## ClutterDragAction

ClutterDragAction — Action enabling dragging on actors

## Synopsis

    struct              ClutterDragAction;
    struct              ClutterDragActionClass;
    ClutterAction *     clutter_drag_action_new             (void);
    void                clutter_drag_action_set_drag_threshold
                                                            (ClutterDragAction *action,
                                                             guint x_threshold,
                                                             guint y_threshold);
    void                clutter_drag_action_get_drag_threshold
                                                            (ClutterDragAction *action,
                                                             guint *x_threshold,
                                                             guint *y_threshold);
    void                clutter_drag_action_set_drag_handle (ClutterDragAction *action,
                                                             ClutterActor *handle);
    ClutterActor *      clutter_drag_action_get_drag_handle (ClutterDragAction *action);
    enum                ClutterDragAxis;
    void                clutter_drag_action_set_drag_axis   (ClutterDragAction *action,
                                                             ClutterDragAxis axis);
    ClutterDragAxis     clutter_drag_action_get_drag_axis   (ClutterDragAction *action);

    void                clutter_drag_action_get_press_coords
                                                            (ClutterDragAction *action,
                                                             gfloat *press_x,
                                                             gfloat *press_y);
    void                clutter_drag_action_get_motion_coords
                                                            (ClutterDragAction *action,
                                                             gfloat *motion_x,
                                                             gfloat *motion_y);

## Object Hierarchy

      GObject
       +----GInitiallyUnowned
             +----ClutterActorMeta
                   +----ClutterAction
                         +----ClutterDragAction

## Properties

      "drag-axis"                ClutterDragAxis       : Read / Write
      "drag-handle"              ClutterActor*         : Read / Write
      "x-drag-threshold"         guint                 : Read / Write
      "y-drag-threshold"         guint                 : Read / Write

## Signals

      "drag-begin"                                     : Run Last
      "drag-end"                                       : Run Last
      "drag-motion"                                    : Run Last

## Description

ClutterDragAction is a sub-class of ClutterAction that implements all the necessary logic for dragging actors.

The simplest usage of ClutterDragAction consists in adding it to a ClutterActor and setting it as reactive; for instance, the following code:

    1
    2

    clutter_actor_add_action (actor, clutter_drag_action_new ());
    clutter_actor_set_reactive (actor, TRUE);

will automatically result in the actor moving to follow the pointer whenever the pointer's button is pressed over the actor and moved across the stage.

The ClutterDragAction will signal the begin and the end of a dragging through the "drag-begin" and "drag-end" signals, respectively. Each pointer motion during a drag will also result in the "drag-motion" signal to be emitted.

It is also possible to set another ClutterActor as the dragged actor by calling `clutter_drag_action_set_drag_handle()` from within a handle of the "drag-begin" signal. The drag handle must be parented and exist between the emission of "drag-begin" and "drag-end".

ClutterDragAction is available since Clutter 1.4

## Details

### struct ClutterDragAction

    struct ClutterDragAction;

The ClutterDragAction structure contains only private data and should be accessed using the provided API

Since 1.4

### struct ClutterDragActionClass

    struct ClutterDragActionClass {
      void (* drag_begin)  (ClutterDragAction   *action,
                            ClutterActor        *actor,
                            gfloat               event_x,
                            gfloat               event_y,
                            ClutterModifierType  modifiers);
      void (* drag_motion) (ClutterDragAction   *action,
                            ClutterActor        *actor,
                            gfloat               delta_x,
                            gfloat               delta_y);
      void (* drag_end)    (ClutterDragAction   *action,
                            ClutterActor        *actor,
                            gfloat               event_x,
                            gfloat               event_y,
                            ClutterModifierType  modifiers);
    };

The ClutterDragActionClass structure contains only private data

`drag_begin` () | class handler of the "drag-begin" signal
`drag_motion` () | class handler of the "drag-motion" signal
`drag_end` () | class handler of the "drag-end" signal

Since 1.4

### clutter_drag_action_new ()

    ClutterAction *     clutter_drag_action_new             (void);

Creates a new ClutterDragAction instance

Returns : | the newly created ClutterDragAction

Since 1.4

### clutter_drag_action_set_drag_threshold ()

    void                clutter_drag_action_set_drag_threshold
                                                            (ClutterDragAction *action,
                                                             guint x_threshold,
                                                             guint y_threshold);

Sets the horizontal and vertical drag thresholds that must be cleared by the pointer before `action` can begin the dragging

`action` : | a ClutterDragAction
`x_threshold` : | a distance on the horizontal axis, in pixels
`y_threshold` : | a distance on the vertical axis, in pixels

Since 1.4

### clutter_drag_action_get_drag_threshold ()

    void                clutter_drag_action_get_drag_threshold
                                                            (ClutterDragAction *action,
                                                             guint *x_threshold,
                                                             guint *y_threshold);

Retrieves the values set by `clutter_drag_action_set_drag_threshold()`

`action` : | a ClutterDragAction
`x_threshold` : | return location for the horizontal drag threshold value, in pixels. [out]
`y_threshold` : | return location for the vertical drag threshold value, in pixels. [out]

Since 1.4

### clutter_drag_action_set_drag_handle ()

    void                clutter_drag_action_set_drag_handle (ClutterDragAction *action,
                                                             ClutterActor *handle);

Sets the actor to be used as the drag handle

`action` : | a ClutterDragHandle
`handle` : | a ClutterActor

Since 1.4

### clutter_drag_action_get_drag_handle ()

    ClutterActor *      clutter_drag_action_get_drag_handle (ClutterDragAction *action);

Retrieves the drag handle set by `clutter_drag_action_set_drag_handle()`

`action` : | a ClutterDragAction
Returns : | a ClutterActor, used as the drag handle, or `NULL` if none was set. [transfer none]

Since 1.4

### enum ClutterDragAxis

    typedef enum { /*< prefix=CLUTTER_DRAG >*/
      CLUTTER_DRAG_AXIS_NONE = 0,

      CLUTTER_DRAG_X_AXIS,
      CLUTTER_DRAG_Y_AXIS
    } ClutterDragAxis;

The axis of the constraint that should be applied on the dragging action

`CLUTTER_DRAG_AXIS_NONE` | No constraint
`CLUTTER_DRAG_X_AXIS` | Set a constraint on the X axis
`CLUTTER_DRAG_Y_AXIS` | Set a constraint on the Y axis

Since 1.4

### clutter_drag_action_set_drag_axis ()

    void                clutter_drag_action_set_drag_axis   (ClutterDragAction *action,
                                                             ClutterDragAxis axis);

Restricts the dragging action to a specific axis

`action` : | a ClutterDragAction
`axis` : | the axis to constraint the dragging to

Since 1.4

### clutter_drag_action_get_drag_axis ()

    ClutterDragAxis     clutter_drag_action_get_drag_axis   (ClutterDragAction *action);

Retrieves the axis constraint set by `clutter_drag_action_set_drag_axis()`

`action` : | a ClutterDragAction
Returns : | the axis constraint

Since 1.4

### clutter_drag_action_get_press_coords ()

    void                clutter_drag_action_get_press_coords
                                                            (ClutterDragAction *action,
                                                             gfloat *press_x,
                                                             gfloat *press_y);

Retrieves the coordinates, in stage space, of the press event that started the dragging

`action` : | a ClutterDragAction
`press_x` : | return location for the press event's X coordinate. [out]
`press_y` : | return location for the press event's Y coordinate. [out]

Since 1.4

### clutter_drag_action_get_motion_coords ()

    void                clutter_drag_action_get_motion_coords
                                                            (ClutterDragAction *action,
                                                             gfloat *motion_x,
                                                             gfloat *motion_y);

Retrieves the coordinates, in stage space, of the latest motion event during the dragging

`action` : | a ClutterDragAction
`motion_x` : | return location for the latest motion event's X coordinate. [out]
`motion_y` : | return location for the latest motion event's Y coordinate. [out]

Since 1.4

## Property Details

### The `"drag-axis"` property

      "drag-axis"                ClutterDragAxis       : Read / Write

Constraints the dragging action to the specified axis

Default value: CLUTTER_DRAG_AXIS_NONE

Since 1.4

### The `"drag-handle"` property

      "drag-handle"              ClutterActor*         : Read / Write

The ClutterActor that is effectively being dragged

A ClutterDragAction will, be default, use the ClutterActor that has been attached to the action; it is possible to create a separate ClutterActor and use it instead.

Setting this property has no effect on the ClutterActor argument passed to the ClutterDragAction signals

Since 1.4

### The `"x-drag-threshold"` property

      "x-drag-threshold"         guint                 : Read / Write

The horizontal threshold, in pixels, that begins a drag action

When set to a non-zero value, ClutterDragAction will only emit "drag-begin" if the pointer has moved horizontally at least of the given amount of pixels since the button press event

Default value: 0

Since 1.4

### The `"y-drag-threshold"` property

      "y-drag-threshold"         guint                 : Read / Write

The vertical threshold, in pixels, that begins a drag action

When set to a non-zero value, ClutterDragAction will only emit "drag-begin" if the pointer has moved vertically at least of the given amount of pixels since the button press event

Default value: 0

Since 1.4

## Signal Details

### The `"drag-begin"` signal

    void                user_function                      (ClutterDragAction  *action,
                                                            ClutterActor       *actor,
                                                            gfloat              event_x,
                                                            gfloat              event_y,
                                                            ClutterModifierType modifiers,
                                                            gpointer            user_data)      : Run Last

The ::drag-begin signal is emitted when the ClutterDragAction starts the dragging

The emission of this signal can be delayed by using the "x-drag-threshold" and "y-drag-threshold" properties

`action` : | the ClutterDragAction that emitted the signal
`actor` : | the ClutterActor attached to the action
`event_x` : | the X coordinate (in stage space) of the press event
`event_y` : | the Y coordinate (in stage space) of the press event
`modifiers` : | the modifiers of the press event
`user_data` : | user data set when the signal handler was connected.

Since 1.4

### The `"drag-end"` signal

    void                user_function                      (ClutterDragAction  *action,
                                                            ClutterActor       *actor,
                                                            gfloat              event_x,
                                                            gfloat              event_y,
                                                            ClutterModifierType modifiers,
                                                            gpointer            user_data)      : Run Last

The ::drag-end signal is emitted at the end of the dragging, when the pointer button's is released

This signal is emitted if and only if the "drag-begin" signal has been emitted first

`action` : | the ClutterDragAction that emitted the signal
`actor` : | the ClutterActor attached to the action
`event_x` : | the X coordinate (in stage space) of the release event
`event_y` : | the Y coordinate (in stage space) of the release event
`modifiers` : | the modifiers of the release event
`user_data` : | user data set when the signal handler was connected.

Since 1.4

### The `"drag-motion"` signal

    void                user_function                      (ClutterDragAction *action,
                                                            ClutterActor      *actor,
                                                            gfloat             delta_x,
                                                            gfloat             delta_y,
                                                            gpointer           user_data)      : Run Last

The ::drag-motion signal is emitted for each motion event after the "drag-begin" signal has been emitted.

The components of the distance between the press event and the latest motion event are computed in the actor's coordinate space, to take into account eventual transformations. If you want the stage coordinates of the latest motion event you can use `clutter_drag_action_get_motion_coords()`.

The default handler of the signal will call `clutter_actor_move_by()` either on `actor` or, if set, of "drag-handle" using the `delta_x` and `delta_y` components of the dragging motion. If you want to override the default behaviour, you can connect to this signal and call `g_signal_stop_emission_by_name()` from within your callback.

`action` : | the ClutterDragAction that emitted the signal
`actor` : | the ClutterActor attached to the action
`delta_x` : | the X component of the distance between the press event that began the dragging and the current position of the pointer, as of the latest motion event
`delta_y` : | the Y component of the distance between the press event that began the dragging and the current position of the pointer, as of the latest motion event
`user_data` : | user data set when the signal handler was connected.

Since 1.4