Visualizza wikitesto di Convertire un file immagine SVG in un file immagine di altro formato con le funzioni esterne delle librerie librsvg e libgdk pixbuf

Utilizzando alcune funzioni esterne delle librerie ''librsvg'' e ''libgdk pixbuf'' di GNOME è possibile convertire un file immagine SVG in un file immagine di altro formato. Tali formati possibili sono di base "jpeg", "png", "ico" e "bmp", ma possono essere installati altri formati.

In particolare la libreria "''librsvg''" è utilizzata per effettuare il ''rendering'' di immagini di formato SVG, mentre la libreria "''libgdk pixbuf''" è utilizzata per caricare e gestire immagini.

E' necessario avere installate nel sistema e richiamare in Gambas le librerie condivise: "''librsvg-2.so.2.50.0'' " e "''libgdk_pixbuf-2.0.so.0.4200.12'' ".

Mostriamo di seguito un esempio, nel quale sarà caricato un file immagine SVG che sarà convertito in formato PNG:
 Library "librsvg-2:2.50.0"
 
 <FONT Color=gray>' ''RsvgHandle * rsvg_handle_new_from_file (const gchar *file_name, GError **error)''
 ' ''Loads the SVG specified by file_name.''</font>
 Private Extern rsvg_handle_new_from_file(file_name As String, gerror As Pointer) As Pointer
 
 <FONT Color=gray>' ''GdkPixbuf * rsvg_handle_get_pixbuf (RsvgHandle *handle)''
 ' Returns the pixbuf loaded by handle.''</font>
 Private Extern rsvg_handle_get_pixbuf(handle As Pointer) As Pointer
 
 <FONT Color=gray>' ''gboolean rsvg_handle_close (RsvgHandle *handle, GError **error)''
 ' ''Closes handle , to indicate that loading the image is complete.''</font>
 Private Extern rsvg_handle_close(handle As Pointer, gerror As Pointer) As Boolean
 
 
 Library "libgdk_pixbuf-2.0:0.4200.12"
 
 <FONT Color=gray>' ''gboolean gdk_pixbuf_save (GdkPixbuf *pixbuf, const char *filename, const char *type, GError **error, ...)''
 ' Saves pixbuf to a file in format type. By default, "jpeg", "png", "ico" and "bmp" are possible file formats to save in.''</font>
 Private Extern gdk_pixbuf_save(pixbuf As Pointer, filename As String, type As String, gerror As Pointer, altro As Pointer) As Boolean
 
 <FONT Color=gray>' ''void g_object_unref (gpointer object)''
 ' Decreases the reference count of object.''</font>
 Private Extern g_object_unref(gobject As Pointer)
 
 
 Public Sub Main()
  
  Dim rsvg, pbf As Pointer
  Dim bo As Boolean
   
 <FONT Color=gray>' ''Carica il file immagine SGV da convertire:''</font>
  rsvg = rsvg_handle_new_from_file("<FONT Color=darkgreen>''/percorso/del/file/immagine.svg''</font>", 0)
  If rsvg == 0 Then Error.Raise("Errore !")
   
  rsvg_handle_close(rsvg, 0)
   
  pbf = rsvg_handle_get_pixbuf(rsvg)
  If pbf == 0 Then Error.Raise("Errore !")
   
 <FONT Color=gray>' ''Converte il file immagine SGV nel nuovo file immagine di formato PNG:''</font>
  bo = gdk_pixbuf_save(pbf, "<FONT Color=gray>''/percorso/del/file/immagine.png''</font>", "png", 0, 0)
  If Not bo Then Error.Raise("ERRORE !")
    
 <FONT Color=gray>' ''In fine libera la memoria occupata dalle due librerie esterne utilizzate:''</font>
  g_object_unref(pbf)
  g_object_unref(rsvg)
   
 End


Un'altra modalità può essere la seguente:
 Library "librsvg-2:2.50.0"
 
 Private Enum RSVG_HANDLE_FLAGS_NONE = 0, RSVG_HANDLE_FLAG_UNLIMITED, RSVG_HANDLE_FLAG_KEEP_IMAGE_DATA
 
 <FONT Color=gray>' ''RsvgHandle * rsvg_handle_new_from_gfile_sync (GFile *file, RsvgHandleFlags flags, GCancellable *cancellable, GError **error)''
 ' ''Creates a new RsvgHandle for file.''</font>
 Private Extern rsvg_handle_new_from_gfile_sync(gfile As Pointer, flags As Integer, cancellable As Pointer, gerror As Pointer) As Pointer
 
 <FONT Color=gray>' ''gboolean rsvg_handle_close (RsvgHandle *handle, GError **error)''
 ' ''Closes handle , to indicate that loading the image is complete.''</font>
 Private Extern rsvg_handle_close(handle As Pointer, gerror As Pointer) As Boolean
 
 <FONT Color=gray>' ''GdkPixbuf * rsvg_handle_get_pixbuf (RsvgHandle *handle)''
 ' Returns the pixbuf loaded by handle.''</font>
 Private Extern rsvg_handle_get_pixbuf(handle As Pointer) As Pointer
 
 
 Library "libgdk_pixbuf-2.0:0.4200.12"
 
 <FONT Color=gray>' ''GFile * g_file_new_for_path (const char *path)''
 ' ''Constructs a GFile for a given path.''</font>
 Private Extern g_file_new_for_path(path As String) As Pointer
 
 <FONT Color=gray>' ''gboolean gdk_pixbuf_save (GdkPixbuf *pixbuf, const char *filename, const char *type, GError **error, ...)''
 ' Saves pixbuf to a file in format type. By default, "jpeg", "png", "ico" and "bmp" are possible file formats to save in.''</font>
 Private Extern gdk_pixbuf_save(pixbuf As Pointer, filename As String, type As String, gerror As Pointer, altro As Pointer) As Boolean
 
 <FONT Color=gray>' ''void g_object_unref (gpointer object)''
 ' Decreases the reference count of object.''</font>
 Private Extern g_object_unref(gobject As Pointer)
 
 
 Public Sub Main()
  
  Dim p, svg, pbf As Pointer
  Dim bo As Boolean
   
 <FONT Color=gray>' ''Carica il file immagine SGV da convertire:''</font>
  p = g_file_new_for_path("<FONT Color=darkgreen>''/percorso/del/file/immagine.svg''</font>", 0)
  If p == 0 Then Error.Raise("Errore !")
   
  svg = rsvg_handle_new_from_gfile_sync(p, 0, 0, 0)
  If svg == 0 Then Error.Raise("Errore !")
   
  bo = rsvg_handle_close(svg, 0)
  If Not bo Then Error.Raise("Errore !")
   
  pbf = rsvg_handle_get_pixbuf(svg)   
  If pbf == 0 Then Error.Raise("Errore !")
   
 <FONT Color=gray>' ''Converte il file immagine SGV nel nuovo file immagine di formato PNG:''</font>
  bo = gdk_pixbuf_save(pbf, "<FONT Color=darkgreen>''/percorso/del/file/immagine.png''</font>", "png", 0, 0)
  If Not bo Then Error.Raise("Errore !")
    
 <FONT Color=gray>' ''In fine libera la memoria occupata dalle due librerie esterne utilizzate:''</font>
  g_object_unref(pbf)
  g_object_unref(svg)
  g_object_unref(p)
   
 End



=Riferimenti=
* https://sourcecodebrowser.com/librsvg/2.26.3/rsvg-base-file-util_8c.html
* https://developer.gnome.org/gdk-pixbuf/stable/gdk-pixbuf-File-saving.html