Alsa e Gambas: Invio dei dati senza connessione della porta del programma con il Softsynth
Da Gambas-it.org - Wikipedia.
Versione del 9 set 2020 alle 13:00 di Vuott (Discussione | contributi)
Per inviare utilmente dati Midi ad altro Client di ALSA, non è necessario connettere i due Client (l'applicativo Gambas ed il Softsynth) mediante la funzione snd_seq_connect_to(), purché si presti attenzione ad alcuni elementi che integrano due casi.
1° caso
Nel primo caso il codice dovrà prevedere:
- la presenza della funzione di ALSA snd_seq_alloc_queue();
- il membro .queue della Struttura relativa agli eventi Midi dovrà essere posto a zero;
- al membro .dest_id e a quello .dest_port della Struttura relativa agli eventi Midi dovranno essere rispettivamente assegnati i valori dell'Id e della porta del Client (Softsynth), al quale l'applicativo Gambas dovrà inviare i dati Midi.
Mostriamo un esempio pratico:
Private sndseq As Pointer Private Const cl_dest As Byte = 128 Private Const po_dest As Byte = 0 Library "libasound:2" Public Struct snd_seq_event_t type As Byte flags As Byte tag As Byte queue As Byte tick_time As Integer real_time As Integer source_client As Byte source_port As Byte dest_client As Byte dest_port As Byte channel As Byte note As Byte velocity As Byte off_velocity As Byte param As Integer value As Integer End Struct Private Const SND_SEQ_OPEN_OUTPUT As Integer = 1 Private Const SND_SEQ_PORT_CAP_READ As Integer = 1 Private Const SND_SEQ_PORT_TYPE_MIDI_GENERIC As Integer = 2 Private Const SND_SEQ_PORT_TYPE_APPLICATION As Integer = 1048576 Private Enum SND_SEQ_EVENT_NOTEON = 6, SND_SEQ_EVENT_NOTEOFF, SND_SEQ_EVENT_KEYPRESS, SND_SEQ_EVENT_CONTROLLER = 10, SND_SEQ_EVENT_PGMCHANGE ' int snd_seq_open (snd_seq_t **handle, const char * name, int streams, int mode) ' Open the ALSA sequencer. Private Extern snd_seq_open(handle As Pointer, name As String, streams As Integer, mode As Integer) As Integer ' const char * snd_strerror (int errnum) ' Returns the message for an error code. Private Extern snd_strerror(err As Integer) As Pointer ' int snd_seq_create_simple_port (snd_seq_t *seq, const char *name, unsigned int caps, unsigned int type) ' Create a port - simple version. Private Extern snd_seq_create_simple_port(seq As Pointer, name As String, caps As Integer, type As Integer) As Integer ' int snd_seq_alloc_queue (snd_seq_t *handle) ' Allocate a queue. Private Extern snd_seq_alloc_queue(handle As Pointer) As Integer ' int snd_seq_event_output (snd_seq_t *handle, snd_seq_event_t *ev) ' Output an event. Private Extern snd_seq_event_output(handle As Pointer, ev As Snd_seq_event_t) ' int snd_seq_drain_output (snd_seq_t * seq) ' Drain output buffer to sequencer. Private Extern snd_seq_drain_output(seq As Pointer) As Integer ' int snd_seq_close (snd_seq_t *handle) ' Close the sequencer. Private Extern snd_seq_close(handle As Pointer) As Integer Public Sub Main() Dim note As Byte[] = [60, 62, 64, 65, 67, 69, 71, 72] Dim porta_source, b As Byte Dim ev As New Snd_seq_event_t porta_source = Connessione() With ev .queue = 0 .source_client = 0 .source_port = porta_source .dest_client = cl_dest .dest_port = po_dest .channel = 0 End With program_change(ev, 48) For b = 0 To note.Max Note_On(ev, note[b]) Wait 1 Note_Off(ev, note[b]) Next snd_seq_close(sndseq) End Private Function Connessione() As Byte Dim rit, porta As Integer rit = snd_seq_open(VarPtr(sndseq), "default", SND_SEQ_OPEN_OUTPUT, 0) If rit < 0 Then Error.Raise("Impossibile aprire il subsistema 'seq' di ALSA: " & String@(snd_strerror(rit))) porta = snd_seq_create_simple_port(sndseq, "porta_", SND_SEQ_PORT_CAP_READ, SND_SEQ_PORT_TYPE_MIDI_GENERIC Or SND_SEQ_PORT_TYPE_APPLICATION) If porta < 0 Then Error.Raise("Impossibile creare la porta di uscita dati ALSA !") snd_seq_alloc_queue(sndseq) Return porta End Private Procedure program_change(ev_prch As Snd_seq_event_t, strum As Integer) With ev_prch .type = SND_SEQ_EVENT_PGMCHANGE .value = strum End With InviaEvento(ev_prch) End Private Procedure Note_On(ev_nton As Snd_seq_event_t, nota As Byte) With ev_nton .type = SND_SEQ_EVENT_NOTEON .note = nota .velocity = 64 End With InviaEvento(ev_nton) End Private Procedure Note_Off(ev_ntoff As Snd_seq_event_t, nota As Byte) With ev_ntoff .type = SND_SEQ_EVENT_NOTEOFF .note = nota .velocity = 0 End With InviaEvento(ev_ntoff) End Private Procedure InviaEvento(evento As Snd_seq_event_t) snd_seq_event_output(sndseq, evento) snd_seq_drain_output(sndseq) End
2° caso
Nel secondo caso si dovrà tenere conto di quanto segue:
- viene eliminata la funzione esterna specifica di Alsa per la creazione della porta del Client applicativo;
- al membro .queue della Struttura relativa agli eventi Midi dovrà essere assegnato il valore della Costante Alsa "SND_SEQ_QUEUE_DIRECT" (253);
- al membro .dest_id e a quello .dest_port della Struttura relativa agli eventi Midi dovranno essere rispettivamente assegnati i valori dell'Id e della porta del Client (Softsynth), al quale l'applicativo Gambas dovrà inviare i dati Midi.
Mostriamo un esempio pratico:
Library "libasound:2" Public Struct snd_seq_event_t type As Byte flags As Byte tag As Byte queue As Byte tick_time As Integer real_time As Integer source_client As Byte source_port As Byte dest_client As Byte dest_port As Byte channel As Byte note As Byte velocity As Byte off_velocity As Byte param As Integer value As Integer End Struct Private Const SND_SEQ_OPEN_OUTPUT As Integer = 1 Private Const SND_SEQ_QUEUE_DIRECT As Byte = 253 Private Enum SND_SEQ_EVENT_NOTEON = 6, SND_SEQ_EVENT_NOTEOFF, SND_SEQ_EVENT_KEYPRESS, SND_SEQ_EVENT_CONTROLLER = 10, SND_SEQ_EVENT_PGMCHANGE ' int snd_seq_open (snd_seq_t **handle, const char * name, int streams, int mode) ' Open the ALSA sequencer. Private Extern snd_seq_open(handle As Pointer, name As String, streams As Integer, mode As Integer) As Integer ' const char * snd_strerror (int errnum) ' Returns the message for an error code. Private Extern snd_strerror(err As Integer) As Pointer ' int snd_seq_event_output (snd_seq_t *handle, snd_seq_event_t *ev) ' Output an event. Private Extern snd_seq_event_output(handle As Pointer, ev As Snd_seq_event_t) ' int snd_seq_drain_output (snd_seq_t * seq) ' Drain output buffer to sequencer. Private Extern snd_seq_drain_output(seq As Pointer) As Integer ' int snd_seq_close (snd_seq_t *handle) ' Close the sequencer. Private Extern snd_seq_close(handle As Pointer) As Integer Public Sub Main() Dim sndseq As Pointer Dim note As Byte[] = [60, 62, 64, 65, 67, 69, 71, 72] Dim b As Byte Dim evento As New Snd_seq_event_t sndseq = Connessione() With evento .queue = SND_SEQ_QUEUE_DIRECT .dest_client = 128 .dest_port = 0 .channel = 0 End With program_change(sndseq, evento, 48) For b = 0 To note.Max Note_On(sndseq, evento, note[b]) InviaEvento(sndseq) Wait 1 Note_Off(sndseq, evento, note[b]) InviaEvento(sndseq) Next snd_seq_close(sndseq) End Private Function Connessione() As Pointer Dim snd As Pointer Dim rit, porta As Integer rit = snd_seq_open(VarPtr(snd), "default", SND_SEQ_OPEN_OUTPUT, 0) If rit < 0 Then Error.Raise("Impossibile aprire il subsistema 'seq' di ALSA: " & String@(snd_strerror(rit))) Return snd End Private Procedure program_change(pc_seq As Pointer, ev_prch As Snd_seq_event_t, strum As Integer) With ev_prch .type = SND_SEQ_EVENT_PGMCHANGE .value = strum End With ' Inserisce l'evento "Program_Change" nel buffer: snd_seq_event_output(pc_seq, ev_prch) End Private Procedure Note_On(nto As Pointer, ev_nton As Snd_seq_event_t, nota As Byte) With ev_nton .type = SND_SEQ_EVENT_NOTEON .note = nota .velocity = 64 End With ' Inserisce l'evento "Note_On" nel buffer: snd_seq_event_output(nto, ev_nton) End Private Procedure Note_Off(ntf As Pointer, ev_ntoff As Snd_seq_event_t, nota As Byte) With ev_ntoff .type = SND_SEQ_EVENT_NOTEOFF .note = nota .velocity = 0 End With ' Inserisce l'evento "Note_Off" nel buffer: snd_seq_event_output(ntf, ev_ntoff) End Private Procedure InviaEvento(seqP As Pointer) ' Invia l'intero contenuto del buffer ad Alsa: snd_seq_drain_output(seqP) End
Esempio più essenziale per invio dati Midi
Mostriamo ora la modalità più breve ed essenziale per inviare ad altro Client di Alsa alcuni eventi Midi, e nella quale non è prevista la creazione di porte del nostro Client applicativo:
Library "libasound:2" Public Struct snd_seq_event_t type As Byte flags As Byte tag As Byte queue As Byte tick_time As Integer real_time As Integer source_client As Byte source_port As Byte dest_client As Byte dest_port As Byte channel As Byte note As Byte velocity As Byte off_velocity As Byte param As Integer value As Integer End Struct Private Const SND_SEQ_OPEN_OUTPUT As Integer = 1 Private Enum SND_SEQ_EVENT_NOTEON = 6, SND_SEQ_EVENT_NOTEOFF Private Const SND_SEQ_QUEUE_DIRECT As Byte = 253 ' int snd_seq_open (snd_seq_t **handle, const char * name, int streams, int mode) ' Open the ALSA sequencer. Private Extern snd_seq_open(handle As Pointer, name As String, streams As Integer, mode As Integer) As Integer ' const char * snd_strerror (int errnum) ' Returns the message for an error code. Private Extern snd_strerror(err As Integer) As Pointer ' int snd_seq_event_output_direct (snd_seq_t *handle, snd_seq_event_t *ev) ' Output an event directly to the sequencer NOT through output buffer. Private Extern snd_seq_event_output_direct(handle As Pointer, ev As Snd_seq_event_t) As Integer ' int snd_seq_close (snd_seq_t *handle) ' Close the sequencer. Private Extern snd_seq_close(handle As Pointer) As Integer Public Sub Main() Dim seq As Pointer Dim evento As New Snd_seq_event_t Dim rit As Integer snd_seq_open(VarPtr(seq), "default", SND_SEQ_OPEN_OUTPUT, 0) If rit < 0 Then Error.Raise("Impossibile aprire il subsistema 'seq' di ALSA: " & String@(snd_strerror(rit))) With evento .type = SND_SEQ_EVENT_NOTEON .queue = SND_SEQ_QUEUE_DIRECT .dest_client = 128 .dest_port = 0 .channel = 0 .note = 64 .velocity = 100 End With snd_seq_event_output_direct(seq, evento) Wait 1 evento.type = SND_SEQ_EVENT_NOTEOFF evento.velocity = 0 snd_seq_event_output_direct(seq, evento) snd_seq_close(seq) End