forked from AuroraMiddleware/gtk
994 lines
29 KiB
XML
994 lines
29 KiB
XML
<?xml version="1.0"?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
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"http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
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]>
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<refentry id="gtk-question-index">
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<refmeta>
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<refentrytitle>Common Questions</refentrytitle>
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<manvolnum>3</manvolnum>
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<refmiscinfo>Common Questions</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>Common Questions</refname>
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<refpurpose>
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Find answers to common questions in the GTK+ manual
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</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Questions and Answers</title>
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<para>
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This is an "index" of the reference manual organized by common "How do
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I..." questions. If you aren't sure which documentation to read for
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the question you have, this list is a good place to start.
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</para>
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<qandaset>
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<qandadiv><title>General</title>
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<qandaentry>
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<question><para>
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How do I get started with GTK+?
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</para></question>
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<answer><para>
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The GTK+ <ulink url="http://www.gtk.org">website</ulink> offers some
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<ulink url="http://www.gtk.org/documentation">tutorials</ulink> and other
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documentation (most of it about GTK+ 2.x, but mostly still applicable).
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More documentation ranging from whitepapers to online books can be found at
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the <ulink url="http://developer.gnome.org">GNOME developer's site</ulink>.
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After studying these materials you should be well prepared to come back to
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this reference manual for details.
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</para></answer>
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</qandaentry>
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<qandaentry>
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<question><para>
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Where can I get help with GTK+, submit a bug report, or make a feature
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request?
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</para></question>
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<answer>
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<para>
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See the <link linkend="gtk-resources">documentation on this topic</link>.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question><para>How do I port from one GTK+
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version to another?</para></question>
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<answer>
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<para>
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See <xref linkend="gtk-migrating-2-to-3"/>.
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You may also find useful information in the documentation for
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specific widgets and functions.
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</para>
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<para>
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If you have a question not covered in the manual, feel free to
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ask on the mailing lists and please <ulink
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url="http://bugzilla.gnome.org">file a bug report</ulink> against the
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documentation.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question><para>
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How does memory management work in GTK+? Should I free data returned
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from functions?
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</para></question>
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<answer>
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<para>
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See the documentation for #GObject and #GInitiallyUnowned. For #GObject note
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specifically g_object_ref() and g_object_unref(). #GInitiallyUnowned is a
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subclass of #GObject so the same points apply, except that it has a "floating"
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state (explained in its documentation).
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</para>
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<para>
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For strings returned from functions, they will be declared "const"
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if they should not be freed. Non-const strings should be
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freed with g_free(). Arrays follow the same rule. If you find an
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undocumented exception to the rules, please report a bug to <ulink
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url="http://bugzilla.gnome.org">http://bugzilla.gnome.org</ulink>.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question>
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<para>
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Why does my program leak memory, if I destroy a widget immediately
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after creating it ?
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</para>
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</question>
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<answer>
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<para>
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If <structname>GtkFoo</structname> isn't a toplevel window, then
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<informalexample><programlisting>
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foo = gtk_foo_new (<!-- -->);
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gtk_widget_destroy (foo);
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</programlisting></informalexample>
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is a memory leak, because no one assumed the initial floating
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reference. If you are using a widget and you aren't immediately
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packing it into a container, then you probably want standard
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reference counting, not floating reference counting.
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</para>
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<para>
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To to get this, you must acquire a reference to the widget and drop the
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floating reference (<quote>ref and sink</quote> in GTK+ parlance) after
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creating it:
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<informalexample><programlisting>
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foo = gtk_foo_new (<!-- -->);
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g_object_ref_sink (foo);
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</programlisting></informalexample>
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When you want to get rid of the widget, you must call gtk_widget_destroy()
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to break any external connections to the widget before dropping your
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reference:
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<informalexample><programlisting>
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gtk_widget_destroy (foo);
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g_object_unref (foo);
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</programlisting></informalexample>
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When you immediately add a widget to a container, it takes care of
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assuming the initial floating reference and you don't have to worry
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about reference counting at all ... just call gtk_widget_destroy()
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to get rid of the widget.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question><para>
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How do I use GTK+ with threads?
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</para></question>
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<answer>
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<para>
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This is covered in the <link linkend="gdk-Threads">GDK threads
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documentation</link>. See also the <link linkend="glib-Threads">GThread</link>
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documentation for portable threading primitives.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question><para>
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How do I internationalize a GTK+ program?
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</para></question>
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<answer>
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<para>
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Most people use <ulink url="http://www.gnu.org/software/gettext/">GNU
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gettext</ulink>, already required in order to install GLib. On a UNIX
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or Linux system with gettext installed, type <literal>info gettext</literal>
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to read the documentation.
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</para>
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<para>
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The short checklist on how to use gettext is: call <literal>bindtextdomain(<!-- -->)</literal> so
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gettext can find the files containing your translations, call textdomain()
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to set the default translation domain, call <literal>bind_textdomain_codeset(<!-- -->)</literal> to
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request that all translated strings are returned in UTF-8, then call
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gettext() to look up each string to be translated in the default domain.
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</para>
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<para>
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<filename>gi18n.h</filename> provides the following shorthand macros for
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convenience.
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Conventionally, people define macros as follows for convenience:
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<informalexample>
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<programlisting>
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#define _(x) gettext (x)
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#define N_(x) x
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#define C_(ctx,x) pgettext (ctx, x)
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</programlisting>
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</informalexample>
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You use N_() (N stands for no-op) to mark a string for translation in
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a location where a function call to gettext() is not allowed, such as
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in an array initializer.
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You eventually have to call gettext() on the string to actually fetch
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the translation. _() both marks the string for translation and actually
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translates it.
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The C_() macro (C stands for context) adds an additional context to
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the string that is marked for translation, which can help to disambiguate
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short strings that might need different translations in different
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parts of your program.
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</para>
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<para>
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Code using these macros ends up looking like this:
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<informalexample>
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<programlisting>
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#include <gi18n.h>
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static const char *global_variable = N_("Translate this string");
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static void
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make_widgets (void)
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{
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GtkWidget *label1;
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GtkWidget *label2;
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label1 = gtk_label_new (_("Another string to translate"));
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label2 = gtk_label_new (_(global_variable));
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...
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</programlisting>
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</informalexample>
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</para>
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<para>
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Libraries using gettext should use dgettext() instead of gettext(), which
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allows them to specify the translation domain each time they ask for a
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translation. Libraries should also avoid calling textdomain(), since
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they will be specifying the domain instead of using the default.
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</para>
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<para>
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With the convention that the macro <literal>GETTEXT_PACKAGE</literal> is
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defined to hold your libraries translation domain,
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<filename>gi18n-lib.h</filename> can be included to provide
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the following convenience:
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<informalexample>
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<programlisting>
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#define _(x) dgettext (GETTEXT_PACKAGE, x)
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</programlisting>
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</informalexample>
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question>
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<para>
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How do I use non-ASCII characters in GTK+ programs ?
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</para>
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</question>
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<answer>
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<para>
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GTK+ uses <ulink url="http://www.unicode.org">Unicode</ulink> (more exactly
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UTF-8) for all text. UTF-8 encodes each Unicode codepoint as a sequence of
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one to six bytes and has a number of nice properties which make it a good
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choice for working with Unicode text in C programs:
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<itemizedlist>
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<listitem><para>
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ASCII characters are encoded by their familiar ASCII codepoints.
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</para></listitem>
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<listitem><para>
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ASCII characters never appear as part of any other character.
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</para></listitem>
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<listitem><para>
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The zero byte doesn't occur as part of a character, so that UTF-8 strings
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can be manipulated with the usual C library functions for handling
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zero-terminated strings.
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</para></listitem>
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</itemizedlist>
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More information about Unicode and UTF-8 can be found in the
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<ulink url="http://www.cl.cam.ac.uk/~mgk25/unicode.html">UTF-8 and Unicode
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FAQ for Unix/Linux</ulink>.
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GLib provides functions for converting strings between UTF-8 and other
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encodings, see g_locale_to_utf8() and g_convert().
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</para>
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<para>
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Text coming from external sources (e.g. files or user input), has to be
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converted to UTF-8 before being handed over to GTK+. The following example
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writes the content of a IS0-8859-1 encoded text file to
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<literal>stdout</literal>:
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<informalexample><programlisting>
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gchar *text, *utf8_text;
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gsize length;
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GError *error = NULL;
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if (g_file_get_contents (filename, &text, &length, NULL))
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{
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utf8_text = g_convert (text, length, "UTF-8", "ISO-8859-1",
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NULL, NULL, &error);
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if (error != NULL)
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{
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fprintf ("Couldn't convert file %s to UTF-8\n", filename);
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g_error_free (error);
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}
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else
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g_print (utf8_text);
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}
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else
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fprintf (stderr, "Unable to read file %s\n", filename);
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</programlisting></informalexample>
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</para>
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<para>
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For string literals in the source code, there are several alternatives for
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handling non-ASCII content:
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<variablelist>
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<varlistentry><term>direct UTF-8</term>
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<listitem><para>
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If your editor and compiler are capable of handling UTF-8 encoded sources,
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it is very convenient to simply use UTF-8 for string literals, since it
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allows you to edit the strings in "wysiwyg". Note that choosing this option
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may reduce the portability of your code.
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</para></listitem>
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</varlistentry>
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<varlistentry><term>escaped UTF-8</term>
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<listitem><para>
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Even if your toolchain can't handle UTF-8 directly, you can still encode
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string literals in UTF-8 by using octal or hexadecimal escapes like
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<literal>\212</literal> or <literal>\xa8</literal> to encode each byte.
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This is portable, but modifying the escaped strings is not very convenient.
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Be careful when mixing hexadecimal escapes with ordinary text;
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<literal>"\xa8abcd"</literal> is a string of length 1 !
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</para></listitem>
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</varlistentry>
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<varlistentry><term>runtime conversion</term>
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<listitem><para>
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If the string literals can be represented in an encoding which your
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toolchain can handle (e.g. IS0-8859-1), you can write your source files
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in that encoding and use g_convert() to convert the strings to UTF-8 at
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runtime. Note that this has some runtime overhead, so you may want to move
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the conversion out of inner loops.
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</para></listitem>
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</varlistentry>
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</variablelist>
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Here is an example showing the three approaches using the copyright sign
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© which has Unicode and ISO-8859-1 codepoint 169 and is represented
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in UTF-8 by the two bytes 194, 169, or <literal>"\302\251"</literal> as
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a string literal:
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<informalexample><programlisting>
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g_print ("direct UTF-8: ©");
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g_print ("escaped UTF-8: \302\251");
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text = g_convert ("runtime conversion: ©", -1, "ISO-8859-1", "UTF-8", NULL, NULL, NULL);
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g_print(text);
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g_free (text);
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</programlisting></informalexample>
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</para>
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<para>
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If you are using gettext() to localize your application, you need to
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call <literal>bind_textdomain_codeset(<!-- -->)</literal> to ensure that translated strings are
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returned in UTF-8 encoding.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question><para>
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How do I use GTK+ with C++?
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</para></question>
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<answer>
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<para>
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There are two ways to approach this. The GTK+ header files use the subset
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of C that's also valid C++, so you can simply use the normal GTK+ API
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in a C++ program. Alternatively, you can use a "C++ binding"
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such as <ulink url="http://gtkmm.sourceforge.net/">gtkmm</ulink>
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which provides a native C++ API.
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</para>
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<para>
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When using GTK+ directly, keep in mind that only functions can be
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connected to signals, not methods. So you will need to use global
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functions or "static" class functions for signal connections.
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</para>
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<para>
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Another common issue when using GTK+ directly is that
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C++ will not implicitly convert an integer to an enumeration.
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This comes up when using bitfields; in C you can write the following
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code:
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<informalexample>
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<programlisting>
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gdk_window_set_events (gdk_window,
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GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK);
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</programlisting>
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</informalexample>
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while in C++ you must write:
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<informalexample>
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<programlisting>
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gdk_window_set_events (gdk_window,
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(GdkEventMask) GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK);
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</programlisting>
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</informalexample>
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There are very few functions that require this cast, however.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question><para>
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How do I use GTK+ with other non-C languages?
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</para></question>
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<answer>
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<para>
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See the <ulink url="http://www.gtk.org/bindings.html">list of language
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bindings</ulink> on <ulink
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url="http://www.gtk.org">http://www.gtk.org</ulink>.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question><para>
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How do I load an image or animation from a file?
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</para></question>
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<answer>
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<para>
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To load an image file straight into a display widget, use
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gtk_image_new_from_file() <footnote><para> If the file load fails,
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gtk_image_new_from_file() will display no image graphic — to detect
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a failed load yourself, use gdk_pixbuf_new_from_file() directly, then
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gtk_image_new_from_pixbuf().</para></footnote>.
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To load an image for another purpose, use gdk_pixbuf_new_from_file(). To i
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load an animation, use gdk_pixbuf_animation_new_from_file().
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gdk_pixbuf_animation_new_from_file() can also load non-animated images, so
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use it in combination with gdk_pixbuf_animation_is_static_image() to load a
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file of unknown type.
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</para>
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<para>
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To load an image or animation file asynchronously (without blocking), use
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#GdkPixbufLoader.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question><para>
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How do I draw text ?
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</para></question>
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<answer>
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<para>
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To draw a piece of text, use a Pango layout and pango_cairo_show_layout().
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<informalexample>
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<programlisting>
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layout = gtk_widget_create_pango_layout (widget, text);
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fontdesc = pango_font_description_from_string ("Luxi Mono 12");
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pango_layout_set_font_description (layout, fontdesc);
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pango_cairo_show_layout (cr, layout);
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pango_font_description_free (fontdesc);
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g_object_unref (layout);
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</programlisting>
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</informalexample>
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</para>
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<para>
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See also the
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<ulink url="http://developer.gnome.org/pango/stable/pango-Cairo-Rendering.html">Cairo Rendering</ulink>
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section of <ulink url="http://developer.gnome.org/pango/stable/">Pango manual</ulink>.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question>
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<para>
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How do I measure the size of a piece of text ?
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</para>
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</question>
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<answer>
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<para>
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To obtain the size of a piece of text, use a Pango layout and
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pango_layout_get_pixel_size(), using code like the following:
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<informalexample>
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<programlisting>
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layout = gtk_widget_create_pango_layout (widget, text);
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fontdesc = pango_font_description_from_string ("Luxi Mono 12");
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pango_layout_set_font_description (layout, fontdesc);
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pango_layout_get_pixel_size (layout, &width, &height);
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pango_font_description_free (fontdesc);
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g_object_unref (layout);
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</programlisting>
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</informalexample>
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</para>
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<para>
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See also the
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<ulink url="http://developer.gnome.org/pango/stable/pango-Layout-Objects.html">Layout Objects</ulink>
|
|
section of <ulink url="http://developer.gnome.org/pango/stable/">Pango manual</ulink>.
|
|
</para>
|
|
</answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question>
|
|
<para>
|
|
Why are types not registered if I use their <literal>GTK_TYPE_BLAH</literal>
|
|
macro ?
|
|
</para>
|
|
</question>
|
|
|
|
<answer>
|
|
<para>
|
|
The <literal>GTK_TYPE_BLAH</literal> macros are defined as calls to
|
|
<literal>gtk_blah_get_type(<!-- -->)</literal>, and the <literal>_get_type(<!-- -->)</literal>
|
|
functions are declared as %G_GNUC_CONST which allows the compiler to optimize
|
|
the call away if it appears that the value is not being used.
|
|
</para>
|
|
|
|
<para>
|
|
A common workaround for this problem is to store the result in a volatile
|
|
variable, which keeps the compiler from optimizing the call away.
|
|
<informalexample><programlisting>
|
|
volatile GType dummy = GTK_TYPE_BLAH;
|
|
</programlisting></informalexample>
|
|
</para>
|
|
</answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question>
|
|
<para>
|
|
How do I create a transparent toplevel window ?
|
|
</para>
|
|
</question>
|
|
|
|
<answer>
|
|
<para>
|
|
To make a window transparent, it needs to use a visual which supports that.
|
|
This is done by getting the RGBA visual of the screen with
|
|
gdk_screen_get_rgba_visual() and setting it on the window. Note that
|
|
gdk_screen_get_rgba_visual() will return %NULL if transparent windows
|
|
are not supported on the screen, you should fall back to
|
|
gdk_screen_get_system_visual() in that case. Additionally, note that this
|
|
will change from screen to screen, so it needs to be repeated whenever the
|
|
window is moved to a different screen.
|
|
<informalexample><programlisting>
|
|
GdkVisual *visual;
|
|
|
|
visual = gdk_screen_get_rgba_visual (screen);
|
|
if (visual == NULL)
|
|
visual = gdk_screen_get_system_visual (screen);
|
|
|
|
gtk_widget_set_visual (GTK_WIDGET (window), visual);
|
|
</programlisting></informalexample>
|
|
To fill the alpha channel on the window simply use cairos
|
|
RGBA drawing capabilities.
|
|
</para>
|
|
<para>
|
|
Note that the presence of an RGBA visual is no guarantee that the
|
|
window will actually appear transparent on screen. On X11, this
|
|
requires a compositing manager to be running. See
|
|
gtk_widget_is_composited() for a way to find out if the alpha
|
|
channel will be respected.
|
|
</para>
|
|
</answer>
|
|
</qandaentry>
|
|
|
|
</qandadiv>
|
|
|
|
<qandadiv><title>Which widget should I use...</title>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
...for lists and trees?
|
|
</para></question>
|
|
|
|
<answer>
|
|
<para>
|
|
See <link linkend="TreeWidget">tree widget overview</link> — you
|
|
should use the #GtkTreeView widget. (A list is just a tree with no branches,
|
|
so the tree widget is used for lists as well).
|
|
</para>
|
|
</answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
...for multi-line text display or editing?
|
|
</para></question>
|
|
|
|
<answer>
|
|
<para>
|
|
See <link linkend="TextWidget">text widget overview</link> — you
|
|
should use the #GtkTextView widget.
|
|
</para>
|
|
<para>
|
|
If you only have a small amount of text, #GtkLabel may also be appropriate
|
|
of course. It can be made selectable with gtk_label_set_selectable(). For a
|
|
single-line text entry, see #GtkEntry.
|
|
</para>
|
|
</answer>
|
|
</qandaentry>
|
|
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
...to display an image or animation?
|
|
</para></question>
|
|
|
|
<answer>
|
|
<para>
|
|
#GtkImage can display images in just about any format GTK+ understands.
|
|
You can also use #GtkDrawingArea if you need to do something more complex,
|
|
such as draw text or graphics over the top of the image.
|
|
</para>
|
|
</answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
...for presenting a set of mutually-exclusive choices, where Windows
|
|
would use a combo box?
|
|
</para></question>
|
|
|
|
<answer>
|
|
<para>
|
|
With GTK+, a #GtkComboBox is the recommended widget to use for this use case.
|
|
This widget looks like either a combo box or the current option menu, depending
|
|
on the current theme. If you need an editable text entry, use the
|
|
#GtkComboBox:has-entry property.
|
|
</para>
|
|
</answer>
|
|
</qandaentry>
|
|
|
|
</qandadiv>
|
|
|
|
<qandadiv><title>GtkWidget</title>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
How do I change the color of a widget?
|
|
</para></question>
|
|
|
|
<answer><para>
|
|
See gtk_widget_override_color() and gtk_widget_override_background_color().
|
|
You can also change the appearance of a widget by installing a
|
|
custom style provider, see gtk_style_context_add_provider().
|
|
</para>
|
|
|
|
<para>To change the background color for widgets such as #GtkLabel that
|
|
have no background, place them in a #GtkEventBox and set the background
|
|
of the event box.
|
|
</para></answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
How do I change the font of a widget?
|
|
</para></question>
|
|
|
|
<answer><para>
|
|
This has several possible answers, depending on what exactly you want to
|
|
achieve. One option is gtk_widget_override_font().
|
|
<informalexample><programlisting>
|
|
PangoFontDesc *font_desc = pango_font_description_new (<!-- -->);
|
|
pango_font_description_set_size (font_desc, 40);
|
|
gtk_widget_override_font (widget, font);
|
|
pango_font_description_free (font_desc);
|
|
</programlisting></informalexample>
|
|
</para>
|
|
<para>
|
|
If you want to make the text of a label larger, you can use
|
|
gtk_label_set_markup():
|
|
<informalexample><programlisting>
|
|
gtk_label_set_markup (label, "<big>big text</big>");
|
|
</programlisting></informalexample>
|
|
This is preferred for many apps because it's a relative size to the
|
|
user's chosen font size. See g_markup_escape_text() if you are
|
|
constructing such strings on the fly.
|
|
</para>
|
|
<para>
|
|
You can also change the font of a widget by putting
|
|
<programlisting>
|
|
.my-widget-class {
|
|
font: Sans 30;
|
|
}
|
|
</programlisting>
|
|
in a CSS file, loading it with gtk_css_provider_load_from_file(), and
|
|
adding the provider with gtk_style_context_add_provider_for_screen().
|
|
To associate this style information with your widget, set a style class
|
|
on its #GtkStyleContext using gtk_style_context_add_class().
|
|
The advantage of this approach is that users can then override the font
|
|
you have chosen. See the #GtkStyleContext documentation for more discussion.
|
|
</para>
|
|
</answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
How do I disable/ghost/desensitize a widget?
|
|
</para></question>
|
|
|
|
<answer><para>
|
|
In GTK+ a disabled widget is termed "insensitive."
|
|
See gtk_widget_set_sensitive().
|
|
</para></answer>
|
|
</qandaentry>
|
|
|
|
</qandadiv>
|
|
|
|
|
|
<qandadiv><title>GtkTextView</title>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
How do I get the contents of the entire text widget as a string?
|
|
</para></question>
|
|
|
|
<answer><para>
|
|
See gtk_text_buffer_get_bounds() and gtk_text_buffer_get_text()
|
|
or gtk_text_iter_get_text().
|
|
</para>
|
|
<para>
|
|
<informalexample><programlisting>
|
|
GtkTextIter start, end;
|
|
GtkTextBuffer *buffer;
|
|
char *text;
|
|
|
|
buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (text_view));
|
|
gtk_text_buffer_get_bounds (buffer, &start, &end);
|
|
text = gtk_text_iter_get_text (&start, &end);
|
|
/* use text */
|
|
g_free (text);
|
|
</programlisting></informalexample>
|
|
</para></answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
How do I make a text widget display its complete contents in a specific font?
|
|
</para></question>
|
|
|
|
<answer><para>
|
|
If you use gtk_text_buffer_insert_with_tags() with appropriate tags to
|
|
select the font, the inserted text will have the desired appearance, but
|
|
text typed in by the user before or after the tagged block will appear in
|
|
the default style.
|
|
</para>
|
|
<para>
|
|
To ensure that all text has the desired appearance, use
|
|
gtk_widget_override_font() to change the default font for the widget.
|
|
</para></answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question>
|
|
<para>
|
|
How do I make a text view scroll to the end of the buffer automatically ?
|
|
</para>
|
|
</question>
|
|
|
|
<answer>
|
|
<para>
|
|
A good way to keep a text buffer scrolled to the end is to place a
|
|
<link linkend="GtkTextMark">mark</link> at the end of the buffer, and
|
|
give it right gravity. The gravity has the effect that text inserted
|
|
at the mark gets inserted <emphasis>before</emphasis>, keeping the mark
|
|
at the end.
|
|
</para>
|
|
|
|
<para>
|
|
To ensure that the end of the buffer remains visible, use
|
|
gtk_text_view_scroll_to_mark() to scroll to the mark after
|
|
inserting new text.
|
|
</para>
|
|
|
|
<para>
|
|
The gtk-demo application contains an example of this technique.
|
|
</para>
|
|
</answer>
|
|
</qandaentry>
|
|
</qandadiv>
|
|
|
|
|
|
|
|
<qandadiv><title>#GtkTreeView</title>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
How do I associate some data with a row in the tree?
|
|
</para></question>
|
|
|
|
<answer>
|
|
<para>
|
|
Remember that the #GtkTreeModel columns don't necessarily have to be
|
|
displayed. So you can put non-user-visible data in your model just
|
|
like any other data, and retrieve it with gtk_tree_model_get().
|
|
See the <link linkend="TreeWidget">tree widget overview</link>.
|
|
</para>
|
|
</answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
How do I put an image and some text in the same column?
|
|
</para></question>
|
|
|
|
<answer>
|
|
<para>
|
|
You can pack more than one #GtkCellRenderer into a single #GtkTreeViewColumn
|
|
using gtk_tree_view_column_pack_start() or gtk_tree_view_column_pack_end().
|
|
So pack both a #GtkCellRendererPixbuf and a #GtkCellRendererText into the
|
|
column.
|
|
</para>
|
|
</answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
I can set data easily on my #GtkTreeStore/#GtkListStore models using
|
|
gtk_list_store_set() and gtk_tree_store_set(), but can't read it back?
|
|
</para></question>
|
|
|
|
<answer>
|
|
<para>
|
|
Both the #GtkTreeStore and the #GtkListStore implement the #GtkTreeModel
|
|
interface. Consequentially, you can use any function this interface
|
|
implements. The easiest way to read a set of data back is to use
|
|
gtk_tree_model_get().
|
|
</para>
|
|
</answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
How do I change the way that numbers are formatted by #GtkTreeView?
|
|
</para></question>
|
|
<answer><para>
|
|
Use gtk_tree_view_insert_column_with_data_func()
|
|
or gtk_tree_view_column_set_cell_data_func() and do the conversion
|
|
from number to string yourself (with, say, g_strdup_printf()).
|
|
</para>
|
|
|
|
<para>
|
|
The following example demonstrates this:
|
|
<informalexample><programlisting>
|
|
enum
|
|
{
|
|
DOUBLE_COLUMN,
|
|
N_COLUMNS
|
|
};
|
|
|
|
GtkListStore *mycolumns;
|
|
GtkTreeView *treeview;
|
|
|
|
void
|
|
my_cell_double_to_text (GtkTreeViewColumn *tree_column,
|
|
GtkCellRenderer *cell,
|
|
GtkTreeModel *tree_model,
|
|
GtkTreeIter *iter,
|
|
gpointer data)
|
|
{
|
|
GtkCellRendererText *cell_text = (GtkCellRendererText *)cell;
|
|
gdouble d;
|
|
gchar *text;
|
|
|
|
/* Get the double value from the model. */
|
|
gtk_tree_model_get (tree_model, iter, (gint)data, &d, -1);
|
|
/* Now we can format the value ourselves. */
|
|
text = g_strdup_printf ("%.2f", d);
|
|
g_object_set (cell, "text", text, NULL);
|
|
g_free (text);
|
|
}
|
|
|
|
void
|
|
set_up_new_columns (GtkTreeView *myview)
|
|
{
|
|
GtkCellRendererText *renderer;
|
|
GtkTreeViewColumn *column;
|
|
GtkListStore *mycolumns;
|
|
|
|
/* Create the data model and associate it with the given TreeView */
|
|
mycolumns = gtk_list_store_new (N_COLUMNS, G_TYPE_DOUBLE);
|
|
gtk_tree_view_set_model (myview, GTK_TREE_MODEL (mycolumns));
|
|
|
|
/* Create a GtkCellRendererText */
|
|
renderer = gtk_cell_renderer_text_new (<!-- -->);
|
|
|
|
/* Create a new column that has a title ("Example column"),
|
|
* uses the above created renderer that will render the double
|
|
* value into text from the associated model's rows.
|
|
*/
|
|
column = gtk_tree_view_column_new (<!-- -->);
|
|
gtk_tree_view_column_set_title (column, "Example column");
|
|
renderer = gtk_cell_renderer_text_new (<!-- -->);
|
|
gtk_tree_view_column_pack_start (column, renderer, TRUE);
|
|
|
|
/* Append the new column after the GtkTreeView's previous columns. */
|
|
gtk_tree_view_append_column (GTK_TREE_VIEW (myview), column);
|
|
/* Since we created the column by hand, we can set it up for our
|
|
* needs, e.g. set its minimum and maximum width, etc.
|
|
*/
|
|
/* Set up a custom function that will be called when the column content
|
|
* is rendered. We use the func_data pointer as an index into our
|
|
* model. This is convenient when using multi column lists.
|
|
*/
|
|
gtk_tree_view_column_set_cell_data_func (column, renderer,
|
|
my_cell_double_to_text,
|
|
(gpointer)DOUBLE_COLUMN, NULL);
|
|
}
|
|
</programlisting></informalexample>
|
|
</para></answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
How do I hide the expander arrows in my tree view ?
|
|
</para></question>
|
|
|
|
<answer><para>
|
|
Set the expander-column property of the tree view to a hidden column.
|
|
See gtk_tree_view_set_expander_column() and gtk_tree_view_column_set_visible().
|
|
</para></answer>
|
|
</qandaentry>
|
|
|
|
</qandadiv>
|
|
|
|
<qandadiv><title>Using cairo with GTK+</title>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
How do I use cairo to draw in GTK+ applications ?
|
|
</para></question>
|
|
|
|
<answer><para>
|
|
The #GtkWidget::draw signal gets a ready-to-use cairo context
|
|
as parameter that you should use.
|
|
</para>
|
|
<para>
|
|
All drawing in GTK+ is normally done in a draw handler, and GTK+
|
|
creates a temporary pixmap for double-buffering the drawing.
|
|
It is possible to turn off double-buffering, with
|
|
gtk_widget_set_double_buffered(), but this is not ideal,
|
|
since it can cause some flickering.
|
|
</para>
|
|
</answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
Can I improve the performance of my application by using the
|
|
Glitz or GL backend of cairo ?
|
|
</para></question>
|
|
|
|
<answer><para>
|
|
No. The GDK X11 backend uses the cairo X backend (and the other
|
|
GDK backends use their respective native cairo backends). The
|
|
GTK+ developers believe that the best way to improving the GDK
|
|
drawing performance is to optimize the cairo X backend and the
|
|
relevant code paths in the X server that is uses (mostly the
|
|
Render extension).
|
|
</para></answer>
|
|
</qandaentry>
|
|
|
|
<qandaentry>
|
|
<question><para>
|
|
Can I use cairo to draw on a #GdkPixbuf ?
|
|
</para></question>
|
|
|
|
<answer><para>
|
|
No, at least not yet. The cairo image surface does not support the
|
|
pixel format used by GdkPixbuf.
|
|
</para></answer>
|
|
</qandaentry>
|
|
|
|
</qandadiv>
|
|
|
|
</qandaset>
|
|
|
|
</refsect1>
|
|
|
|
</refentry>
|