Why is a freshly created screen initialized with sizes LV_HOR_RES_MAX,LV_VER_RES_MAX?

H_Schwarz · June 8, 2021, 1:20am

Description

If I create a new screen, then it will have the size LV_HOR_RES_MAX*LV_VER_RES_MAX. I would assume it has the size of the particular display, which it is created for.

What MCU/Processor/Board and compiler are you using?

Linux Simulator (SDL)

What LVGL version are you using?

7.11

What do you want to achieve?

I would expect, when I create a new screen, that it has the dimensions of the used display initially. (Seems to be synchronisation error after setting the default display).

What have you tried so far?

Just create a screen after setting the default display, but the display is apparently NULL in lv_disp_get_hor_res(lv_disp_t * disp).
Is there a way to prevent it being NULL in lv_disp_get_hor_res ?

Code to reproduce

client code :

        lv_disp_set_default(disp);
        lv_obj_t* s  = lv_obj_create(NULL,NULL);
        lv_coord_t screen_width = lv_obj_get_width(s);
        lv_coord_t screen_height = lv_obj_get_height(s);

        cout << screen_width << endl;
        cout << screen_height << endl;

lv_hal_disp.c

lv_coord_t lv_disp_get_hor_res(lv_disp_t * disp)
{
    if(disp == NULL) disp = lv_disp_get_default();

    if(disp == NULL)
        return LV_HOR_RES_MAX;
    else {
        switch(disp->driver.rotated) {
            case LV_DISP_ROT_90:
            case LV_DISP_ROT_270:
                return disp->driver.ver_res;
            default:
                return disp->driver.hor_res;
        }
    }
}

Screenshot and/or video

If possible, add screenshots and/or videos about the current state.

embeddedt · June 8, 2021, 2:05am

Smells like memory corruption.

lv_obj_create won’t create a screen unless there is actually a default display. Therefore, the fact that it gets into lv_disp_get_hor_res and reaches the return LV_HOR_RES_MAX line suggests that the default display reference is being corrupted along the way.

github.com

lvgl/lvgl/blob/3bafa5a8a385d482d4c600d4e0f233f34f0407d3/src/lv_core/lv_obj.c#L274-L300

    
      
                  lv_disp_t * disp = lv_disp_get_default();
                  if(!disp) {
                      LV_LOG_WARN("lv_obj_create: not display created to so far. No place to assign the new screen");
                      return NULL;
                  }
          
          
        new_obj = _lv_ll_ins_head(&disp->scr_ll);
                  LV_ASSERT_MEM(new_obj);
                  if(new_obj == NULL) return NULL;
          
          
        _lv_memset_00(new_obj, sizeof(lv_obj_t));
          
          
#if LV_USE_BIDI
                  new_obj->base_dir     = LV_BIDI_BASE_DIR_DEF;
          #else
                  new_obj->base_dir     = LV_BIDI_DIR_LTR;
          #endif
          
          
        /*Set the callbacks*/
                  new_obj->signal_cb = lv_obj_signal;

This file has been truncated. show original

H_Schwarz · June 8, 2021, 2:25am

Sorry, seems it was my fault , I forgot to set disp_drv.hor_res (disp_drv.ver_res) in one of my displays. Anyway I am getting confused about when LV_HOR_RES (LV_HOR_RES_MAX) and MONITOR_HOR_RES etc. are used by the driver hal and driver implementation. At least when it comes to the simulator.