Updating label text clips - maybe related to kerning?


Using lv_label_set_text() to update the date, and it clips the text for some dates. Issue may be related to positive kerning offset.

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

MCU = PSoC 6
Board = CY8CKIT-062
Compiler = GCC 5.4

What do you experience?

Expect to see a label that says:

January 1, 2021

but I see

January 1,

It fails for the months of January and February, but no others. The day of month, or year, does not seem to matter – only determining factor seems to be month. The glyph ‘ry’ has positive kerning, which is rare – could that be a clue?

I have also seen similar issue when using the / for dates – there it would sometimes cut off only the last number of the year.

If I initialize the ROBOTO_16 array ckern_class_values to zero, the problem goes away.

What do you expect?

I expect to see the entire date string passed to lv_label_set_text()

Code to reproduce

When I create the label, I give it initial text string:

    btn_dat = lv_btn_create(lv_scr_act(), NULL);                        /*Add a button the current screen*/
    lv_obj_set_pos(btn_dat, h_ban_1, v_ban_1);                          /*Set its position*/
    lv_obj_set_size(btn_dat, ban_wid, ban_hgt);                         /*Set its size*/
    lv_obj_set_event_cb(btn_dat,  date_activity_action);                /*Assign a callback to the button*/
    label_dat = lv_label_create(btn_dat, NULL);
    lv_label_set_text( label_dat, "Wednesday, January 20  2021" );
    lv_obj_align( label_dat, NULL, LV_ALIGN_IN_TOP_MID, 0,0 );
    lv_label_set_long_mode(label_dat, LV_LABEL_LONG_EXPAND);

Then later change it based on Calendar widget:

static void calendar_event_handler(lv_obj_t * obj, lv_event_t event)
    static char date_str[64];
    if(event == LV_EVENT_CLICKED) 
        lv_calendar_date_t * date = lv_calendar_get_pressed_date(obj);
            lv_calendar_set_today_date(obj, date);
            today = *date;

            sprintf( date_str, "%s %2d, %4d", months[today.month-1], today.day, today.year );
            lv_label_set_text( label_dat, date_str );


Screenshot and/or video

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

The spacing between January and 1 looks somewhat larger than I would expect. You may be right about the kerning being broken here.

I have some vague memories that there was a sneaky issue with an over/underflow when calculating kern values, however, couldn’t find it now :frowning:

Could you try it in v7?