WIDM_OPEN

See also WIDM_CLOSE, WAVEOPENDESC

Sent to a waveform input device driver to allocate a specified device for use by a client application.

The return value is an error code, or zero (MMSYSERR_NOERROR) if the operation is successful. Possible error codes are:

MMSYSERR_NOTENABLED	The driver failed to load or initialize.
MMSYSERR_ALLOCATED	The device is already allocated by the maximum number of clients the driver supports, or the device cannot be opened because of system resource limitations other than memory.
MMSYSERR_NOMEM	The device cannot be opened because of a failure allocating or locking memory.
WAVERR_BADFORMAT	The device cannot be opened using the specified data format.

DWORD dwParam1

Specifies a far pointer to a WAVEOPENDESC structure. This structure contains additional information for the driver such as the waveform data format, instance data from the client, and a callback for the client.

DWORD dwParam2

Specifies option flags for opening the device.

WAVE_FORMAT_QUERY	If this flag is specified, the device driver determines if it supports the format specified by lpFormat in the WAVEOPENDESC structure, but does not actually open the device. If the driver supports the requested format, it should return MMSYSERR_NOERROR, otherwise it should return WAVERR_BADFORMAT.
CALLBACK_EVENT	If this flag is specified, dwCallback in the WAVEOPENDESC structure is assumed to be the handle of an event.
CALLBACK_FUNCTION	If this flag is specified, dwCallback in the WAVEOPENDESC structure is assumed to be the address of a callback function.
CALLBACK_THREAD	If this flag is specified, dwCallback in the WAVEOPENDESC structure is assumed to be a handle of a thread.
CALLBACK_WINDOW	If this flag is specified, dwCallback in the WAVEOPENDESC structure is assumed to be a window handle.

It is up to the driver to determine the number of clients allowed to use a particular device. Once a device is opened for the maximum number of clients the driver supports, the driver should return MMSYSERR_ALLOCATED for any additional open requests. If the open operation is successful, the driver should use the DriverCallback function to send the client a WIM_OPEN message.