Ruotare un'immagine mediante le funzioni esterne del API di ImageMagick
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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-7.Q16HDRI.so.10.0.2 ".
Mostriamo di seguito un semplice esempio pratico per ruotare un'immagine:
Library "libMagickWand-7.Q16HDRI:10.0.2"
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
' 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
' PixelWand *NewPixelWand(void)
' Returns a new pixel wand.
Private Extern NewPixelWand() As Pointer
' void PixelSetRed(PixelWand *wand, const double red)
' Sets the normalized red color of the pixel wand.
Private Extern PixelSetRed(Pwand As Pointer, red As Float)
' void PixelSetGreen(PixelWand *wand, const double green)
' Sets the normalized green color of the pixel wand.
Private Extern PixelSetGreen(Pwand As Pointer, green As Float)
' void PixelSetBlue(PixelWand *wand, const double blue)
' Sets the normalized blue color of the pixel wand.
Private Extern PixelSetBlue(Pwand As Pointer, blue As Float)
' void PixelSetAlpha(PixelWand *wand, const double alpha)
' Sets the normalized alpha color of the pixel wand.
Private Extern PixelSetAlpha(Pwand As Pointer, alpha As Float)
' MagickBooleanType MagickRotateImage(MagickWand *wand, const PixelWand *background,const double degrees)
' Rotates an image the specified number of degrees.
Private Extern MagickRotateImage(wand As MagickWand, background As Pointer, degrees 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
' PixelWand *DestroyPixelWand(PixelWand *wand)
' Deallocates resources associated with a PixelWand.
Private Extern DestroyPixelWand(Pwand As Pointer) As Pointer
' 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 Integer
Dim mwand As MagickWand
Dim fileimmagine, nuovofile As String
Dim pw As Pointer
fileimmagine = "/percorso/del/file/immagine"
nuovofile = "/percorso/del/nuovo/file/dell'immagine/ruotata"
MagickWandGenesis()
' I triangoli lasciati vuoti dalla rotazione dell'immagine sono riempiti da un colore di fondo:
pw = ColorFondo()
mwand = NewMagickWand()
bo = MagickReadImage(mwand, fileimmagine)
If bo = MagickFalse Then
Termina(mwand, pw)
Error.Raise("Impossibile caricare l'immagine !")
Endif
' Ruota l'immegine di 135,00° a destra:
MagickRotateImage(mwand, pw, 135.00)
bo = MagickWriteImages(mwand, nuovofile, MagickTrue)
If bo = MagickFalse Then
Termina(mwand, pw)
Error.Raise("Impossibile creare il nuovo file dell'immagine ruotata !")
Endif
Termina(mwand, pw)
End
Private Function ColorFondo() As Pointer
Dim pxw As Pointer
pxw = NewPixelWand()
PixelSetRed(pxw, 255.0)
PixelSetGreen(pxw, 255.0)
PixelSetBlue(pxw, 255.0)
' Imposta il canale Alfa a zero per la trasparenza:
PixelSetAlpha(pxw, 0.0)
Return pxw
End
Private Procedure Termina(mw As MagickWand, pixw As Pointer) ' Libera la memoria e termina il programma
DestroyPixelWand(pixw)
DestroyMagickWand(mw)
Wait 0.01
MagickWandTerminus()
End