acid-drop

- Hacking the planet from a LilyGo T-Deck using custom firmware
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animation.md (5455B)
      1 ```eval_rst
      2 .. include:: /header.rst
      3 :github_url: |github_link_base|/overview/animation.md
      4 ```
      5 # Animations
      6 
      7 You can automatically change the value of a variable between a start and an end value using animations.
      8 Animation will happen by periodically calling an "animator" function with the corresponding value parameter.
      9 
     10 The *animator* functions have the following prototype:
     11 ```c
     12 void func(void * var, lv_anim_var_t value);
     13 ```
     14 This prototype is compatible with the majority of the property *set* functions in LVGL. For example `lv_obj_set_x(obj, value)` or `lv_obj_set_width(obj, value)`
     15 
     16 
     17 ## Create an animation
     18 To create an animation an `lv_anim_t` variable has to be initialized and configured with `lv_anim_set_...()` functions.
     19 
     20 ```c
     21 
     22 /* INITIALIZE AN ANIMATION
     23  *-----------------------*/
     24 
     25 lv_anim_t a;
     26 lv_anim_init(&a);
     27 
     28 /* MANDATORY SETTINGS
     29  *------------------*/
     30 
     31 /*Set the "animator" function*/
     32 lv_anim_set_exec_cb(&a, (lv_anim_exec_xcb_t) lv_obj_set_x);
     33 
     34 /*Set target of the animation*/
     35 lv_anim_set_var(&a, obj);
     36 
     37 /*Length of the animation [ms]*/
     38 lv_anim_set_time(&a, duration);
     39 
     40 /*Set start and end values. E.g. 0, 150*/
     41 lv_anim_set_values(&a, start, end);
     42 
     43 /* OPTIONAL SETTINGS
     44  *------------------*/
     45 
     46 /*Time to wait before starting the animation [ms]*/
     47 lv_anim_set_delay(&a, delay);
     48 
     49 /*Set path (curve). Default is linear*/
     50 lv_anim_set_path(&a, lv_anim_path_ease_in);
     51 
     52 /*Set a callback to indicate when the animation is ready (idle).*/
     53 lv_anim_set_ready_cb(&a, ready_cb);
     54 
     55 /*Set a callback to indicate when the animation is started (after delay).*/
     56 lv_anim_set_start_cb(&a, start_cb);
     57 
     58 /*When ready, play the animation backward with this duration. Default is 0 (disabled) [ms]*/
     59 lv_anim_set_playback_time(&a, time);
     60 
     61 /*Delay before playback. Default is 0 (disabled) [ms]*/
     62 lv_anim_set_playback_delay(&a, delay);
     63 
     64 /*Number of repetitions. Default is 1. LV_ANIM_REPEAT_INFINITE for infinite repetition*/
     65 lv_anim_set_repeat_count(&a, cnt);
     66 
     67 /*Delay before repeat. Default is 0 (disabled) [ms]*/
     68 lv_anim_set_repeat_delay(&a, delay);
     69 
     70 /*true (default): apply the start value immediately, false: apply start value after delay when the anim. really starts. */
     71 lv_anim_set_early_apply(&a, true/false);
     72 
     73 /* START THE ANIMATION
     74  *------------------*/
     75 lv_anim_start(&a);                             /*Start the animation*/
     76 ```
     77 
     78 
     79 You can apply multiple different animations on the same variable at the same time.
     80 For example, animate the x and y coordinates with `lv_obj_set_x` and `lv_obj_set_y`. However, only one animation can exist with a given variable and function pair and `lv_anim_start()` will remove any existing animations for such a pair.
     81 
     82 ## Animation path
     83 
     84 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.
     85 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:
     86 
     87 - `lv_anim_path_linear` linear animation
     88 - `lv_anim_path_step` change in one step at the end
     89 - `lv_anim_path_ease_in` slow at the beginning
     90 - `lv_anim_path_ease_out` slow at the end
     91 - `lv_anim_path_ease_in_out` slow at the beginning and end
     92 - `lv_anim_path_overshoot` overshoot the end value
     93 - `lv_anim_path_bounce` bounce back a little from the end value (like hitting a wall)
     94 
     95 
     96 ## Speed vs time
     97 By default, you set the animation time directly. But in some cases, setting the animation speed is more practical.
     98 
     99 The `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.
    100 The speed is interpreted in _unit/sec_ dimension. For example,  `lv_anim_speed_to_time(20,0,100)` will yield 5000 milliseconds. For example, in the case of `lv_obj_set_x` *unit* is pixels so *20* means *20 px/sec* speed.
    101 
    102 ## Delete animations
    103 
    104 You can delete an animation with `lv_anim_del(var, func)` if you provide the animated variable and its animator function.
    105 
    106 ## Timeline
    107 A timeline is a collection of multiple animations which makes it easy to create complex composite animations.
    108 
    109 Firstly, create an animation element but don’t call `lv_anim_start()`.
    110 
    111 Secondly, create an animation timeline object by calling `lv_anim_timeline_create()`.
    112 
    113 Thirdly, add animation elements to the animation timeline by calling `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`.
    114 
    115 Finally, call `lv_anim_timeline_start(at)` to start the animation timeline.
    116 
    117 It supports forward and backward playback of the entire animation group, using `lv_anim_timeline_set_reverse(at, reverse)`.
    118 
    119 Call `lv_anim_timeline_stop(at)` to stop the animation timeline.
    120 
    121 Call `lv_anim_timeline_set_progress(at, progress)` function to set the state of the object corresponding to the progress of the timeline.
    122 
    123 Call `lv_anim_timeline_get_playtime(at)` function to get the total duration of the entire animation timeline.
    124 
    125 Call `lv_anim_timeline_get_reverse(at)` function to get whether to reverse the animation timeline.
    126 
    127 Call `lv_anim_timeline_del(at)` function to delete the animation timeline.
    128 
    129 ![](/misc/anim-timeline.png "timeline diagram")
    130 
    131 ## Examples
    132 
    133 ```eval_rst
    134 
    135 .. include:: ../../examples/anim/index.rst
    136 
    137 ```
    138 ## API
    139 
    140 ```eval_rst
    141 
    142 .. doxygenfile:: lv_anim.h
    143   :project: lvgl
    144 
    145 ```