Animations - rockcastle/lvgl GitHub Wiki

Written for v5.1

You can automatically change the value (animate) of a variable between a start and an end value using an animator function with void func(void* var,int32_t value) prototype. The animation will happen by the periodical calling of the animator function with the corresponding value parameter.

To create an animation you have to initializes an lv_anim_t variable (there is a template in lv_anim.h):

lv_anim_t a;								
a.var = button1;							 /*Variable to animate*/						
a.start = 100;								 /*Start value*/
a.end = 300;								 /*End value*/
a.fp = (lv_anim_fp_t)lv_obj_set_height;		                         /*Function to be used to animate*/
a.path = lv_anim_path_linear;                                            /*Path of animation*/
a.end_cb = NULL; 						 	 /*Callback when the animation is ready*/
a.act_time = 0;								 /*Set < 0 to make a delay [ms]*/
a.time = 200;								 /*Animation length [ms]*/
a.playback = 0;								 /*1: animate in reverse direction too when the normal is ready*/
a.playback_pause = 0;						         /*Wait before playback [ms]*/
a.repeat = 0;								 /*1: Repeat the animation (with or without playback)*/
a.repeat_pause = 0;							 /*Wait before repeat [ms]*/

lv_anim_create(&a);                          /*Start the animation*/

The anim_create(&a) will register the animation and immediately applies the start value regardless to the set delay.

You can determinate the path of animation. In most simple case it is linear which means the current value between start and end is changed linearly. A path is a function which calculates the next value to set based on the current state of the animation. Currently, there are two built-in paths:

• lv_anim_path_linear linear animation
• lv_anim_path_step change in one step at the end

By default, you can set the animation time. But in some cases, the animation speed is more practical. 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. The speed is interpreted in unit/sec dimension. For example lv_anim_speed_to_time(20,0,100) will give 5000 milliseconds.

You can apply multiple different animations on the same variable at the same time. (For example animate the x and y coordinates with lv_obj_set_x end lv_obj_set_y). But only one animation can exist with a given variable and function pair. Therefore the lv_anim_create() function will delete the already existing variable-function animations.

You can delete an animation by lv_anim_del(var, func) with providing the animated variable and its animator function.