Using ExtDeviceMode() to Modify Printer Settings

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Extdev2.exe

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Beginning with Windows version 3.0, many printer drivers implement a convention for controlling print settings on a job-by-job basis, without requiring user intervention via a dialog box. This is accomplished via the ExtDeviceMode() function as described in Chapter 17 of the Microsoft Windows SDK "Guide to Programming" for both versions 3.0 and 3.1. The DeviceCapabilities() function, also introduced in Windows 3.0, provides information about the print settings supported by a given driver. As of Windows version 3.1, changes to printer settings are allowed on a page-by-page basis via the use of the ResetDC() API.

ExtDeviceMode() and DeviceCapabilities() are supplied by the printer drivers rather than GDI. Because not all drivers support these functions, applications must ensure that the driver supports these functions before attempting to use them.

Because of the Universal Printer Driver (UNIDRV), almost all Windows 3.1 printer drivers support these functions. The HP Plotter driver (HPPLOT.DRV) is a notable exception. The only way to change the settings on the HP Plotter is to display the driver's print setup dialog box, which is accomplished by calling the driver's DeviceMode function.

Correct usage of ExtDeviceMode() and DeviceCapabilities() to query and/or modify printer settings is a multistep process that is not fully explained in the SDK documentation.

Because these functions reside in the printer driver rather than GDI, applications must first get a handle to the driver, typically by calling LoadLibrary(), and then use GetProcAddress() to get the address of the driver's ExtDeviceMode() and/or DeviceCapabilities() functions. If GetProcAddress() returns NULL for either of these functions, then that function is not supported by the driver.

Furthermore, because ExtDeviceMode() and DeviceCapabilities() are not Windows APIs, they are not prototyped in WINDOWS.H. Instead, function pointer types are defined for both of these functions in PRINT.H included in the Windows 3.1 SDK and in DRIVINIT.H included in the Windows 3.0 SDK. Use LPFNDEVMODE for ExtDeviceMode(); use LPFNDEVCAPS for DeviceCapabilities(). Using these types is important for compiler type-checking and ensures that the correct arguments are passed on the stack. Not using these types (for example, using FARPROC) can lead to general protection (GP) faults in some circumstances.

PRINT.H (or DRIVINIT.H) also defines the device-independent part of the DEVMODE structure used for manipulating printer settings. Note that the DEVMODE structure actually used by a printer driver contains the device-independent part followed by a driver-specific part that varies in size and content with each driver and driver version.

Because of this driver-dependence, it is very important for applications to query the driver for the correct size of the DEVMODE structure before allocating a buffer for it.

The following code fragment loads a printer driver, calls ExtDeviceMode() (if supported) to get the full DEVMODE size, and allocates a buffer for the full DEVMODE structure:

   #include <print.h>            // Formerly DRIVINIT.H in 3.0

   HINSTANCE hDriver;            // Handle to driver
   LPFNDEVMODE ExtDeviceMode;    // Function pointer variable
   PDEVMODE pdm;                 // Pointer to DEVMODE struct
   int nSize;                    // Size of printer's DEVMODE struct

   hDriver = LoadLibrary(szDriver);
   if (hDriver < HINSTANCE_ERROR)

     return;                     // Error

   ExtDeviceMode = (LPFNDEVMODE) GetProcAddress(hDriver, "EXTDEVICEMODE");
   if (!ExtDeviceMode)

     {
     FreeLibrary(hDriver);       // ExtDeviceMode() not supported
     return;
     }

   // Get size of DEVMODE
   nSize = ExtDeviceMode(hWnd, hDriver, NULL, szDevice, szPort,
                         NULL, NULL, 0);

   // Allocate buffer for DEVMODE
   pdm = (PDEVMODE) LocalAlloc(LPTR, nSize);  // check for failure!
				

Often, it is desirable to query the driver for the current printer settings. This can be accomplished by allocating a buffer for the DEVMODE structure as above, and then calling ExtDeviceMode() a second time, passing the address of the output buffer and using the DM_OUT_BUFFER flag (also known as DM_COPY). For example:

  ExtDeviceMode(hWnd, hDriver, pdm, szDevice, szPort, NULL, NULL, DM_COPY);
				

Once the current settings are obtained, applications should use the dmFields member of the DEVMODE structure to determine which of the subsequent DEVMODE fields were initialized by the driver. Only fields with the corresponding bit set in dmFields should be used by the application; other fields are not supported by the driver.

To change printer settings, the application should not only change the appropriate fields of DEVMODE, but also indicate which fields were changed by setting the corresponding bits in dmFields. For example, the following code fragment sets landscape printing:

   DWORD dwFields;

   ...

   dwFields = pdm->dmFields;     // Save this
   pdm->dmFields = 0             // We haven't changed anything yet

   if (dwFields & DM_ORIENTATION)

     {
     pdm->dmFields |= DM_ORIENTATION;
     pdm->dmOrientation = DMORIENT_LANDSCAPE;
     }

   // Continue changing other settings
				

A driver may support modifying a certain DEVMODE field without supporting all of the available settings for that field. For example, an application cannot use ExtDeviceMode() to switch to Executive paper if the printer only supports Letter, Legal, and A4 paper sizes. Applications should use DeviceCapabilities() to query the driver for this type of information. For an example of using DeviceCapabilities(), please see the following article in the Microsoft Knowledge Base:

When the application is done modifying DEVMODE, it is necessary to call ExtDeviceMode() again to allow the driver to merge the new settings and to update the driver-dependent part of the DEVMODE structure if necessary. This is done by providing both an input and an output DEVMODE (a single buffer can be used) and by using both the DM_OUT_BUFFER and DM_IN_BUFFER (also known as DM_COPY and DM_MODIFY) flags.

   ExtDeviceMode(hWnd, hDriver, pdm, szDevice, szPort,

                 pdm, NULL, DM_IN_BUFFER|DM_OUT_BUFFER);
				

DEVMODE is now ready for use in CreateDC() or ResetDC() for printing.

Changes made to printer settings in this manner are specific to the particular print job. It is also possible to change the system-wide default settings for a printer by using DM_OUT_DEFAULT (also known as DM_UPDATE) in addition to DM_IN_BUFFER and DM_OUT_BUFFER in the final call to ExtDeviceMode() above. However, this is discouraged. It is more appropriate for the user to make changes to default settings through the Control Panel.

The following function from the EXTDEV2 sample demonstrates the above method for changing the printer orientation to landscape:

Code Sample

   #include <windows.h>
   #include <print.h>    // Formerly DRIVINIT.H in 3.0

/**************************************************************************
**
   FUNCTION: GetPrinterDC()

    PURPOSE:  Get hDC for default device according to information in the
              "device" entry in the "windows" section of WIN.INI. Set
              the device context to landscape orientation if supported.

    COMMENTS: Calls ExtDeviceMode() in printer driver to set the device
              context to landscape if supported.

              See the documentation for ExtDeviceMode() and the DEVMODE
              structure for more information.

    RETURNS:  hDC > 0 if success
              hDC = 0 if failure

***************************************************************************

*/ 

   HANDLE GetPrinterDC()
   {

    char          pPrintInfo[80];
    LPSTR         lpTemp;
    LPSTR         lpPrintType;
    LPSTR         lpPrintDriver;
    LPSTR         lpPrintPort;
    char          pmodule[32];
    HANDLE        hDriver = 0;
    HANDLE        hDevMode = 0;
    LPDEVMODE     lpDevMode = NULL;
    LPFNDEVMODE   lpfnExtDeviceMode;
    HDC           hDC;
    int           count;

    // Get the default printer information from WIN.ini.
    // The string contains the printer name, driver filename, and port.
    if (!GetProfileString("windows", "Device", (LPSTR)"", pPrintInfo, 80))
        return (NULL);

    // Parse the string we just got from WIN.INI.
    // lpPrintDriver will be the driver filename (for example, HPPCL5MS).
    // lpPrintType will be the printer name (for example, HP Laserjet III).
    // lpPrintPort will be the port (for example, LPT1:).

    lpTemp = lpPrintType = pPrintInfo;
    lpPrintDriver = lpPrintPort = 0;

    while (*lpTemp)
    {
        if (*lpTemp == ',')
        {
            *lpTemp++ = 0;
            while (*lpTemp == ' ')
                lpTemp = AnsiNext(lpTemp);
            if (!lpPrintDriver)
                lpPrintDriver = lpTemp;
            else
            {
                lpPrintPort = lpTemp;
                break;
            }
        }
        else
            lpTemp = AnsiNext(lpTemp);
    }

    // Build driver name
    wsprintf (pmodule, "%s.drv",(LPSTR)lpPrintDriver);

    // Load driver
    if ((hDriver = LoadLibrary(pmodule)) > 31)
    {
        // Get a function pointer to the ExtDeviceMode() function.
        // ExtDeviceMode() resides in the driver so we can't call it
        // directly.
        if (lpfnExtDeviceMode = (LPFNDEVMODE)GetProcAddress(hDriver,
                                               (LPSTR)"EXTDEVICEMODE"))
        {
           // Get the number of bytes in the full DEVMODE buffer.
           // This includes the device-dependent part at the end
           // of the DEVMODE struct.
           count = lpfnExtDeviceMode(0,
                                     hDriver,
                                     NULL,
                                     lpPrintType,
                                     lpPrintPort,
                                     NULL,
                                     NULL,
                                     0);    // 0 = get buffer size

           if (count != -1)
           {
               // Allocate storage for the DEVMODE buffer.
               hDevMode = GlobalAlloc(GHND, count);

               if (hDevMode)
               {
                  lpDevMode = (LPDEVMODE)GlobalLock(hDevMode);

                  // Get the current printer settings.
                  count = lpfnExtDeviceMode(0,
                                            hDriver,
                                            lpDevMode,   // Output buffer
                                            lpPrintType,
                                            lpPrintPort,
                                            NULL,
                                            NULL,
                                            DM_OUT_BUFFER); // aka DM_COPY

                  // Check to see if this printer supports changing
                  // the orientation. You should check dmFields
                  // before changing any printer setting.

                  if (lpDevMode->dmFields & DM_ORIENTATION)
                  {
                     // Pass lpDevMode as both the input and output
                     // DEVMODE buffers. It is important to pass
                     // in the full DEVMODE from the previous call
                     // to ExtDeviceMode() as the input buffer because
                     // it has been completely initialized by the
                     // driver. If you do not do this, the results
                     // are sporadic--sometimes it works and sometimes
                     // it doesn't depending on the printer driver and
                     // the setting you are trying to change.

                     // Zero out all the fields and then set the bit(s)
                     // for the field(s) we want to change.
                     lpDevMode->dmFields = 0;
                     lpDevMode->dmFields = DM_ORIENTATION;

                     // Change to landscape.
                     lpDevMode->dmOrientation = DMORIENT_LANDSCAPE;

                     // Call ExtDeviceMode() once more to allow the driver
                     // to change the device-dependent portion of the
                     // DEVMODE buffer if it needs to.

                     count = lpfnExtDeviceMode(0,
                                             hDriver,
                                             lpDevMode,  //Output buffer
                                             lpPrintType,
                                             lpPrintPort,
                                             lpDevMode,  // Input buffer
                                             NULL,
                                             DM_OUT_BUFFER | DM_IN_BUFFER);

                                             // aka DM_COPY | DM_MODIFY

                     hDC = CreateDC(lpPrintDriver,
                                    lpPrintType,
                                    lpPrintPort,
                                    (void FAR*)lpDevMode);
                  }
                  else
                  {
                     // The printer doesn't support the field you're
                     // trying to change. Just use the current printer
                     // settings.
                     hDC = CreateDC(lpPrintDriver,
                                    lpPrintType,
                                    lpPrintPort,
                                    (void FAR*)lpDevMode);
                  }
                  GlobalUnlock(hDevMode);
                  GlobalFree(hDevMode);
                  FreeLibrary(hDriver);
                  return hDC;

               } // end hDevMode
           }  // end count != -1
        } // end lpfnExtDeviceMode != 0
    } // end hDriver > 31

// If we got here, an error has occurred so finish cleanup and return NULL.

    if (hDriver)
       FreeLibrary(hDriver);

    return NULL;

   } // end GetPrinterDC
				

There are some common variations to the above method when calling ExtDeviceMode(). For example, if you just want to create a printer HDC using the current printer settings, you only need to call ExtDeviceMode() twice, as described above. The first call is to get the size of the full DEVMODE and the second call is to get the current printer settings. You then just pass the initialized LPDEVMODE to CreateDC.

ExtDeviceMode() can also be used to display the printer driver's setup dialog box. Note that this dialog box is driver-specific, and may be slightly different than the common dialog box's (COMMDLG.dll) setup dialog box, which is displayed by calling the PrintDlg function.

To display the driver's setup dialog box with the current printer settings, you only need to call ExtDeviceMode() twice as describe above but with one minor change. On the second call to ExtDeviceMode(), use the flags DM_IN_PROMPT | DM_OUT_BUFFER (also known as DM_PROMPT | DM_COPY). The DM_IN_PROMPT flag displays the dialog box and the DM_OUT_BUFFER flag copies the settings from the dialog box into the LPDEVMODE.

You can also display the driver's setup dialog box and change which dialog box controls are selected when the dialog box is displayed. For example, if you want to display the printer driver's setup dialog box but have the dialog box displayed with the landscape control selected, use the above approach with one minor change. On the third call to ExtDeviceMode(), specify the flags DM_OUT_BUFFER | DM_IN_BUFFER | DM_IN_PROMPT. DM_IN_BUFFER initializes the dialog box controls, DM_IN_PROMPT displays the setup dialog box, and DM_OUT_BUFFER copies the settings from the dialog box into the LPDEVMODE.