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Applying visual effects to the desktop - Shoot

, 31 Jul 2003
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This article discusses how an application can apply visual effects to the desktop, by copying desktop contents, applying effects on it and then re-displaying it.

Sample Image

Introduction

This article discusses how an application can apply visual effects to the desktop, by copying desktop contents, applying effects on it using GDI functions and then re-displaying it. Additionally this application also demonstrates how to play wav files using Win32 API.

Shoot comes in handy when you are frustrated with your computer and would like to literally shoot the brains out of it. This application when run, converts your mouse pointer to a gun's target finder and wherever you click, it makes a gun shot sound and burns a hole through the desktop. To close the application just hit the escape key.

Background

Like all other windows, the desktop window also has a device context associated with it. The Win32 API GetDCEx(...) can be used to get a handle to this desktop device context. Using this handle, you can copy the desktop window contents to some device context of your application. Then using any combination of GDI operations, various visual effects can be applied to it.

Using the code

We start copying the desktop window in the constructor of the dialog class, since we need to do this before, the window for this application comes up. We first get a handle to the desktop device context and then convert it to a pointer to a CDC object. We also get the screen resolution.

CDC *pDesktopDC = CDC::FromHandle (::GetDCEx(NULL, NULL, 0));
int screenMaxX = GetSystemMetrics(SM_CXSCREEN);
int screenMaxY = GetSystemMetrics(SM_CYSCREEN);

Then we create a device context in memory that is compatible with the desktop device context.

m_pProcDC = new CDC;
m_pProcDC->CreateCompatibleDC (pDesktopDC);

When a memory device context is created, a 1x1 pixel sized bitmap is selected to it and hence GDI operations on it do not produce the required effect. We circumvent this by creating a bitmap of the same dimension as the desktop and selecting it to the memory device context.

m_pBMP = new CBitmap;
m_pBMP->CreateCompatibleBitmap (pDesktopDC, screenMaxX, screenMaxY);
m_pProcDC->SelectObject (m_pBMP);

The memory device context is now ready for use and we can copy the contents of the desktop device context to it.

 m_pProcDC->BitBlt(0, 0, screenMaxX, screenMaxY, pDesktopDC, 0, 0, SRCCOPY);

Once this is done you can apply any visual effect to the memory device context and then redisplay it.

However in this application we will not apply the visual effect right now. We need to create a bullet mark on the screen when the user clicks. For that we use a bitmap resource named IDB_SHOTMARK which is like a gunshot mark. To use this bitmap, we load it and select it to another device context created in memory.

m_pShotDC = new CDC;
m_pShotDC->CreateCompatibleDC(pDesktopDC);

m_pShotBmp = new CBitmap;
m_pShotBmp->LoadBitmap ( IDB_SHOTMARK );

m_pShotDC->SelectObject ( m_pShotBmp );

When we are done with copying desktop contents and loading bitmaps, we are ready to display them.

In the OnInitDialog we make the dialog cover the whole desktop, by giving it the size of the desktop and making it stay always on top using a call to SetWindowPos.

::SetWindowPos( this->GetSafeHwnd(), HWND_TOPMOST, 0, 0,
                 GetSystemMetrics(SM_CXSCREEN), GetSystemMetrics(SM_CYSCREEN),
                 SWP_SHOWWINDOW);

We also keep the gun's view finder cursor, which is another resource, ready, by loading it.

HINSTANCE hInstResource = AfxFindResourceHandle (MAKEINTRESOURCE(IDC_TF),
                                                  RT_GROUP_CURSOR);
m_hCursor = ::LoadCursor(hInstResource, MAKEINTRESOURCE(IDC_TF));

In the OnPaint handler we display the desktop window by copying it from the device context in memory where we had stored it previously to the dialog's device context.

CDC *pDC = GetDC();
pDC->BitBlt (0, 0, screenMaxX, screenMaxY, m_pProcDC, 0, 0, SRCCOPY );
ReleaseDC(pDC);

The only thing that is left is to show the gunshot mark and make the sound, when the user clicks. For this we handle the message WM_LBUTTONDOWN where we copy the contents of the gunshot bitmap loaded in the m_pShotDC device context to the point where the user clicked. We also play the wav file using the PlaySound function. To use this function you need to link the VC98\Lib\WINMM.LIB with your application and include the mmsystem.h header file in your application.

void CShootDlg::OnLButtonDown(UINT nFlags, CPoint point)
{
 ...
 //  Show gunshot mark
 CDC *pDC = GetDC();
 pDC->BitBlt (point.x - 10, point.y - 10, 48, 48, m_pShotDC, 0, 0, SRCAND);
 ReleaseDC(pDC);
 ...

 //  Play gunshot sound
 ::PlaySound((LPCTSTR)soundFile, NULL,
             SND_FILENAME | SND_ASYNC | SND_NODEFAULT | SND_PURGE);
 ...

}

Points of interest

The project assumes that the winmm.lib is available as ..\..\VC98\Lib\WINMM.LIB. So you need to extract the shoot sources in the MyProjects folder or change the relative path before building the application.

The application assumes that the gunshot.wav file is present in the same folder as the executable. If it does not find the wav file, the gunshot sound will not be made.

History

  • v1.0 - This is the initial version.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

abhinaba
Web Developer
United States United States
I just love coding. I started programming in 1995 with BASIC and then moved through Cobol, Pascal, Prolog, C, C++, VB, VC++ and now C#/.NET.
 
I received a Bachelor of Technology degree in Computer Science from University of Calcutta in 2001.
 
I worked for some time in Texas Instruments, Adobe Systems and now in Microsoft India Development Center in the Visual Studio Team Systems.
 
I am from the City of Joy, Kolkata in India, but now live and code Hyderabad.

Comments and Discussions

 
Generalcapturing the mouse cursor Pinmemberstealth kid1-Nov-04 0:54 
Generalerror MFC42D.DLL Pinsusselmic30-Aug-03 12:29 
GeneralRe: error MFC42D.DLL Pinmemberabhinaba31-Aug-03 9:51 
GeneralRe: error MFC42D.DLL Pinsusselmic1-Sep-03 5:38 
GeneralBombs out when I run it Pinmembertufwheels6-Aug-03 11:12 
GeneralRe: Bombs out when I run it Pinmemberabhinaba7-Aug-03 21:11 
GeneralRe: Bombs out when I run it Pinmembertufwheels23-Aug-03 10:45 
GeneralRe: Bombs out when I run it PinmemberPhilippe Lhoste8-Jun-04 1:29 
GeneralAnother Way PinmemberSuperEric4-Aug-03 9:45 
GeneralRe: Another Way Pinmemberabhinaba4-Aug-03 18:51 
GeneralLinkage error. PinmemberWREY2-Aug-03 22:50 
The sample failed to link due to its inability to open file:
 
"..\..\VC98\Lib\WINMM.LIB"
 
The thing is, I already have \Microsoft Visual Studio\VC98\LIB set in Tools->Options->Directories->Library files, and I also checked that directory to make sure WINMM.LIB was present there (and it was).
 
AFAIK, everything is in order. So why the linkage failed with that error is beyond me.
 
Confused | :confused:
 
William
 
Fortes in fide et opere!
GeneralRe: Linkage error. Pinmemberabhinaba3-Aug-03 18:09 
GeneralIt's working now!! Thanks!! PinmemberWREY3-Aug-03 21:29 
QuestionHow 2 Close IT?!! PinmemberSuperEric2-Aug-03 11:40 
AnswerRe: How 2 Close IT?!! PinmemberJohann Gerell2-Aug-03 11:50 
GeneralRe: How 2 Close IT?!! PinmemberSuperEric2-Aug-03 20:41 
AnswerRe: How 2 Close IT?!! Pinmemberabhinaba3-Aug-03 17:58 
GeneralRe: How 2 Close IT?!! PinmemberSuperEric4-Aug-03 9:32 

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