Migrating from GTK+ 2.x to GTK+ 3
GTK+ 3 is a major new version of GTK+ that breaks both API and ABI
compared to GTK+ 2.x, which has remained API- and ABI-stable for a
long time. Thankfully, most of the changes are not hard to adapt to
and there are a number of steps that you can take to prepare your
GTK+ 2.x application for the switch to GTK+ 3. After that, there's
a small number of adjustments that you may have to do when you actually
switch your application to build against GTK+ 3.
Preparation in GTK+ 2.x
The steps outlined in the following sections assume that your
application is working with GTK+ 2.24, which is the final stable
release of GTK+ 2.x. It includes all the necessary APIs and tools
to help you port your application to GTK+ 3. If you are still using
an older version of GTK+ 2.x, you should first get your application
to build and work with 2.24.
Do not include individual headers
With GTK+ 2.x it was common to include just the header files for
a few widgets that your application was using, which could lead
to problems with missing definitions, etc. GTK+ 3 tightens the
rules about which header files you are allowed to include directly.
The allowed header files are are
gtk/gtk.hfor GTKgtk/gtkunixprint.hfor low-level, UNIX-specific printing functionsgdk/gdk.hfor GDKgdk/gdkx.hfor GDK functions that are X11-specificgdk/gdkwin32.hfor GDK functions that are Windows-specific
(these relative paths are assuming that you are using the include
paths that are specified in the gtk+-2.0.pc file, as returned by
pkg-config --cflags gtk+-2.0.pc.)
To check that your application only includes the allowed headers,
you can use defines to disable inclusion of individual headers,
as follows:
make CFLAGS+="-DGTK_DISABLE_SINGLE_INCLUDES"
Do not use deprecated symbols
Over the years, a number of functions, and in some cases, entire
widgets have been deprecated. These deprecations are clearly spelled
out in the API reference, with hints about the recommended replacements.
The API reference also includes an
index of all deprecated
symbols.
To verify that your program does not use any deprecated symbols,
you can use defines to remove deprecated symbols from the header files,
as follows:
make CFLAGS+="-DGDK_DISABLE_DEPRECATED -DGTK_DISABLE_DEPRECATED"
Use accessor functions instead of direct access
GTK+ 3 removes many implementation details and struct members from
its public headers.
To ensure that your application does not have problems with this, you
define the preprocessor symbol GSEAL_ENABLE. This
will make the compiler catch all uses of direct access to struct fields
so that you can go through them one by one and replace them with a call
to an accessor function instead.
make CFLAGS+="-DGSEAL_ENABLE"
Replace GDK_<keyname> with GDK_KEY_<keyname>
Key constants have gained a _KEY_ infix.
For example, GDK_a is now
GDK_KEY_a. In GTK+ 2, the old names continue
to be available. In GTK+ 3 however, the old names will require
an explicit include of the gdkkeysyms-compat.h header.
Use cairo for drawing
In GTK+ 3, the GDK drawing API (which closely mimics the X
drawing API, which is itself modeled after PostScript) has been
removed. All drawing in GTK+ 3 is done via cairo.
The #GdkGC and #GdkImage objects, as well as all the functions using
them, are gone. This includes the gdk_draw family
of functions like gdk_draw_rectangle() and gdk_draw_drawable(). As
#GdkGC is roughly equivalent to #cairo_t and #GdkImage was used for
drawing images to GdkDrawables, which cairo supports automatically,
a transition is usually straightforward.
The following examples show a few common drawing idioms used by
applications that have been ported to use cairo and how the code
was replaced.
Drawing a GdkPixbuf onto a GdkDrawable
Drawing a pixbuf onto a drawable used to be done like this:
black_gc,
pixbuf,
0, 0
x, y,
gdk_pixbuf_get_width (pixbuf),
gdk_pixbuf_get_height (pixbuf),
GDK_RGB_DITHER_NORMAL,
0, 0);
]]>
Doing the same thing with cairo:
Note that very similar code can be used for drawing pixmaps
by using gdk_cairo_set_source_pixmap() instead of
gdk_cairo_set_source_pixbuf().
Drawing a tiled GdkPixmap to a GdkDrawable
Tiled pixmaps are often used for drawing backgrounds.
Old code looked something like this:
black_gc;
gdk_gc_set_tile (gc, pixmap);
gdk_gc_set_fill (gc, GDK_TILED);
gdk_gc_set_ts_origin (gc, x_origin, y_origin);
/* use */
gdk_draw_rectangle (drawable, gc, TRUE, 0, 0, width, height);
/* restore */
gdk_gc_set_tile (gc, NULL);
gdk_gc_set_fill (gc, GDK_SOLID);
gdk_gc_set_ts_origin (gc, 0, 0);
]]>
The equivalent cairo code looks like this:
Again, you can exchange pixbufs and pixmaps by using
gdk_cairo_set_source_pixbuf() instead of
gdk_cairo_set_source_pixmap().
Drawing a PangoLayout to a clipped area
Drawing layouts clipped is often used to avoid overdraw or to
allow drawing selections. Code would have looked like this:
text_gc[state];
gdk_gc_set_clip_rectangle (gc, &area);
/* use */
gdk_draw_layout (drawable, gc, x, y, layout);
/* restore */
gdk_gc_set_clip_rectangle (gc, NULL);
]]>
With cairo, the same effect can be achieved using:
text[state]);
/* draw the text */
cairo_move_to (cr, x, y);
pango_cairo_show_layout (cr, layout);
cairo_destroy (cr);
]]>
Clipping using cairo_clip() is of course not restricted to text
rendering and can be used everywhere where GC clips were used.
And using gdk_cairo_set_source_color() with style colors should
be used in all the places where a style’s GC was used to achieve
a particular color.
What should you be aware of ?No more stippling
Stippling is the usage of a bi-level mask, called a #GdkBitmap.
It was often used to achieve a checkerboard effect. You can use
cairo_mask() to achieve this effect. To get a checkerbox mask,
you can use code like this:
Note that stippling looks very outdated in UIs, and is rarely
used in modern applications. All properties that made use of
stippling have been removed from GTK+ 3. Most prominently,
stippling is absent from text rendering, in particular #GtkTextTag.
Using the the target drawable also as source or mask
The gdk_draw_drawable() function allowed using the same drawable
as source and target. This was often used to achieve a scrolling
effect. Cairo does not allow this yet. You can however use
cairo_push_group() to get a different intermediate target that
you can copy to. So you can replace this code:
By using this code:
The cairo developers plan to add self-copies in the future to allow
exactly this effect, so you might want to keep up on cairo
development to be able to change your code.
Using pango_cairo_show_layout(<!-- -->) instead of gdk_draw_layout_with_colors(<!-- -->)
GDK provided a way to ignore the color attributes of text and use
a hardcoded text color with the gdk_draw_layout_with_colors()
function. This is often used to draw text shadows or selections.
Pango’s cairo support does not yet provide this functionality. If
you use Pango layouts that change colors, the easiest way to achieve
a similar effect is using pango_cairo_layout_path() and cairo_fill()
instead of gdk_draw_layout_with_colors(). Note that this results in
a slightly uglier-looking text, as subpixel anti-aliasing is not
supported.
Changes that need to be done at the time of the switch
This section outlines porting tasks that you need to tackle when
you get to the point that you actually build your application against
GTK+ 3. Making it possible to prepare for these in GTK+ 2.24 would
have been either impossible or impractical.
Replace size_request by get_preferred_width/height
The request-phase of the traditional GTK+ geometry management
has been replaced by a more flexible height-for-width system,
which is described in detail in the API documentation
(see ). As a consequence,
the ::size-request signal and vfunc has been removed from
#GtkWidgetClass. The replacement for size_request() can
take several levels of sophistication:
As a minimal replacement to keep current functionality,
you can simply implement the get_preferred_width() and
get_preferred_height() vfuncs by calling your existing
size_request() function. So you go from
static void
my_widget_class_init (MyWidgetClass *class)
{
GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (class);
/* ... */
widget_class->size_request = my_widget_size_request;
/* ... */
}
to something that looks more like this:
static void
my_widget_get_preferred_width (GtkWidget *widget,
gint *minimal_width,
gint *natural_width)
{
GtkRequisition requisition;
my_widget_size_request (widget, &requisition);
*minimal_width = *natural_width = requisition.width;
}
static void
my_widget_get_preferred_height (GtkWidget *widget,
gint *minimal_height,
gint *natural_height)
{
GtkRequisition requisition;
my_widget_size_request (widget, &requisition);
*minimal_height = *natural_height = requisition.height;
}
/* ... */
static void
my_widget_class_init (MyWidgetClass *class)
{
GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (class);
/* ... */
widget_class->get_preferred_width = my_widget_get_preferred_width;
widget_class->get_preferred_height = my_widget_get_preferred_height;
/* ... */
}
Sometimes you can make things a little more streamlined
by replacing your existing size_request() implementation by
one that takes an orientation parameter:
static void
my_widget_get_preferred_size (GtkWidget *widget,
GtkOrientation orientation,
gint *minimal_size,
gint *natural_size)
{
/* do things that are common for both orientations ... */
if (orientation == GTK_ORIENTATION_HORIZONTAL)
{
/* do stuff that only applies to width... */
*minimal_size = *natural_size = ...
}
else
{
/* do stuff that only applies to height... */
*minimal_size = *natural_size = ...
}
}
static void
my_widget_get_preferred_width (GtkWidget *widget,
gint *minimal_width,
gint *natural_width)
{
my_widget_get_preferred_size (widget,
GTK_ORIENTATION_HORIZONTAL,
minimal_width,
natural_width);
}
static void
my_widget_get_preferred_height (GtkWidget *widget,
gint *minimal_height,
gint *natural_height)
{
my_widget_get_preferred_size (widget,
GTK_ORIENTATION_VERTICAL,
minimal_height,
natural_height);
}
/* ... */
If your widget can cope with a small size,
but would appreciate getting some more space (a common
example would be that it contains ellipsizable labels),
you can do that by making your get_preferred_width()/height()
functions return a smaller value for @minimal than for @natural.
For @minimal, you probably want to return the same value
that your size_request() function returned before (since
size_request() was defined as returning the minimal size
a widget can work with). A simple way to obtain good
values for @natural, in the case of containers, is to use
gtk_widget_get_preferred_width() and
gtk_widget_get_preferred_height() on the children of the
container, as in the following example:
static void
gtk_fixed_get_preferred_height (GtkWidget *widget,
gint *minimum,
gint *natural)
{
GtkFixed *fixed = GTK_FIXED (widget);
GtkFixedPrivate *priv = fixed->priv;
GtkFixedChild *child;
GList *children;
gint child_min, child_nat;
*minimum = 0;
*natural = 0;
for (children = priv->children; children; children = children->next)
{
child = children->data;
if (!gtk_widget_get_visible (child->widget))
continue;
gtk_widget_get_preferred_height (child->widget, &child_min, &child_nat);
*minimum = MAX (*minimum, child->y + child_min);
*natural = MAX (*natural, child->y + child_nat);
}
}
To make full use of the new capabilities of the
height-for-width geometry management, you need to additionally
implement the get_preferred_height_for_width() and
get_preferred_width_for_height(). For details on these functions,
see .
Replace GdkRegion by cairo_region_t
Starting with version 1.10, cairo provides a region API that is
equivalent to the GDK region API (which was itself copied from
the X server). Therefore, the region API has been removed in GTK+ 3.
Porting your application to the cairo region API should be a straight
find-and-replace task. Please refer to the following table:
GDKcairo#GdkRegion#cairo_region_t#GdkRectangle#cairo_rectangle_int_tgdk_rectangle_intersect()this function is still theregdk_rectangle_union()this function is still theregdk_region_new()cairo_region_create()gdk_region_copy()cairo_region_copy()gdk_region_destroy()cairo_region_destroy()gdk_region_rectangle()cairo_region_create_rectangle()gdk_region_get_clipbox()cairo_region_get_extents()gdk_region_get_rectangles()cairo_region_num_rectangles() and
cairo_region_get_rectangle()gdk_region_empty()cairo_region_is_empty()gdk_region_equal()cairo_region_equal()gdk_region_point_in()cairo_region_contains_point()gdk_region_rect_in()cairo_region_contains_rectangle()gdk_region_offset()cairo_region_translate()gdk_region_union_with_rect()cairo_region_union_rectangle()gdk_region_intersect()cairo_region_intersect()gdk_region_union()cairo_region_union()gdk_region_subtract()cairo_region_subtract()gdk_region_xor()cairo_region_xor()gdk_region_shrink()no replacementgdk_region_polygon()no replacement, use cairo paths instead
Replace GdkPixmap by cairo surfaces
The #GdkPixmap object and related functions have been removed.
In the cairo-centric world of GTK+ 3, cairo surfaces take over
the role of pixmaps.
Creating custom cursors
One place where pixmaps were commonly used is to create custom
cursors:
GdkCursor *cursor;
GdkPixmap *pixmap;
cairo_t *cr;
GdkColor fg = { 0, 0, 0, 0 };
pixmap = gdk_pixmap_new (NULL, 1, 1, 1);
cr = gdk_cairo_create (pixmap);
cairo_rectangle (cr, 0, 0, 1, 1);
cairo_fill (cr);
cairo_destroy (cr);
cursor = gdk_cursor_new_from_pixmap (pixmap, pixmap, &fg, &fg, 0, 0);
g_object_unref (pixmap);
The same can be achieved without pixmaps, by drawing onto
an image surface:
GdkCursor *cursor;
cairo_surface_t *s;
cairo_t *cr;
GdkPixbuf *pixbuf;
s = cairo_image_surface_create (CAIRO_FORMAT_A1, 3, 3);
cr = cairo_create (s);
cairo_arc (cr, 1.5, 1.5, 1.5, 0, 2 * M_PI);
cairo_fill (cr);
cairo_destroy (cr);
pixbuf = gdk_pixbuf_get_from_surface (NULL, s,
0, 0, 0, 0,
3, 3);
cairo_surface_destroy (s);
cursor = gdk_cursor_new_from_pixbuf (display, pixbuf, 0, 0);
g_object_unref (pixbuf);
Replace colormaps by visuals
For drawing with cairo, it is not necessary to allocate colors, and
a #GdkVisual provides enough information for cairo to handle colors
in 'native' surfaces. Therefore, #GdkColormap and related functions
have been removed in GTK+ 3, and visuals are used instead. The
colormap-handling functions of #GtkWidget (gtk_widget_set_colormap(),
etc) have been removed and gtk_window_set_visual() has been added.
Setting up a translucent windowYou might have a screen-changed handler like the following
to set up a translucent window with an alpha-channel:
static void
on_alpha_screen_changed (GtkWidget *widget,
GdkScreen *old_screen,
GtkWidget *label)
{
GdkScreen *screen = gtk_widget_get_screen (widget);
GdkColormap *colormap = gdk_screen_get_rgba_colormap (screen);
if (colormap == NULL)
colormap = gdk_screen_get_default_colormap (screen);
gtk_widget_set_colormap (widget, colormap);
}
With visuals instead of colormaps, this will look as follows:
static void
on_alpha_screen_changed (GtkWindow *window,
GdkScreen *old_screen,
GtkWidget *label)
{
GdkScreen *screen = gtk_widget_get_screen (GTK_WIDGET (window));
GdkVisual *visual = gdk_screen_get_rgba_visual (screen);
if (visual == NULL)
visual = gdk_screen_get_system_visual (screen);
gtk_window_set_visual (window, visual);
}
The GtkWidget::draw signal
The GtkWidget #GtkWidget::expose-event signal has been replaced by
a new #GtkWidget::draw signal, which takes a #cairo_t instead of
an expose event. The cairo context is being set up so that the origin
at (0, 0) coincides with the upper left corner of the widget, and
is properly clipped.
In other words, the cairo context of the draw signal is set
up in 'widget coordinates', which is different from traditional expose
event handlers, which always assume 'window coordinates'.
The widget is expected to draw itself with its allocated size, which
is available via the new gtk_widget_get_allocated_width() and
gtk_widget_get_allocated_height() functions. It is not necessary to
check for GTK_WIDGET_IS_DRAWABLE(), since GTK+ already does this check
before emitting the ::draw signal.
There are some special considerations for widgets with multiple windows.
Expose events are window-specific, and widgets with multiple windows
could expect to get an expose event for each window that needs to be
redrawn. Therefore, multi-window expose event handlers typically look
like this:
if (event->window == widget->window1)
{
/* ... draw window1 ... */
}
else if (event->window == widget->window2)
{
/* ... draw window2 ... */
}
...
In contrast, the ::draw signal handler may have to draw multiple
windows in one call. GTK+ has a convenience function
gtk_cairo_should_draw_window() that can be used to find out if
a window needs to be drawn. With that, the example above would look
like this (note that the 'else' is gone):
if (gtk_cairo_should_draw_window (cr, widget->window1)
{
/* ... draw window1 ... */
}
if (gtk_cairo_should_draw_window (cr, widget->window2)
{
/* ... draw window2 ... */
}
...
Another convenience function that can help when implementing
::draw for multi-window widgets is gtk_cairo_transform_to_window(),
which transforms a cairo context from widget-relative coordinates
to window-relative coordinates.
All GtkStyle drawing functions (gtk_paint_box(), etc) have been changed
to take a #cairo_t instead of a window and a clip area. ::draw
implementations will usually just use the cairo context that has been
passed in for this.
A simple ::draw function
gboolean
gtk_arrow_draw (GtkWidget *widget,
cairo_t *cr)
{
gint x, y;
gint width, height;
gint extent;
width = gtk_widget_get_allocated_width (widget);
height = gtk_widget_get_allocated_height (widget);
extent = MIN (width - 2 * PAD, height - 2 * PAD);
x = PAD;
y = PAD;
gtk_paint_arrow (gtk_widget_get_style (widget),
cr,
gtk_widget_get_state (widget),
GTK_SHADOW_OUT,
widget,
"arrow",
widget->priv->arrow_type,
TRUE,
x, y, extent, extent);
}
GtkProgressBar orientation
In GTK+ 2.x, #GtkProgressBar and #GtkCellRendererProgress were using the
GtkProgressBarOrientation enumeration to specify their orientation and
direction. In GTK+ 3, both the widget and the cell renderer implement
#GtkOrientable, and have an additional 'inverted' property to determine
their direction. Therefore, a call to gtk_progress_bar_set_orientation()
needs to be replaced by a pair of calls to
gtk_orientable_set_orientation() and gtk_progress_bar_set_inverted().
The following values correspond:
GtkScrolledWindow policy
The default values for the #GtkScrolledWindow:hscrollbar-policy and
#GtkScrolledWindow:vscrollbar-policy properties have been changed from
'never' to 'automatic'. If your application was relying on the default
value, you will have explicitly set it explicitly.
GtkObject is gone
GtkObject has been removed in GTK+ 3. Its remaining functionality,
the ::destroy signal, has been moved to GtkWidget. If you have non-widget
classes that are directly derived from GtkObject, you have to make
them derive from #GInitiallyUnowned (or, if you don't need the floating
functionality, #GObject). If you have widgets that override the
destroy class handler, you have to adust your class_init function,
since destroy is now a member of GtkWidgetClass:
GtkObjectClass *object_class = GTK_OBJECT_CLASS (class);
object_class->destroy = my_destroy;
becomes
GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (class);
widget_class->destroy = my_destroy;
In the unlikely case that you have a non-widget class that is derived
from GtkObject and makes use of the destroy functionality, you have
to implement ::destroy yourself.
Resize grips
The resize grip functionality has been moved from #GtkStatusbar
to #GtkWindow. Any window can now have resize grips, regardless whether
it has a statusbar or not. The functions
gtk_statusbar_set_has_resize_grip() and gtk_statusbar_get_has_resize_grip()
have disappeared, and instead there are now
gtk_window_set_has_resize_grip() and gtk_window_get_has_resize_grip().
Prevent mixed linkage
Linking against GTK+ 2.x and GTK+ 3 in the same process is problematic
and can lead to hard-to-diagnose crashes. The gtk_init() function in
both GTK+ 2.22 and in GTK+ 3 tries to detect this situation and abort
with a diagnostic message, but this check is not 100% reliable (e.g. if
the problematic linking happens only in loadable modules).
Direct linking of your application against both versions of GTK+ is
easy to avoid; the problem gets harder when your application is using
libraries that are themselves linked against some version of GTK+.
In that case, you have to verify that you are using a version of the
library that is linked against GTK+ 3.
If you are using packages provided by a distributor, it is likely that
parallel installable versions of the library exist for GTK+ 2.x and
GTK+ 3, e.g for vte, check for vte3; for webkitgtk look for webkitgtk3,
and so on.
Install GTK+ modules in the right place
Some software packages install loadable GTK+ modules such as theme engines,
gdk-pixbuf loaders or input methods. Since GTK+ 3 is parallel-installable
with GTK+ 2.x, the two GTK+ versions have separate locations for their
loadable modules. The location for GTK+ 2.x is
libdir/gtk-2.0
(and its subdirectories), for GTK+ 3 the location is
libdir/gtk-3.0
(and its subdirectories).
For some kinds of modules, namely input methods and pixbuf loaders,
GTK+ keeps a cache file with extra information about the modules.
For GTK+ 2.x, these cache files are located in
sysconfdir/gtk-2.0.
For GTK+ 3, they have been moved to
libdir/gtk-3.0/3.0.0/.
The commands that create these cache files have been renamed with a -3
suffix to make them parallel-installable.
Note that GTK+ modules often link against libgtk, libgdk-pixbuf, etc.
If that is the case for your module, you have to be careful to link the
GTK+ 2.x version of your module against the 2.x version of the libraries,
and the GTK+ 3 version against hte 3.x versions. Loading a module linked
against libgtk 2.x into an application using GTK+ 3 will lead to
unhappiness and must be avoided.