Estrarre immagini da un file PDF con le risorse del API di libpoppler-glib e di libcairo
Da Gambas-it.org - Wikipedia.
Se un file PDF possiede delle immagini, queste possono essere estratte.
E' necessario avere installate nel sistema e richiamare nel programma Gambas le librerie condivise: "libpoppler-glib.so.8.26.0 " e "libcairo.so.2.11800.0 ".
Mostriamo un semplice esempio:
Private Const URI As String = "file://"
Library "libpoppler-glib:8.26.0"
Private poppler_error As String[] = [Null, "INVALID", "ENCRYPTED", "OPEN_FILE", "BAD_CATALOG", "DAMAGED"]
' popplerDocument *poppler_document_new_from_file (const char *uri, const char *password, GError **error)
' Creates a new PopplerDocument.
Private Extern poppler_document_new_from_file(uri As String, password As String, GError As Pointer) As Pointer
' PopplerPage * poppler_document_get_page (PopplerDocument *document, int index)
' Returns the PopplerPage indexed at index.
Private Extern poppler_document_get_page(document As Pointer, index As Integer) As Pointer
' cairo_surface_t * poppler_page_get_image (PopplerPage *page, gint image_id)
' Returns a cairo surface for the image of the page.
Private Extern poppler_page_get_image(page As Pointer, image_id As Integer) As Pointer
' void g_object_unref (gpointer object)
' Decreases the reference count of object.
Private Extern g_object_unref(gobject As Pointer)
Library "libcairo:2.11800.0"
Private cairo_format As String[] = ["CAIRO_FORMAT_ARGB32", "CAIRO_FORMAT_RGB24", "CAIRO_FORMAT_A8",
"CAIRO_FORMAT_A1", "CAIRO_FORMAT_RGB16_565", "CAIRO_FORMAT_RGB30"]
' int cairo_image_surface_get_width (cairo_surface_t *surface)
' Get the width of the image surface in pixels.
Private Extern cairo_image_surface_get_width(surface As Pointer) As Integer
' int cairo_image_surface_get_height (cairo_surface_t *surface)
' Get the height of the image surface in pixels.
Private Extern cairo_image_surface_get_height(surface As Pointer) As Integer
' cairo_format_t cairo_image_surface_get_format (cairo_surface_t *surface)
' Get the format of the surface.
Private Extern cairo_image_surface_get_format(surface As Pointer) As Integer
' cairo_status_t cairo_surface_write_to_png(cairo_surface_t *surface, const char *filename)
' Writes the contents of surface to a new file filename as a PNG image.
Private Extern cairo_surface_write_to_png(cairo_surface As Pointer, filename As String) As Integer
' void cairo_surface_destroy (cairo_surface_t *surface)
' Decreases the reference count on surface by one.
Private Extern cairo_surface_destroy(cairo_surface As Pointer)
Public Sub Main()
Dim percorso, en As String
Dim p, doc, pag, cai As Pointer
Dim w, h, frm, err As Integer
percorso = "/percorso/del/file.pdf"
' Carica il file PDF:
doc = poppler_document_new_from_file(URI & percorso, Null, VarPtr(p))
If doc == 0 Then Error.Raise("Errore: " & poppler_error[Val(String@(p))])
' Prende in considerazione la prima pagina (indice 0) del file pdf:
pag = poppler_document_get_page(doc, 0)
If pag == 0 Then Error.Raise("Errore !")
' Estrae la prima immagine (indice 0) presente nella pagina del file pdf:
cai = poppler_page_get_image(pag, 0)
If cai == 0 Then Error.Raise("Errore !")
''''''''''''''''
' Ottiene alcune informazioni sull'immagine estratta:
w = cairo_image_surface_get_width(cai)
h = cairo_image_surface_get_height(cai)
Print "Informazioni sull'immagine estratta"
Print "Dimensioni: "; w; " x "; h; " pixel"
frm = cairo_image_surface_get_format(cai)
If frm = -1 Then
en = "CAIRO_FORMAT_INVALID"
Else
en = cairo_format[frm]
Endif
Print "Formato: "; en
' Salva i dati dell'immagine estratta in un'immagine di tipo PNG:
err = cairo_surface_write_to_png(cai, "/tmp/immagine.png")
If err > 0 Then Error.Raise("Errore nella creazione del file immagine .png !")
' Al termine libera la memoria precedentemente occupata:
cairo_surface_destroy(cai)
g_object_unref(pag)
g_object_unref(doc)
End
