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Posted 6 Sep 2007


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Screen Capture (Simple Win32 Dialog Based)

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4.57/5 (18 votes)
11 Nov 2007CPOL3 min read
It's a simple dialog based Screen Capture that uses Global Mouse Hooks to capture the area selected by user, controls( i.e. Buttons, etc.), and any other Window.


I have just started programming in VC++, and this is my first article on CodeProject. I have created this project after reading the materials from CodeProject itself.

Everybody knows about the Screen Capture (Prt Scr Button) utility that comes with each and every Microsoft Windows. So what is the necessity of another Screen Capture application. But the Screen Capture utility that ships with Windows is very simple, you can only capture the whole screen. But what if you have to capture the part of the screen or say only a particular control on other window. Don't worry; here is the application for that. Using this application, you can capture the Selected area rather than the whole window. You can also capture any window or control by just clicking on it. (You can even capture only the start button or clock on task bar). Isn't it good! And it uses a simple Win32 API function for that.


This article uses the two main functions of the Win32 API:

  1. SetWindowsHookEx(): To Set the global Mouse Hook (see MSDN for more help about this.) Global Mouse Hook is necessary to capture the Mouse Event from outside of our window.
  2. BitBlt() (pronounced as Bitblit): Used to transfer color data between source device context and destination device context. It is used here to Capture the Screen.

Using the Code


Below is the code from MyMouseHook.cpp. Here we are sending MOUSE_DOWN message when user presses the left Mouse Button and MOUSE_UP when user leaves the left Mouse Button. Both of these are user messages.

LRESULT CALLBACK MyMouseHookProc(int nCode, WPARAM wParam, LPARAM lParam)
     //Below Function will Return the Handle of window whose Caption is "Capture "
     //We will use this handle to send Message.(Handle is handle to Our Application )

            HWND hWndApp = FindWindow(0,L"Capture");
              //Wpram will contain which mouse event has been generated 
              // We will send the User Message for each event we require.
            if(wParam== WM_LBUTTONDOWN || wParam == WM_NCLBUTTONDOWN)
            if(wParam == WM_LBUTTONUP)


Below is the part of the code used in ScreenCaptureDlg.cpp File. When the user first presses the Mouse Button after pressing the Capture button, we take that point as the starting point in Begpt as a starting point. And after dragging the Mouse when the user releases the button, we take the End points of the Selected Rectangle in Endpt. Then we capture the area between this Begpt and Endpt from Desktop to MemDC and send it to the SaveBitmap()function which will save DC into .bmp file. And then we will create a process to show the .bmp file into PAIN application. Don't worry about the other function I haven't explain here. I have explained all the things well in the code:

    if(CaptureActWnd == TRUE)
        GetCursorPos(&Begpt);              	//Will take the Cursor Position
        hWndActWnd= WindowFromPoint(Begpt);	//Will get the Handle of Window 
					//Where Your Mouse is Currently
        CaptureActiveWindow();            	//Will Call the Function to Capture 
					//That Window    
        EndDialog(hWndDlg,LOWORD(lParam)); 	//Will End the Dialog
        PostQuitMessage(0);                 	//Will destroy Window
        OutputDebugString( L"Desktop -GDI, MOUSE_DOWN");
        GetCursorPos(&Begpt);        	// Will Store the Current Cursor 
					// position in Begpt
        break;                        	// Mouse is Down Begpt.x = left, 
					// Begpt.y = Top     

case MOUSE_UP:
    if(CaptureActWnd == FALSE)
        GetCursorPos(&Endpt);	//As the Mouse is UP We will get Out Bottom 
				//Right Points in EndPt.
        DrawBox();            	//Will Draw the Rectangle Around selected area
        // Create a memory device context Compatible with Dialog DC
        MemDC = CreateCompatibleDC(DlgDC);
        // Create a compatible bitmap 
        hBitmap = CreateCompatibleBitmap(DlgDC,width,height);
        // Select the bitmap into the memory context
        // This will copy the our Selected Area into MemDC
        BitBlt(MemDC,0,0,width,height ,DeskDC,Begpt.x,Begpt.y,SRCCOPY);    
        //Will Save the Device Context into Sample.bmp
        SaveBitmap(MemDC, hBitmap,"Sample.bmp");
         //Will show you the Capture Area Into MSPAINT
         //Send Message to Quit the Window.

Points of Interest

I tried to capture WM_MOUSEMOVE event to draw the rectangle on screen rather than capture only WM_LBUTTONDOWN and WM_LBUTTONUP but it was making the application very sluggish. So I left it and took only Starting Point and End Points to draw the rectangle and capture the screen. So you will not be able to see the rectangle when you will be selecting the area, but the rectangle will appear when you will complete your selection.

Special Thanks

To Arun Krishnan for his nice article on Desktop Calendar from where I came to know how to save the DC(Device Context)in .bmp file.

To Mumtaz Zaheer for his nice project about Sweep the Minesweeper from where I came to know about global hook.


There was a little flaw in the previous version of the application. When it was capturing the Window, it was failing to capture the Title bar which is also important. I have fixed the problem in the updated version.


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


About the Author

GauranG Shah
Tester / Quality Assurance
India India
His name is Gaurang Shah. He has completed his bachelor in computer science.Has worked as a System programmer. Currently working as QA Analyst in Pune.

Comments and Discussions

Suggestionoption without needing DLL Pin
Member 147526384-Mar-20 9:05
MemberMember 147526384-Mar-20 9:05 
QuestionALT+PRINT prints the activated window Pin
francwalter16-Feb-14 19:06
Memberfrancwalter16-Feb-14 19:06 
QuestionWill it work for Multiple screens? Pin
Member-42540443-Sep-13 8:06
MemberMember-42540443-Sep-13 8:06 
Questioncapture Pin
zeppp24-Apr-12 20:06
Memberzeppp24-Apr-12 20:06 
GeneralBLOWUP.C -- Video Magnifier Program by Charles Petzold, is very very better!!! Pin
merdaig1211-Jul-10 10:07
Membermerdaig1211-Jul-10 10:07 
GeneralThank you share Pin
JoshuaTsai2-Dec-09 21:19
MemberJoshuaTsai2-Dec-09 21:19 
QuestionDid you test your updated version ? Pin
Member 427768226-Jun-09 12:01
MemberMember 427768226-Jun-09 12:01 
GeneralDraw Rectangle Pin
Render Plus9-May-09 13:04
MemberRender Plus9-May-09 13:04 
GeneralRe: Draw Rectangle Pin
GauranG Shah24-Jun-09 2:29
MemberGauranG Shah24-Jun-09 2:29 
GeneralFirst straightforward code Pin
bulg23-Oct-08 12:24
Memberbulg23-Oct-08 12:24 
GeneralThank you for share! Pin
cigogo1-Jul-08 17:34
Membercigogo1-Jul-08 17:34 
GeneralThank you Pin
wenzis6-May-08 16:07
Memberwenzis6-May-08 16:07 
Question::FindWindow problem.. Pin
shizu looi16-Dec-07 21:21
Membershizu looi16-Dec-07 21:21 
QuestionSave Bitmap to another format Pin
dubbele onzin21-Nov-07 22:06
Memberdubbele onzin21-Nov-07 22:06 
QuestionHow can I modify this to Capture the Desktop? Pin
dubbele onzin16-Nov-07 1:08
Memberdubbele onzin16-Nov-07 1:08 
AnswerRe: How can I modify this to Capture the Desktop? Pin
GauranG Shah19-Nov-07 19:34
MemberGauranG Shah19-Nov-07 19:34 
GeneralRe: How can I modify this to Capture the Desktop? Pin
dubbele onzin21-Nov-07 22:07
Memberdubbele onzin21-Nov-07 22:07 
AnswerRe: How can I modify this to Capture the Desktop? Pin
Manikandan22-Sep-08 17:49
MemberManikandan22-Sep-08 17:49 
GeneralVery good Pin
nirdhar22-Oct-07 23:04
Membernirdhar22-Oct-07 23:04 
GeneralRe: Very good Pin
GauranG Shah23-Oct-07 2:51
MemberGauranG Shah23-Oct-07 2:51 
GeneralCapture the active window in windows Pin
GurliGebis6-Sep-07 23:00
MemberGurliGebis6-Sep-07 23:00 
GeneralRe: Capture the active window in windows Pin
GauranG Shah7-Sep-07 19:31
MemberGauranG Shah7-Sep-07 19:31 
GeneralNice Work !!! Pin
DharmeshC6-Sep-07 3:39
MemberDharmeshC6-Sep-07 3:39 

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