Each message received by the midMessage function comes with two DWORD parameters. For some messages, one of these parameters points to a data structure containing additional information from the client, or to an empty data structure for the driver to fill with information for the client.
MIDI input device drivers use the data structures listed in the following table. See “Audio Device Driver Reference,” later in this chapter, for details on these messages.
A client-filled structure identifying a MIDI data block.
A client-filled structure providing information about opening a MIDI device.
A driver-filled structure providing a client with information about the capabilities of a MIDI input device.