Choose user mode or kernel mode
Important
The modern print platform is Windows' preferred means of communicating with printers. 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 Modern print platform and 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:
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.