Versione delle 19:07, 28 ago 2016

Canberra è una libreria che mette a disposizione funzioni e risorse utilizzate principalmente per l'esecuzione di suoni nel caso vengano sollevati eventi (click, avvio di programma, chiusura di finestre ed applicazioni, etc). Per questa ragione è progettata per eseguire file non eccessivamente grandi, aventi dimensioni non superiori a circa 65 Mbyte.
Un suono-evento viene attivato tramite libcanberra chiamando la funzione ca_context_play () su un oggetto ca_context creato in precedenza.

I formati di file audio supportati sono soltanto: .wav e .ogg .

Per utilizzare le risorse di Canberra nella propria applicazione Gambas, si dovrà richiamare la libreria dinamica condivisa: "libcanberra.so.0.2.5."

Esempio in ambiente grafico

Mostriamo di seguito un semplice codice in ambiente grafico:

Private ca As Pointer


Library "libcanberra:0.2.5"

Private Const CA_PROP_MEDIA_FILENAME As String = "media.filename"

' int ca_context_create (ca_context **c)
' Create an (unconnected) context object.
Private Extern ca_context_create(c As Pointer) As Integer

' const char * ca_strerror (int code)
' Converts a numerical error code as returned by most libcanberra API functions into a human readable error string.
Private Extern ca_strerror(code As Integer) As String
 
' int ca_context_set_driver (ca_context *c, const char *driver)
' Specify the backend driver used. "driver": the backend driver to use (e.g."alsa", "pulse", "null", ...)
Private Extern ca_context_set_driver(c As Pointer, driver As String) As Integer

' int ca_context_open (ca_context *c)
' Connect the context to the sound system.
Private Extern ca_context_open(c As Pointer) As Integer

' int ca_context_play (ca_context *c, uint32_t id, ...)
' Play one event sound
Private Extern ca_context_play(c As Pointer, id As Integer, cpmf As String, sfile As String, nl As String) As Integer

' int ca_context_destroy (ca_context *c)
' Destroy a (connected or unconnected) context object.
Private Extern ca_context_destroy(c As Pointer) As Integer


Public Sub Button1_Click()

 Dim err As Integer
 Dim nomefile As String

   nomefile = "/percorso/del/file/audio"

   err = ca_context_create(VarPtr(ca))
   If err < 0 Then Error.Raise("Impossibile creare un contesto media: " & ca_strerror(err))
   
   ca_context_set_driver(ca, "alsa")
   If err < 0 Then Error.Raise("Impossibile impostare il driver audio da utilizzare: " & ca_strerror(err))
   
   err = ca_context_open(ca)
   If err < 0 Then Error.Raise("Impossibile aprire un contesto media: " & ca_strerror(err))
   
   err = ca_context_play(ca, 0, CA_PROP_MEDIA_FILENAME, nomefile, Null)
   If err < 0 Then Error.Raise("Impossibile eseguire il file audio: " & ca_strerror(err))

End


Public Sub Button2_Click()

 Dim err As Integer

' Arresta l'esecuzione del file audio, e cancella il contesto media:
   err = ca_context_destroy(ca)
   If err < 0 Then Error.Raise("Impossibile arrestare il file audio: " & ca_strerror(err))

End

Esempio con applicazione a riga di comando

Mostriamo di seguito un semplice codice con un'applicazione a riga di comando:

Library "libcanberra:0.2.5"

Private Const CA_PROP_MEDIA_FILENAME As String = "media.filename"

' int ca_context_create (ca_context **c)
' Create an (unconnected) context object.
Private Extern ca_context_create(c As Pointer) As Integer

' const char * ca_strerror (int code)
' Converts a numerical error code as returned by most libcanberra API functions into a human readable error string.
Private Extern ca_strerror(code As Integer) As String
 
' int ca_context_set_driver (ca_context *c, const char *driver)
' Specify the backend driver used. "driver": the backend driver to use (e.g."alsa", "pulse", "null", ...)
Private Extern ca_context_set_driver(c As Pointer, driver As String) As Integer

' int ca_context_open (ca_context *c)
' Connect the context to the sound system.
Private Extern ca_context_open(c As Pointer) As Integer

' int ca_context_play (ca_context *c, uint32_t id, ...)
' Play one event sound
Private Extern ca_context_play(c As Pointer, id As Integer, cpmf As String, sfile As String, nl As String) As Integer

' int ca_context_playing(ca_context *c, uint32_t id, int *playing)
' Check if at least one sound with the specified id is still playing.
Private Extern ca_context_playing(c As Pointer, id As Integer, playing As Pointer) As Integer

' int ca_context_destroy (ca_context *c)
' Destroy a (connected or unconnected) context object.
Private Extern ca_context_destroy(c As Pointer) As Integer


Public Sub Button1_Click()

 Dim err As Integer
 Dim nomefile As String
 Dim ca As Pointer
 
   nomefile = "/percorso/del/file/audio"

   err = ca_context_create(VarPtr(ca))
   If err < 0 Then Error.Raise("Impossibile creare un contesto media: " & ca_strerror(err))
   
   ca_context_set_driver(ca, "alsa")
   If err < 0 Then Error.Raise("Impossibile impostare il driver audio da utilizzare: " & ca_strerror(err))
   
   err = ca_context_open(ca)
   If err < 0 Then Error.Raise("Impossibile aprire un contesto media: " & ca_strerror(err))
   
   err = ca_context_play(ca, 0, CA_PROP_MEDIA_FILENAME, nomefile, Null)
   If err < 0 Then Error.Raise("Impossibile eseguire il file audio: " & ca_strerror(err))
   
' Il ciclo consente l'esecuzione del file audio. Si esce dal ciclo, quando l'esecuzione è terminata.
   Do 
     ca_context_playing(ca, 0, VarPtr(eseg))
   Loop Until Int(eseg) = 0
   
   ca_context_destroy(ca)

End

Riferimenti

• https://developer.gnome.org/libcanberra/unstable/libcanberra-canberra.html
• http://sourcecodebrowser.com/libcanberra/0.3/index.html
• http://0pointer.de/lennart/projects/libcanberra
• http://libcanberra.sourcearchive.com/documentation/0.15/main.html