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− | Mostreremo di seguito il codice di un semplice Client Midi di Alsa capace di ricevere dati Midi (a titolo esemplificativo sono stati individuati i quattro tipi più importanti e frequenti) da un altro Client di Alsa (ad esempio da una tastiera Midi esterna) e di inviarli immediatamente ad un altro Client (ad esempio ad un ''softsynth'' per l'ascolto sonoro).
| + | #REDIRECT [[ALSA_e_Gambas:_Esempio_di_semplice_Client_Midi_di_Alsa_in_ricezione_ed_invio_dati]] |
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− | Al terzo parametro della funzione ''snd_seq_open()'', necessaria per l'apertura del subsistema ''Seq'' di Alsa, va inserita la costante ''SND_SEQ_OPEN_DUPLEX'' per consentire il flusso di dati sia in Entrata che in Uscita.
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− | <BR>I dati Midi ricevuti sono assegnati ad una variabile di tipo ''Struttura'' organizzata secondo lo schema tipico di un "''Evento''" Midi Alsa.
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− | Dopo l'avvio del ''softsynth'' e del seguente applicativo, sarà necessario connettere via Alsa la tastiera Midi ed ''softsynth'' al presente applicativo Midi rispettivamente in entrata ed in uscita.
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− | Public Struct snd_seq_event_t
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− | type As Byte <FONT color=gray>' ''byte n° 0''</font>
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− | flag As Byte
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− | tag As Byte
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− | queue As Byte
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− | timestamp1 As Integer
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− | timestamp2 As Integer
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− | source_id As Byte
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− | source_porta As Byte
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− | dest_id As Byte
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− | dest_porta As Byte
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− | channel As Byte <FONT color=gray>' ''byte n° 16''</font>
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− | note As Byte
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− | velocity As Byte
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− | off_velocity As Byte
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− | parametro As Integer <FONT color=gray>' ''byte n° 20''</font>
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− | valore As Integer <FONT color=gray>' ''byte n° 24''</font>
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− | End Struct
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− | Library "libasound:2.0.0"
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− | Private Const SND_SEQ_OPEN_DUPLEX As Integer = 3
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− | Private Const SND_SEQ_PORT_CAP_WRITE As Integer = 2
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− | Private Const SND_SEQ_PORT_CAP_SUBS_WRITE As Integer = 64
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− | Private Const SND_SEQ_PORT_CAP_READ As Integer = 1
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− | Private Const SND_SEQ_PORT_CAP_SUBS_READ As Integer = 32
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− | Private Const SND_SEQ_PORT_TYPE_APPLICATION As Integer = 1048576
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− | Private Const SND_SEQ_ADDRESS_UNKNOWN As Byte = 253
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− | Private Const SND_SEQ_ADDRESS_SUBSCRIBERS As Byte = 254
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− | Private Const SND_SEQ_EVENT_NOTEON As Byte = 6
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− | Private Const SND_SEQ_EVENT_NOTEOFF As Byte = 7
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− | Private Const SND_SEQ_EVENT_CONTROLLER As Byte = 10
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− | Private Const SND_SEQ_EVENT_PGMCHANGE As Byte = 11
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− | <FONT color=gray>' ''const char * snd_strerror(int errnum)''
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− | ' ''Returns the message for an error code.''</font>
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− | Private Extern snd_strerror(errnum As Integer) As String
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− |
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− | <FONT color=gray>' ''int snd_seq_open (snd_seq_t **handle, const char *name, int streams, int mode)
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− | ' ''Open the ALSA sequencer.''</font>
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− | Private Extern snd_seq_open(handle As Pointer, name As String, streams As Integer, mode As Integer) As Integer
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− |
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− | <FONT color=gray>' ''int snd_seq_set_client_name(snd_seq_t* seq, const char* name)''
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− | ' ''Set client name.''</font>
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− | Private Extern snd_seq_set_client_name(handle As Pointer, name As String) As Integer
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− |
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− | <FONT color=gray>' ''int snd_seq_client_id (snd_seq_t *seq)''
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− | ' ''Get the client id.''</font>
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− | Private Extern snd_seq_client_id(handle As Pointer) As Integer
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− |
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− | <FONT color=gray>' ''int snd_seq_create_simple_port(snd_seq_t *seq, const char *name, unsigned int caps, unsigned int type)''
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− | ' ''Create a port - simple version.''</font>
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− | Private Extern snd_seq_create_simple_port(handle As Pointer, name As String, caps As Integer, type As Integer) As Integer
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− |
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− | <FONT color=gray>' ''int snd_seq_event_input(snd_seq_t *handle, snd_seq_event_t **ev)''
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− | ' ''Retrieve an event from sequencer.''</font>
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− | Private Extern snd_seq_event_input(handle As Pointer, ev As Snd_seq_event_t) As Integer
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− |
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− | <FONT color=gray>' ''int snd_seq_event_output_direct (snd_seq_t *handle, snd_seq_event_t *ev)''
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− | ' ''Output an event directly to the sequencer NOT through output buffer.''</font>
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− | Private Extern snd_seq_event_output_direct(handle As Pointer, ev As Snd_seq_event_t) As Integer
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− | '''Public''' Sub Main()
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− | Dim seq As Pointer
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− | Dim idportaE, idportaU, err, id As Integer
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− | err = snd_seq_open(VarPtr(seq), "default", SND_SEQ_OPEN_DUPLEX, 0)
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− | If err < 0 Then Error.Raise("Impossibile inizializzare il subsistema 'seq' di ALSA: " & snd_strerror(err))
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− | Print "Apertura del dispositivo 'seq' di Alsa: regolare\nNome del dispositivo 'seq': "; "'default'"
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− | err = snd_seq_set_client_name(seq, "Sequencer dimostrativo di ALSA")
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− | If err < 0 Then Error.Raise("Impossibile assegnare un nome al Client applicativo di ALSA: " & snd_strerror(err))
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− | id = snd_seq_client_id(seq)
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− | Print "Numero identificativo del sequencer dimostrativo: "; id
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− | idportaE = snd_seq_create_simple_port(seq, "Porta di Entrata del sequencer dimostrativo di ALSA", SND_SEQ_PORT_CAP_WRITE Or SND_SEQ_PORT_CAP_SUBS_WRITE, SND_SEQ_PORT_TYPE_APPLICATION)
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− | If idportaE < 0 Then Error.Raise("Impossibile creare una porta del Client applicativo di ALSA: " & snd_strerror(err))
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− | Print "Numero identificativo della porta di Entrata: "; idportaE
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− | idportaU = snd_seq_create_simple_port(seq, "Porta di Uscita del sequencer dimostrativo di ALSA", SND_SEQ_PORT_CAP_READ Or SND_SEQ_PORT_CAP_SUBS_READ, SND_SEQ_PORT_TYPE_APPLICATION)
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− | If idportaU < 0 Then Error.Raise("Impossibile creare una porta del Client applicativo di ALSA: " & snd_strerror(err))
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− | Print "Numero identificativo della porta di Uscita: "; idportaU
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− | Print
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− | intercettaMessaggiMidi(seq, id, idportaU)
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− | '''End'''
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− | '''Public''' Procedure intercettaMessaggiMidi(seqiM As Pointer, idC As Integer, portEx As Integer)
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− | Dim ev As Pointer
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− | Dim midi@ As Snd_seq_event_t
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− | While True
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− | snd_seq_event_input(seqiM, VarPtr(ev))
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− | midi@ = ev
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− | With midi@
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− | Select Case midi@.type
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− | Case SND_SEQ_EVENT_NOTEON
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− | Print "Evento 'NoteOn' sul canale: "; .channel, .note, .velocity
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− | Case SND_SEQ_EVENT_NOTEOFF
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− | Print "Evento 'NoteOff' sul canale: "; .channel, .note, .velocity
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− | Case SND_SEQ_EVENT_CONTROLLER
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− | Print "Evento 'Control' sul canale: "; .channel, .parametro, .valore
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− | Case SND_SEQ_EVENT_PGMCHANGE
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− | Print "Evento 'Program Change' sul canale: "; .channel, .valore
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− | End Select
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− | .source_id = idC
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− | .source_porta = portEx
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− | .dest_id = SND_SEQ_ADDRESS_SUBSCRIBERS
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− | .dest_porta = SND_SEQ_ADDRESS_UNKNOWN
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− | End With
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− | snd_seq_event_output_direct(seqiM, midi@)
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− | Wend
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− | '''End'''
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