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Choose user mode or kernel mode

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Important

We recommend that you use Microsoft's IPP inbox class driver, along with Print Support Apps (PSA), to customize the print experience in Windows 10 and 11 for printer device development.

For more information, see the Print support app design guide.

User-mode execution of printer graphics DLLs provides the following advantages over kernel-mode execution:

  • Unlimited stack space.

  • Access to Win32 APIs.

  • Less potential for causing system crashes.

  • Easier debugging, with user-mode debuggers.

  • Better floating-point capabilities, since use of graphics DDI floating-point functions isn't required.

  • Ability to call any customized, vendor-supplied user-mode DLLs that aren't part of the described Microsoft Windows 2000 and later printer driver architecture

In Windows Vista, it isn't possible to install a kernel-mode printer driver. If an application attempts to do so, the AddPrinterDriver and AddprinterDriverEx functions (described in the Windows SDK documentation) will fail with the error code ERROR_KM_DRIVER_BLOCKED.

The following table shows allowed printer driver execution modes:

Operating system version Allowed execution mode of printer graphics DLL
Windows NT 4.0 kernel
Windows 2000 user or kernel
Windows XP and Server 2003 kernel mode available for existing printers; user mode required for new printer installations
Windows Vista user

Using the graphics DDI in user mode

A user-mode printer graphics DLL isn't limited to calling the GDI Support Services and other Eng-prefixed graphics DDI callback functions. However, there are some rules that must be followed:

  • Like kernel-mode graphics DLLs, user-mode graphics DLLs must call the graphics DDIs that create or modify a drawing surface. These callback functions are the GDI Support Services, and calling Win32 equivalents of these drawing functions isn't allowed.

    For user-mode DLLs, calls to these drawing callback functions are intercepted by the user-mode GDI client, which then passes the calls to GDI's kernel-mode graphics rendering engine (GRE).

  • The following list of Eng-prefixed graphics DDI functions can't be called by user-mode DLLs:

    EngCreatePath

    EngGetType1FontList

    EngMapModule

    EngDebugBreak

  • User-mode printer graphics DLLs can continue to use graphics DDI functions for GDI floating-point services.

Converting an existing printer graphics DLL to user mode

If you've previously developed a printer graphics DLL that executes in kernel mode, you can convert the DLL to user-mode execution. To convert, add a DrvQueryDriverInfo function to the DLL, and then follow the rules for building a printer graphics DLL.

Creating a new printer graphics DLL in user mode

To develop a new printer graphics DLL that executes in user mode, you can continue to use all the graphics DDI functions used by kernel-mode DLLs. However, you also have the following options:

  • For Eng-prefixed functions that have exact Win32 equivalents, it's recommended that you call the Win32 functions. The following table lists these Eng-prefixed functions, along with their Win32 equivalents.

    Eng-prefixed function Win32 equivalent
    EngAllocMem HeapAlloc
    EngAllocUserMem HeapAlloc
    EngEnumForms EnumForms
    EngFreeMem HeapFree
    EngFreeUserMem HeapFree
    EngFindImageProcAddress GetProcAddress
    EngGetForm GetForm
    EngGetLastError GetLastError
    EngGetPrinter GetPrinter
    EngGetPrinterData GetPrinterData
    EngGetPrinterDriver GetPrinterDriver
    EngLoadImage LoadLibrary
    EngMulDiv MulDiv
    EngSetLastError SetLastError
    EngSetPrinterData SetPrinterData
    EngUnloadImage FreeLibrary
    EngWritePrinter WritePrinter

  • For Eng-prefixed functions that correspond to Win32 functions with similar functionality, it's also recommended that you call the Win32 functions. The following table lists several of these Eng-prefixed functions, together with their Win32 counterparts.

    Eng-prefixed function Win32 equivalent
    EngAcquireSemaphore EnterCriticalSection
    EngCreateSemaphore Allocate a CRITICAL_SECTION object, and initialize it using a call to the Win32 InitializeCriticalSection function.
    EngDeleteSemaphore DeleteCriticalSection
    EngFindResource FindResource
    EngFreeModule FreeLibrary
    EngLoadModule LoadLibrary
    EngMultiByteToWideChar MultiByteToWideChar
    EngQueryLocalTime GetLocalTime
    EngReleaseSemaphore ReleaseSemaphore
    EngWideCharToMultiByte WideCharToMultiByte

  • For functions that create or modify a drawing service, new drivers must continue to call GDI support services and not their Win32 equivalents.

  • Instead of using graphics DDI functions for GDI Floating-Point Services, you can use the FLOAT data type.