Canvas Events

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Functions relating to canvas events, which are mainly reports on its internal states changing (an object got focused, the rendering is updated, etc).

Some of the functions in this group are exemplified here.

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Function Documentation

void evas_event_callback_add	(	Evas *	e,
		Evas_Callback_Type	type,
		Evas_Event_Cb	func,
		const void *	data
	)

Add (register) a callback function to a given canvas event.

Parameters:

e	Canvas to attach a callback to
type	The type of event that will trigger the callback
func	The (callback) function to be called when the event is triggered
data	The data pointer to be passed to func

This function adds a function callback to the canvas e when the event of type type occurs on it. The function pointer is func.

In the event of a memory allocation error during the addition of the callback to the canvas, evas_alloc_error() should be used to determine the nature of the error, if any, and the program should sensibly try and recover.

A callback function must have the ::Evas_Event_Cb prototype definition. The first parameter (data) in this definition will have the same value passed to evas_event_callback_add() as the data parameter, at runtime. The second parameter e is the canvas pointer on which the event occurred. The third parameter event_info is a pointer to a data structure that may or may not be passed to the callback, depending on the event type that triggered the callback. This is so because some events don't carry extra context with them, but others do.

The event type type to trigger the function may be one of EVAS_CALLBACK_RENDER_FLUSH_PRE, EVAS_CALLBACK_RENDER_FLUSH_POST, EVAS_CALLBACK_CANVAS_FOCUS_IN, EVAS_CALLBACK_CANVAS_FOCUS_OUT, EVAS_CALLBACK_CANVAS_OBJECT_FOCUS_IN and EVAS_CALLBACK_CANVAS_OBJECT_FOCUS_OUT. This determines the kind of event that will trigger the callback to be called. Only the last two of the event types listed here provide useful event information data -- a pointer to the recently focused Evas object. For the others the event_info pointer is going to be NULL.

Example:

   evas_event_callback_add(d.canvas, EVAS_CALLBACK_RENDER_FLUSH_PRE,
                           _render_flush_cb, NULL);
   if (evas_alloc_error() != EVAS_ALLOC_ERROR_NONE)
     {
        fprintf(stderr, "ERROR: Callback registering failed! Aborting.\n");
        goto panic;
     }

   evas_event_callback_add(d.canvas, EVAS_CALLBACK_CANVAS_OBJECT_FOCUS_IN,
                           _object_focus_in_cb, NULL);
   if (evas_alloc_error() != EVAS_ALLOC_ERROR_NONE)
     {
        fprintf(stderr, "ERROR: Callback registering failed! Aborting.\n");
        goto panic;
     } /* two canvas event callbacks */

Looking to the callbacks registered above,

/* called when our rectangle gets focus */
static void
_object_focus_in_cb(void *data EINA_UNUSED,
                    Evas *e,
                    void *event_info)
{
   fprintf(stdout, "An object got focused: %s\n",
           evas_object_name_get(event_info));

   fprintf(stdout, "Let's recheck it: %s\n",
           evas_object_name_get(evas_focus_get(e)));

   fprintf(stdout, "And again: %s\n", evas_object_focus_get(event_info) ?
           "OK!" : "Oops, something is bad.");
}

/* render flush callback */
static void
_render_flush_cb(void *data EINA_UNUSED,
                 Evas *e EINA_UNUSED,
                 void *event_info EINA_UNUSED)
{
   fprintf(stdout, "Canvas is about to flush its rendering pipeline!\n");
}

/* put some action in the canvas */
static Eina_Bool
_resize_cb(void *data EINA_UNUSED)
{
   int w, h, cw, ch;

   evas_object_geometry_get(d.img, NULL, NULL, &w, &h);
   ecore_evas_geometry_get(d.ee, NULL, NULL, &cw, &ch);

   if (w < cw)
     evas_object_resize(d.img, cw, ch);
   else
     evas_object_resize(d.img, cw / 2, ch / 2);

   return EINA_TRUE; /* re-issue the timer */
}

/* let's have our events back */

we see that the canvas flushes its rendering pipeline (EVAS_CALLBACK_RENDER_FLUSH_PRE) whenever the _resize_cb routine takes place: it has to redraw that image at a different size. Also, the callback on an object being focused comes just after we focus it explicitly, on code.

See the full example.

Note:

Be careful not to add the same callback multiple times, if that's not what you want, because Evas won't check if a callback existed before exactly as the one being registered (and thus, call it more than once on the event, in this case). This would make sense if you passed different functions and/or callback data, only.

Since :

2.3

Examples:

ecore_imf_example.c, and evas-events.c.

void* evas_event_callback_del	(	Evas *	e,
		Evas_Callback_Type	type,
		Evas_Event_Cb	func
	)

Delete a callback function from the canvas.

Parameters:

e	Canvas to remove a callback from
type	The type of event that was triggering the callback
func	The function that was to be called when the event was triggered

Returns:

The data pointer that was to be passed to the callback

This function removes the most recently added callback from the canvas e which was triggered by the event type type and was calling the function func when triggered. If the removal is successful it will also return the data pointer that was passed to evas_event_callback_add() when the callback was added to the canvas. If not successful NULL will be returned.

Example:

 extern Evas *e;
 void *my_data;
 void focus_in_callback(void *data, Evas *e, void *event_info);

 my_data = evas_event_callback_del(ebject, EVAS_CALLBACK_CANVAS_FOCUS_IN, focus_in_callback);

Since :

2.3

void* evas_event_callback_del_full	(	Evas *	e,
		Evas_Callback_Type	type,
		Evas_Event_Cb	func,
		const void *	data
	)

Delete (unregister) a callback function registered to a given canvas event.

Parameters:

e	Canvas to remove an event callback from
type	The type of event that was triggering the callback
func	The function that was to be called when the event was triggered
data	The data pointer that was to be passed to the callback

Returns:

The data pointer that was to be passed to the callback

This function removes the first added callback from the canvas e matching the event type type, the registered function pointer func and the callback data pointer data. If the removal is successful it will also return the data pointer that was passed to evas_event_callback_add() (that will be the same as the parameter) when the callback(s) was(were) added to the canvas. If not successful NULL will be returned. A common use would be to remove an exact match of a callback.

Example:

        evas_event_callback_del_full(evas, EVAS_CALLBACK_RENDER_FLUSH_PRE,
                                     _render_flush_cb, NULL);
        evas_event_callback_del_full(
          evas, EVAS_CALLBACK_CANVAS_OBJECT_FOCUS_IN,
          _object_focus_in_cb, NULL);

See the full example.

Note:

For deletion of canvas events callbacks filtering by just type and function pointer, user evas_event_callback_del().

Since :

2.3

Examples:

ecore_imf_example.c, and evas-events.c.

void evas_event_callback_priority_add	(	Evas *	e,
		Evas_Callback_Type	type,
		Evas_Callback_Priority	priority,
		Evas_Event_Cb	func,
		const void *	data
	)

Add (register) a callback function to a given canvas event with a non-default priority set. Except for the priority field, it's exactly the same as evas_event_callback_add

Parameters:

e	Canvas to attach a callback to
type	The type of event that will trigger the callback
priority	The priority of the callback, lower values called first.
func	The (callback) function to be called when the event is triggered
data	The data pointer to be passed to func

See also:

evas_event_callback_add

Since (EFL) :

1.1

Since :

2.3

void evas_post_event_callback_push	(	Evas *	e,
		Evas_Object_Event_Post_Cb	func,
		const void *	data
	)

Push a callback on the post-event callback stack

Parameters:

e	Canvas to push the callback on
func	The function that to be called when the stack is unwound
data	The data pointer to be passed to the callback

Evas has a stack of callbacks that get called after all the callbacks for an event have triggered (all the objects it triggers on and all the callbacks in each object triggered). When all these have been called, the stack is unwound from most recently to least recently pushed item and removed from the stack calling the callback set for it.

This is intended for doing reverse logic-like processing, example - when a child object that happens to get the event later is meant to be able to "steal" functions from a parent and thus on unwind of this stack have its function called first, thus being able to set flags, or return 0 from the post-callback that stops all other post-callbacks in the current stack from being called (thus basically allowing a child to take control, if the event callback prepares information ready for taking action, but the post callback actually does the action).

Since :

2.3

void evas_post_event_callback_remove	(	Evas *	e,
		Evas_Object_Event_Post_Cb	func
	)

Remove a callback from the post-event callback stack

Parameters:

e	Canvas to push the callback on
func	The function that to be called when the stack is unwound

This removes a callback from the stack added with evas_post_event_callback_push(). The first instance of the function in the callback stack is removed from being executed when the stack is unwound. Further instances may still be run on unwind.

Since :

2.3

void evas_post_event_callback_remove_full	(	Evas *	e,
		Evas_Object_Event_Post_Cb	func,
		const void *	data
	)

Remove a callback from the post-event callback stack

Parameters:

e	Canvas to push the callback on
func	The function that to be called when the stack is unwound
data	The data pointer to be passed to the callback

This removes a callback from the stack added with evas_post_event_callback_push(). The first instance of the function and data in the callback stack is removed from being executed when the stack is unwound. Further instances may still be run on unwind.

Since :

2.3