SetPenHook

1. 0 2.0

Installs and removes a pen packet hook. This function is typically used by system-level applications such as Control Panel applications.

BOOL SetPenHook( HKP hkpOp, LPFNRAWHOOK lpfn )

Parameters

hkpOp

Operation to be performed. This parameter can be HKP_SETHOOK to install a hook or HKP_UNHOOK to remove a function from the hook list.

lpfn

Pointer to callback function to handle pen packets.

Return Value

Returns TRUE if successful or FALSE if GetPenInput is unable to set or remove the hook. The callback function returns FALSE to cancel the processing of a pen packet.

Comments

The pen device generates approximately 100 hardware interrupts per second. At each interrupt, the device sends data to the pen driver, which organizes the data into a pen packet. Each packet contains the x- and y-coordinates of the current pen position, the time, and possibly extra OEM data such as pen pressure, angle, and so forth. The pen device may require more than one hardware interrupt to send all the information for a single packet, so the rate at which the driver sends pen packets may be less than the rate of interrupts generated by the pen hardware.

When it has created a pen packet, the driver passes it to the system, which buffers the packets in an internal queue as they arrive from the pen driver. The internal queue is informally known as the "ten-second buffer" to indicate how much data it can hold before overflowing. An application must call GetPenInput regularly to remove data from the queue.

SetPenHook enables an application to examine, modify, or cancel pen packets as they arrive from the pen driver before GetPenInput sees them.

See Also

SetPenHookCallback, SetResultsHookHREC, GetPenInput

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