Height for width geometry management

GTK+ uses a height-for-width (and width-for-height) geometry management system. Height-for-width means that a widget can change how much vertical space it needs, depending on the amount of horizontal space that it is given (and similar for width-for-height).

There are some things to keep in mind when implementing container widgets that make use of GTK+’s height for width geometry management system. First, it’s important to note that a container must prioritize one of its dimensions, that is to say that a widget or container can only have a GtkSizeRequestMode that is GTK_SIZE_REQUEST_HEIGHT_FOR_WIDTH or GTK_SIZE_REQUEST_WIDTH_FOR_HEIGHT. However, every widget and container must be able to respond to the APIs for both dimensions, i.e. even if a widget has a request mode that is height-for-width, it is possible that its parent will request its sizes using the width-for-height APIs.

To ensure that everything works properly, here are some guidelines to follow when implementing height-for-width (or width-for-height) containers.

Each request mode involves 2 virtual methods. Height-for-width apis run through gtk_widget_get_preferred_width() and then through gtk_widget_get_preferred_height_for_width(). When handling requests in the opposite GtkSizeRequestMode it is important that every widget request at least enough space to display all of its content at all times.

When gtk_widget_get_preferred_height() is called on a container that is height-for-width, the container must return the height for its minimum width. This is easily achieved by simply calling the reverse apis implemented for itself as follows:

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static void
foo_container_get_preferred_height (GtkWidget *widget,
                                    gint *min_height,
                                    gint *nat_height)
{
   if (i_am_in_height_for_width_mode)
     {
       gint min_width;

       GTK_WIDGET_GET_CLASS (widget)->get_preferred_width (widget,
                                                           &min_width,
                                                           NULL);
       GTK_WIDGET_GET_CLASS (widget)->get_preferred_height_for_width
                                                          (widget,
                                                           min_width,
                                                           min_height,
                                                           nat_height);
     }
   else
     {
       ... many containers support both request modes, execute the
       real width-for-height request here by returning the
       collective heights of all widgets that are stacked
       vertically (or whatever is appropriate for this container)
       ...
     }
}

Similarly, when gtk_widget_get_preferred_width_for_height() is called for a container or widget that is height-for-width, it then only needs to return the base minimum width like so:

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static void
foo_container_get_preferred_width_for_height (GtkWidget *widget,
                                              gint for_height,
                                              gint *min_width,
                                              gint *nat_width)
{
   if (i_am_in_height_for_width_mode)
     {
       GTK_WIDGET_GET_CLASS (widget)->get_preferred_width (widget,
                                                           min_width,
                                                           nat_width);
     }
   else
     {
       ... execute the real width-for-height request here based on
       the required width of the children collectively if the
       container were to be allocated the said height ...
     }
}

Height for width requests are generally implemented in terms of a virtual allocation of widgets in the input orientation. Assuming an height-for-width request mode, a container would implement the get_preferred_height_for_width() virtual function by first calling gtk_widget_get_preferred_width() for each of its children.

For each potential group of children that are lined up horizontally, the values returned by gtk_widget_get_preferred_width() should be collected in an array of GtkRequestedSize structures. Any child spacing should be removed from the input for_width and then the collective size should be allocated using the gtk_distribute_natural_allocation() convenience function.

The container will then move on to request the preferred height for each child by using gtk_widget_get_preferred_height_for_width() and using the sizes stored in the GtkRequestedSize array.

To allocate a height-for-width container, it’s again important to consider that a container must prioritize one dimension over the other. So if a container is a height-for-width container it must first allocate all widgets horizontally using a GtkRequestedSize array and gtk_distribute_natural_allocation() and then add any extra space (if and where appropriate) for the widget to expand.

After adding all the expand space, the container assumes it was allocated sufficient height to fit all of its content. At this time, the container must use the total horizontal sizes of each widget to request the height-for-width of each of its children and store the requests in a GtkRequestedSize array for any widgets that stack vertically (for tabular containers this can be generalized into the heights and widths of rows and columns). The vertical space must then again be distributed using gtk_distribute_natural_allocation() while this time considering the allocated height of the widget minus any vertical spacing that the container adds. Then vertical expand space should be added where appropriate and available and the container should go on to actually allocating the child widgets.

See GtkWidget’s geometry management section to learn more about implementing height-for-width geometry management for widgets.

Child properties

GtkContainer introduces child properties. These are object properties that are not specific to either the container or the contained widget, but rather to their relation. Typical examples of child properties are the position or pack-type of a widget which is contained in a GtkBox.

Use gtk_container_class_install_child_property() to install child properties for a container class and gtk_container_class_find_child_property() or gtk_container_class_list_child_properties() to get information about existing child properties.

To set the value of a child property, use gtk_container_child_set_property(), gtk_container_child_set() or gtk_container_child_set_valist(). To obtain the value of a child property, use gtk_container_child_get_property(), gtk_container_child_get() or gtk_container_child_get_valist(). To emit notification about child property changes, use gtk_widget_child_notify().

GtkContainer as GtkBuildable

The GtkContainer implementation of the GtkBuildable interface supports a <packing> element for children, which can contain multiple <property> elements that specify child properties for the child.

An example of child properties in UI definitions:

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<object class="GtkVBox">
  <child>
    <object class="GtkLabel"/>
    <packing>
      <property name="pack-type">start</property>
    </packing>
  </child>
</object>

Since 2.16, child properties can also be marked as translatable using the same “translatable”, “comments” and “context” attributes that are used for regular properties.

GTK_IS_RESIZE_CONTAINER()

#define             GTK_IS_RESIZE_CONTAINER(widget)

GTK_CONTAINER_WARN_INVALID_CHILD_PROPERTY_ID()

#define             GTK_CONTAINER_WARN_INVALID_CHILD_PROPERTY_ID(object, property_id, pspec)

This macro should be used to emit a standard warning about unexpected properties in set_child_property() and get_child_property() implementations.

gtk_container_add ()

void
gtk_container_add (GtkContainer *container,
                   GtkWidget *widget);

Adds widget to container . Typically used for simple containers such as GtkWindow, GtkFrame, or GtkButton; for more complicated layout containers such as GtkBox or GtkGrid, this function will pick default packing parameters that may not be correct. So consider functions such as gtk_box_pack_start() and gtk_grid_attach() as an alternative to gtk_container_add() in those cases. A widget may be added to only one container at a time; you can’t place the same widget inside two different containers.

Note that some containers, such as GtkScrolledWindow or GtkListBox, may add intermediate children between the added widget and the container.

gtk_container_remove ()

void
gtk_container_remove (GtkContainer *container,
                      GtkWidget *widget);

Removes widget from container . widget must be inside container . Note that container will own a reference to widget , and that this may be the last reference held; so removing a widget from its container can destroy that widget. If you want to use widget again, you need to add a reference to it while it’s not inside a container, using g_object_ref(). If you don’t want to use widget again it’s usually more efficient to simply destroy it directly using gtk_widget_destroy() since this will remove it from the container and help break any circular reference count cycles.

gtk_container_add_with_properties ()

void
gtk_container_add_with_properties (GtkContainer *container,
                                   GtkWidget *widget,
                                   const gchar *first_prop_name,
                                   ...);

Adds widget to container , setting child properties at the same time. See gtk_container_add() and gtk_container_child_set() for more details.

gtk_container_get_resize_mode ()

GtkResizeMode
gtk_container_get_resize_mode (GtkContainer *container);

Returns the resize mode for the container. See gtk_container_set_resize_mode().

gtk_container_set_resize_mode ()

void
gtk_container_set_resize_mode (GtkContainer *container,
                               GtkResizeMode resize_mode);

Sets the resize mode for the container.

The resize mode of a container determines whether a resize request will be passed to the container’s parent, queued for later execution or executed immediately.

gtk_container_check_resize ()

void
gtk_container_check_resize (GtkContainer *container);

gtk_container_foreach ()

void
gtk_container_foreach (GtkContainer *container,
                       GtkCallback callback,
                       gpointer callback_data);

Invokes callback on each non-internal child of container . See gtk_container_forall() for details on what constitutes an “internal” child. Most applications should use gtk_container_foreach(), rather than gtk_container_forall().

gtk_container_get_children ()

GList *
gtk_container_get_children (GtkContainer *container);

Returns the container’s non-internal children. See gtk_container_forall() for details on what constitutes an "internal" child.

gtk_container_get_path_for_child ()

GtkWidgetPath *
gtk_container_get_path_for_child (GtkContainer *container,
                                  GtkWidget *child);

Returns a newly created widget path representing all the widget hierarchy from the toplevel down to and including child .

gtk_container_set_reallocate_redraws ()

void
gtk_container_set_reallocate_redraws (GtkContainer *container,
                                      gboolean needs_redraws);

Sets the reallocate_redraws flag of the container to the given value.

Containers requesting reallocation redraws get automatically redrawn if any of their children changed allocation.

gtk_container_get_focus_child ()

GtkWidget *
gtk_container_get_focus_child (GtkContainer *container);

Returns the current focus child widget inside container . This is not the currently focused widget. That can be obtained by calling gtk_window_get_focus().

Since 2.14

gtk_container_set_focus_child ()

void
gtk_container_set_focus_child (GtkContainer *container,
                               GtkWidget *child);

Sets, or unsets if child is NULL, the focused child of container .

This function emits the GtkContainer::set_focus_child signal of container . Implementations of GtkContainer can override the default behaviour by overriding the class closure of this signal.

This is function is mostly meant to be used by widgets. Applications can use gtk_widget_grab_focus() to manualy set the focus to a specific widget.

gtk_container_get_focus_vadjustment ()

GtkAdjustment *
gtk_container_get_focus_vadjustment (GtkContainer *container);

Retrieves the vertical focus adjustment for the container. See gtk_container_set_focus_vadjustment().

gtk_container_set_focus_vadjustment ()

void
gtk_container_set_focus_vadjustment (GtkContainer *container,
                                     GtkAdjustment *adjustment);

Hooks up an adjustment to focus handling in a container, so when a child of the container is focused, the adjustment is scrolled to show that widget. This function sets the vertical alignment. See gtk_scrolled_window_get_vadjustment() for a typical way of obtaining the adjustment and gtk_container_set_focus_hadjustment() for setting the horizontal adjustment.

The adjustments have to be in pixel units and in the same coordinate system as the allocation for immediate children of the container.

gtk_container_get_focus_hadjustment ()

GtkAdjustment *
gtk_container_get_focus_hadjustment (GtkContainer *container);

Retrieves the horizontal focus adjustment for the container. See gtk_container_set_focus_hadjustment().

gtk_container_set_focus_hadjustment ()

void
gtk_container_set_focus_hadjustment (GtkContainer *container,
                                     GtkAdjustment *adjustment);

Hooks up an adjustment to focus handling in a container, so when a child of the container is focused, the adjustment is scrolled to show that widget. This function sets the horizontal alignment. See gtk_scrolled_window_get_hadjustment() for a typical way of obtaining the adjustment and gtk_container_set_focus_vadjustment() for setting the vertical adjustment.

The adjustments have to be in pixel units and in the same coordinate system as the allocation for immediate children of the container.

gtk_container_resize_children ()

void
gtk_container_resize_children (GtkContainer *container);

gtk_container_child_type ()

GType
gtk_container_child_type (GtkContainer *container);

Returns the type of the children supported by the container.

Note that this may return G_TYPE_NONE to indicate that no more children can be added, e.g. for a GtkPaned which already has two children.

gtk_container_child_get ()

void
gtk_container_child_get (GtkContainer *container,
                         GtkWidget *child,
                         const gchar *first_prop_name,
                         ...);

Gets the values of one or more child properties for child and container .

gtk_container_child_set ()

void
gtk_container_child_set (GtkContainer *container,
                         GtkWidget *child,
                         const gchar *first_prop_name,
                         ...);

Sets one or more child properties for child and container .

gtk_container_child_get_property ()

void
gtk_container_child_get_property (GtkContainer *container,
                                  GtkWidget *child,
                                  const gchar *property_name,
                                  GValue *value);

Gets the value of a child property for child and container .

gtk_container_child_set_property ()

void
gtk_container_child_set_property (GtkContainer *container,
                                  GtkWidget *child,
                                  const gchar *property_name,
                                  const GValue *value);

Sets a child property for child and container .

gtk_container_child_get_valist ()

void
gtk_container_child_get_valist (GtkContainer *container,
                                GtkWidget *child,
                                const gchar *first_property_name,
                                va_list var_args);

Gets the values of one or more child properties for child and container .

gtk_container_child_set_valist ()

void
gtk_container_child_set_valist (GtkContainer *container,
                                GtkWidget *child,
                                const gchar *first_property_name,
                                va_list var_args);

Sets one or more child properties for child and container .

gtk_container_child_notify ()

void
gtk_container_child_notify (GtkContainer *container,
                            GtkWidget *child,
                            const gchar *child_property);

Emits a “child-notify” signal for the child property child_property on widget.

This is an analogue of g_object_notify() for child properties.

Also see gtk_widget_child_notify().

Since 3.2

gtk_container_forall ()

void
gtk_container_forall (GtkContainer *container,
                      GtkCallback callback,
                      gpointer callback_data);

Invokes callback on each child of container , including children that are considered “internal” (implementation details of the container). “Internal” children generally weren’t added by the user of the container, but were added by the container implementation itself. Most applications should use gtk_container_foreach(), rather than gtk_container_forall().

gtk_container_get_border_width ()

guint
gtk_container_get_border_width (GtkContainer *container);

Retrieves the border width of the container. See gtk_container_set_border_width().

gtk_container_set_border_width ()

void
gtk_container_set_border_width (GtkContainer *container,
                                guint border_width);

Sets the border width of the container.

The border width of a container is the amount of space to leave around the outside of the container. The only exception to this is GtkWindow; because toplevel windows can’t leave space outside, they leave the space inside. The border is added on all sides of the container. To add space to only one side, use a specific “margin” property on the child widget, for example “margin-top”.

gtk_container_propagate_draw ()

void
gtk_container_propagate_draw (GtkContainer *container,
                              GtkWidget *child,
                              cairo_t *cr);

When a container receives a call to the draw function, it must send synthetic “draw” calls to all children that don’t have their own GdkWindows. This function provides a convenient way of doing this. A container, when it receives a call to its “draw” function, calls gtk_container_propagate_draw() once for each child, passing in the cr the container received.

gtk_container_propagate_draw() takes care of translating the origin of cr , and deciding whether the draw needs to be sent to the child. It is a convenient and optimized way of getting the same effect as calling gtk_widget_draw() on the child directly.

In most cases, a container can simply either inherit the “draw” implementation from GtkContainer, or do some drawing and then chain to the ::draw implementation from GtkContainer.

gtk_container_get_focus_chain ()

gboolean
gtk_container_get_focus_chain (GtkContainer *container,
                               GList **focusable_widgets);

Retrieves the focus chain of the container, if one has been set explicitly. If no focus chain has been explicitly set, GTK+ computes the focus chain based on the positions of the children. In that case, GTK+ stores NULL in focusable_widgets and returns FALSE.

gtk_container_set_focus_chain ()

void
gtk_container_set_focus_chain (GtkContainer *container,
                               GList *focusable_widgets);

Sets a focus chain, overriding the one computed automatically by GTK+.

In principle each widget in the chain should be a descendant of the container, but this is not enforced by this method, since it’s allowed to set the focus chain before you pack the widgets, or have a widget in the chain that isn’t always packed. The necessary checks are done when the focus chain is actually traversed.

gtk_container_unset_focus_chain ()

void
gtk_container_unset_focus_chain (GtkContainer *container);

Removes a focus chain explicitly set with gtk_container_set_focus_chain().

gtk_container_class_find_child_property ()

GParamSpec *
gtk_container_class_find_child_property
                               (GObjectClass *cclass,
                                const gchar *property_name);

Finds a child property of a container class by name.

gtk_container_class_install_child_property ()

void
gtk_container_class_install_child_property
                               (GtkContainerClass *cclass,
                                guint property_id,
                                GParamSpec *pspec);

Installs a child property on a container class.

gtk_container_class_list_child_properties ()

GParamSpec **
gtk_container_class_list_child_properties
                               (GObjectClass *cclass,
                                guint *n_properties);

Returns all child properties of a container class.

gtk_container_class_handle_border_width ()

void
gtk_container_class_handle_border_width
                               (GtkContainerClass *klass);

Modifies a subclass of GtkContainerClass to automatically add and remove the border-width setting on GtkContainer. This allows the subclass to ignore the border width in its size request and allocate methods. The intent is for a subclass to invoke this in its class_init function.

gtk_container_class_handle_border_width() is necessary because it would break API too badly to make this behavior the default. So subclasses must “opt in” to the parent class handling border_width for them.

struct GtkContainer

struct GtkContainer;

struct GtkContainerClass

struct GtkContainerClass {
  GtkWidgetClass parent_class;


  void    (*add)       		(GtkContainer	 *container,
				 GtkWidget	 *widget);
  void    (*remove)    		(GtkContainer	 *container,
				 GtkWidget	 *widget);
  void    (*check_resize) (GtkContainer	 *container);
  void    (*forall)    		(GtkContainer	 *container,
				 gboolean	  include_internals,
				 GtkCallback	  callback,
				 gpointer	  callback_data);
  void    (*set_focus_child) (GtkContainer	 *container,
				 GtkWidget	 *child);
  GType   (*child_type)		(GtkContainer	 *container);
  gchar*  (*composite_name) (GtkContainer	 *container,
				 GtkWidget	 *child);
  void    (*set_child_property) (GtkContainer    *container,
				 GtkWidget       *child,
				 guint            property_id,
				 const GValue    *value,
				 GParamSpec      *pspec);
  void    (*get_child_property) (GtkContainer    *container,
                                 GtkWidget       *child,
				 guint            property_id,
				 GValue          *value,
				 GParamSpec      *pspec);
  GtkWidgetPath * (*get_path_for_child) (GtkContainer *container,
                                         GtkWidget    *child);
};

Base class for containers.

enum GtkResizeMode

The “border-width” property

  “border-width”             guint

The width of the empty border outside the containers children.

Flags: Read / Write

Allowed values: <= 65535

Default value: 0

The “child” property

  “child”                    GtkWidget *

Can be used to add a new child to the container.

Flags: Write

The “resize-mode” property

  “resize-mode”              GtkResizeMode

Specify how resize events are handled.

Flags: Read / Write

Default value: GTK_RESIZE_PARENT

The “add” signal

void
user_function (GtkContainer *container,
               GtkWidget    *widget,
               gpointer      user_data)

Flags: Run First

The “check-resize” signal

void
user_function (GtkContainer *container,
               gpointer      user_data)

Flags: Run Last

The “remove” signal

void
user_function (GtkContainer *container,
               GtkWidget    *widget,
               gpointer      user_data)

Flags: Run First

The “set-focus-child” signal

void
user_function (GtkContainer *container,
               GtkWidget    *widget,
               gpointer      user_data)

Flags: Run First