How to add tactile feedback in lvgl 9?

lewisxhe · May 18, 2025, 2:07am

In lvgl8, you can set the feedback_cb callback function when lv_indev_drv_register, and this callback function can be called when touching any widget.
In lvgl9, feedback_cb has been removed, so how can I listen to the event callback of the global widget? I want this method to perform the tactile feedback function.

Thank you

Marian_M · May 18, 2025, 1:16pm

From where you have info v9 no have cb???

  lv_indev_t * indev_drv = lv_indev_create();
  lv_indev_set_type(indev_drv, LV_INDEV_TYPE_POINTER);
  lv_indev_set_read_cb(indev_drv, my_touchpad_read);

lewisxhe · May 22, 2025, 8:47am

This is just a callback function for reading touches, and it cannot get which widgets triggered the events.
There is feedback in v8, but it is gone in v9.

github.com

lvgl/lvgl/blob/e8b95b3f9c91a8b186d5705cb7705c72e6f5aea7/src/core/lv_event.c#L427


      
              return &obj->spec_attr->event_dsc[id];
          }
          
          static lv_res_t event_send_core(lv_event_t * e)
          {
              EVENT_TRACE("Sending event %d to %p with %p param", e->code, (void *)e->current_target, e->param);
          
              /*Call the input device's feedback callback if set*/
              lv_indev_t * indev_act = lv_indev_get_act();
              if(indev_act) {
                  if(indev_act->driver->feedback_cb) indev_act->driver->feedback_cb(indev_act->driver, e->code);
                  if(e->stop_processing) return LV_RES_OK;
                  if(e->deleted) return LV_RES_INV;
              }
          
              lv_res_t res = LV_RES_OK;
              lv_event_dsc_t * event_dsc = lv_obj_get_event_dsc(e->current_target, 0);
          
              uint32_t i = 0;
              while(event_dsc && res == LV_RES_OK) {
                  if(event_dsc->cb  && ((event_dsc->filter & LV_EVENT_PREPROCESS) == LV_EVENT_PREPROCESS)

krembed · May 22, 2025, 12:41pm

I am not sure if I understand correctly as I havent used LVGL 8 a lot, but I’m not sure if something like that would exist in LVGL 9? You implemented it to have global feedback regardless of the widget? What about adding a callback to the active screen with LV_EVENT_ALL?

kdschlosser · May 22, 2025, 9:28pm

That could be done and also it could be done from inside of the indev read callback function as well. There are multiple ways to actually handle this one of them being to disable the polling of the indev driver and set your own timer to handle the process this would allow the user to step in the middle of the processing of the input so they can capture any inputs that actually triggered a response from any of the elements in LVGL.