Versione delle 12:25, 7 giu 2017

Il sistema ImageMagick consente di creare, modificare e convertire immagini bitmap. Può altresì leggere e scrivere immagini di oltre 200 formati.

Per poter fruire in Gambas delle risorse, è necessario avere installata nel sistema e richiamare la seguente libreria dinamica condivisa: "libMagickWand-6.Q16.so.2.0.0" (o altra versione).

Mostriamo di seguito un semplice esempio pratico per creare da una immagine iniziale una sua copia ridimensionata come un thumbnail:

Library "libMagickWand-6.Q16:2.0.0"

Private Enum MagickFalse = 0, MagickTrue
Private Enum UndefinedFilter = 0, PointFilter, BoxFilter, TriangleFilter, HermiteFilter,
  HanningFilter, HammingFilter, BlackmanFilter, GaussianFilter, QuadraticFilter,
  CubicFilter, CatromFilter, MitchellFilter, JincFilter, SincFilter, SincFastFilter,
  KaiserFilter, WelshFilter, ParzenFilter, BohmanFilter, BartlettFilter, LagrangeFilter,
  LanczosFilter, LanczosSharpFilter, Lanczos2Filter, Lanczos2SharpFilter, RobidouxFilter,
  RobidouxSharpFilter, CosineFilter, SplineFilter, LanczosRadiusFilter, SentinelFilter
 
' void MagickWandGenesis(void)
' Initializes the MagickWand environment.
Private Extern MagickWandGenesis()
 
' MagickWand *NewMagickWand(void)
' Returns a wand required for all other methods in the API.
Private Extern NewMagickWand() As Pointer
 
' MagickBooleanType MagickReadImage(MagickWand *wand,const char *filename)
' Reads an image or image sequence.
Private Extern MagickReadImage(wand As Pointer, filename As String) As Boolean

' MagickBooleanType MagickResizeImage(MagickWand *wand, const size_t columns,const size_t rows,const FilterType filter)
' Scales an image to the desired dimensions with a filter.
Private Extern MagickResizeImage(wand As Pointer, columns As Long, rows As Long, filter As Integer, blur As Float) As Boolean

' MagickBooleanType MagickWriteImages(MagickWand *wand, const char *filename,const MagickBooleanType adjoin)
' Writes an image or image sequence.
Private Extern MagickWriteImages(wand As Pointer, filename As String, adjoin As Boolean) As Boolean

' MagickWand *DestroyMagickWand(MagickWand *wand)
' Deallocates memory associated with an MagickWand.
Private Extern DestroyMagickWand(wand As Pointer) As Pointer

' void MagickWandTerminus(void)
' Terminates the MagickWand environment.
Private Extern MagickWandTerminus()


Public Sub Main()
 
 Dim bo As Boolean
 Dim magick_wand As Pointer
 Dim fileimmagine, nuovofile As String  
 
  fileimmagine = "/percorso/del/file/immagine"
  nuovofile = "/percorso/del/file/immagine/ridimensionata"
  
  MagickWandGenesis()
  
  magick_wand = NewMagickWand()
  
  bo = MagickReadImage(magick_wand, fileimmagine)
  If bo = MagickFalse Then
    Error.Raise("Impossibile caricare il file immagine !")
    Chiude()
  Endif
  
' Ridimensiona l'immagine:
  MagickResizeImage(magick_wand, 106, 80, LanczosFilter, 1.0)
     
  bo = MagickWriteImages(magick_wand, nuovofile, MagickTrue)
  If bo = MagickFalse Then
    Error.Raise("Impossibile creare il nuovo file dell'immagine ridimensionata !")
    Chiude()
  Endif
 
  Chiude()
  
End


Private Procedure Chiude(mw As Pointer)
 
' Libera la memoria e chiude la libreria "ImageMagick":
  DestroyMagickWand(mw)
  Wait 0.01
  MagickWandTerminus()
  
End

Riferimenti

• http://imagemagick.org/api/magick-wand.php
• http://www.ummon.org/Linux/index/ImageMagick_R.html