Creare un file PS con le risorse del API di Cairo
Da Gambas-it.org - Wikipedia.
La libreria Cairo consente, fra l'altro, di creare un file immagine di formato PS (PostScript)..
Per fare ciò, si dovranno utilizzare alcune funzioni esterne della libreria condivisa: "libcairo.so.2.11802.2 ".
Va considerato che la libreria Cairo sviluppa il disegno dell'immagine in tre fasi:
1) viene creata una maschera, che comprende uno o più primitive o forme vettoriali, cioè cerchi, quadrati, i font TrueType, curve di Bézier, ecc;
2) viene quindi definito un sorgente, che può essere un colore, una sfumatura di colore, una bitmap o qualche grafica vettoriale;
3) infine il risultato viene trasferito al file di destinazione o alla superficie di un oggetto grafico.
Mostriamo un semplice esempio, nel quale verrà creato un file PS:
Library "libcairo:2.11802.2" Private Enum CAIRO_FONT_SLANT_NORMAL = 0, CAIRO_FONT_SLANT_ITALIC, CAIRO_FONT_SLANT_OBLIQUE Private Enum CAIRO_FONT_WEIGHT_NORMAL = 0, CAIRO_FONT_WEIGHT_BOLD ' cairo_surface_t *cairo_ps_surface_create(const char * filename, double width_in_points, double height_in_points) ' Creates a PostScript surface of the specified size in points to be written to filename. Private Extern cairo_ps_surface_create(filename As String, width_in_points As Float, height_in_points As Float) As Pointer ' cairo_t* cairo_create(cairo_surface_t *target) ' Creates a new cairo_t with all graphics state parameters set to default values and with target as a target surface. Private Extern cairo_create(target As Pointer) As Pointer ' void cairo_rectangle(cairo_t *cr, double x, double y, double width, double height) ' Adds a closed sub-path rectangle of the given size to the current path at position (x, y) in user-space coordinates. Private Extern cairo_rectangle(cr As Pointer, xF As Float, yF As Float, width As Float, height As Float) ' cairo_pattern_t * cairo_pattern_create_radial(double cx0, double cy0, double radius0, double cx1, double cy1, double radius1) ' Creates a new radial gradient cairo_pattern_t between the two circles defined by (cx0, cy0, radius0) and (cx1, cy1, radius1). Private Extern cairo_pattern_create_radial(cx0 As Float, cy0 As Float, radius0 As Float, cx1 As Float, cy1 As Float, radius1 As Float) As Pointer ' void cairo_pattern_add_color_stop_rgb(cairo_pattern_t *pattern, double offset, double red, double green, double blue) ' Adds an opaque color stop to a gradient pattern. Private Extern cairo_pattern_add_color_stop_rgb(patternP As Pointer, offset As Float, red As Float, green As Float, blue As Float) ' void cairo_set_source(cairo_t *cr, cairo_pattern_t *source) ' Sets the source pattern within cr to source. Private Extern cairo_set_source(cr As Pointer, patternP As Pointer) ' void cairo_fill(cairo_t *cr) ' A drawing operator that fills the current path according to the current fill rule. Private Extern cairo_fill(cr As Pointer) ' void cairo_set_font_size(cairo_t *cr, double size) ' Sets the current font matrix to a scale by a factor of size. Private Extern cairo_set_font_size(cr As Pointer, size As Float) ' void cairo_select_font_face(cairo_t *cr, const char *family, cairo_font_slant_t slant, cairo_font_weight_t weight) ' Selects a family and style of font from a simplified description as a family name, slant and weight. Private Extern cairo_select_font_face(cr As Pointer, family As String, slant As Integer, font_weight As Integer) ' void cairo_set_source_rgb(cairo_t *cr, double red, double green, double blue) ' Sets the source pattern within cr to an opaque color. Private Extern cairo_set_source_rgb(cr As Pointer, red As Float, green As Float, blue As Float) ' void cairo_move_to(cairo_t *cr, double x, double y) ' Begin a new sub-path. Private Extern cairo_move_to(cr As Pointer, xF As Float, yF As Float) ' void cairo_show_text(cairo_t *cr, const char *utf8) ' A drawing operator that generates the shape from a string of UTF-8 characters. Private Extern cairo_show_text(cr As Pointer, utf8 As String) ' void cairo_destroy(cairo_t *cr) ' Decreases the reference count on cr by one. Private Extern cairo_destroy(cr As Pointer) ' 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 surface, cairo, pattern As Pointer Dim x, y As Byte ' Crea la superficie grafica per il file "PostScript" e il percorso ove esso sarà generato (il 2° e il 3° argomento sono espressi in pixel): surface = cairo_ps_surface_create("/tmp/esempio_Cairo.ps", 100.0, 100.0) If surface == 0 Then Error.Raise("Errore !") cairo = cairo_create(surface) If cairo == 0 Then Error.Raise("Errore !") ' Disegna i quadrati sullo sfondo: For x = 0 To 9 For y = 0 To 9 cairo_rectangle(cairo, x * 10.0, y * 10.0, 5, 5) Next Next pattern = cairo_pattern_create_radial(50, 50, 5, 50, 50, 50) If pattern == 0 Then Error.Raise("Errore !") cairo_pattern_add_color_stop_rgb(pattern, 0, 0.75, 0.15, 0.99) cairo_pattern_add_color_stop_rgb(pattern, 0.9, 1, 1, 1) cairo_set_source(cairo, pattern) cairo_fill(cairo) ' Scrive in primo piano. ' Imposta la dimensione del font: cairo_set_font_size(cairo, 14) ' Imposta il font del testo: cairo_select_font_face(cairo, "Ubuntu", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD) ' Attribuisce un colore al testo: cairo_set_source_rgb(cairo, 0, 0, 0) ' Imposta le coordinate ove sarà disegnato il testo: cairo_move_to(cairo, 12, 25) ' Imposta il testo: cairo_show_text(cairo, "Crea un PS") cairo_set_source_rgb(cairo, 255, 0, 0) cairo_move_to(cairo, 0, 75) cairo_show_text(cairo, "Testo qualsiasi") ' Per generare il file PS, è necessario distruggere il contesto grafico "cairo_t" e la superficie dell'immagine: cairo_destroy(cairo) cairo_surface_destroy(surface) End