pygtk

PyGTK built on four libraries:

• GLib, a low-level core library that provides wrappers and interfaces for such run-time functionality as an event loop, threads, dynamic loading and an object system.
• Pango, a library for layout and rendering of text
• Cairo, a library for 2D graphics.
• ATK, a library that provides a set of interfaces for accessibility.

http://www.gtk.org/overview.html

Drawing text

n the getting started example, we showed how simple it can be to display a few text characters with cairo:

cairo_select_font_face (cr, "serif",
                        CAIRO_FONT_SLANT_NORMAL,
                        CAIRO_FONT_WEIGHT_BOLD);
cairo_set_font_size (cr, 32.0);
cairo_set_source_rgb (cr, 0.0, 0.0, 1.0);
cairo_move_to (cr, 10.0, 50.0);
cairo_show_text (cr, "Hello, world");

But as you read the cairo documentation and talk to expert cairo users, you learn that cairo_show_text is part of cairo's "toy" text API. It's fine for quick demos, and for learning how to use cairo, but it's not intended for use in actual applications.

It's not hard to run into some of the limitations of cairo_show_text. For example, it will only display glyphs from a single font. So if you happen to choose a font that doesn't provide glyphs covering every character in your string, then some characters just won't appear. It has a host of other limitations with respect to layout, ligatures, and shaping. We won't go into all of those details here, but suffice it to say that if you have any aspirations of having reasonable, internationalized text display in your application, then you don't want to be using cairo_show_text.

Meanwhile, the non-toy APIs in cairo, (cairo_show_glyphs and cairo_show_text_glyphs), are really hard to use. Compared to cairo_show_text, these still don't do any of the heavy lifting of text, but instead expect that the caller has done all of that already. So you could use these as the basis of a sophisticated text-layout engine, but chances are that you'd rather spend the next several years on your application instead.

Fortunately, the pango library exists and does do sophisticated text layout, shaping, etc. and integrates very nicely with cairo. We heartily recommend that "real" applications wanting to display text with cairo use pango to do it.

And it's really not that hard to get started using pango. The pango-using equivalent of our code above is:

#include <pango/pangocairo.h>
PangoLayout *layout;
PangoFontDescription *font_description;

font_description = pango_font_description_new ();
pango_font_description_set_family (font_description, "serif");
pango_font_description_set_weight (font_description, PANGO_WEIGHT_BOLD);
pango_font_description_set_absolute_size (font_description,
                                          32 * PANGO_SCALE);

layout = pango_cairo_create_layout (cr);
pango_layout_set_font_description (layout, font_description);
pango_layout_set_text (layout, "Hello, world", -1);

cairo_set_source_rgb (cr, 0.0, 0.0, 1.0);
cairo_move_to (cr, 10.0, 50.0);
pango_cairo_show_layout (cr, layout);

g_object_unref (layout);
pango_font_description_free (font_description);

Note that this does have slightly different text placement from the previous example. To get the same text origin as cairo_show_text, (baseline left, instead of Pango's top left), replace the pango_cairo_show_layout line with this:

pango_cairo_show_layout_line (cr, pango_layout_get_line (layout, 0))

http://cairographics.org/FAQ/#using_pango