Gdk – 4.0: Pango Interaction
Description: Reference for Gdk-4.0: Pango Interaction

Pango is the text layout system used by GDK and GTK. The functions and types in this section are used to obtain clip regions for `PangoLayout`s, and to get `PangoContext`s that can be used with GDK.

## Using Pango in GDK

Creating a `PangoLayout` object is the first step in rendering text, and requires getting a handle to a `PangoContext`. For GTK programs, you’ll usually want to use Gtk.Widget.get_pango_context, or Gtk.Widget.create_pango_layout. Once you have a `PangoLayout`, you can set the text and attributes of it with Pango functions like `pango_layout_set_text()` and get its size with `pango_layout_get_size()`.

Note: Pango uses a fixed point system internally, so converting between Pango units and pixels using `PANGO_SCALE` or the `PANGO_PIXELS()` macro.

Rendering a Pango layout is done most simply with `pango_cairo_show_layout()`; you can also draw pieces of the layout with `pango_cairo_show_layout_line()`.

### Draw transformed text with Pango and cairo

    #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_surface_get_width (surface);
    height = gdk_surface_get_height (surface);
    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_display (display);
    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);

The example code above will yield the following result: