Each message received by the widMessage function comes with two DWORD parameters. For some messages, one of these parameters points to a structure containing additional information from the client, or to an empty structure for the driver to fill with information for the client.
Waveform input device drivers use the structures listed in the following table. For detailed information on these structures, see the reference section later in this chapter.
PCMWAVEFORMAT | A client-filled structure providing specific information about the format for PCM waveform data. |
WAVEFORMAT | A client-filled structure providing general information about the format of waveform data. |
WAVEHDR | A client-filled structure identifying a waveform data block. |
WAVEINCAPS | A driver-filled structure providing a client with information about the capabilities of a waveform input device. |
WAVEOPENDESC | A client-filled structure providing information about opening a waveform device. |
With the exception of WAVEINCAPS, these are the same structures used by waveform output drivers.