]> GTK+ 3 has seen considerable development over multiple stable releases. While we try to maintain compatibility as far as possible, some minor adjustments may be necessary when moving an application from one release of GTK+ 3 to the next. The following sections list noteworthy changes in GTK+ 3.x release that may or may not require applications to be updated.

The accessible implementations for GTK+ widgets have been integrated into libgtk itself, and the gail module does not exist anymore. This change should not affect applications very much.

Scroll events have been separated from button events, and smooth scrolling has been added with a separate event mask. Widgets now need to have either GDK_SCROLL_MASK or GDK_SMOOTH_SCROLL_MASK in their event mask to receive scroll events. In addition, the GdkScrollDirection enumeration has gained a new member, GDK_SCROLL_SMOOTH, so switch statements will have to be amended to cover this case. GTK+ now uses <Primary> instead of <Control> in keyboard accelerators, for improved cross-platform handling. This should not affect applications, unless they parse or create these accelerator manually. The tacit assumption that the Alt key corresponds to the MOD1 modifier under X11 is now a hard requirement. The beagle search backend for the file chooser has been dropped. Tracker is the only supported search backend on Linux now. GtkNotebook has been changed to destroy its action widgets when it gets destroyed itself. If your application is using action widgets in notebooks, you may have to adjust your code to take this into account. GtkApplication no longer uses the gtk_ mainloop wrappers, so it is no longer possible to use gtk_main_quit() to stop it. The -uninstalled variants of the pkg-config files have been dropped. Excessive dependencies have been culled from Requires: lines in .pc files. Dependent modules may have to declare dependencies that there were getting 'for free' in the past.

The accessibility bridge code that exports accessible objects on the bus is now used by default; atk-bridge has been converted into a library that GTK+ links against. To void the linking, pass --without-atk-bridge when configuring GTK+. GDK threading support has been deprecated. It is recommended to use g_idle_add(), g_main_context_invoke() and similar funtions to make all GTK+ calls from the main thread. GTK+ now follows the XDG Base Directory specification for user configuration and data files. In detail, $XDG_CONFIG_HOME/gtk-3.0/custom-papers is the new location for $HOME/.gtk-custom-papers $XDG_CONFIG_HOME/gtk-3.0/bookmarks is the new location for $HOME/.gtk-bookmarks $XDG_DATA_HOME/themes is preferred over $HOME/.themes $XDG_DATA_HOME/icons is preferred over $HOME/.icons. Existing files from the old location will still be read if the new location does not exist. $HOME/.gtk-3.0 is no longer in the default module load path. If you want to load modules from there, add it to the GTK_PATH environment variable.

GtkIconInfo has changed from being a boxed type to a GObject. This is technically an ABI change, but basically all existing code will keep working if its used as a boxed type, and it is not possible to instantiate GtkIconInfos outside GTK+, so this is not expected to be a big problem.

GDK has been changed to allow only a single screen per display. Only the X11 backend had multiple screens before, and multi-screen setups (not multi-monitor!) are very rare nowadays. If you really need multiple X screens, open them as separate displays. The behavior of GtkBox::expand has been changed to never propagate up. Previously, this was happening inconsistently. If you want the expand to propagate, use the GtkWidget h/v expand properties. If you experience sizing problems with widgets in ported code, carefully check the expand and fill flags of your boxes. GtkBin no longer provides default implementations for get_height_for_width, subclasses now have to provide their own implementation if they need height-for-width functionality. Widget state propagation has been changed. Historically, all of active, prelight, selected, insensitive, inconsistent and backdrop have been propagated to children. This has now been restricted to just the insensitive and backdrop states. This mostly affects theming. The way widget drawing happens has changed. Earlier versions handled one expose event per GdkWindow, each with a separate cairo_t. Now we only handle the expose event on the toplevel and reuse the same cairo_t (with the right translation and clipping) for the entire widget hierarchy, recursing down via the GtkWidget::draw signal. Having all rendering in the same call tree allows effects like opacity and offscreen rendering of entire widget sub-hierarchies. Generally this should not require any changes in widgets, but code looking at e.g. the current expose event may see different behavior than before. The Gtk+ scrolling implementation has changed. gdk_window_scroll() and gdk_window_move_region() no longer copy the region on the window, but rather invalidate the entire scrolled region. This is slightly slower, but allowed us to implement a offscreen surface scrolling method which better fits modern hardware. Most scrolling widgets in Gtk+ have been converted to use this model for scrolling, but external widgets implementing scrolling using GdkWindow may see some slowdown.

GtkWidget had a hack where if opacity is 0.999 we set up an opacity group when rendering the widget. This is no longer needed in 3.10, and GtkStack doesn't use it anymore. It has been removed in 3.12. GdStack is using it, so applications should be ported from GdStack to GtkStack in 3.12. GtkHeaderBar in 3.10 was not ordering its pack-end children in the right way. This has been fixed in 3.12. Applications which pack multiple widgets at the end of a headerbar will have to be updated. gtk_text_view_add_child_in_window has changed behaviour a bit. It now always positions the child in buffer coordinates, where it used to inconsistently scroll with the buffer but then go reposition to a window-relative position on redraw. A number of container widgets have been made more compliant with the uniform CSS rendering model by making them render backgrounds and borders. This may require some adjustments in applications that were making assumptions about containers never rendering backgrounds.

A new state, GTK_STATE_FLAG_CHECKED, has been added for checked states of radio and check buttons and menuitems. Applications that are using GTK+ styles without widgets will need adjustments. Adwaita is now the default theme on all platforms. The icon theme code has become a little pickier about sizes and is not automatically scaling icons beyond the limits defined in the icon theme unless explicitly asked to do so with GTK_ICON_LOOKUP_FORCE_SIZE. GTK+ now includes an interactive debugger which can be activated with the keyboard shortcuts Ctrl-Shift-d or Ctrl-Shift-i. If these shortcuts interfere with application keybindings, they can be disabled with the setting org.gtk.Settings.Debug.enable-inspector-keybinding. Most widgets have been ported to use the new gesture framework internally for event handling. Traditional event handlers in derived widgets are still being called. Using GTK+ under X11 without the X Render extension has been observed to be problematic. This combination is using code paths in cairo and graphics drivers which are rarely tested and likely buggy. GtkTextView is now using a pixel-cache internally, and is drawing a background underneath the text. This can cause problems for applications which assumed that they could draw things below and above the text by chaining up in the ::draw implementation of their GtkTextView subclass. As a short-term workaround, you can make the application apply a custom theme to the text view with a transparent background. For a proper fix, use the new ::draw_layer vfunc.

GTK+ now includes an OpenGL rendering widget. To support GL on various platforms, GTK+ uses libepoxy. GTK+ no longer uses gtk-update-icon-cache during its build. The --enable-gtk2-dependency configure option has been removed. The introspection annotations for the x and y parameters of GtkMenuPositionFunc have been corrected from 'out' to 'inout'. If you are using such a function from language-bindings, this may require adjustments. The lookup order for actions that are activated via keyboard accelerators has been changed to start at the currently focused widget. If your application is making use fo nested action groups via gtk_widget_insert_action_group, you may want to check that this change does not upset your accelerators. The GtkScrollable interface has gained a new vfunc, get_border, that is used to position overshoot and undershoot indications that are drawn over the content by GtkScrolledWindow. Unless your scrollable has non-scrolling parts similar to treeview headers, there is no need to implement this vfunc. The GtkSearchEntry widget has gained a number of new signals that are emitted when certain key sequences are seen. In particular, it now handles the Escape key and emits ::stop-search. Applications that expect to handle Escape themselves will need to be updated.

The GtkListBox model support that was introduced in 3.16 has been changed to no longer call gtk_widget_show_all on rows created by the create_widget_func. You need to manage the visibility of child widgets yourself in your create_widget_func. The alpha component of foreground colors that are applied to GtkCellRendererText is no longer ignored. If you don't want your text to be translucent, use opaque colors.

The way theming works in GTK+ has been reworked fundamentally, to implement many more CSS features and make themes more expressive. As a result, custom CSS that is shipped with applications and third-party themes will need adjustments. Widgets now use element names much more than style classes; type names are no longer used in style matching. Every widget now documents the element names it has and the style classes it uses. The GTK+ inspector can also help with finding this information. GTK+ now uses internal subobjects (also known as gadgets) for allocating and drawing widget parts. Applications that subclass GTK+ widgets may see warnings if they override the size_allocate vfunc and don't chain up. The proper way to subclass is to chain up in size_allocate. If you do not want to do that for some reason, you have to override the draw vfunc as well. Several fixes for window sizing and window placement with client-side decorations may affect applications that are saving and restoring window sizes. The recommended best practice for this which is known to work with client-side and server-side decorations and with older and newer versions of GTK+ is to use gtk_window_get_size() to save window sizes and gtk_window_set_default_size() to restore it. See https://wiki.gnome.org/HowDoI/SaveWindowState for a detailed example. Geometry handling in GtkWindow has been removed. If you are using the functions gtk_window_resize_to_geometry, gtk_window_set_default_geometry, gtk_window_parse_geometry or gtk_window_set_geometry_hints, you may need to make some changes to your code. GtkDrawingArea used to implicitly render the theme background before calling the ::draw handler. This is no longer the case. If you rely on having a theme-provided background, call gtk_render_background() from your ::draw handler. The GtkFileChooser interface prerequisite changed from GtkWidget to GObject, allowing non-widget implementations of this interface. This is a minor change in ABI, as applications are no longer guaranteed that a GtkFileChooser also supports all GtkWidget methods. However, all previously existing implementations still derive from GtkWidget, so no existing code should break. The way in which GtkLevelBar determines the offset to apply was a bit inconsistent in the past; this has been fixed. Applications that are using custom offsets should double-check that their levels look as expected.

The CSS parser has gotten a bit more selective in what it accepts as valid values for the font: shorthand. Following the CSS specification, at least a size and a family name are required now. If you want to change an individual facet of the font, like the weight, use the individual CSS properties: font-weight, font-size, font-family, etc. The CSS parser now warns about some more constructs that are not according to the CSS spec, such as gradients with a single color stop. Instead, you can just use image(<color>). The #GtkSizeGroup:ignore-hidden property has not been working properly for a long time, and we've not documented it as broken and deprecated. The recommended alternative for reserving space of widgets that are not currently shown in the UI is to use a #GtkStack (with some 'filler' widget, e.g. an empty #GtkBox, in another page). GtkHeaderBar now respects the hexpand property for its custom title widget and its packed children. This change may inadvertently cause the layout of those children to change, if they unintentionally had hexpand set before. The behavior of the expand flag in #GtkTables #GtkAttachOptions has been changed to (again) match the behavior in #GtkBox and in GTK+ 2.x. These options don't cause the table itself to expand. The way GtkPopover behaved during a call to gtk_widget_hide() violated some of the internal assumptions GTK+ makes about widget visibility. gtk_popover_popup() and gtk_popover_popdown() have been introduced to show or hide the popover with a transition, while gtk_widget_show() and gtk_widget_hide() on a GtkPopover now work the same way they do on any other widget and immediately hide (or show) the popover.