WIDM_OPEN

This message is used in an MMDRV_MESSAGE_PARAMS structure passed to the WAV_IOControl function to request a waveform input driver to open an instance of a specified device.

Parameters

uDeviceId

Device identifier—0, 1, 2, and so on—for the target device.

uMsg

Specifies this message.

dwUser

Specifies a pointer to a location to receive the device instance identifier.

dwParam1

Specifies a pointer to a WAVEOPENDESC structure containing the client’s device handle, notification target, and instance identifier.

dwParam2

Contains one or both of the following flags:

WAVE_FORMAT_DIRECT

Data compression and decompression should take place in hardware.

WAVE_FORMAT_QUERY

The driver indicates whether or not it supports the specified format.

Return Values

MMSYSERR_NOERROR indicates success. Otherwise, the driver returns one of the error values MMSYSERR or WAVERR declared in the Mmsystem.h header file.

Remarks

The ACM sends this message by calling the audio driver’s WAV_IOControl entry point through the DeviceIoControl function.

The driver assigns a device instance identifier and returns it in the location pointed to by the parameter dwUser. The driver receives this value as the input parameter dwUser to all other wave input driver messages.

The driver determines the number of clients that it enables to use a particular device. If a device is opened by the maximum number of clients, it returns MMSYSERR_ALLOCATED for subsequent open requests.

The flag WAVE_FORMAT_DIRECT is meant for use with a wave mapper. If the flag is set in dwParam2, the driver does not call the ACM to handle compression and decompression operations—the caller sets that flag to indicate that the driver uses the hardware to perform these operations directly. If the hardware is not capable of performing the operations, the driver returns MMSYSERR_NOTSUPPORTED when WAVE_FORMAT_DIRECT is set.

If the WAVE_FORMAT_QUERY flag is set in dwParam2, the driver does not open the device. Instead, it determines whether it supports the format specified by the lpFormat member of WAVEOPENDESC. If the driver supports the requested format, it returns MMSYSERR_NOERROR. Otherwise, the driver returns WAVERR_BADFORMAT.

If the open operation succeeds, the Wave API Manager sends the ACM the WIM_OPEN message by calling the PostThreadMessage function on the callback thread handle.