Label (lv_label)

Overview

The Labels are the basic objects to display text.

Set text

You can modify the text in run-time at any time with lv_label_set_text(label, "New text"). It will allocate the text dynamically.

With lv_label_set_text_fmt(label, "Value: %d", 15)a printf-like formatting can used to set the text.

Labels are able to show text from a static array. Use: lv_label_set_static_text(label, char_array). In this case, the text is not stored in the dynamic memory but the given array is used directly instead. Keep in mind that the array can’t be a local variable which destroys when the function exits.

You can also use a raw character array as label text. The array doesn’t have to be \0 terminated. In this case, the text will be saved to the dynamic memory. To set a raw character array use the lv_label_set_array_text(label, char_array) function.

Line break

You can use \n to make line break. For example: "line1\nline2\n\nline4"

Long modes

The size of the label object can be automatically expanded to the text size or the text can be manipulated according to several long mode policies:

  • LV_LABEL_LONG_EXPAND Expand the object size to the text size (Default)

  • LV_LABEL_LONG_BREAK Keep the object width, break (wrap) the too long lines and expand the object height

  • LV_LABEL_LONG_DOTS Keep the object size, break the text and write dots in the last line

  • LV_LABEL_LONG_SROLL Keep the size and scroll the label back and forth

  • LV_LABEL_LONG_SROLL_CIRC Keep the size and scroll the label circularly

  • LV_LABEL_LONG_CROP Keep the size and crop the text out of it.

You can specify the long mode with: lv_label_set_long_mode(label, LV_LABEL_LONG_...)

It’s important to note that when a label is created and its test is set the label’s size already expanded to the text size. In addition with the default LV_LABEL_LONG_EXPAND long mode lv_obj_set_width/height/size() has no effect. So you need to change the long mode first and then set the size with lv_obj_set_width/height/size() .

Text align

The label’s text can be aligned to the left, right or middle with lv_label_set_align(label, LV_LABEL_ALIGN_LEFT/RIGHT/CENTER)

Draw background

You can enable to draw a background for the label with lv_label_set_body_draw(label, draw)

The background will be larger in every direction with body.padding.top/bottom/left/right values. However, the background is drawn only “virtually” and doesn’t make the label really larger. There for when the label is positioned the label’s coordinates will be taken into account and not background’s.

Text recolor

In the text, you can use commands to re-color parts of the text. For example: "Write a #ff0000 red# word". This feature can be enabled individually for each label by lv_label_set_recolor() function.

Note that, recoloring work only in a single line. I.e. there can’t be \n in a recolored text or it can be wrapped by LV_LABEL_LONG_BREAK else the text in the new line won’t be recolored.

Very long texts

LittlevGL can effectively handle very long (> 40k characters) by saving some extra data (~12 bytes) to speed up drawing. To enable this feature set LV_LABEL_LONG_TXT_HINT   1 in lv_conf.h.

Symbols

The labels can display symbols besides letters. Read the Font section to learn more about the symbols.

Styles

The Label uses one style which can be set by lv_label_set_style(label, LV_LABEL_STYLE_MAIN, &style). Form the style the following properties are used:

  • all properties from style.text

  • for background drawing style.body properties. padding will increase the size only visually, the real object’s size won’t be changed.

The labels’ default style is NULL so they inherit the parent’s style.

Events

Only the Generic events are sent by the object type.

Learn more about Events.

Keys

No Keys are processed by the object type.

Learn more about Keys.

Example

C

Label recoloring and scrolling

Label example in LittlevGL

code

#include "lvgl/lvgl.h"

void lv_ex_label_1(void)
{
    lv_obj_t * label1 = lv_label_create(lv_scr_act(), NULL);
    lv_label_set_long_mode(label1, LV_LABEL_LONG_BREAK);     /*Break the long lines*/
    lv_label_set_recolor(label1, true);                      /*Enable re-coloring by commands in the text*/
    lv_label_set_align(label1, LV_LABEL_ALIGN_CENTER);       /*Center aligned lines*/
    lv_label_set_text(label1, "#000080 Re-color# #0000ff words# #6666ff of a# label "
                              "and  wrap long text automatically.");
    lv_obj_set_width(label1, 150);
    lv_obj_align(label1, NULL, LV_ALIGN_CENTER, 0, -30);

    lv_obj_t * label2 = lv_label_create(lv_scr_act(), NULL);
    lv_label_set_long_mode(label2, LV_LABEL_LONG_SROLL_CIRC);     /*Circular scroll*/
    lv_obj_set_width(label2, 150);
    lv_label_set_text(label2, "It is a circularly scrolling text. ");
    lv_obj_align(label2, NULL, LV_ALIGN_CENTER, 0, 30);
}

Text shadow

Label with shadow in LittlevGL

code

#include "lvgl/lvgl.h"

void lv_ex_label_2(void)
{
    /* Create a style for the shadow*/
    static lv_style_t label_style;
    lv_style_copy(&label_style, &lv_style_plain);
    label_style.text.opa = LV_OPA_50;

    /*Create a label for the shadow first (it's in the background) */
    lv_obj_t * shadow_label = lv_label_create(lv_scr_act(), NULL);
    lv_label_set_style(shadow_label, LV_LABEL_STYLE_MAIN, &label_style);

    /* Create the main label */
    lv_obj_t * main_label = lv_label_create(lv_scr_act(), NULL);
    lv_label_set_text(main_label, "A simple method to create\n"
                                  "shadows on text\n"
                                  "It even works with\n\n"
                                  "newlines     and spaces.");

    /*Set the same text for the shadow label*/
    lv_label_set_text(shadow_label, lv_label_get_text(main_label));

    /* Position the main label */
    lv_obj_align(main_label, NULL, LV_ALIGN_CENTER, 0, 0);
    
    /* Shift the second label down and to the right by 1 pixel */
    lv_obj_align(shadow_label, main_label, LV_ALIGN_IN_TOP_LEFT, 1, 1);
}

Align labels

Align labels in LittlevGL

code

#include "lvgl/lvgl.h"

static void text_changer(lv_task_t * t);

lv_obj_t * labels[3];

/**
 * Create three labels to demonstrate the alignments.
 */
void lv_ex_label_3(void)
{
    /*`lv_label_set_align` is not required to align the object itslef.
     * It's used only when the text has multiple lines*/

    /* Create a label on the top.
     * No additional alignment so it will be the reference*/
    labels[0] = lv_label_create(lv_scr_act(), NULL);
    lv_obj_align(labels[0], NULL, LV_ALIGN_IN_TOP_MID, 0, 5);
    lv_label_set_align(labels[0], LV_LABEL_ALIGN_CENTER);

    /* Create a label in the middle.
     * `lv_obj_align` will be called every time the text changes
     * to keep the middle position */
    labels[1] = lv_label_create(lv_scr_act(), NULL);
    lv_obj_align(labels[1], NULL, LV_ALIGN_CENTER, 0, 0);
    lv_label_set_align(labels[1], LV_LABEL_ALIGN_CENTER);

    /* Create a label in the bottom.
     * Enable auto realign. */
    labels[2] = lv_label_create(lv_scr_act(), NULL);
    lv_obj_set_auto_realign(labels[2], true);
    lv_obj_align(labels[2], NULL, LV_ALIGN_IN_BOTTOM_MID, 0, -5);
    lv_label_set_align(labels[2], LV_LABEL_ALIGN_CENTER);

    lv_task_t * t = lv_task_create(text_changer, 1000, LV_TASK_PRIO_MID, NULL);
    lv_task_ready(t);
}

static void text_changer(lv_task_t * t)
{
    const char * texts[] = {"Text", "A very long text", "A text with\nmultiple\nlines", NULL};
    static uint8_t i = 0;

    lv_label_set_text(labels[0], texts[i]);
    lv_label_set_text(labels[1], texts[i]);
    lv_label_set_text(labels[2], texts[i]);

    /*Manually realaign `labels[1]`*/
    lv_obj_align(labels[1], NULL, LV_ALIGN_CENTER, 0, 0);

    i++;
    if(texts[i] == NULL) i = 0;

}

MicroPython

Label recoloring and scrolling

Label example in LittlevGL with MicroPython

code

label1 = lv.label(lv.scr_act())
label1.set_long_mode(lv.label.LONG.BREAK)     # Break the long lines
label1.set_recolor(True)                      # Enable re-coloring by commands in the text
label1.set_align(lv.label.ALIGN.CENTER)       # Center aligned lines
label1.set_text("#000080 Re-color# #0000ff words# #6666ff of a# label " +
                "and  wrap long text automatically.")
label1.set_width(150)
label1.align(None, lv.ALIGN.CENTER, 0, -30)

label2 = lv.label(lv.scr_act())
label2.set_long_mode(lv.label.LONG.SROLL_CIRC)     # Circular scroll
label2.set_width(150)
label2.set_text("It is a circularly scrolling text. ")
label2.align(None, lv.ALIGN.CENTER, 0, 30)

Text shadow

Label with shadow in LittlevGL with MicroPython

code

# Create a style for the shadow
label_style = lv.style_t()
lv.style_copy(label_style, lv.style_plain)
label_style.text.opa = lv.OPA._50

# Create a label for the shadow first (it's in the background)
shadow_label = lv.label(lv.scr_act())
shadow_label.set_style(lv.label.STYLE.MAIN, label_style)

# Create the main label
main_label = lv.label(lv.scr_act())
main_label.set_text("A simple method to create\n" +
                              "shadows on text\n" +
                              "It even works with\n\n" +
                              "newlines     and spaces.")

# Set the same text for the shadow label
shadow_label.set_text(main_label.get_text())

# Position the main label
main_label.align(None, lv.ALIGN.CENTER, 0, 0)

# Shift the second label down and to the right by 1 pixel
shadow_label.align(main_label, lv.ALIGN.IN_TOP_LEFT, 1, 1)

Align labels

Align labels in LittlevGL with MicroPython

code

# Create three labels to demonstrate the alignments.
labels = []

# `lv_label_set_align` is not required to align the object itslef.
# It's used only when the text has multiple lines

# Create a label on the top.
# No additional alignment so it will be the reference
label = lv.label(lv.scr_act())
label.align(None, lv.ALIGN.IN_TOP_MID, 0, 5)
label.set_align(lv.label.ALIGN.CENTER)
labels.append(label)

# Create a label in the middle.
# `lv_obj_align` will be called every time the text changes
# to keep the middle position
label = lv.label(lv.scr_act())
label.align(None, lv.ALIGN.CENTER, 0, 0)
label.set_align(lv.label.ALIGN.CENTER)
labels.append(label)

# Create a label in the bottom.
# Enable auto realign.
label = lv.label(lv.scr_act())
label.set_auto_realign(True)
label.align(None, lv.ALIGN.IN_BOTTOM_MID, 0, -5)
label.set_align(lv.label.ALIGN.CENTER)
labels.append(label)

class TextChanger:
    """Changes texts of all labels every second"""
    def __init__(self, labels, 
                texts=["Text", "A very long text", "A text with\nmultiple\nlines"],
                rate=1000):
        self.texts = texts
        self.labels = labels
        self.rate = rate
        self.counter = 0

    def start(self):
        lv.task_create(self.task_cb, self.rate, lv.TASK_PRIO.LOWEST, None)

    def task_cb(self, task):
        for label in labels:
            label.set_text(self.texts[self.counter])

        # Manually realaign `labels[1]`
        if len(self.labels) > 1:
            self.labels[1].align(None, lv.ALIGN.CENTER, 0, 0)

        self.counter = (self.counter + 1) % len(self.texts)

text_changer = TextChanger(labels)
text_changer.start()

API

Typedefs

typedef uint8_t lv_label_long_mode_t
typedef uint8_t lv_label_align_t
typedef uint8_t lv_label_style_t

Enums

enum [anonymous]

Long mode behaviors. Used in ‘lv_label_ext_t

Values:

LV_LABEL_LONG_EXPAND

Expand the object size to the text size

LV_LABEL_LONG_BREAK

Keep the object width, break the too long lines and expand the object height

LV_LABEL_LONG_DOT

Keep the size and write dots at the end if the text is too long

LV_LABEL_LONG_SROLL

Keep the size and roll the text back and forth

LV_LABEL_LONG_SROLL_CIRC

Keep the size and roll the text circularly

LV_LABEL_LONG_CROP

Keep the size and crop the text out of it

enum [anonymous]

Label align policy

Values:

LV_LABEL_ALIGN_LEFT

Align text to left

LV_LABEL_ALIGN_CENTER

Align text to center

LV_LABEL_ALIGN_RIGHT

Align text to right

LV_LABEL_ALIGN_AUTO

Use LEFT or RIGHT depending on the direction of the text (LTR/RTL)

enum [anonymous]

Label styles

Values:

LV_LABEL_STYLE_MAIN

Functions

LV_EXPORT_CONST_INT(LV_LABEL_DOT_NUM)
LV_EXPORT_CONST_INT(LV_LABEL_POS_LAST)
LV_EXPORT_CONST_INT(LV_LABEL_TEXT_SEL_OFF)
lv_obj_t *lv_label_create(lv_obj_t *par, const lv_obj_t *copy)

Create a label objects

Return

pointer to the created button

Parameters
  • par: pointer to an object, it will be the parent of the new label

  • copy: pointer to a button object, if not NULL then the new object will be copied from it

void lv_label_set_text(lv_obj_t *label, const char *text)

Set a new text for a label. Memory will be allocated to store the text by the label.

Parameters
  • label: pointer to a label object

  • text: ‘\0’ terminated character string. NULL to refresh with the current text.

void lv_label_set_text_fmt(lv_obj_t *label, const char *fmt, ...)

Set a new formatted text for a label. Memory will be allocated to store the text by the label.

Parameters
  • label: pointer to a label object

  • fmt: printf-like format

void lv_label_set_array_text(lv_obj_t *label, const char *array, uint16_t size)

Set a new text for a label from a character array. The array don’t has to be ‘\0’ terminated. Memory will be allocated to store the array by the label.

Parameters
  • label: pointer to a label object

  • array: array of characters or NULL to refresh the label

  • size: the size of ‘array’ in bytes

void lv_label_set_static_text(lv_obj_t *label, const char *text)

Set a static text. It will not be saved by the label so the ‘text’ variable has to be ‘alive’ while the label exist.

Parameters
  • label: pointer to a label object

  • text: pointer to a text. NULL to refresh with the current text.

void lv_label_set_long_mode(lv_obj_t *label, lv_label_long_mode_t long_mode)

Set the behavior of the label with longer text then the object size

Parameters
  • label: pointer to a label object

  • long_mode: the new mode from ‘lv_label_long_mode’ enum. In LV_LONG_BREAK/LONG/ROLL the size of the label should be set AFTER this function

void lv_label_set_align(lv_obj_t *label, lv_label_align_t align)

Set the align of the label (left or center)

Parameters
  • label: pointer to a label object

  • align: ‘LV_LABEL_ALIGN_LEFT’ or ‘LV_LABEL_ALIGN_LEFT’

void lv_label_set_recolor(lv_obj_t *label, bool en)

Enable the recoloring by in-line commands

Parameters
  • label: pointer to a label object

  • en: true: enable recoloring, false: disable

void lv_label_set_body_draw(lv_obj_t *label, bool en)

Set the label to draw (or not draw) background specified in its style’s body

Parameters
  • label: pointer to a label object

  • en: true: draw body; false: don’t draw body

void lv_label_set_anim_speed(lv_obj_t *label, uint16_t anim_speed)

Set the label’s animation speed in LV_LABEL_LONG_SROLL/SCROLL_CIRC modes

Parameters
  • label: pointer to a label object

  • anim_speed: speed of animation in px/sec unit

static void lv_label_set_style(lv_obj_t *label, lv_label_style_t type, const lv_style_t *style)

Set the style of an label

Parameters
  • label: pointer to an label object

  • type: which style should be get (can be only LV_LABEL_STYLE_MAIN)

  • style: pointer to a style

void lv_label_set_text_sel_start(lv_obj_t *label, uint16_t index)

Set the selection start index.

Parameters
  • label: pointer to a label object.

  • index: index to set. LV_LABEL_TXT_SEL_OFF to select nothing.

void lv_label_set_text_sel_end(lv_obj_t *label, uint16_t index)

Set the selection end index.

Parameters
  • label: pointer to a label object.

  • index: index to set. LV_LABEL_TXT_SEL_OFF to select nothing.

char *lv_label_get_text(const lv_obj_t *label)

Get the text of a label

Return

the text of the label

Parameters
  • label: pointer to a label object

lv_label_long_mode_t lv_label_get_long_mode(const lv_obj_t *label)

Get the long mode of a label

Return

the long mode

Parameters
  • label: pointer to a label object

lv_label_align_t lv_label_get_align(const lv_obj_t *label)

Get the align attribute

Return

LV_LABEL_ALIGN_LEFT or LV_LABEL_ALIGN_CENTER

Parameters
  • label: pointer to a label object

bool lv_label_get_recolor(const lv_obj_t *label)

Get the recoloring attribute

Return

true: recoloring is enabled, false: disable

Parameters
  • label: pointer to a label object

bool lv_label_get_body_draw(const lv_obj_t *label)

Get the body draw attribute

Return

true: draw body; false: don’t draw body

Parameters
  • label: pointer to a label object

uint16_t lv_label_get_anim_speed(const lv_obj_t *label)

Get the label’s animation speed in LV_LABEL_LONG_ROLL and SCROLL modes

Return

speed of animation in px/sec unit

Parameters
  • label: pointer to a label object

void lv_label_get_letter_pos(const lv_obj_t *label, uint16_t index, lv_point_t *pos)

Get the relative x and y coordinates of a letter

Parameters
  • label: pointer to a label object

  • index: index of the letter [0 … text length]. Expressed in character index, not byte index (different in UTF-8)

  • pos: store the result here (E.g. index = 0 gives 0;0 coordinates)

uint16_t lv_label_get_letter_on(const lv_obj_t *label, lv_point_t *pos)

Get the index of letter on a relative point of a label

Return

the index of the letter on the ‘pos_p’ point (E.g. on 0;0 is the 0. letter) Expressed in character index and not byte index (different in UTF-8)

Parameters
  • label: pointer to label object

  • pos: pointer to point with coordinates on a the label

bool lv_label_is_char_under_pos(const lv_obj_t *label, lv_point_t *pos)

Check if a character is drawn under a point.

Return

whether a character is drawn under the point

Parameters
  • label: Label object

  • pos: Point to check for characte under

static const lv_style_t *lv_label_get_style(const lv_obj_t *label, lv_label_style_t type)

Get the style of an label object

Return

pointer to the label’s style

Parameters
  • label: pointer to an label object

  • type: which style should be get (can be only LV_LABEL_STYLE_MAIN)

uint16_t lv_label_get_text_sel_start(const lv_obj_t *label)

Get the selection start index.

Return

selection start index. LV_LABEL_TXT_SEL_OFF if nothing is selected.

Parameters
  • label: pointer to a label object.

uint16_t lv_label_get_text_sel_end(const lv_obj_t *label)

Get the selection end index.

Return

selection end index. LV_LABEL_TXT_SEL_OFF if nothing is selected.

Parameters
  • label: pointer to a label object.

void lv_label_ins_text(lv_obj_t *label, uint32_t pos, const char *txt)

Insert a text to the label. The label text can not be static.

Parameters
  • label: pointer to a label object

  • pos: character index to insert. Expressed in character index and not byte index (Different in UTF-8) 0: before first char. LV_LABEL_POS_LAST: after last char.

  • txt: pointer to the text to insert

void lv_label_cut_text(lv_obj_t *label, uint32_t pos, uint32_t cnt)

Delete characters from a label. The label text can not be static.

Parameters
  • label: pointer to a label object

  • pos: character index to insert. Expressed in character index and not byte index (Different in UTF-8) 0: before first char.

  • cnt: number of characters to cut

struct lv_label_ext_t
#include <lv_label.h>

Data of label

Public Members

char *text
char *tmp_ptr
char tmp[LV_LABEL_DOT_NUM + 1]
union lv_label_ext_t::[anonymous] dot
uint16_t dot_end
lv_point_t offset
lv_draw_label_hint_t hint
uint16_t anim_speed
uint16_t txt_sel_start
uint16_t txt_sel_end
lv_label_long_mode_t long_mode
uint8_t static_txt
uint8_t align
uint8_t recolor
uint8_t expand
uint8_t body_draw
uint8_t dot_tmp_alloc