C / C++ / MFC

22-Jun-05 17:58

Hi,

I am new to MFC and Windows Service. I am trying write a Windows Service Program, its job is to take Screen Capture once in while and save it as a bitmap. For this I am using BitBlt() function. It is failing with "Invalid Handle", but I checked all the handles and they are valid.

I used same code to capture screen which uses BitBlt in a normal Windows apllication and it is working fine.

So , BitBlt is only failing in Windows Service.

Please help me to resolve this issue.

Thanks
VV

John R. Shaw22-Jun-05 18:07

John R. Shaw

22-Jun-05 18:07

Please post some code. There are so many articles on capturing the sceen that it will probably be nothing new. It may be just a minor mistake in the code.

The smaller the example the better.

INTP
"The more help VB provides VB programmers, the more miserable your life as a C++ programmer becomes."
Andrew W. Troelsen

ThatsAlok22-Jun-05 18:18

ThatsAlok

22-Jun-05 18:18

vegeakhil wrote:
I am trying write a Windows Service Program, its job is to take Screen Capture once in while and save it as a bitmap

Is your service is DESKTOP INTERECTIVE SERVICE? if not, you always get BLANK IMAGE or Invalid HANDLE Frown | :(

"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

cheers,
Alok Gupta

vegeakhil23-Jun-05 5:00

23-Jun-05 5:00

Yes, the service is created with SERVICE_INTERACTIVE_PROCESS property. Give me some more time I will post the code also. Thanks

vegeakhil23-Jun-05 5:02

23-Jun-05 5:02

The same Screen Capture function is working fine if I call from simple application (normal application not a service application). So I am thinking it is something to do with service.

vegeakhil23-Jun-05 18:13

23-Jun-05 18:13

Hi Guys

Pls help me...the code is , just to remind you again, if I call this function from simple application it is fine, but if I call from windows service, BitBlt is failing with "Invalid Handle".

Thanks

BOOL CFrameBuffer::CaptureScreen(CRect rectScreen, BYTE *scrBuff)
{
HBITMAP hDesktopCompatibleBitmap=NULL;
HDC hDesktopCompatibleDC=NULL;
HDC hDesktopDC=NULL;
HWND hDesktopWnd=NULL;

int nHeight=rectScreen.bottom-rectScreen.top;/GetSystemMetrics(SM_CXSCREEN);
int nWidth=rectScreen.right-rectScreen.left;//GetSystemMetrics(SM_CYSCREEN);

hDesktopWnd=GetDesktopWindow();

hDesktopDC=::GetDC(NULL);

hDesktopCompatibleDC=CreateCompatibleDC(hDesktopDC);

hDesktopCompatibleBitmap=CreateCompatibleBitmap(hDesktopDC,nWidth,nHeight);

BOOL bRet = FALSE;
HBITMAP oldbitmap;
oldbitmap = (HBITMAP)SelectObject(hDesktopCompatibleDC,hDesktopCompatibleBitmap);

if(hDesktopCompatibleDC && hDesktopDC)
{
bRet = BitBlt(hDesktopCompatibleDC,0,0,nWidth,nHeight,hDesktopDC,0,0,SRCCOPY);
}

OPENFILENAME ofn;
char szFileName[512]; szFileName[0]='\0';
ZeroMemory(&ofn,sizeof(ofn));
ofn.lStructSize=sizeof(OPENFILENAME);
ofn.Flags=OFN_HIDEREADONLY|OFN_PATHMUSTEXIST;
ofn.lpstrFilter="Bitmap Files (*.bmp)\0*.bmp\0";
ofn.lpstrDefExt="bmp";
strcpy(szFileName,"C:\\temp\\MyBitmap.bmp");
ofn.lpstrFile=szFileName;
ofn.nMaxFile=512;

CFileFind finder;
if(finder.FindFile(szFileName))
{
DeleteFile(szFileName);
}

SetCursor(LoadCursor(NULL,IDC_WAIT));

BITMAPINFO bi;
void *pBits=NULL;

ZeroMemory(&bi,sizeof(bi));
bi.bmiHeader.biSize=sizeof(bi.bmiHeader);
bi.bmiHeader.biHeight=nHeight;
bi.bmiHeader.biWidth=nWidth;
bi.bmiHeader.biPlanes=1;
bi.bmiHeader.biBitCount=32;//16 bit
bi.bmiHeader.biCompression=BI_RGB;
bi.bmiHeader.biSizeImage=nWidth*nHeight *sizeof(DWORD);
bi.bmiHeader.biHeight = abs(nHeight);
HDC hBmpFileDC=CreateCompatibleDC(hDesktopCompatibleDC);

HBITMAP hBmpFileBitmap=CreateDIBSection(hDesktopCompatibleDC,&bi,DIB_RGB_COLORS,&pBits,NULL,0);

SelectObject(hBmpFileDC,hBmpFileBitmap);
BitBlt(hBmpFileDC,0,0,nWidth,nHeight,hDesktopCompatibleDC,0,0,SRCCOPY);

HANDLE hFile=CreateFile(szFileName,GENERIC_WRITE,FILE_SHARE_WRITE,NULL,CREATE_ALWAYS,FILE_ATTRIBUTE_NORMAL,NULL);
if(hFile!=INVALID_HANDLE_VALUE)
{
DWORD dwRet=0;
BITMAPFILEHEADER bmfHeader;
ZeroMemory(&bmfHeader,sizeof(bmfHeader));
bmfHeader.bfOffBits=sizeof(BITMAPFILEHEADER)+sizeof(BITMAPINFOHEADER);
bmfHeader.bfSize=bi.bmiHeader.biSizeImage+bmfHeader.bfOffBits;
bmfHeader.bfType='MB';

WriteFile(hFile,&bmfHeader,sizeof(bmfHeader),&dwRet,NULL);
WriteFile(hFile,&bi.bmiHeader,sizeof(bi.bmiHeader),&dwRet,NULL);
WriteFile(hFile,pBits,bi.bmiHeader.biSizeImage,&dwRet,NULL);
CloseHandle(hFile);
AddToMessageLog(" Inside 2 CaptureScreen() is called", 1 );
}

if(scrBuff!=NULL)
{
memcpy(scrBuff,pBits,bi.bmiHeader.biSizeImage);
}

SelectObject(hDesktopCompatibleDC,oldbitmap);
DeleteDC(hBmpFileDC);
DeleteObject(hBmpFileBitmap);
ReleaseDC(hDesktopWnd,hDesktopDC);
return TRUE;
}

printf(...) clone

Weiye Chen22-Jun-05 17:49

22-Jun-05 17:49

How do i create a function which accepts the same parameters as printf(...)?

In stdio.h, printf is declared as

_CRTIMP int __cdecl printf(const char *, ...);

I tried creating a similar function

void test(const char *pStr, ...)
{
    // Display string
    printf(pStr);
}

However, test(...) display differently from the actual printf(...) call. What am i missing? Confused | :confused:

<font=arial>Weiye Chen
Life is hard, yet we are made of flesh...

Christian Graus22-Jun-05 18:16

Christian Graus

22-Jun-05 18:16

The ... represents a parameter collection of unknown size. Zero is an acceptable size, so your code ends up calling successfully, but gives printf nothing to do.

This[^] took me ages to find, none of the words I was searching on was specific enough to avoid a thousand hits to basic C++ pages, as ... appears all over the place.

Christian Graus - Microsoft MVP - C++

Weiye Chen22-Jun-05 19:57

22-Jun-05 19:57

Thanks for the link. It certainly explains some 'behind the scene' stuff. Smile | :)

<font=arial>Weiye Chen
Life is hard, yet we are made of flesh...

John R. Shaw22-Jun-05 18:25

John R. Shaw

22-Jun-05 18:25

The fuction below represents that last time I remember having to do this:

int my_printf( const char *format,... )
{
    int n=-1;
    char *buf=NULL;
    size_t size=0;
    va_list ap;
    va_start( ap,format );
    while( n == -1 ) {
        size += 128;                                /* change size */
        if( buf ) free(buf);                        /* free old buffer */
        buf = (char *)malloc(size);                 /* allocate new buffer */
        if( !buf ) n = 0;                           /* allocation failer */
        else n = _vsnprintf(buf,size,format,ap);    /* do basic formating */
    }
    va_end(ap);
    my_print(buf);
    return n;
}

The _vsnprintf() function is still supported by VC6, so it still works. The key is the va_list(), va_start() and va_end() (macros I believe). You'll need to look them all up and may be bring them upto date (this was written around 1992).

INTP
"The more help VB provides VB programmers, the more miserable your life as a C++ programmer becomes."
Andrew W. Troelsen

Weiye Chen22-Jun-05 19:42

22-Jun-05 19:42

Thanks. Your code works just like printf. Now i need to see if this would run well on unix. Smile | :)

<font=arial>Weiye Chen
Life is hard, yet we are made of flesh...

ThatsAlok22-Jun-05 18:30

ThatsAlok

22-Jun-05 18:30

Weiye Chen wrote:
However, test(...) display differently from the actual printf(...) call. What am i missing?

See if this help
http://www.codeproject.com/cpp/argfunctions.asp[^]

http://www.codeproject.com/cpp/C___Variable_Arguments.asp[^]

"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

cheers,
Alok Gupta

Weiye Chen22-Jun-05 19:59