detach();

void ClipRectToMonitor( LPRECT lprc, 
                        const BOOL UseWorkAreaRect = FALSE ) const;
void CenterRectToMonitor( LPRECT lprc, 
                          const BOOL UseWorkAreaRect = FALSE ) const;
void CenterWindowToMonitor( CWnd* const pWnd,
                            const BOOL UseWorkAreaRect = FALSE ) const;

//creates a device context for the monitor - the client is responsible for DeleteDC
HDC CreateDC() const;

void GetMonitorRect( LPRECT lprc ) const;
//the work area is the monitor rect minus the start bar
void GetWorkAreaRect( LPRECT lprc ) const;

void GetName( CString& string ) const;

int GetBitsPerPixel() const;

//determines if the specified item on the monitor
BOOL IsOnMonitor( const POINT pt ) const;
BOOL IsOnMonitor( const CWnd* pWnd ) const;
BOOL IsOnMonitor( const LPRECT lprc ) const;

BOOL IsPrimaryMonitor() const;
BOOL IsMonitor() const;        

CMonitorDC is a CDC derived class that represents a monitor specific device context. I haven't really gone too far with this class but it seemed like a logical part of the library.

Known Limitations

CMonitor and CMonitors rely on the assumption that a monitor handle does not change. This has proved to be a safe assumption empirically but isn't necessarily a guarantee.


  • 02/20/2003 - Initial release
  • 08/25/2003 - Made changes to make compatible with VC6 environment


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Don Kackman
Team Leader Starkey Laboratories
United States United States
The first computer program I ever wrote was in BASIC on a TRS-80 Model I and it looked something like:
10 PRINT "Don is cool"
20 GOTO 10

It only went downhill from there.

Hey look, I've got a blog

Comments and Discussions

QuestionNice work. Pin
Kim Moung Soo29-May-13 21:29
MemberKim Moung Soo29-May-13 21:29 
AnswerRe: Nice work. Pin
Don Kackman30-May-13 2:43
MemberDon Kackman30-May-13 2:43 
GeneralMy vote of 5 Pin
Kim Moung Soo29-May-13 21:23
MemberKim Moung Soo29-May-13 21:23 
Questionversion Pin
Member 1005080919-May-13 15:50
MemberMember 1005080919-May-13 15:50 
AnswerRe: version Pin
Don Kackman19-May-13 16:04
MemberDon Kackman19-May-13 16:04 
GeneralMy vote of 5 Pin
Georgy Meshkov15-Oct-12 1:57
MemberGeorgy Meshkov15-Oct-12 1:57 
QuestionMultimon Code Project Licensing Pin
DonaldJLucas17-May-09 17:40
MemberDonaldJLucas17-May-09 17:40 
AnswerRe: Multimon Code Project Licensing Pin
Don Kackman18-May-09 6:59
MemberDon Kackman18-May-09 6:59 
QuestionRe: Multimon Code Project Licensing Pin
DonaldJLucas18-May-09 19:17
MemberDonaldJLucas18-May-09 19:17 
AnswerRe: Multimon Code Project Licensing Pin
Don Kackman19-May-09 2:00
MemberDon Kackman19-May-09 2:00 
GeneralDual Monitor problem Pin
Member 469378711-Aug-08 21:00
MemberMember 469378711-Aug-08 21:00 or c# version please ? Pin
UltraWhack12-May-08 9:43
MemberUltraWhack12-May-08 9:43 
AnswerRe: or c# version please ? PinPopular
Don Kackman5-Aug-08 1:27
MemberDon Kackman5-Aug-08 1:27 
Questionmirror display Pin
furry2223-Apr-08 1:40
Memberfurry2223-Apr-08 1:40 
QuestionMFC Classes Pin
kannettan15-Sep-06 20:49
Memberkannettan15-Sep-06 20:49 
GeneralBits per pixel Pin
akorka17-Jul-06 9:39
Memberakorka17-Jul-06 9:39 
GeneralRe: Bits per pixel Pin
Don Kackman17-Jul-06 11:02
MemberDon Kackman17-Jul-06 11:02 
GeneralProblem Pin
akorka17-Jul-06 8:40
Memberakorka17-Jul-06 8:40 
GeneralSplitterWND question Pin
Karl Bahr26-Nov-05 6:02
MemberKarl Bahr26-Nov-05 6:02 
GeneralNice classes, one fix Pin
Hans Dietrich24-Feb-05 15:48
mentorHans Dietrich24-Feb-05 15:48 
GeneralRe: Nice classes, one fix Pin
Don Kackman19-Mar-05 15:18
MemberDon Kackman19-Mar-05 15:18 
GeneralRe: Nice classes, one fix Pin
Hans Dietrich19-Mar-05 18:43
mentorHans Dietrich19-Mar-05 18:43 
GeneralRe: Nice classes, one fix Pin
FreeDragon8029-May-08 9:22
MemberFreeDragon8029-May-08 9:22 
GeneralNice! What about turning on/off the second monitor Pin
AORD17-Feb-05 21:48
MemberAORD17-Feb-05 21:48 
GeneralCMonitor not defined Pin
bujal20-Dec-04 13:58
Memberbujal20-Dec-04 13:58 

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Posted 19 Feb 2003


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