----- makefile -----

# Nmake macros for building Windows 32-Bit apps

!include <ntwin32.mak>

all: display.exe

display.obj: display.c
    $(cc) $(cflags) $(cvars) $(cdebug) display.c

logonid.obj: logonid.c
    $(cc) $(cflags) $(cvars) $(cdebug) -Ic:\ddk\inc logonid.c

display.exe: display.obj logonid.obj
    $(link) $(linkdebug) $(conflags) -out:display.exe display.obj 
logonid.obj $(conlibs) c:\ddk\lib\i386\free\ntdll.lib


----- display.c -----

#include <stdio.h>
#include <windows.h>

extern ULONG GetWinCenterLogonId(HANDLE);

char *
GetWinCenterDisplay(char *display)
{
    HANDLE          shmem = 0;
    ULONG          *shmemBase,
                    ipaddr,
                    dpy,
                    screen;
    char            string[25];

    sprintf(string, "XDisplayAddress-%d",
	    GetWinCenterLogonId(GetCurrentProcess()));

    if (!(shmem = OpenFileMapping(FILE_MAP_READ, FALSE, string)) ||
	!(shmemBase = MapViewOfFile(shmem, FILE_MAP_READ, 0, 0, 0)))
    {
	if (shmem)
	    CloseHandle(shmem);
	return NULL;
    }

    ipaddr = shmemBase[0];
    dpy = shmemBase[1];
    screen = shmemBase[2];

    UnmapViewOfFile(shmemBase);
    CloseHandle(shmem);

    sprintf(display, "%d.%d.%d.%d:%d.%d",
	    (ipaddr >> 24) & 0xff, (ipaddr >> 16) & 0xff,
	    (ipaddr >> 8) & 0xff, ipaddr & 0xff, dpy, screen);

    return display;
}

int
main(int argc, char **argv)
{
    char display[50];

    printf("%s\n", GetWinCenterDisplay(display) ? display :
	   "Couldn't get display");

    return 1;
}

----- logonid.c -----

#include <ntddk.h>

//
// Citrix specific Process Information
// NtQueryInformationProcess using ProcessCitrixInformation
//

typedef struct _PROCESS_CITRIX_INFORMATION
{
    ULONG LogonId;
} PROCESS_CITRIX_INFORMATION, *PPROCESS_CITRIX_INFORMATION;

#define ProcessCitrixInformation 19 /* hopefully this won't change... */

ULONG
GetWinCenterLogonId(HANDLE ProcessHandle)
{
    PROCESS_CITRIX_INFORMATION 	ProcessInfo;
    NTSTATUS        		Status;

    Status = NtQueryInformationProcess(ProcessHandle,
				       ProcessCitrixInformation,
				       &ProcessInfo, 
sizeof(ProcessInfo),
				       NULL);

    return NT_SUCCESS(Status) ? ProcessInfo.LogonId : 0;
}