pango_cairo_update_layout()

[Theo Veenker <Theo Veenker let uu nl>]

Hi,

A question regarding pango_cairo_update_layout(). The example in
http://library.gnome.org/devel/pango/stable/pango-Cairo-Rendering.html
contains the following fragment:

  for (i = 0; i < N_WORDS; i++)
    {
      int width, height;
      double angle = (360. * i) / N_WORDS;
      double red;

      cairo_save (cr);

      /* Gradient from red at angle == 60 to blue at angle == 240 */
      red   = (1 + cos ((angle - 60) * G_PI / 180.)) / 2;
      cairo_set_source_rgb (cr, red, 0, 1.0 - red);

      cairo_rotate (cr, angle * G_PI / 180.);

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

      pango_layout_get_size (layout, &width, &height);
      cairo_move_to (cr, - ((double)width / PANGO_SCALE) / 2, - RADIUS);
      pango_cairo_show_layout (cr, layout);

      cairo_restore (cr);
    }

Why is it that it doesn't make a difference whether pango_cairo_update_layout()
is called or not. The output is the same. Is it really necessary to call this
function if only the cairo context changes? Why? In my own code I also don't
notice any diffrence if I just drop the pango_cairo_update_layout() call.

Theo