Creare un file Midi con le funzioni esterne del API di Libsmf
Da Gambas-it.org - Wikipedia.
Libsmf è una libreria per la lettura e la scrittura dei file Midi standard (.mid).
Per poter fruire delle sue risorse è necessario avere installata nel sistema e richiamare in Gambas la libreria dinamica condivisa: "libsmf.so.0.0.0 ".
La libreria possiede, fra l'altro, specifiche risorse per la gestione di dati Midi, anche finalizzata alla creazione di file Midi.
Mostriamo di seguito un semplice esempio per costruire un file Midi formato da una sola traccia:
Library "libsmf:0.0.0"
Public Struct smf_struct
formati As Integer
ppqn As Integer
frames_per_second As Integer
resolution As Integer
number_of_tracks As Integer
streamf As Pointer
file_buffer As Pointer
file_buffer_length As Integer
next_chunk_offset As Integer
expected_number_of_tracks As Integer
tracks_array As Pointer
last_seek_position As Float
tempo_array As Pointer
End Struct
Public Struct smf_track_struct
smf_t As Pointer
track_number As Integer
number_of_events As Integer
file_buffer As Pointer
file_buffer_length As Integer
last_status As Integer
next_event_offset As Integer
next_event_number As Integer
time_of_next_event As Integer
events_array As Pointer
user_pointer As Pointer
End Struct
Public Struct smf_event_struct
track As Pointer
event_number As Integer
delta_time_pulses As Integer
time_pulses As Integer
time_seconds As Float
track_number As Integer
midi_buffer As Pointer
midi_buffer_length As Integer
user_pointer As Pointer
End Struct
' smf_t * smf_new (void)
' Allocates new smf_t structure.
Private Extern smf_new() As Smf_struct
' smf_track_t * smf_track_new (void)
' Allocates new smf_track_t structure.
Private Extern smf_track_new() As Smf_track_struct
' void smf_add_track (smf_t *smf, smf_track_t *track)
' Appends smf_track_t to smf.
Private Extern smf_add_track(smf As Smf_struct, track As Smf_track_struct)
' smf_event_t * smf_event_new_from_pointer (void *midi_data, int len)
' Allocates an smf_event_t structure and fills it with "len" bytes copied from "midi_data".
Private Extern smf_event_new_from_pointer(midi_data As Pointer, leni As Integer) As Smf_event_struct
' void smf_track_add_event_seconds (smf_track_t *track, smf_event_t *event, double seconds)
' Adds event to the track at the time "seconds" seconds from the start of song.
Private Extern smf_track_add_event_seconds(track As Smf_track_struct, evento As Smf_event_struct, seconds As Float)
' int smf_save (smf_t *smf, const char *file_name)
' Writes the contents of SMF to the file given.
Private Extern smf_save(smf As Smf_struct, file_name As String) As Integer
' void smf_delete (smf_t *smf)
' Frees smf and all it's descendant structures.
Private Extern smf_delete(smf As Smf_struct)
Public Sub Main()
Dim sm As Smf_struct
Dim tr As Smf_track_struct
Dim ev As Smf_event_struct
Dim i As Integer
Dim nota As Byte
Dim byte_evento As New Byte[3]
Dim pausa As Float
sm = smf_new()
tr = smf_track_new()
smf_add_track(sm, tr)
For i = 0 To 15
nota = &3C + i
If i = 8 Then
' Imposta i dati necessari per il Messaggio Midi "Program Change":
byte_evento[0] = &C0
byte_evento[1] = 48
' Inserisce i dati del singolo evento Midi nella Struttura dell'evento:
ev = smf_event_new_from_pointer(byte_evento.Data, 2)
' Questo evento sarà posto nella traccia ad una posizione pari alla somma dei secondi trascorsi dall'inizio della traccia medesima, definito dal terzo parametro della seguente funzione:
smf_track_add_event_seconds(tr, ev, i)
pausa = 1.0
Endif
' Imposta i dati necessari per il Messaggio Midi "NoteOn":
byte_evento[0] = &90
byte_evento[1] = nota
byte_evento[2] = 100
Print "Note-On: "; nota
ev = smf_event_new_from_pointer(byte_evento.Data, 3)
smf_track_add_event_seconds(tr, ev, i + pausa)
' Imposta i dati necessari per il Messaggio Midi "NoteOff":
byte_evento[0] = &80
byte_evento[1] = nota
byte_evento[2] = 0
Print "Note-Off: "; nota
ev = smf_event_new_from_pointer(byte_evento.Data, 3)
smf_track_add_event_seconds(tr, ev, i + 1 + pausa)
Next
smf_save(sm, "/tmp/midi.mid")
smf_delete(sm)
End
