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<chapter id="gtk-migrating-3-to-4">
  <title>Migrating from GTK 3.x to GTK 4</title>

  <para>
    GTK 4 is a major new version of GTK that breaks both API and ABI
    compared to GTK 3.x. 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 3.x application for the switch to GTK 4. After
    that, there's a number of adjustments that you may have to do
    when you actually switch your application to build against GTK 4.
  </para>

  <section>
    <title>Preparation in GTK 3.x</title>

    <para>
      The steps outlined in the following sections assume that your
      application is working with GTK 3.24, which is the final stable
      release of GTK 3.x. It includes all the necessary APIs and tools
      to help you port your application to GTK 4. If you are using
      an older version of GTK 3.x, you should first get your application
      to build and work with the latest minor release in the 3.24 series.
    </para>

    <section>
      <title>Do not use deprecated symbols</title>
      <para>
        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 for GTK 3 also includes an
        <ulink url="https://developer.gnome.org/gtk3/3.24/api-index-deprecated.html">index</ulink> of all deprecated symbols.
      </para>
      <para>
        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:
        <programlisting>
        make CFLAGS+="-DGDK_DISABLE_DEPRECATED -DGTK_DISABLE_DEPRECATED"
        </programlisting>
      </para>
      <para>
        Note that some parts of our API, such as enumeration values, are
        not well covered by the deprecation warnings. In most cases, using
        them will require you to also use deprecated functions, which will
        trigger warnings.
      </para>
    </section>

    <section>
      <title>Enable diagnostic warnings</title>
      <para>
        Deprecations of properties and signals cannot be caught at compile
        time, as both properties and signals are installed and used after
        types have been instantiated. In order to catch deprecations and
        changes in the run time components, you should use the
        <envar>G_ENABLE_DIAGNOSTIC</envar> environment variable when
        running your application, e.g.:
        <programlisting>
          G_ENABLE_DIAGNOSTIC=1 ./your-app
        </programlisting>
      </para>
    </section>

    <section>
      <title>Do not use widget style properties</title>
      <para>
        Style properties do not exist in GTK 4. You should stop using them in
        your custom CSS and in your code.
      </para>
    </section>

    <section>
      <title>Review your window creation flags</title>
      <para>
        GTK 4 removes the GDK_WA_CURSOR flag. Instead, just use
        gdk_window_set_cursor() to set a cursor on the window after
        creating it. GTK 4 also removes the GDK_WA_VISUAL flag, and
        always uses an RGBA visual for windows. To prepare your code
         for this, use
        <literal>gdk_window_set_visual (gdk_screen_get_rgba_visual ())</literal>
        after creating your window.
        GTK 4 also removes the GDK_WA_WMCLASS flag. If you need this
        X11-specific functionality, use XSetClassHint() directly.
      </para>
    </section>

    <section>
      <title>Stop using direct access to GdkEvent structs</title>
      <para>
        In GTK 4, event structs are opaque and immutable. Many fields already
        have accessors in GTK 3, and you should use those to reduce the amount
        of porting work you have to do at the time of the switch.
      </para>
    </section>

    <section>
      <title>Stop using gdk_pointer_warp()</title>
      <para>
        Warping the pointer is disorienting and unfriendly to users.
        GTK 4 does not support it. In special circumstances (such as when
        implementing remote connection UIs) it can be necessary to
        warp the pointer; in this case, use platform APIs such as
        <function>XWarpPointer()</function> directly.
      </para>
    </section>

    <section>
      <title>Stop using non-RGBA visuals</title>
      <para>
        GTK 4 always uses RGBA visuals for its windows; you should make
        sure that your code works with such visuals. At the same time,
        you should stop using GdkVisual APIs, since this object not longer
        exists in GTK 4. Most of its APIs are deprecated already and not
        useful when dealing with RGBA visuals.
      </para>
    </section>

    <section>
      <title>Stop using GtkBox padding, fill and expand child properties</title>
      <para>
        GTK 4 removes these #GtkBox child properties, so you should stop using
        them. You can replace GtkBox:padding using the #GtkWidget:margin properties
        on your #GtkBox child widgets.
      </para>
     <para>
        The fill child property can be replaced by setting appropriate values
        for the #GtkWidget:halign and #GtkWidget:valign properties of the child
        widgets. If you previously set the fill child property to %TRUE, you can
        achieve the same effect by setting the halign or valign properties to
        %GTK_ALIGN_FILL, depending on the parent box -- halign for a horizontal
        box, valign for a vertical one.
      </para>
      <para>
        #GtkBox also uses the expand child property. It can be replaced by setting
        #GtkWidget:hexpand or #GtkWidget:vexpand on the child widgets. To match the
        old behavior of the #GtkBox's expand child property, you need to set
        #GtkWidget:hexpand on the child widgets of a horizontal #GtkBox and
        #GtkWidget:vexpand on the child widgets of a vertical #GtkBox.
      </para>
      <para>
        Note that there's a subtle but important difference between #GtkBox's
        expand and fill child properties and the ones in #GtkWidget: setting
        #GtkWidget:hexpand or #GtkWidget:vexpand to %TRUE will propagate up
        the widget hierarchy, so a pixel-perfect port might require you to reset
        the expansion flags to %FALSE in a parent widget higher up the hierarchy.
      </para>
    </section>

    <section>
      <title>Stop using the state argument of GtkStyleContext getters</title>
      <para>
        The getters in the GtkStyleContext API, such as
        gtk_style_context_get_property(), gtk_style_context_get(),
        or gtk_style_context_get_color() only accept the context's current
        state for their state argument. You should update all callers to pass
        the current state.
      </para>
    </section>

    <section>
      <title>Stop using gdk_pixbuf_get_from_window() and gdk_cairo_set_source_surface()</title>
      <para>
        These functions are not supported in GTK 4. Instead, either use
        backend-specific APIs, or render your widgets using
        #GtkWidgetClass.snapshot() (once you are using GTK 4).
      </para>
    </section>

    <section>
      <title>Stop using GtkButton's image-related API</title>
      <para>
        The functions and properties related to automatically add a GtkImage
        to a GtkButton, and using a GtkSetting to control its visibility, are
        not supported in GTK 4. Instead, you can just pack a GtkImage inside
        a GtkButton, and control its visibility like you would for any other
        widget. If you only want to add a named icon to a GtkButton, you can
        use gtk_button_new_from_icon_name().
      </para>
    </section>

    <section>
      <title>Stop using GtkWidget event signals</title>
      <para>
        Event controllers and #GtkGestures replace event signals in GTK 4.
        They have been backported to GTK 3.x so you can prepare for this change.
      </para>
    </section>

    <section>
      <title>Set a proper application ID</title>
      <para>
        In GTK 4 we want the application's #GApplication 'application-id'
        (and therefore the D-Bus name), the desktop file basename and Wayland's
        xdg-shell app_id to match. In order to achieve this with GTK 3.x call
        g_set_prgname() with the same application ID you passed to #GtkApplication.
        Rename your desktop files to match the application ID if needed.
      </para>
      <para>
        The call to g_set_prgname() can be removed once you fully migrated
        to GTK 4.
      </para>
      <para>
        You should be aware that changing the application ID makes your
        application appear as a new, different app to application installers.
        You should consult the appstream documentation for best practices
        around renaming applications.
      </para>
    </section>

    <section>
      <title>Stop using gtk_main() and related APIs</title>

      <para>
        GTK 4 removes the gtk_main_ family of APIs. The recommended replacement
        is GtkApplication, but you can also iterate the GLib mainloop directly,
        using GMainContext APIs. The replacement for gtk_events_pending() is
        g_main_context_pending(), the replacement for gtk_main_iteration() is
        g_main_context_iteration().
      </para>
    </section>

    <section>
      <title>Reduce the use of gtk_widget_destroy()</title>
      <para>
        GTK 4 introduces a gtk_window_destroy() api. While that is not available
        in GTK 3, you can prepare for the switch by using gtk_widget_destroy()
        only on toplevel windows, and replace all other uses with
        gtk_container_remove() or g_object_unref().
      </para>
    </section>

    <section>
      <title>Reduce the use of generic container APIs</title>
      <para>
        GTK 4 removes gtk_container_add() and gtk_container_remove(). While there
        is not always a replacement for gtk_container_remove() in GTK 3, you can
        replace many uses of gtk_container_add() with equivalent container-specific
        APIs such as gtk_box_pack_start() or gtk_grid_attach(), and thereby reduce
        the amount of work you have to do at the time of the switch.
      </para>
    </section>
  </section>

  <section>
    <title>Changes that need to be done at the time of the switch</title>

    <para>
      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.
    </para>

    <section>
      <title>Stop using GdkScreen</title>
      <para>
        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.
      </para>
    </section>

    <section>
      <title>Stop using the root window</title>
      <para>
        The root window is an X11-centric concept that is no longer exposed in the
        backend-neutral GDK API. If you need to interact with the X11 root window,
        you can use gdk_x11_display_get_xrootwindow() to get its XID.
      </para>
    </section>

    <section>
      <title>Stop using GdkVisual</title>
      <para>
        This object is not useful with current GTK drawing APIs and has been removed
        without replacement.
      </para>
    </section>

    <section>
      <title>Stop using GdkDeviceManager</title>
      <para>
        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.
      </para>
    </section>

    <section>
      <title>Adapt to GdkWindow API changes</title>
      <para>
        GdkWindow has been renamed to GdkSurface.
      </para>
      <para>
        In GTK 4, the two roles of a standalone toplevel window and of a popup
        that is placed relative to a parent window have been separated out into
        two interfaces, #GdkToplevel and #GdkPopup. Surfaces implementing these
        interfaces are created with gdk_surface_new_toplevel() and
        gdk_surface_new_popup(), respectively, and they are presented on screen
        using gdk_toplevel_present() and gdk_popup_present(). The present()
        functions take parameters in the form of an auxiliary layout struct,
        #GdkPopupLayout or #GdkToplevelLayout. If your code is dealing directly
        with surfaces, you may have to change it to call the API in these
        interfaces, depending on whether the surface you are dealing with
        is a toplevel or a popup.
      </para>
      <para>
        As part of this reorganization, X11-only concepts such as sticky or
        keep-below have been removed. If you need to use them on your X11 windows,
        you will have to set the corresponding X11 properties (as specified in the
        EWMH) yourself. Subsurfaces are only supported with the Wayland backend,
        using gdk_wayland_surface_new_subsurface(). Native and foreign subwindows
        are no longer supported. These concepts were complicating the code and
        could not be supported across backends.
      </para>
      <para>
        gdk_window_reparent() is no longer available.
      </para>
      <para>
        A number of minor API cleanups have happened in GdkSurface
        as well. For example, gdk_surface_input_shape_combine_region()
        has been renamed to gdk_surface_set_input_region(), and
        gdk_surface_begin_resize_drag() has been renamed to
        gdk_toplevel_begin_resize().
      </para>
    </section>

    <section>
      <title>The "iconified" window state has been renamed to "minimized"</title>
      <para>
        The <literal>GDK_SURFACE_STATE_ICONIFIED</literal> value of the
        #GdkSurfaceState enumeration is now %GDK_SURFACE_STATE_MINIMIZED.
      </para>
      <para>
        The #GdkWindow functions <function>gdk_window_iconify()</function>
        and <function>gdk_window_deiconify()</function> have been renamed to
        gdk_toplevel_minimize() and gdk_toplevel_present(), respectively.
      </para>
      <para>
        The behavior of the minimization and unminimization operations have
        not been changed, and they still require support from the underlying
        windowing system.
      </para>
    </section>

    <section>
      <title>Adapt to GdkEvent API changes</title>
      <para>
        Direct access to GdkEvent structs is no longer possible in GTK 4.
        GdkEvent is now a strictly read-only type, and you can no longer
        change any of its fields, or construct new events. All event fields
        have accessors that you will have to use.
      </para>
      <para>
        Event compression is always enabled in GTK 4. If you need to see
        the uncoalesced motion history, use gdk_motion_event_get_history()
        on the latest motion event.
      </para>
    </section>

    <section>
      <title>Stop using grabs</title>
      <para>
        GTK 4 no longer provides the gdk_device_grab() or gdk_seat_grab()
        apis. If you need to dismiss a popup when the user clicks outside
        (the most common use for grabs), you can use the GdkPopup
        #GdkPopup:autohide property instead. GtkPopover also has a
        #GtkPopover:autohide property for this. If you need to prevent
        the user from interacting with a window while a dialog is open,
        use the #GtkWindow:modal property of the dialog.
      </para>
    </section>

    <section>
      <title>Adapt to coordinate API changes</title>
      <para>
        A number of coordinate APIs in GTK 3 had _double variants: 
        gdk_device_get_position(), gdk_device_get_surface_at_position(),
        gdk_surface_get_device_position(). These have been changed to use
        doubles, and the _double variants have been removed. Update your
        code accordingly.
      </para>
      <para>
        Any APIs that deal with global (or root) coordinates have been
        removed in GTK 4, since not all backends support them. You should
        replace your use of such APIs with surface-relative equivalents.
        Examples of this are gdk_surface_get_origin(), gdk_surface_move()
        or gdk_event_get_root_coords().
      </para>
    </section>

    <section>
      <title>Adapt to GdkKeymap API changes</title>
      <para>
        GdkKeymap no longer exists as an independent object.
      </para>
      <para>
        If you need access to keymap state, it is now exposed as properties
        on the #GdkDevice representing the keyboard: #GdkDevice:direction,
        #GdkDevice:has-bidi-layouts, #GdkDevice:caps-lock-state,
        #GdkDevice:num-lock-state, #GdkDevice:scroll-lock-state and
        #GdkDevice:modifier-state. To obtain the keyboard device, you can use
        <literal>gdk_seat_get_keyboard (gdk_display_get_default_seat (display))</literal>.
      </para>
      <para>
        If you need access to translated keys for event handling, #GdkEvent
        now includes all of the translated key state, including consumed
        modifiers, group and shift level, so there should be no need to
        manually call gdk_keymap_translate_keyboard_state() (which has
        been removed).
      </para>
      <para>
        If you need to do forward or backward mapping between key codes
        and key values, use gdk_display_map_keycode() and gdk_display_map_keyval(),
        which are the replacements for gdk_keymap_get_entries_for_keycode()
        and gdk_keymap_get_entries_for_keyval().
      </para>
    </section>

    <section>
      <title>Adapt to changes in keyboard modifier handling</title>
      <para>
        GTK 3 has the idea that use of modifiers may differ between different
        platforms, and has a #GdkModifierIntent api to let platforms provide
        hint about how modifiers are expected to be used. It also promoted
        the use of &lt;Primary&gt; instead of &lt;Control&gt; to specify
        accelerators that adapt to platform conventions.
      </para>
      <para>
        In GTK 4, the meaning of modifiers has been fixed, and backends are
        expected to map the platform conventions to the existing modifiers.
        The expected use of modifiers in GTK 4 is:
        <simplelist>
          <member>GDK_CONTROL_MASK - Primary accelerators</member>
          <member>GDK_ALT_MASK - Mnemonics</member>
          <member>GDK_SHIFT_MASK - Extending selections</member>
          <member>GDK_CONTROL_MASK - Modifying selections</member>
          <member>GDK_CONTROL_MASK|GDK_ALT_MASK - Prevent text input</member>
        </simplelist>
      </para>
      <para>
        Consequently, #GdkModifierIntent and related APIs have been removed,
        and &lt;Control&gt; is preferred over &lt;Primary&gt; in accelerators.
      </para>
      <para>
        A related change is that GTK 4 no longer supports the use of archaic
        X11 'real' modifiers with the names Mod1,..., Mod5, and %GDK_MOD1_MASK
        has been renamed to %GDK_ALT_MASK.
      </para>
    </section>

    <section>
      <title>Stop using gtk_get_current_... APIs</title>
      <para>
        The function gtk_get_current_event() and its variants have been
        replaced by equivalent event controller APIs:
        gtk_event_controller_get_current_event(), etc.
      </para>
    </section>

    <section>
      <title>Convert your ui files</title>

      <para>
        A number of the changes outlined below affect .ui files. The
        gtk4-builder-tool simplify command can perform many of the
        necessary changes automatically, when called with the --3to4
        option. You should always review the resulting changes.
      </para>
    </section>

    <section>
      <title>Adapt to event controller API changes</title>
      <para>
        A few changes to the event controller and #GtkGesture APIs
        did not make it back to GTK 3, and have to be taken into account
        when moving to GTK 4. One is that the #GtkEventControllerMotion::enter
        and #GtkEventControllerMotion::leave signals have gained new arguments.
        Another is that #GtkGestureMultiPress has been renamed to #GtkGestureClick,
        and has lost its area property. A #GtkEventControllerFocus has been
        split off from #GtkEventcontrollerKey.
      </para>
    </section>

    <section>
      <title>Focus handling changes</title>
      <para>
        The semantics of the #GtkWidget:can-focus property have changed.
        In GTK 3, this property only meant that the widget itself would not
        accept keyboard input, but its children still might (in the case of
        containers). In GTK 4, if :can-focus is %FALSE, the focus cannot enter
        the widget or any of its descendents, and the default value has changed
        from %FALSE to %TRUE. In addition, there is a #GtkWidget:focusable
        property, which controls whether an individual widget can receive
        the input focus.
      </para>
      <para>
        The feature to automatically keep the focus widget scrolled into view
        with gtk_container_set_focus_vadjustment() has been removed together with
        GtkContainer, and is provided by scrollable widgets instead. In the common
        case that the scrollable is a #GtkViewport, use #GtkViewport:scroll-to-focus.
      </para>
    </section>

    <section>
      <title>Stop using GtkEventBox</title>
      <para>
        GtkEventBox is no longer needed and has been removed.
        All widgets receive all events.
      </para>
    </section>

    <section>
      <title>Stop using GtkButtonBox</title>
      <para>
        GtkButtonBox has been removed. Use a GtkBox instead.
      </para>
    </section>

    <section>
      <title>Adapt to GtkBox API changes</title>
      <para>
        The GtkBox pack-start and -end methods have been replaced by gtk_box_prepend()
        and gtk_box_append(). You can also reorder box children as necessary.
      </para>
    </section>

    <section>
      <title>Adapt to GtkHeaderBar and GtkActionBar API changes</title>
      <para>
        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.
      </para>
      <para>
        The gtk_header_bar_set_custom_title() function has been renamed to
        the more accurate name gtk_header_bar_set_title_widget(). The
        corresponding getter and the property itself have also been renamed.
      </para>
      <para>
        The gtk_header_bar_set_title() function has been removed along with its
        corresponding getter and the property. By default #GtkHeaderBar shows
        the title of the window, so if you were setting the title of the header
        bar, consider setting the window title instead. If you need to show a
        title that's different from the window title, use the
        #GtkHeaderBar:title-widget property to add a #GtkLabel as shown in the
        example in #GtkHeaderBar documentation.
      </para>
      <para>
        The gtk_header_bar_set_subtitle() function has been removed along with
        its corresponding getter and the property. The old "subtitle" behavior
        can be replicated by setting the #GtkHeaderBar:title-widget property to
        a #GtkBox with two labels inside, with the title label matching the
        example in #GtkHeaderBar documentation, and the subtitle label being
        similar, but with "subtitle" style class instead of "title".
      </para>
      <para>
        The gtk_header_bar_set_has_subtitle() function has been removed along
        with its corresponding getter and the property. Its behavior can be
        replicated by setting the #GtkHeaderBar:title-widget property to a
        #GtkStack with #GtkStack:vhomogeneous property set to %TRUE and two
        pages, each with a #GtkBox with title and subtitle as described above.
      </para>
      <para>
        The ::pack-type child properties of GtkHeaderBar and GtkActionBar have
        been removed. If you need to programmatically place children, use the
        pack_start() and pack_end() APIs. In ui files, use the type attribute
        on the child element.
      </para>
      <para>
        gtk4-builder-tool can help with this conversion, with the --3to4 option
        of the simplify command.
      </para>
    </section>

    <section>
      <title>Adapt to GtkStack, GtkAssistant and GtkNotebook API changes</title>
      <para>
        The child properties of GtkStack, GtkAssistant and GtkNotebook have been
        converted into child meta objects.
        Instead of gtk_container_child_set (stack, child, …), you can now use
        g_object_set (gtk_stack_get_page (stack, child), …). In .ui files, the
        GtkStackPage objects must be created explicitly, and take the child widget
        as property. GtkNotebook and GtkAssistant are similar.
      </para>
      <para>
        gtk4-builder-tool can help with this conversion, with the --3to4 option
        of the simplify command.
      </para>
    </section>

    <section>
      <title>Adapt to GtkBin removal</title>
      <para>
        The abstract base class GtkBin for single-child containers has been
        removed. The former subclasses are now derived directly from GtkWidget,
        and have a "child" property for their child widget. To add a child, use
        the setter for the "child" property (e.g. gtk_frame_set_child()) instead
        of gtk_container_add(). Adding a child in a ui file with
        <tag class="starttag">child</tag> still works.
        The affected classes are:
      </para>
      <simplelist>
        <member>GtkAspectFrame</member>
        <member>GtkButton (and subclasses)</member>
        <member>GtkComboBox</member>
        <member>GtkFlowBoxChild</member>
        <member>GtkFrame</member>
        <member>GtkListBoxRow</member>
        <member>GtkOverlay</member>
        <member>GtkPopover</member>
        <member>GtkRevealer</member>
        <member>GtkScrolledWindow</member>
        <member>GtkSearchBar</member>
        <member>GtkViewport</member>
        <member>GtkWindow (and subclasses)</member>
      </simplelist>
      <para>
        If you have custom widgets that were derived from GtkBin, you should
        port them to derive from GtkWidget. Notable vfuncs that you will have
        to implement include dispose() (to unparent your child), compute_expand()
        (if you want your container to propagate expand flags) and
        get_request_mode() (if you want your container to support height-for-width.
      </para>
      <para>
        You may also want to implement the GtkBuildable interface, to support
        adding children with <tag class="starttag">child</tag> in ui files.
      </para>
    </section>

    <section>
      <title>Adapt to GtkContainer removal</title>
      <para>
        The abstract base class GtkContainer for general containers has been
        removed. The former subclasses are now derived directly from GtkWidget,
        and have class-specific add() and remove() functions.
        The most noticable change is the use of gtk_box_append() or gtk_box_prepend()
        instead of gtk_container_add() for adding children to GtkBox, and the change
        to use container-specific remove functions, such as gtk_stack_remove() instead
        of gtk_container_remove(). Adding a child in a ui file with
        <tag class="starttag">child</tag> still works.
        The affected classes are:
      </para>
      <simplelist>
        <member>GtkActionBar</member>
        <member>GtkBox (and subclasses)</member>
        <member>GtkExpander</member>
        <member>GtkFixed</member>
        <member>GtkFlowBox</member>
        <member>GtkGrid</member>
        <member>GtkHeaderBar</member>
        <member>GtkIconView</member>
        <member>GtkInfoBar</member>
        <member>GtkListBox</member>
        <member>GtkNotebook</member>
        <member>GtkPaned</member>
        <member>GtkStack</member>
        <member>GtkTextView</member>
        <member>GtkTreeView</member>
      </simplelist>
      <para>
        Without GtkContainer, there are no longer facilities for defining and
        using child properties. If you have custom widgets using child properties,
        they will have to be converted either to layout properties provided
        by a layout manager (if they are layout-related), or handled in some
        other way. One possibility is to use child meta objects, as seen with
        GtkAssistantPage, GtkStackPage and the like.
      </para>
    </section>

    <section>
      <title>Stop using GtkContainer::border-width</title>
      <para>
        GTK 4 has removed the #GtkContainer::border-width property (together
        with the rest of GtkContainer). Use other means to influence the spacing
        of your containers, such as the CSS margin and padding properties on child
        widgets.
      </para>
    </section>

    <section>
      <title>Adapt to gtk_widget_destroy() removal</title>
      <para>
        The function gtk_widget_destroy() has been removed. To explicitly destroy
        a toplevel window, use gtk_window_destroy(). To destroy a widget that is
        part of a hierarchy, remove it from its parent using a container-specific
        remove api, such as gtk_box_remove() or gtk_stack_remove(). To destroy
        a freestanding non-toplevel widget, use g_object_unref() to drop your
        reference.
      </para>
    </section>

    <section>
      <title>Adapt to GtkStyleContext API changes</title>
      <para>
        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.
      </para>
      <para>
        The most commonly used GtkStyleContext API, gtk_style_context_add_class(),
        has been moved to GtkWidget as gtk_widget_add_css_class(), as have the
        corresponding gtk_style_context_remove_class() and
        gtk_style_context_has_class() APIs.
      </para>
    </section>

    <section>
      <title>Adapt to GtkCssProvider API changes</title>
      <para>
        In GTK 4, the various #GtkCssProvider load functions have lost their
        #GError argument. If you want to handle CSS loading errors, use the
        #GtkCssProvider::parsing-error signal instead. gtk_css_provider_get_named()
        has been replaced by gtk_css_provider_load_named().
      </para>
    </section>

    <section>
      <title>Stop using GtkShadowType and GtkRelief properties</title>
      <para>
        The shadow-type properties in GtkScrolledWindow, GtkViewport,
        and GtkFrame, as well as the relief properties in GtkButton
        and its subclasses have been removed. GtkScrolledWindow, GtkButton
        and GtkMenuButton have instead gained a boolean has-frame
        property.
      </para>
    </section>

    <section>
      <title>Adapt to GtkWidget's size request changes</title>
      <para>
        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. gtk_widget_measure() replaces the various
        gtk_widget_get_preferred_ functions for querying sizes.
      </para>
    </section>

    <section>
      <title>Adapt to GtkWidget's size allocation changes</title>
      <para>
        The #GtkWidget.size_allocate() vfunc takes the baseline as an argument
        now, so you no longer need to call gtk_widget_get_allocated_baseline()
        to get it.
      </para>
      <para>
        The ::size-allocate signal has been removed, since it is easy
        to misuse. If you need to learn about sizing changes of custom
        drawing widgets, use the #GtkDrawingArea::resize or #GtkGLArea::resize
        signals.
      </para>
    </section>

    <section>
      <title>Switch to GtkWidget's children APIs</title>
      <para>
        In GTK 4, any widget can have children (and GtkContainer is gone).
        There is new API to navigate the widget tree, for use in widget
        implementations: gtk_widget_get_first_child(), gtk_widget_get_last_child(),
        gtk_widget_get_next_sibling(), gtk_widget_get_prev_sibling().
      </para>
    </section>

    <section>
      <title>Don't use -gtk-gradient in your CSS</title>
      <para>
        GTK now supports standard CSS syntax for both linear and radial
        gradients, just use those.
      </para>
    </section>

    <section>
      <title>Don't use -gtk-icon-effect in your CSS</title>
      <para>
        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);.
      </para>
    </section>

    <section>
      <title>Don't use -gtk-icon-theme in your CSS</title>
      <para>
        GTK now uses the current icon theme, without a way to change this.
      </para>
    </section>

    <section>
      <title>Don't use -gtk-outline-...-radius in your CSS</title>
      <para>
        These non-standard properties have been removed from GTK
        CSS. Just use regular border radius.
      </para>
    </section>

    <section>
      <title>Adapt to drawing model changes</title>
      <para>
        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 #GtkWidget::draw signal handler for custom
        drawing will need to be converted to use gtk_snapshot_append_cairo().
      </para>
      <para>
        The auxiliary #GtkSnapshot object has APIs to help with creating render
        nodes.
      </para>
      <para>
        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 #GtkWidget::draw signal.
      </para>
    </section>

    <section>
      <title>Stop using APIs to query GdkSurfaces</title>
      <para>
        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().
      </para>
    </section>

    <section>
      <title>Widgets are now visible by default</title>
      <para>
        The default value of #GtkWidget: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.
        The only widgets that still need to be explicitly shown are toplevel
        windows, dialogs and popovers.
      </para>
      <para>
        A convenient way to remove unnecessary property assignments like this
        from ui files it run the command <command>gtk4-builder-tool simplify --replace</command>
        on them.
      </para>
      <para>
        The function gtk_widget_show_all(), the #GtkWidget:no-show-all property
        and its getter and setter have been removed in  GTK 4, so you should stop
        using them.
      </para>
    </section>

    <section>
      <title>Adapt to changes in animated hiding and showing of widgets</title>
      <para>
        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.
      </para>
    </section>

    <section>
      <title>Stop passing commandline arguments to gtk_init</title>
      <para>
        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.
      </para>
    </section>

    <section>
      <title>GdkPixbuf is deemphasized</title>
      <para>
        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.
      </para>
    </section>

    <section>
      <title>GtkWidget event signals are removed</title>
      <para>
        Event controllers and #GtkGestures have already been introduced in GTK 3 to handle
        input for many cases. In GTK 4, the traditional widget signals for handling input,
        such as #GtkWidget::motion-event or #GtkWidget::event have been removed.
      </para>
    </section>

    <section>
      <title>Invalidation handling has changed</title>
      <para>
        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.
      </para>
    </section>

    <section>
      <title>Stop using GtkWidget::draw</title>
      <para>
        The #GtkWidget::draw signal has been removed. Widgets need to implement the
        #GtkWidgetClass.snapshot() function now. Connecting draw signal handlers is
        no longer possible. If you want to keep using cairo for drawing, use
        gtk_snaphot_append_cairo().
      </para>
    </section>

    <section>
      <title>Window content observation has changed</title>
      <para>
        Observing widget contents and widget size is now done by using the
        #GtkWidgetPaintable object instead of connecting to widget signals.
      </para>
    </section>

    <section>
      <title>Monitor handling has changed</title>
      <para>
        Instead of a monitor number, #GdkMonitor is now used throughout. 
        gdk_display_get_monitors() returns the list of monitors that can be queried
        or observed for monitors to pass to APIs like gtk_window_fullscreen_on_monitor().
      </para>
    </section>

    <section>
      <title>Adapt to cursor API changes</title>
      <para>
        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.
      </para>
      <para>
        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.
      </para>
    </section>

    <section>
      <title>Adapt to icon size API changes</title>
      <para>
        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.
      </para>
      <para>
        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.
      </para>
      <para>
        The :stock-size property of GtkCellRendererPixbuf has been renamed to
        #GtkCellRendererPixbuf:icon-size.
      </para>
    </section>

    <section>
      <title>Adapt to changes in the GtkAssistant API</title>
      <para>
        The :has-padding property is gone, and GtkAssistant no longer adds padding
        to pages. You can easily do that yourself.
      </para>
    </section>

    <section>
      <title>Adapt to changes in the API of GtkEntry, GtkSearchEntry and GtkSpinButton</title>
      <para>
        The GtkEditable interface has been made more useful, and the core functionality of
        GtkEntry has been broken out as a GtkText widget. GtkEntry, GtkSearchEntry,
        GtkSpinButton and the new GtkPasswordEntry now use a GtkText widget internally
        and implement GtkEditable. In particular, this means that it is no longer
        possible to use GtkEntry API such as gtk_entry_grab_focus_without_selecting()
        on a search entry.
      </para>
      <para>
        Use GtkEditable API for editable functionality, and widget-specific APIs for
        things that go beyond the common interface. For password entries, use
        GtkPasswordEntry. As an example, gtk_spin_button_set_max_width_chars()
        has been removed in favor of gtk_editable_set_max_width_chars().
      </para>
    </section>

    <section>
      <title>Adapt to changes in GtkOverlay API</title>
      <para>
        The GtkOverlay :pass-through child property has been replaced by the
        #GtkWidget:can-target property. Note that they have the opposite sense:
        pass-through == !can-target.
      </para>
    </section>

    <section>
      <title>Use GtkFixed instead of GtkLayout</title>
      <para>
        Since GtkScrolledWindow can deal with widgets that do not implement
        the GtkScrollable interface by automatically wrapping them into a
        GtkViewport, GtkLayout is redundant, and has been removed in favor
        of the existing GtkFixed container widget.
      </para>
    </section>

    <section>
      <title>Adapt to search entry changes</title>
      <para>
        The way search entries are connected to global events has changed;
        gtk_search_entry_handle_event() has been dropped and replaced by
        gtk_search_entry_set_key_capture_widget() and
        gtk_event_controller_key_forward().
      </para>
    </section>

    <section>
      <title>Stop using gtk_window_activate_default()</title>
      <para>
        The handling of default widgets has been changed, and activating
        the default now works by calling gtk_widget_activate_default()
        on the widget that caused the activation. If you have a custom widget
        that wants to override the default handling, you can provide an
        implementation of the default.activate action in your widgets' action
        groups.
      </para>
    </section>

    <section>
      <title>Stop setting ::has-default and ::has-focus in .ui files</title>
      <para>
        The special handling for the ::has-default and ::has-focus properties
        has been removed. If you want to define the initial focus or the
        the default widget in a .ui file, set the ::default-widget or
        ::focus-widget properties of the toplevel window.
      </para>
    </section>

    <section>
      <title>Stop using the GtkWidget::display-changed signal</title>
      <para>
        To track the current display, use the #GtkWidget::root property
        instead.
      </para>
    </section>

    <section>
      <title>GtkPopover::modal has been renamed to autohide</title>
      <para>
        The modal property has been renamed to autohide.
        gtk-builder-tool can assist with the rename in ui files.
      </para>
    </section>

    <section>
      <title>gtk_widget_get_surface has been removed</title>
      <para>
        gtk_widget_get_surface() has been removed.
        Use gtk_native_get_surface() in combination with
        gtk_widget_get_native() instead.
      </para>
    </section>

    <section>
      <title>gtk_widget_is_toplevel has been removed</title>
      <para>
        gtk_widget_is_toplevel() has been removed.
        Use GTK_IS_ROOT, GTK_IS_NATIVE or GTK_IS_WINDOW
        instead, as appropriate.
      </para>
    </section>

    <section>
      <title>gtk_widget_get_toplevel has been removed</title>
      <para>
        gtk_widget_get_toplevel() has been removed.
        Use gtk_widget_get_root() or gtk_widget_get_native()
        instead, as appropriate.
      </para>
    </section>

    <section>
      <title>GtkEntryBuffer ::deleted-text has changed</title>
      <para>
        To allow signal handlers to access the deleted text before it
        has been deleted #GtkEntryBuffer::deleted-text has changed from
        %G_SIGNAL_RUN_FIRST to %G_SIGNAL_RUN_LAST. The default handler
        removes the text from the #GtkEntryBuffer.
      </para>
      <para>
        To adapt existing code, use g_signal_connect_after() or
        %G_CONNECT_AFTER when using g_signal_connect_data() or
        g_signal_connect_object().
      </para>
    </section>

    <section>
      <title>GtkMenu, GtkMenuBar and GtkMenuItem are gone</title>
      <para>
        These widgets were heavily relying on X11-centric concepts such as
        override-redirect windows and grabs, and were hard to adjust to other
        windowing systems.
      </para>
      <para>
        Menus can already be replaced using GtkPopoverMenu in GTK 3. Additionally,
        GTK 4 introduces GtkPopoverMenuBar to replace menubars. These new widgets
        can only be constructed from menu models, so the porting effort involves
        switching to menu models and actions.
      </para>
      <para>
        Tabular menus were rarely used and complicated the menu code,
        so they have not been brought over to #GtkPopoverMenu. If you need
        complex layout in menu-like popups, consider directly using a
        #GtkPopover instead.
      </para>
      <para>
        Since menus are gone, GtkMenuButton also lost its ability to show menus,
        and needs to be used with popovers in GTK 4.
      </para>
    </section>

    <section>
      <title>GtkToolbar has been removed</title>
      <para>
        Toolbars were using outdated concepts such as requiring special toolitem
        widgets. Toolbars should be replaced by using a GtkBox with regular widgets
        instead and the "toolbar" style class.
      </para>
    </section>

    <section>
      <title>GtkAspectFrame is no longer a frame</title>
      <para>
        GtkAspectFrame is no longer derived from GtkFrame and does not
        place a label and frame around its child anymore. It still lets
        you control the aspect ratio of its child.
      </para>
    </section>

    <section>
      <title>Stop using custom tooltip windows</title>
      <para>
        Tooltips no longer use GtkWindows in GTK 4, and it is no longer
        possible to provide a custom window for tooltips. Replacing the content
        of the tooltip with a custom widget is still possible, with
        gtk_tooltip_set_custom().
      </para>
    </section>

    <section>
      <title>Switch to the new Drag-and-Drop api</title>
      <para>
        The source-side Drag-and-Drop apis in GTK 4 have been changed to use an event
        controller, #GtkDragSource. Instead of calling gtk_drag_source_set()
        and connecting to #GtkWidget signals, you create a #GtkDragSource object,
        attach it to the widget with gtk_widget_add_controller(), and connect
        to #GtkDragSource signals. Instead of calling gtk_drag_begin() on a widget
        to start a drag manually, call gdk_drag_begin().
        The ::drag-data-get signal has been replaced by the #GtkDragSource::prepare
        signal, which returns a #GdkContentProvider for the drag operation.
      </para>
      <para>
        The destination-side Drag-and-Drop  apis in GTK 4 have also been changed
        to use an event controller, #GtkDropTarget. Instead of calling
        gtk_drag_dest_set() and connecting to #GtkWidget signals, you create
        a #GtkDropTarget object, attach it to the widget with
        gtk_widget_add_controller(), and connect to #GtkDropTarget signals.
        The ::drag-motion signal has been renamed to #GtkDropTarget::accept, and
        instead of ::drag-data-received, you need to use async read methods on the
        #GdkDrop object, such as gdk_drop_read_async() or gdk_drop_read_value_async().
      </para>
    </section>

    <section>
      <title>Adapt to GtkIconTheme API changes</title>
      <para>
        gtk_icon_theme_lookup_icon() returns a #GtkIconPaintable object now, instead
        of a #GtkIconInfo. It always returns a paintable in the requested size, and
        never fails. A number of no-longer-relevant lookup flags and API variants
        have been removed.
      </para>
    </section>

    <section>
      <title>Update to GtkFileChooser API changes</title>
      <para>
        GtkFileChooser moved to a GFile-based API. If you need to convert a
        path or a URI, use g_file_new_for_path(), g_file_new_for_commandline_arg(),
        or g_file_new_for_uri(); similarly, if you need to get a path or a URI
        from a GFile, use g_file_get_path(), or g_file_get_uri(). With the
        removal or path and URI-based functions, the "local-only" property has
        been removed; GFile can be used to access non-local as well as local
        resources.
      </para>
      <para>
        The GTK_FILE_CHOOSER_ACTION_CREATE_FOLDER action has been removed. Use
        %GTK_FILE_CHOOSER_ACTION_SELECT_FOLDER, instead. If a new folder is needed,
        the user can create one.
      </para>
      <para>
        The "confirm-overwrite" signal, and the "do-overwrite-confirmation"
        property have been removed from GtkFileChooser. The file chooser widgets
        will automatically handle the confirmation of overwriting a file when
        using GTK_FILE_CHOOSER_ACTION_SAVE.
      </para>
      <para>
        GtkFileChooser does not support a custom extra widget any more. If you
        need to add extra widgets, use gtk_file_chooser_add_choice() instead.
      </para>
      <para>
        GtkFileChooser does not support a custom preview widget any more. If
        you need to show a custom preview, you can create your own GtkDialog
        with a GtkFileChooserWidget and your own preview widget that you
        update whenever the #GtkFileChooser::selection-changed signal is
        emitted.
      </para>
    </section>

    <section>
      <title>Stop using blocking dialog functions</title>
      <para>
        GtkDialog, GtkNativeDialog, and GtkPrintOperation removed their
        blocking API using nested main loops. Nested main loops present
        re-entrancy issues and other hard to debug issues when coupled
        with other event sources (IPC, accessibility, network operations)
        that are not under the toolkit or the application developer's
        control. Additionally, "stop-the-world" functions do not fit
        the event-driven programming model of GTK.
      </para>
      <para>
        You can replace calls to <function>gtk_dialog_run()</function>
        by specifying that the #GtkDialog must be modal using
        gtk_window_set_modal() or the %GTK_DIALOG_MODAL flag, and
        connecting to the #GtkDialog::response signal.
      </para>
    </section>
  </section>
</chapter>
