Versione attuale delle 20:42, 30 nov 2021

La libreria GifLib, scritta da Eric Steven Raymond, consente di leggere e scrivere file immagine in formato GIF.

E' possibile ottenere anche alcune informazioni generali su un'immagine GIF.

Per poter utilizzare le risorse della libreria GifLib, utilizzeremo la libreria condivisa: "libgif.so.7.1.0 "

Mostriamo un semplice esempio:

The GIFLIB distribution is Copyright (c) 1997  Eric S. Raymond

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.


' GifFileType *DGifOpenFileHandle(int GifFileHandle)
' Update a New GIF file, given its file handle.
Private Extern DGifOpenFileHandle(FileHandle As Integer) As Pointer In "libgif:7.1.0"


Public Sub Main()

 Dim GifFile1, GifFile2 As Pointer
 Dim fl As File
 Dim percorso As String = "/percorso/del/file.gif"
 Dim i As Integer
 Dim st As Stream
 
 fl = Open percorso For Read
    
 GifFile1 = DGifOpenFileHandle(fl.Handle)
 If GifFile1 == 0 Then Print "Impossibile ottenere il descrittore dell'immagine !"

 Print "== Dati generali dell'immagine ==\n"
 Print "File immagine: "; Null, percorso
 st = Memory GifFile1 For Read
 Read #st, i
 Print "Larghezza: "; Null, i; " pixel"
 Read #st, i
 Print "Altezza: "; Null, i; " pixel"
 Read #st, i
 Print "Risol. colore: "; Null, i
 Seek #st, 16
 Read #st, GifFile2
 st.Close

 st = Memory GifFile2 For Read
 Seek #st, 4
 Read #st, i
 Print "Bit per Pixel: "; Null, i; " bit"
   
' Va in chiusura:
 st.Close
 fl.Close

End

Riferimenti

• http://giflib.sourceforge.net/gif_lib.html
• http://wwwcdf.pd.infn.it/libgif/index.html
• http://fossies.org/dox/giflib-5.1.1/index.html