Genearting screenshot (BMP) with Windows Service and CreateProcessWithLogonW

Question

I'm trying to create a screenshot application using windows service, that can capture complete screen at regular time intervals. To get started with, I took basic window service example (http://code.msdn.microsoft.com/windowsdesktop/CppWindowsService-cacf4948) and included screenshot utility class in the project and called the capture function in the onStart method of sample windows service. However, I got blank screen shots. Later I realized that windows service runs in different session and hence the screenshots are blank.

S, I decoupled the screenshot utility class and made it as a seperate project and generated a .exe out of it (which is capable of writing logs to a file where ever needed). This time, I used createProcessWithLogonW function to call the executable, so that it will run the exe in specified user domain than the default service session. The following is the code snippet I have been using.

void CSampleService::StartProcess()
{
    DWORD dwSize; HANDLE hToken=NULL;
    LPVOID lpvEnv; PROCESS_INFORMATION pi = {0};
    STARTUPINFO si = {0};
    WCHAR szUserProfile[256] = L"";
    si.cb = sizeof(STARTUPINFO);

    if (!CreateEnvironmentBlock(&lpvEnv, hToken, TRUE))
    {
        logger::Wlog(logger::fileName,"CreateEnvironmentBlock Error");
    }

    dwSize = sizeof(szUserProfile)/sizeof(WCHAR);

    GetUserProfileDirectory(hToken, szUserProfile, &dwSize);

    CreateProcessWithLogonW(L"admin", L"MyDomain",L"mypassword",
        LOGON_WITH_PROFILE, NULL, L"C:\\Temp\\application.exe",
        CREATE_UNICODE_ENVIRONMENT, lpvEnv, NULL, &si, &pi);

    DestroyEnvironmentBlock(lpvEnv);
    CloseHandle(hToken);
    CloseHandle(pi.hProcess);
    CloseHandle(pi.hThread);
    WaitForSingleObject(pi.hProcess, INFINITE);
    CloseHandle(pi.hProcess);
    CloseHandle(pi.hThread);
}

I have no errors from the logs i got. when the services get initiated, it gives a warning of interactive service trying to show a message. When I click that, I received a black screenshot again. I know that there are many things involved here, I just gave a high level view of what I'm doing. Also, i'm pretty new to windows programming. Any kind of help is appreciated.

Answer 1

yes, i got that working. we have to acquire the active session-ID (perhaps from opened desktop) and run the process as interactive service in that session context. This should probably solve the capturing screenshots issue. If someone is looking for GUI and service interactions perhaps IPC will be the most convenient way.