More info about particular GDK and GdkPixbuf functions and methods can be found at the following URLs: http://developer.gnome.org/doc/API/gdk/index.html http://developer.gnome.org/doc/API/2.0/gdk/index.html http://developer.gnome.org/doc/API/2.0/gdk-pixbuf/index.html PHP-GTK currently supports only GDK 1.x but GDK 2.x documentation may have better documentation for methods existing in 1.x as well.