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This section outlines porting tasks that you need to tackle when you get to the point that you actually build your application against GTK+ 4. Making it possible to prepare for these in GTK+ 3 would have been either impossible or impractical.
The GdkScreen object has been removed in GTK+ 4. Most of its APIs already had replacements in GTK+ 3 and were deprecated, a few remaining replacements have been added to GdkDisplay.
The root window is an X11-centric concept that is no longer exposed in the
backend-neutral GDK API. gdk_surface_get_parent()
will return NULL
for toplevel
windows. If you need to interact with the X11 root window, you can use
gdk_x11_display_get_xrootwindow()
to get its XID.
This object is not useful with current GTK+ drawing APIs and has been removed without replacement.
The GdkDeviceManager object has been removed in GTK+ 4. Most of its APIs already had replacements in GTK+ 3 and were deprecated in favor of GdkSeat.
GdkWindow has been renamed to GdkSurface.
The gdk_window_new()
function has been replaced by a number of more
specialized constructors: gdk_surface_new_toplevel()
, gdk_surface_new_popup()
,
gdk_surface_new_temp()
, gdk_surface_new_child()
, gdk_surface_new_input()
,
gdk_wayland_surface_new_subsurface()
. Use the appropriate ones to create
your windows.
Native and foreign subwindows are no longer supported. These concepts were complicating the code and could not be supported across backends.
gdk_window_reparent()
is no longer available.
Direct access to GdkEvent structs is no longer possible in GTK+ 4. Some frequently-used fields already had accessors in GTK+ 3, and the remaining fields have gained accessors in GTK+ 4.
Event compression is now always enabled. If you need to see the uncoalesced
motion history, use gdk_event_get_motion_history()
.
The way to get a keymap has changed slightly. gdk_keymap_get_for_display()
has
been renamed to gdk_display_get_keymap()
.
The gtk_header_bar_set_show_close_button()
function has been renamed to
the more accurate name gtk_header_bar_set_show_title_buttons()
. The corresponding
getter and the property itself have also been renamed.
The getters in the GtkStyleContext API, such as
gtk_style_context_get_property()
, gtk_style_context_get()
,
or gtk_style_context_get_color()
have lost their state argument,
and always use the context's current state. Update all callers
to omit the state argument.
In GTK+ 4, the various GtkCssProvider load functions have lost their GError argument. If you want to handle CSS loading errors, use the “parsing-error” signal instead.
GTK+ 4 has removed the “border-width” property. Use other means to influence the spacing of your containers, such as the CSS margin and padding properties on child widgets.
GTK+ 3 used five different virtual functions in GtkWidget to
implement size requisition, namely the gtk_widget_get_preferred_width()
family of functions. To simplify widget implementations, GTK+4 uses
only one virtual function, GtkWidgetClass::measure()
that widgets
have to implement.
Instead of the GtkContainer subclass, in GTK+ 4, any widget can
have children, and there is new API to navigate the widget tree:
gtk_widget_get_first_child()
, gtk_widget_get_last_child()
,
gtk_widget_get_next_sibling()
, gtk_widget_get_prev_sibling()
.
The GtkContainer API still works, but if you are implementing
your own widgets, you should consider using the new APIs.
GTK+ now supports standard CSS syntax for both linear and radial gradients, just use those.
GTK+ now supports a more versatile -gtk-icon-filter instead. Replace -gtk-icon-effect: dim; with -gtk-icon-filter: opacity(0.5); and -gtk-icon-effect: hilight; with -gtk-icon-filter: brightness(1.2);.
gtk_widget_measure()
replaces the various gtk_widget_get_preferred_ functions
for querying sizes.
This area has seen the most radical changes in the transition from GTK+ 3
to GTK+ 4. Widgets no longer use a draw()
function to render their contents
to a cairo surface. Instead, they have a snapshot()
function that creates
one or more GskRenderNodes to represent their content. Third-party widgets
that use a draw()
function or a “draw” signal handler for custom
drawing will need to be converted to use gtk_snapshot_append_cairo()
.
The auxiliary GtkSnapshot object has APIs to help with creating render nodes.
If you are using a GtkDrawingArea for custom drawing, you need to switch
to using gtk_drawing_area_set_draw_func()
to set a draw function instead
of connnecting a handler to the “draw” signal.
A number of APIs for querying special-purpose windows have been removed,
since these windows are no longer publically available:
gtk_tree_view_get_bin_window()
, gtk_viewport_get_bin_window()
,
gtk_viewport_get_view_window()
.
The default value of “visible” in GTK+ 4 is TRUE
, so you no
longer need to explicitly show all your widgets. On the flip side, you
need to hide widgets that are not meant to be visible from the start.
A convenient way to remove unnecessary property assignments like this from ui files it run the command gtk4-builder-tool simplify --replace on them.
Widgets that appear and disappear with an animation, such as GtkPopover,
GtkInfoBar, GtkRevealer no longer use gtk_widget_show()
and gtk_widget_hide()
for this, but have gained dedicated APIs for this purpose that you should
use.
The gtk_init()
and gtk_init_check()
functions no longer accept commandline
arguments. Just call them without arguments. Other initialization functions
that were purely related to commandline argument handling, such as
gtk_parse_args()
and gtk_get_option_group()
, are gone. The APIs to
initialize GDK separately are also gone, but it is very unlikely
that you are affected by that.
A number of GdkPixbuf-based APIs have been removed. The available replacements are either using GIcon, or the newly introduced GdkTexture or GdkPaintable classes instead.
If you are dealing with pixbufs, you can use gdk_texture_new_for_pixbuf()
to convert them to texture objects where needed.
Event controllers and GtkGestures have already been introduced in GTK+ 3 to handle input for many cases. In GTK+ 4, even more are available, such as GtkEventControllerScroll and GtkEventControllerMotion, and the traditional widget signals for handling input, such as “motion-event” or “event” have been removed.
Only gtk_widget_queue_draw()
is left to mark a widget as needing redraw.
Variations like gtk_widget_queue_draw_rectangle()
or gtk_widget_queue_draw_region()
are no longer available.
The “draw” signal has been removed. Widgets need to implement the “snapshot” function now. Connecting draw signal handlers is no longer possible.
Observing widget contents and widget size is now done by using the GtkWidgetPaintable object instead of connecting to widget signals.
Instead of a monitor number, gtk_window_fullscreen_on_monitor()
now takes a
GdkMonitor argument.
Use the new gtk_widget_set_cursor()
function to set cursors, instead of
setting the cursor on the underlying window directly. This is necessary
because most widgets don't have their own window anymore, turning any
such calls into global cursor changes.
For creating standard cursors, gdk_cursor_new_for_display()
has been removed,
you have to use cursor names instead of GdkCursorType. For creating custom cursors,
use gdk_cursor_new_from_texture()
. The ability to get cursor images has been removed.
Instead of the existing extensible set of symbolic icon sizes, GTK+ now only supports normal and large icons with the GtkIconSize enumeration. The actual sizes can be defined by themes via the CSS property -gtk-icon-size.
GtkImage setters like gtk_image_set_from_icon_name()
no longer take a GtkIconSize
argument. You can use the separate gtk_image_set_icon_size()
setter if you need
to override the icon size.
The ::stock-size property of GtkCellRendererPixbuf has been renamed to “icon-size”.