Adding PrintTicket support to a monolithic driver
I’ve been getting a number of questions lately about various aspects of adding support for PrintTicket to a monolithic driver. In response, I’ve put together a short ‘how to article that I hope you’ll find helpful. This walkthrough is basically geared towards getting a minimal implementation up and running, though there will be much more work involved in making a complete implementation.
First, you're going to need to provide implementations for a couple of COM-style classes. One class is the class factory, and the other is the class that actually implements the PrintTicket support. The class that implements the PrintTicket support should implement the interface IPrintTicketProvider. The class factory should implement support for IClassFactory. Second, you need a DLL method called DllGetClassObject that returns your class factory. The DllGetClassObject routine should return an instance of your class factory object in response to a query for CLSID_PTPROVIDER. Definitions for both IPrintTicketProvider and CLSID_PTPROVIDER can both be found in the Vista DDK in a file called 'prdrvcom.h'.
Your driver should not register the class in the Windows Registry as a COM server. All drivers are implementing the same class ID. The OS support for PrintTicket will directly query the driver's config DLL to obtain the interface. It will never attempt to access your provider implementation via CoCreateInstance. In fact, you don't even need a DllRegisterServer method.
When implementing the provider, you're going to need to support a few routines just to get through the PTOpenProvider API:
- GetPrintCapabilities (releases prior to Beta 2)
GetSupportedVersions(THIS_ HANDLE hPrinter,
if ( (*ppVersions = (INT*)CoTaskMemAlloc(sizeof(INT))) != NULL)
(*ppVersions) = 1; // Version 1
*pcVersions = 1; // 1 supported version
That's it. Because v.1 is the only version that exists for now, this implementation should work for any PrintTicket provider being written at this time.
BindPrinter is a bit more involved. There are a number of parameters that the driver needs to handle.
BindPrinter( THIS_ HANDLE hPrinter,
- hPrinter is a standard printer handle given to the provider. The provider can use if for the lifetime of the provider object, but the plug-in does not need to release the handle. The system will take care of that.
- Version indicates the version of PrintSchema support that the system is requesting. This should be one of the versions that the provider indicated support for in GetSupportedVersions. If it’s not, the provider should fail the bind call. In practical terms, this means if it's not '1', it's time to return failure.
- pOptions allows the provider to control behavior that the system will provider on behalf of the PrintTicketProvider object. At the time of writing, the only allowed option is to enable / disable support for encoding a base64 representation of the DEVMODE in the PrintTicket. If you're just starting your implementation, I recommend you leave this on. It'll retain any DEVMODE settings that you haven't added PrintTicket support for. Only turn this off if you're confident that everything that your driver can do is fully represented and configurable from a PrintTicket.
- pDevModeFlags is an out parameter that indicates which features in the public DEVMODE your PrintTicket provider has support for. The values are the same as the values used in the dmFields member of the DEVMODE structure. If your provider indicates support for a field, the shim will not provide any default conversion handling. If you support all of your DEVMODE handling in your PrintTicket code, just set this value to 0xFFFFFFFF to disable all of the shim'd default conversions.
- pcNamespaces – out parameter, set value to 0
- ppNamespaces – out parameter, set value to NULL
This routine provides the default namespace that the shim handling will use if it needs to put a feature or option in a driver-private namespace (such as the base64 encoding of the DEVMODE). For a discussion of how to pick a namespace, see my previous post here: http://blogs.msdn.com/benkuhn/archive/2005/12/29/508056.aspx
A typical implementation might look something like this:
*pDefaultNamespace = SysAllocString(TEXT("http://schemas.fabrikam.com/printers/seriesA/v.1.0"));
This routine is a bit harder to implement. You're going to need to return valid PrintCapabilities content. To get your provider up & running, it doesn't need to have much, but you won't be able to support any features in your PrintTicket that aren't exposed in the PrintCapabilities, so you'll need to keep coming back to this routing to add features to the capabilities document as you add features to other routines.
The details of implementing this routine are best saved for another article, at least for now. If you're running on Vista Beta 2, you won't see this method called during PTOpenProvider. However, on releases prior to Beta 2, you will need to implement this to get past the PTOpenProviderCall.
One important thing to make note of here is that the system does not populate anything in the PrintCapabilities. This means that even for featuers that the system converts between DEVMODE PrintTicket, the driver needs to supply the corresponding PrintCapabilities. The reason for this is that the shim's method of populating this data is to call the win32 DeviceCapabilities API, and it needs to do this many times, which can cause performance issues. The driver can implement the support internally with much more efficiency.