Draw transformed text with Pango and cairo

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#define RADIUS 100
#define N_WORDS 10
#define FONT "Sans Bold 18"

PangoContext *context;
PangoLayout *layout;
PangoFontDescription *desc;

double radius;
int width, height;
int i;

// Set up a transformation matrix so that the user space coordinates for
// where we are drawing are [-RADIUS, RADIUS], [-RADIUS, RADIUS]
// We first center, then change the scale

width = gdk_window_get_width (window);
height = gdk_window_get_height (window);
radius = MIN (width, height) / 2.;

cairo_translate (cr,
                 radius + (width - 2 * radius) / 2,
                 radius + (height - 2 * radius) / 2);
                 cairo_scale (cr, radius / RADIUS, radius / RADIUS);

// Create a PangoLayout, set the font and text
context = gdk_pango_context_get_for_screen (screen);
layout = pango_layout_new (context);
pango_layout_set_text (layout, "Text", -1);
desc = pango_font_description_from_string (FONT);
pango_layout_set_font_description (layout, desc);
pango_font_description_free (desc);

// Draw the layout N_WORDS times in a circle
for (i = 0; i < N_WORDS; i++)
  {
    double red, green, blue;
    double angle = 2 * G_PI * i / n_words;

    cairo_save (cr);

    // Gradient from red at angle == 60 to blue at angle == 300
    red = (1 + cos (angle - 60)) / 2;
    green = 0;
    blue = 1 - red;

    cairo_set_source_rgb (cr, red, green, blue);
    cairo_rotate (cr, angle);

    // Inform Pango to re-layout the text with the new transformation matrix
    pango_cairo_update_layout (cr, layout);

    pango_layout_get_size (layout, &width, &height);

    cairo_move_to (cr, - width / 2 / PANGO_SCALE, - DEFAULT_TEXT_RADIUS);
    pango_cairo_show_layout (cr, layout);

    cairo_restore (cr);
  }

g_object_unref (layout);
g_object_unref (context);

Output of the example above.

gdk_pango_layout_get_clip_region ()

cairo_region_t *
gdk_pango_layout_get_clip_region (PangoLayout *layout,
                                  gint x_origin,
                                  gint y_origin,
                                  const gint *index_ranges,
                                  gint n_ranges);

Obtains a clip region which contains the areas where the given ranges of text would be drawn. x_origin and y_origin are the top left point to center the layout. index_ranges should contain ranges of bytes in the layout’s text.

Note that the regions returned correspond to logical extents of the text ranges, not ink extents. So the drawn layout may in fact touch areas out of the clip region. The clip region is mainly useful for highlightling parts of text, such as when text is selected.

[skip]

gdk_pango_layout_line_get_clip_region ()

cairo_region_t *
gdk_pango_layout_line_get_clip_region (PangoLayoutLine *line,
                                       gint x_origin,
                                       gint y_origin,
                                       const gint *index_ranges,
                                       gint n_ranges);

Obtains a clip region which contains the areas where the given ranges of text would be drawn. x_origin and y_origin are the top left position of the layout. index_ranges should contain ranges of bytes in the layout’s text. The clip region will include space to the left or right of the line (to the layout bounding box) if you have indexes above or below the indexes contained inside the line. This is to draw the selection all the way to the side of the layout. However, the clip region is in line coordinates, not layout coordinates.

Note that the regions returned correspond to logical extents of the text ranges, not ink extents. So the drawn line may in fact touch areas out of the clip region. The clip region is mainly useful for highlightling parts of text, such as when text is selected.

[skip]

gdk_pango_context_get ()

PangoContext *
gdk_pango_context_get (void);

Creates a PangoContext for the default GDK screen.

The context must be freed when you’re finished with it.

When using GTK+, normally you should use gtk_widget_get_pango_context() instead of this function, to get the appropriate context for the widget you intend to render text onto.

The newly created context will have the default font options (see cairo_font_options_t) for the default screen; if these options change it will not be updated. Using gtk_widget_get_pango_context() is more convenient if you want to keep a context around and track changes to the screen’s font rendering settings.

gdk_pango_context_get_for_screen ()

PangoContext *
gdk_pango_context_get_for_screen (GdkScreen *screen);

Creates a PangoContext for screen .

The context must be freed when you’re finished with it.

When using GTK+, normally you should use gtk_widget_get_pango_context() instead of this function, to get the appropriate context for the widget you intend to render text onto.

The newly created context will have the default font options (see cairo_font_options_t) for the screen; if these options change it will not be updated. Using gtk_widget_get_pango_context() is more convenient if you want to keep a context around and track changes to the screen’s font rendering settings.

Since: 2.2

gdk_pango_context_get_for_display ()

PangoContext *
gdk_pango_context_get_for_display (GdkDisplay *display);

Creates a PangoContext for display .

The context must be freed when you’re finished with it.

When using GTK+, normally you should use gtk_widget_get_pango_context() instead of this function, to get the appropriate context for the widget you intend to render text onto.

The newly created context will have the default font options (see cairo_font_options_t) for the display; if these options change it will not be updated. Using gtk_widget_get_pango_context() is more convenient if you want to keep a context around and track changes to the font rendering settings.

Since: 3.22