Visualizza wikitesto di Mostrare un'immagine con funzioni del API di GStreamer

La risorsa '''GStreamer''' dà la possibilità anche semplicemente di caricare un file immagine e mostrarne il contenuto.

Per poter fruire delle risorse di ''GStreamer'', sarà necessario avere installata nel sistema e richiamare in Gambas la libreria condivisa: "''libgstreamer-1.0:0.2407.0'' ".

L'immagine potrà essere mostrata in una finestra automaticamente creata dalla risorsa ''GStreamer'', oppure in una ''DrawingArea''.


==Immagine mostrata in una finestra creata da ''GStreamer''==
Di seguito mostreremo un esempio, nel quale verrà caricato un file immagine in un'applicazione ''a riga di comando''. L'immagine sarà mostrata in una finestra creata da ''GStreamer''.
 Private immago As Pointer
 Private ciclo As Byte = 1
 
 
 Library "libgstreamer-1.0:0.2407.0"
 
 Private Enum GST_STATE_VOID_PENDING = 0, GST_STATE_NULL, GST_STATE_READY, GST_STATE_PAUSED, GST_STATE_PLAYING
 
 <FONT Color=gray>' ''gst_init (int *argc, char **argv[])''
 ' ''Initializes the GStreamer library, setting up internal path lists, registering built-in elements, and loading standard plugins.''</font>
 Private Extern gst_init(argc As Pointer, argv As Pointer)
 
 <FONT Color=gray>' ''GstElement * gst_element_factory_make(const gchar *factoryname, Const gchar * name)''
 ' ''Create a new element of the type defined by the given element factory.''</font>
 Private Extern gst_element_factory_make(factoryname As String, name As String) As Pointer
 
 <FONT Color=gray>' ''gchar * g_filename_to_uri (const gchar *filename, const gchar *hostname, GError **error)''
 ' ''Converts an absolute filename to an escaped ASCII-encoded URI.''</font>
 Private Extern g_filename_to_uri(filename As String, hostname As String, GError As Pointer) As String
 
 <FONT Color=gray>' ''void g_object_set(gpointer object, const gchar *first_property_name, ...)''
 ' ''Sets properties on an object.''</font>
 Private Extern g_object_set(gobject As Pointer, key As String, value As String, tertium As String)
 
 <FONT Color=gray>' ''GstStateChangeReturn gst_element_set_state(GstElement *element, GstState state)''
 ' ''Sets the state of the element.''</font>
 Private Extern gst_element_set_state(gstelement As Pointer, state As Integer) As Integer''
 
 <FONT Color=gray>' ''void gst_object_unref(gpointer object)''
 ' ''Decrements the reference count on object.''</font>
 Private Extern gst_object_unref(gobject As Pointer)
 
 
 Public Sub Main()
  
   Dim fileImmagine As String
      
   gst_init(0, 0)
   
   immago = gst_element_factory_make("playbin", "immagine")
   If IsNull(immago) Then Error.Raise("Impossibile creare un elemento 'playbin' !")
   
   fileImmagine = "<FONT Color=darkgreen>''/percorso/del/file/immagine''</font>"
   
   g_object_set(immago, "uri", g_filename_to_uri(fileImmagine, Null, 0), Null)
  
 <FONT Color=gray>' ''Mostra l'immagine:''</font>
   gst_element_set_state(immago, GST_STATE_PLAYING)
   
   While ciclo
     Wait 0.01
   Wend
   
   gst_object_unref(immago)
      
   Quit
    
 End
 
 
 Public Sub Application_Read()
  
   Dim s As String
   
   Input #File.In, s
   
 <FONT Color=gray>' ''Arresta la riproduzione del file immagine:''</font>
   If s = "c" Then ciclo = 0
   
 End



==Immagine mostrata in una ''DrawingArea''==
Di seguito mostreremo un esempio, nel quale verrà caricato un file immagine in un'applicazione grafica.
<BR>L'immagine sarà mostrata in una ''DrawingArea''. posta sul ''Form'' dell'applicazione Gambas.
 Private immago As Pointer
  
 
 Library "<FONT Color=blue>libgstreamer-1.0:0.2407.0</font>"
 
 Private Enum GST_STATE_VOID_PENDING = 0, GST_STATE_NULL, GST_STATE_READY, GST_STATE_PAUSED, GST_STATE_PLAYING
 
 <FONT Color=gray>' ''gst_init (int *argc, char **argv[])''
 ' ''Initializes the GStreamer library, setting up internal path lists, registering built-in elements, and loading standard plugins.''</font>
 Private Extern gst_init(argc As Pointer, argv As Pointer)
 
 <FONT Color=gray>' ''GstElement * gst_element_factory_make(const gchar *factoryname, Const gchar * name)''
 ' ''Create a new element of the type defined by the given element factory.''</font>
 Private Extern gst_element_factory_make(factoryname As String, name As String) As Pointer
 
 <FONT Color=gray>' ''gchar * g_filename_to_uri (const gchar *filename, const gchar *hostname, GError **error)''
 ' ''Converts an absolute filename to an escaped ASCII-encoded URI.''</font>
 Private Extern g_filename_to_uri(filename As String, hostname As String, GError As Pointer) As String
 
 <FONT Color=gray>' ''void g_object_set(gpointer object, const gchar *first_property_name, ...)''
 ' ''Sets properties on an object.''</font>
 Private Extern g_object_set(gobject As Pointer, key As String, value As String, tertium As String)
 
 <FONT Color=gray>' ''GstStateChangeReturn gst_element_set_state(GstElement *element, GstState state)''
 ' ''Sets the state of the element.''</font>
 Private Extern gst_element_set_state(gstelement As Pointer, state As Integer) As Integer''
 
 <FONT Color=gray>' ''void gst_object_unref(gpointer object)''
 ' ''Decrements the reference count on object.''</font>
 Private Extern gst_object_unref(gobject As Pointer)
 
 
 Library "<FONT Color=red>libgstvideo-1.0:0.2403.0</font>"
 
 <FONT Color=gray>' ''void gst_video_overlay_set_window_handle (GstVideoOverlay *overlay, guintptr handle)''
 ' ''Calls the video overlay's set_window_handle method.''</font>
 Private Extern gst_video_overlay_set_window_handle(overlay As Pointer, handle As Integer)
 
 
 Public Sub Form_Open()
    
   Dim fileImmagine As String
      
   gst_init(0, 0)
   
   immago = gst_element_factory_make("playbin", "immagine")
   If IsNull(immago) Then Error.Raise("Impossibile creare un elemento 'playbin' !")
   
   fileImmagine = "<FONT Color=gray>''/percorso/del/file/immagine''</font>"
   
   g_object_set(immago, "uri", g_filename_to_uri(fileImmagine, Null, 0), Null)
   
 <FONT Color=gray>' ''Imposta la "DrawingArea" come superficie per la riproduzione dell'immagine:''</font>
   gst_video_overlay_set_window_handle(immago, DrawingArea1.Handle)
  
 <FONT Color=gray>' ''Mostra l'immagine:''</font>
   gst_element_set_state(immago, GST_STATE_PLAYING)
         
 End
 
 
 Public Sub Button1_Click()
  
  Me.Close
  
 End
 
 
 Public Sub Form_Close()
  
  gst_object_unref(immago)
  
 End



=Riferimenti=
* http://gstreamer.freedesktop.org/
* https://developer.gnome.org/gstreamer/stable/
* https://developer.gnome.org/gstreamer-libs/stable/