DOCEVENT_FILTER structure (winddiui.h)

The DOCEVENT_FILTER structure contains a list of document events to which the printer driver will respond. See DrvDocumentEvent for a complete list of the document events.

Syntax

typedef struct _DOCEVENT_FILTER {
  UINT  cbSize;
  UINT  cElementsAllocated;
  UINT  cElementsNeeded;
  UINT  cElementsReturned;
  DWORD aDocEventCall[ANYSIZE_ARRAY];
} DOCEVENT_FILTER, *PDOCEVENT_FILTER;

Members

cbSize

Spooler-supplied size, in bytes, of this structure. The spooler initializes this member to sizeof(DOCEVENT_FILTER).

cElementsAllocated

Spooler-supplied number of elements in the aDocEventCall array member. The spooler initializes this member to DOCUMENTEVENT_LAST - 1. (The DOCUMENTEVENT_LAST constant is defined in header file Winddiui.h.)

cElementsNeeded

Driver-supplied total number of elements needed in the aDocEventCall array member. The spooler initializes this member to 0XFFFFFFFF. For more information, see the following Remarks section.

cElementsReturned

Driver-supplied number of DOCUMENTEVENT_**XXX **events that it placed in the aDocEventCall array member. The spooler initializes this member to 0XFFFFFFFF. For more information, see the following Remarks section.

aDocEventCall[ANYSIZE_ARRAY]

Driver-filled array of DWORDs listing all of the DOCUMENTEVENT_XXX events to which the printer driver will respond. The spooler initializes this member to 0.

Remarks

The printer driver lists the events to which it will respond in the DOCEVENT_FILTER structure. Because this limits the number of calls to the driver the spooler needs to make, printer performance is enhanced. When the spooler makes a call to the DrvDocumentEvent DDI with its iEsc parameter set to DOCUMENTEVENT_QUERYFILTER, the spooler allocates a buffer that contains a DOCEVENT_FILTER structure, including its aDocEventCall array. The amount of memory allocated for the buffer is:

sizeof(DOCEVENT_FILTER) + sizeof(DWORD) * (DOCUMENTEVENT_LAST - 2)

After allocating a buffer that contains a DOCEVENT_FILTER structure, the spooler initializes the structure members to the following values:

Member	Initialized to
cbSize	0
cElementsAllocated	DOCUMENTEVENT_LAST - 1 The DOCUMENTEVENT_LAST constant is defined in winddiui.h.
cElementsNeeded	0XFFFFFFFF
cElementsReturned	0XFFFFFFFF
aDocEventCall	0

After the spooler has initialized the structure members to the values shown in the preceding table, it then calls DrvDocumentEvent. When this function returns, the spooler inspects the cElementsNeeded and cElementsReturned members to see if either has been changed. If the driver has written to one of these members, but not the other, the spooler interprets the unwritten-to member as having the value 0.

If the driver supports DOCUMENTEVENT_QUERYFILTER:

• If the aDocEventCall array is large enough to contain all of the DOCUMENTEVENT_XXX events the printer driver intends to place in it, the printer driver:

  • Fills the array with those events

  • Sets the cElementsReturned member to that number of events (which should be less than or equal to cElementsAllocated)

  • Leaves cElementsNeeded unchanged

  • Returns DOCUMENTEVENT_SUCCESS

In this case, the spooler uses the first cElementsReturned values in the aDocEventCall array.

The DOCUMENTEVENT_CREATEDCPRE event is treated in a special way. When the spooler calls DrvDocumentEvent with the iEsc parameter set to DOCUMENTEVENT_CREATEDCPRE, the spooler uses the return value to determine whether future calls to this function are necessary. Unlike other DOCUMENTEVENT_XXX events, the printer driver always receives calls to DrvDocumentEvent with DOCUMENTEVENT_CREATEDCPRE, whether this event is filtered out or not.

• If the aDocEventCall array is not large enough to contain all of the DOCUMENTEVENT_XXX events the printer driver intends to place in it, the printer driver should:

  • Set cElementsNeeded to the number of events to which it intends to respond (which should be greater than cElementsAllocated)

  • Leave cElementsReturned unchanged

  • Return DOCUMENTEVENT_SUCCESS

In this case, the spooler then allocates a new buffer that is sufficiently large, and then makes another call to DrvDocumentEvent with DOCUMENTEVENT_QUERYFILTER.

If the driver does not support the DOCUMENTEVENT_QUERYFILTER event, it should return DOCUMENTEVENT_UNSUPPORTED. If the driver does support DOCUMENTEVENT_QUERYFILTER, but encounters internal errors when it handles this event, it should return DOCUMENTEVENT_FAILURE. In either case, the spooler is not able to retrieve the event filter from the driver, so it continues in its behavior of calling DrvDocumentEvent for all events.

Requirements

Requirement	Value
Header	winddiui.h (include Winddiui.h)

See also

DrvDocumentEvent