How do I tell if a screen-change animation is running?

How-to
1

Description

How can I tell if a screen-change is currently animating? My LVGL main loop has two possible actions:

  1. Call lv_timer_handler()
  2. If present, pop a command-packet from a FreeRTOS queue and process it. This may involve calling lv_scr_load_anim()

What LVGL version are you using?

8.3.x

What do you want to achieve?

I’d like to defer processing a command packet while a screen animation is running, so that my screen changes can occur back-to-back, rather than a new screen change destroying the old screen immediately while a screen change is already in progress.

What have you tried so far?

I’ve tried stashing the current screen pointer and waiting for it to update, but this is tedious. Do I need to wait until disp->scr_to_load is NULL? Is there a direct way to do so?

2

what if you try to use events?

3

That’s an interesting idea! Just to confirm, you mean I should monitor for LV_EVENT_SCREEN_UNLOAD_START to notice that the animation has begun, then perhaps LV_EVENT_SCREEN_UNLOADED to notice when the previous screen was unloaded?

4

Are both of your actions processed in one thread?

5

Yes. Other threads submit work using the queue that the main thread processes.

6

I can offer you create semaphore when lv_scr_load_anim() is called.Give it when new screen loaded (in LV_EVENT_SCREEN_LOADED event handler). And skip action 2 if semaphore not taken (xSemaphoreTake in non-blocking mode - TickToWait=0).
EDIT: delete semaphore if it successfully taken.

7

I think something like that should work, since all LVGL calls and queue processing are all on the same thread, I think a simple boolean should work, something like this:

bool animationRunning = false;

void threadFunc(){
    if(queueHasItem() && !animationRunning){
        queuePopAndProcessItem();
    }
    //This would trigger calls to update animationRunning accordingly
    lv_timer_handler();
}

Is there a way to listen for all calls to lv_scr_load_anim() by LV_EVENT_SCREEN_UNLOAD_START ? Or, would I have to wrap all calls to lv_scr_load_anim()? Is there a root object I could listen to where all LV_EVENT_SCREEN_UNLOAD_START would trigger, maybe the display object?

8

In principle, you can do it without a semaphore, and use a regular variable - since as far as I remember, event handlers are called inside lv_timer_handler()

9

I have not used such events, but I can assume that you can use lv_obj_add_event_cb() for root screen objects - which you use when call lv_scr_load_anim().
EDIT: and as far as I understand you need to use

  • LV_EVENT_SCREEN_LOADED A screen was loaded, called when all animations are finished
10

I can call lv_obj_add_event_cb() on the root screen object, but it seems I need to then enable event bubbling for the event target, which means I’d need to wrap each call to lv_scr_load_anim() before LV_EVENT_SCREEN_LOADED would bubble up to the root screen object.

11

I think I’ve got it(would need disp param for multiple displays):

bool lv_disp_anim_running(void)
{
    lv_obj_t * act_scr = lv_scr_act();
    if(!act_scr) return false;

    lv_disp_t * d = lv_obj_get_disp(act_scr);
    if(!d) return false;

    return d->scr_to_load != NULL;
}