Visualizza wikitesto di Eseguire un file audio mediante le funzioni di Alure

'''ALURE''' è una libreria di utilità per aiutare a gestire le operazioni più comuni con applicazioni ''OpenAL''. Questo include l'enumerazione e l'inizializzazione del dispositivo, il caricamento del file, e l'esecuzione. Lo scopo di questa [http://it.wikipedia.org/wiki/Application_programming_interface API] è quello di fornire funzionalità pre-organizzate per facilitare e velocizzare la programmazione dello sviluppatore.

La libreria condivisa contenente le funzioni esterne dell'API di OpenAlure, e che dovrà essere richiamata in Gambas, è attualmente la seguente: "''libalure.so.1.2.0'' ".

I tipi di file audio eseguibili sono:
* WAV;
* MP3;
* OGG.

Mostriamo di seguito un semplice codice per ottenere l'esecuzione, la pausa, la ripresa e l'arresto di file audio:
 Private isdone As Integer
 Private src As Integer
 Private streamP As Pointer
  
 Library "libalure:1.2.0"
 
 <FONT color=gray>' ''ALboolean alureInitDevice(const ALCchar * name, Const ALCint * attribs)''
 ' ''Opens the named device, creates a context with the given attributes, and sets that context as current.''
 ' ''The name and attribute list would be the same as what’s passed to alcOpenDevice and alcCreateContext respectively.''
 ' ''Returns: AL_FALSE On error.''</font>
 Private Extern alureInitDevice(name As String, attribs As String) As Boolean
 
 <FONT color=gray>' ''void alGenSources(Alsizei n, ALuint *sources)''</font>
 Private Extern alGenSources(n As Integer, sources As Pointer) In "libalut:0.1.0"
 
 <FONT color=gray>' ''alureStream* alureCreateStreamFromFile(Const ALchar * fname, ALsizei chunkLength, ALsizei numBufs, ALuint * bufs)''
 ' ''Opens a file and sets it up for streaming.  The given chunkLength is the number of bytes, or microseconds worth of bytes if alureStreamSizeIsMicroSec was last called with AL_TRUE,''
 ' ''each buffer will fill with.  ALURE will optionally generate the specified number of buffer objects, fill them with the beginning of the data,''
 ' ''then place the new IDs into the provided storage, before returning.  Requires an active context.''
 ' ''Returns: An opaque handle used To control the opened stream, Or Null On error.''</font>
 Private Extern alureCreateStreamFromFile(fname As String, chunkLength As Integer, numBufs As Integer, bufs As Pointer) As Pointer
 
 <FONT color=gray>' ''ALboolean alurePlaySourceStream(ALuint source, alureStream * stream, ALsizei numBufs, ALsizei loopcount, void( * eos_callback)(void * userdata, ALuint source), void * userdata)''
 ' ''Starts playing a stream, using the specified source ID.  A stream can only be played if it is not already playing.
 ' ''<SPAN style="text-decoration:underline">You must call alureUpdate at regular intervals to keep the stream playing, or else the stream will underrun</span>
 ' ''and cause a break in the playback until an update call can restart it.
 ' ''If an underrun occurs, the source will enter a stopped state until it is automatically restarted.  Instead, set a flag using the callback to indicate the stream being stopped.''
 ' ''"'''eos_callback'''": This callback will be called when the stream reaches the end, no more loops are pending, and the source reaches a stopped state.''
 ' ''It will also be called if an error occured and playback terminated.''
 ' ''Returns: AL_FALSE On error.''</font>
 Private Extern alurePlaySourceStream(source As Integer, strePnt As Pointer, numBufs As Integer, loopcount As Integer, eos_callback As Pointer, userdata As Pointer) As Boolean
 
 <FONT color=gray>' ''void alureUpdate(void)''
 ' ''Updates the running list of streams, and checks for stopped sources.''
 ' ''This makes sure that sources played with alurePlaySourceStream are kept fed from their associated stream, and sources played with alurePlaySource are still playing.''
 ' ''It will call their callbacks as needed.''</font>
 Private Extern alureUpdate()
 
 <FONT color=gray>' ''ALboolean alureStopSource(ALuint source, ALboolean run_callback)''
 ' ''Stops the specified source ID, and any associated stream.''
 ' ''Returns: AL_FALSE On error.''</font>
 Private Extern alureStopSource(source As Integer, run_callback As Boolean) As Boolean
 
 <FONT color=gray>' ''void alDeleteSources(ALsizei n, ALuint * sources)''
 ' ''This function deletes one or more sources.''</font>
 Private Extern alDeleteSources(n As Integer, sources As Pointer) In "libalut:0.1.0"
 
 <FONT color=gray>' ''ALboolean alureDestroyStream(alureStream * stream, ALsizei numBufs, ALuint * bufs)'
 ' ''Closes an opened stream.''
 ' ''Returns: AL_FALSE On error.''</font>
 Private Extern alureDestroyStream(strePnt As Pointer, numBufs As Integer, bufs As Pointer) As Boolean
 
 <FONT color=gray>' ''ALboolean alureShutdownDevice(void)''
 ' ''Destroys the current context and closes its associated device.''
 ' ''Returns: AL_FALSE On error.''</font>
 Private Extern alureShutdownDevice() As Boolean
 
 <FONT color=gray>' ''ALboolean alurePauseSource(ALuint source)''
 ' ''Pauses the specified source ID, and any associated stream. Returns AL_FALSE On Error.''</font>
 Private Extern alurePauseSource(source As Integer) As Boolean
 
 <FONT color=gray>' ''ALboolean alureResumeSource(ALuint source)''
 ' ''Resumes the specified source ID after being paused. Returns AL_FALSE On Error.''</font>
 Private Extern alureResumeSource(source As Integer) As Boolean
  
 
 Public Sub Button1_Click()
 
  Dim ver As Boolean
  Dim percorsoFile As String = "<FONT color=gray>''/percorso/del/file/audio''</font>"
  Dim lungh As Integer
  Dim tm As Date
 
  ver = alureInitDevice(Null, Null)
  If ver == False Then Error.Raise("Impossibile inizializzare la libreria 'Alure' !")
 
  alGenSources(1, VarPtr(src))
  
  lungh = Stat(percorsoFile).Size
  
 <FONT color=gray>' ''Se si preferisce impostare la durata in base alla dimensione del file audio da eseguire, è opportuno passare il valore del secondo parametro almeno pari alla dimensione del file:''</font>
  streamP = alureCreateStreamFromFile(percorsoFile, lungh, 0, Null)
  If streamP == 0 Then Error.Raise("Impossibile caricare il file Audio !")
 
 <FONT color=B22222>' ''Il terzo parametro della seguente funzionerappresenta il numero dei buffer utilizzati da accodare alla fonte di "OpenAL".''
 ' ''Ogni buffer verrà riempito con la lunghezza del "chunk" specificato quando il flusso è stato creato.''
 ' ''Tale valore nell'esecuzione di un file audio deve essere di almeno 2.''</font>
  ver = alurePlaySourceStream(src, streamP, <FONT color=#B22222>3</font>, 0, <FONT color=darkgreen>eos_callback</font>, Null)
  If ver = False Then Error.Raise("Impossibile eseguire il flusso dati audio !")
 
  tm = Now
 
  While isdone = 0
    Write "\r\e[0mTempo trascorso: \e[31m" & Str(Time(0, 0, 0, DateDiff(tm, Now, gb.Millisecond)))
    Wait 0.01
    alureUpdate()
  Wend
 
 <FONT color=gray>' ''Va in chiusura:''</font>
  AlureStop()
  isdone = 0
 
 End
 
  
 Private Function eos_callback(unused As Pointer, unused2 As Integer)
 
  isdone = 1
  
 End
 
 
 <FONT color=gray>' ''Mette in pausa l'esecuzione:''</font>
 Public Sub Button2_Click()
 
  alurePauseSource(src)
 
 End
 
 
 <FONT color=gray>' ''Riprende l'esecuzione:''</font>
 Public Sub Button3_Click()
 
  alureResumeSource(src)
 
 End
 
 
 <FONT color=gray>' ''Arresta l'esecuzione:''</font>
 Public Sub Button4_Click()
 
  AlureStop()
 
 End
 
 
 <FONT color=gray>' ''Arresta l'esecuzione e chiude la finestra del programma:''</font>
 Public Sub Button5_Click()
 
  isdone = 1
  Me.Close
      
 End
 
 
 Private Procedure AlureStop()
 
  alureStopSource(src, False)
  alDeleteSources(1, VarPtr(src))
  alureDestroyStream(streamP, 0, Null)
  alureShutdownDevice()
  
 End



=Riferimenti=
* https://kcat.tomasu.net/alure-docs/index/Functions.html