Re: pango_cairo_update_layout()

[Behdad Esfahbod <behdad behdad org>]

Theo Veenker wrote:
> Hi,

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.

It's very delicate.  For example, if you have hinting enabled, then the size
of a layout with identity matrix may be different from one of a rotated matrix
as hinting is only done with axis-aligned transforms.  And for pango to pick
up the matrix from your cairo_t you need to make that function call.

behdad

> Theo
> 
> 
> _______________________________________________
> gtk-i18n-list mailing list
> gtk-i18n-list gnome org
> http://mail.gnome.org/mailman/listinfo/gtk-i18n-list
>