==========
Animations
==========

You can automatically change the value of a variable between a start and
an end value using animations. Animation will happen by periodically
calling an "animator" function with the corresponding value parameter.

The *animator* functions have the following prototype:

.. code:: c

   void func(void * var, lv_anim_var_t value);

This prototype is compatible with the majority of the property *set*
functions in LVGL. For example :cpp:expr:`lv_obj_set_x(obj, value)` or
:cpp:expr:`lv_obj_set_width(obj, value)`

Create an animation
*******************

To create an animation an :cpp:type:`lv_anim_t` variable has to be initialized
and configured with ``lv_anim_set_...()`` functions.

.. code:: c


   /* INITIALIZE AN ANIMATION
    *-----------------------*/

   lv_anim_t a;
   lv_anim_init(&a);

   /* MANDATORY SETTINGS
    *------------------*/

   /*Set the "animator" function*/
   lv_anim_set_exec_cb(&a, (lv_anim_exec_xcb_t) lv_obj_set_x);

   /*Set target of the animation*/
   lv_anim_set_var(&a, obj);

   /*Length of the animation [ms]*/
   lv_anim_set_time(&a, duration);

   /*Set start and end values. E.g. 0, 150*/
   lv_anim_set_values(&a, start, end);

   /* OPTIONAL SETTINGS
    *------------------*/

   /*Time to wait before starting the animation [ms]*/
   lv_anim_set_delay(&a, delay);

   /*Set path (curve). Default is linear*/
   lv_anim_set_path(&a, lv_anim_path_ease_in);

   /*Set a callback to indicate when the animation is ready (idle).*/
   lv_anim_set_ready_cb(&a, ready_cb);

   /*Set a callback to indicate when the animation is deleted (idle).*/
   lv_anim_set_deleted_cb(&a, deleted_cb);

   /*Set a callback to indicate when the animation is started (after delay).*/
   lv_anim_set_start_cb(&a, start_cb);

   /*When ready, play the animation backward with this duration. Default is 0 (disabled) [ms]*/
   lv_anim_set_playback_time(&a, time);

   /*Delay before playback. Default is 0 (disabled) [ms]*/
   lv_anim_set_playback_delay(&a, delay);

   /*Number of repetitions. Default is 1. LV_ANIM_REPEAT_INFINITE for infinite repetition*/
   lv_anim_set_repeat_count(&a, cnt);

   /*Delay before repeat. Default is 0 (disabled) [ms]*/
   lv_anim_set_repeat_delay(&a, delay);

   /*true (default): apply the start value immediately, false: apply start value after delay when the anim. really starts. */
   lv_anim_set_early_apply(&a, true/false);

   /* START THE ANIMATION
    *------------------*/
   lv_anim_start(&a);                             /*Start the animation*/

You can apply multiple different animations on the same variable at the
same time. For example, animate the x and y coordinates with
:cpp:func:`lv_obj_set_x` and :cpp:func:`lv_obj_set_y`. However, only one animation can
exist with a given variable and function pair and :cpp:func:`lv_anim_start`
will remove any existing animations for such a pair.

Animation path
**************

You can control the path of an animation. The most simple case is
linear, meaning the current value between *start* and *end* is changed
with fixed steps. A *path* is a function which calculates the next value
to set based on the current state of the animation. Currently, there are
the following built-in path functions:

-  :cpp:func:`lv_anim_path_linear`: linear animation
-  :cpp:func:`lv_anim_path_step`: change in one step at the end
-  :cpp:func:`lv_anim_path_ease_in`: slow at the beginning
-  :cpp:func:`lv_anim_path_ease_out`: slow at the end
-  :cpp:func:`lv_anim_path_ease_in_out`: slow at the beginning and end
-  :cpp:func:`lv_anim_path_overshoot`: overshoot the end value
-  :cpp:func:`lv_anim_path_bounce`: bounce back a little from the end value (like
   hitting a wall)

Speed vs time
*************

By default, you set the animation time directly. But in some cases,
setting the animation speed is more practical.

The :cpp:expr:`lv_anim_speed_to_time(speed, start, end)` function calculates the
required time in milliseconds to reach the end value from a start value
with the given speed. The speed is interpreted in *unit/sec* dimension.
For example, :cpp:expr:`lv_anim_speed_to_time(20, 0, 100)` will yield 5000
milliseconds. For example, in the case of :cpp:func:`lv_obj_set_x` *unit* is
pixels so *20* means *20 px/sec* speed.

Delete animations
*****************

You can delete an animation with :cpp:expr:`lv_anim_del(var, func)` if you
provide the animated variable and its animator function.

Timeline
********

A timeline is a collection of multiple animations which makes it easy to
create complex composite animations.

Firstly, create an animation element but don't call :cpp:func:`lv_anim_start`.

Secondly, create an animation timeline object by calling
:cpp:func:`lv_anim_timeline_create`.

Thirdly, add animation elements to the animation timeline by calling
:cpp:expr:`lv_anim_timeline_add(at, start_time, &a)`. ``start_time`` is the
start time of the animation on the timeline. Note that ``start_time``
will override the value of ``delay``.

Finally, call :cpp:expr:`lv_anim_timeline_start(at)` to start the animation
timeline.

It supports forward and backward playback of the entire animation group,
using :cpp:expr:`lv_anim_timeline_set_reverse(at, reverse)`.

Call :cpp:expr:`lv_anim_timeline_stop(at)` to stop the animation timeline.

Call :cpp:expr:`lv_anim_timeline_set_progress(at, progress)` function to set the
state of the object corresponding to the progress of the timeline.

Call :cpp:expr:`lv_anim_timeline_get_playtime(at)` function to get the total
duration of the entire animation timeline.

Call :cpp:expr:`lv_anim_timeline_get_reverse(at)` function to get whether to
reverse the animation timeline.

Call :cpp:expr:`lv_anim_timeline_del(at)` function to delete the animation
timeline.

.. image:: /misc/anim-timeline.png

Examples
********

.. include:: ../examples/anim/index.rst

API
***
