Ridimensionare un'immagine mediante le funzioni esterne del API di ImageMagick
Da Gambas-it.org - Wikipedia.
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 condivisa: "libMagickWand-6.Q16.so.6.0.0 ".
Mostriamo di seguito un semplice esempio pratico per creare da una immagine iniziale una sua copia ridimensionata come un thumbnail:
Library "libMagickWand-6.Q16:6.0.0"
Private Const MagickPathExtent As Integer = 4096
Public Struct MagickWand
id As Long
name[MagickPathExtent] As Byte
images As Pointer
image_info As Pointer
exception As Pointer
insert_before As Integer
image_pending As Integer
debug_ As Integer
signature As Long
End Struct
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 MagickWand
' MagickBooleanType MagickReadImage(MagickWand *wand,const char *filename)
' Reads an image or image sequence.
Private Extern MagickReadImage(wand As MagickWand, filename As String) As Integer
' 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 MagickWand, columns As Long, rows As Long, filter As Integer, blur As Float) As Integer
' MagickBooleanType MagickWriteImages(MagickWand *wand, const char *filename,const MagickBooleanType adjoin)
' Writes an image or image sequence.
Private Extern MagickWriteImages(wand As MagickWand, filename As String, adjoin As Boolean) As Integer
' MagickWand *DestroyMagickWand(MagickWand *wand)
' Deallocates memory associated with an MagickWand.
Private Extern DestroyMagickWand(wand As MagickWand) As MagickWand
' void MagickWandTerminus(void)
' Terminates the MagickWand environment.
Private Extern MagickWandTerminus()
Public Sub Main()
Dim bo As Boolean
Dim mwand As MagickWand
Dim fileimmagine, nuovofile As String
fileimmagine = "/percorso/del/file/immagine"
nuovofile = "/percorso/del/file/immagine/ridimensionata"
MagickWandGenesis()
mwand = NewMagickWand()
bo = MagickReadImage(mwand, fileimmagine)
If bo = MagickFalse Then
Error.Raise("Impossibile caricare il file immagine !")
Chiude(mwand)
Endif
' Ridimensiona l'immagine:
MagickResizeImage(mwand, 128, 64, LanczosFilter, 1.0)
bo = MagickWriteImages(mwand, nuovofile, MagickTrue)
If bo = MagickFalse Then
Error.Raise("Impossibile creare il nuovo file dell'immagine ridimensionata !")
Chiude(mwand)
Endif
Chiude(mwand)
End
Private Procedure Chiude(mw As MagickWand)
' Libera la memoria e chiude la libreria "ImageMagick":
DestroyMagickWand(mw)
Wait 0.01
MagickWandTerminus()
End
