Label (lv_label)

Overview

A label is the basic object type that is used to display text.

Parts and Styles

The label has only a main part, called LV_LABEL_PART_MAIN. It uses all the typical background properties and the text properties. The padding values can be used to make the area for the text small in the related direction.

Usage

Set text

You can set the text on a label at runtime with lv_label_set_text(label, "New text"). It will allocate a buffer dynamically, and the provided string will be copied into that buffer. Therefore, you don't need to keep the text you pass to lv_label_set_text in scope after that function returns.

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

Labels are able to show text from a static character buffer which is \0-terminated. To do so, use lv_label_set_text_static(label, "Text"). In this case, the text is not stored in the dynamic memory and the given buffer is used directly instead. This means that the array can't be a local variable which goes out of scope when the function exits. Constant strings are safe to use with lv_label_set_text_static (except when used with LV_LABEL_LONG_DOT, as it modifies the buffer in-place), as they are stored in ROM memory, which is always accessible.

Line break

Line breaks are handled automatically by the label object. You can use \n to make a line break. For example: "line1\nline2\n\nline4"

Long modes

By default, the width of the label object automatically expands to the text size. Otherwise, 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_DOT - Keep the object size, break the text and write dots in the last line (not supported when using lv_label_set_text_static)

  • 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 text 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 set the new long mode and then set the size with lv_obj_set_width/height/size().

Another important note is that LV_LABEL_LONG_DOT manipulates the text buffer in-place in order to add/remove the dots. When lv_label_set_text or lv_label_set_array_text are used, a separate buffer is allocated and this implementation detail is unnoticed. This is not the case with lv_label_set_text_static! The buffer you pass to lv_label_set_text_static must be writable if you plan to use LV_LABEL_LONG_DOT.

Text align

The lines of the text can be aligned to the left, right or center with lv_label_set_align(label, LV_LABEL_ALIGN_LEFT/RIGHT/CENTER). Note that, it will align only the lines, not the label object itself.

Vertical alignment is not supported by the label itself; you should place the label inside a larger container and align the whole label object instead.

Text recolor

In the text, you can use commands to recolor 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. Therefore, \n should not use in a recolored text or it should be wrapped by LV_LABEL_LONG_BREAK else, the text in the new line won't be recolored.

Very long texts

Lvgl can efficiently 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 alongside letters (or on their own). Read the Font section to learn more about the symbols.

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

code

#include "../../../lv_examples.h"
#if LV_USE_LABEL

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, "#0000ff Re-color# #ff00ff words# #ff0000 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);
}

#endif

Text shadow

code

#include "../../../lv_examples.h"
#if LV_USE_LABEL

void lv_ex_label_2(void)
{
    /* Create a style for the shadow*/
    static lv_style_t label_shadow_style;
    lv_style_init(&label_shadow_style);
    lv_style_set_text_opa(&label_shadow_style, LV_STATE_DEFAULT, LV_OPA_50);
    lv_style_set_text_color(&label_shadow_style, LV_STATE_DEFAULT, LV_COLOR_RED);

    /*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_obj_add_style(shadow_label, LV_LABEL_PART_MAIN, &label_shadow_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 2 pixel */
    lv_obj_align(shadow_label, main_label, LV_ALIGN_IN_TOP_LEFT, 1, 1);
}

#endif

Align labels

code

#include "../../../lv_examples.h"
#if LV_USE_LABEL

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;
}

#endif

MicroPython

Label recoloring and scrolling

Click to try in the simulator!
lv_ex_label_1

code

label1 = lv.label(lv.scr_act(),None)
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(
"""#0000ff Re-color# #ff00ff words# #ff0000 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(), None)
label2.set_long_mode(lv.label.LONG.SROLL_CIRC)
label2.set_width(150)
label2.set_text("It is a circularly scrolling text. ")
label2.align(None, lv.ALIGN.CENTER, 0, 30)

Text shadow

Click to try in the simulator!
lv_ex_label_2

code

from lv_colors import lv_colors

# Create a style for the shadow
label_shadow_style = lv.style_t()
label_shadow_style.init()
label_shadow_style.set_text_opa(lv.STATE.DEFAULT,lv.OPA._50)
label_shadow_style.set_text_color(lv.STATE.DEFAULT, lv_colors.RED);

# Create a label for the shadow first (it's in the background)
shadow_label = lv.label(lv.scr_act())
shadow_label.add_style(lv.label.PART.MAIN, label_shadow_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)

while True:
    lv.task_handler()
    time.sleep_ms(5)

Align labels

Click to try in the simulator!
lv_ex_label_3

code

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

# `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.
# `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_part_t

Enums

enum [anonymous]

Long mode behaviors. Used in 'lv_label_ext_t'

Values:

enumerator LV_LABEL_LONG_EXPAND

Expand the object size to the text size

enumerator LV_LABEL_LONG_BREAK

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

enumerator LV_LABEL_LONG_DOT

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

enumerator LV_LABEL_LONG_SROLL

Keep the size and roll the text back and forth

enumerator LV_LABEL_LONG_SROLL_CIRC

Keep the size and roll the text circularly

enumerator LV_LABEL_LONG_CROP

Keep the size and crop the text out of it

enum [anonymous]

Label align policy

Values:

enumerator LV_LABEL_ALIGN_LEFT

Align text to left

enumerator LV_LABEL_ALIGN_CENTER

Align text to center

enumerator LV_LABEL_ALIGN_RIGHT

Align text to right

enumerator LV_LABEL_ALIGN_AUTO

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

enum [anonymous]

Label styles

Values:

enumerator LV_LABEL_PART_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

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

Returns

pointer to the created button

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_text_static(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_anim_speed(lv_obj_t *label, uint16_t anim_speed)

Set the label's animation speed in LV_LABEL_LONG_SROLL/SROLL_CIRC modes

Parameters

  • label -- pointer to a label object

  • anim_speed -- speed of animation in px/sec unit

void lv_label_set_text_sel_start(lv_obj_t *label, uint32_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, uint32_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

Parameters

label -- pointer to a label object

Returns

the text of the label

lv_label_long_mode_t lv_label_get_long_mode(const lv_obj_t *label)

Get the long mode of a label

Parameters

label -- pointer to a label object

Returns

the long mode

lv_label_align_t lv_label_get_align(const lv_obj_t *label)

Get the align attribute

Parameters

label -- pointer to a label object

Returns

LV_LABEL_ALIGN_LEFT or LV_LABEL_ALIGN_CENTER

bool lv_label_get_recolor(const lv_obj_t *label)

Get the recoloring attribute

Parameters

label -- pointer to a label object

Returns

true: recoloring is enabled, false: disable

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

Parameters

label -- pointer to a label object

Returns

speed of animation in px/sec unit

void lv_label_get_letter_pos(const lv_obj_t *label, uint32_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)

uint32_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

Parameters

  • label -- pointer to label object

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

Returns

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)

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.

Parameters

  • label -- Label object

  • pos -- Point to check for character under

Returns

whether a character is drawn under the point

uint32_t lv_label_get_text_sel_start(const lv_obj_t *label)

Get the selection start index.

Parameters

label -- pointer to a label object.

Returns

selection start index. LV_LABEL_TXT_SEL_OFF if nothing is selected.

uint32_t lv_label_get_text_sel_end(const lv_obj_t *label)

Get the selection end index.

Parameters

label -- pointer to a label object.

Returns

selection end index. LV_LABEL_TXT_SEL_OFF if nothing is selected.

lv_style_list_t *lv_label_get_style(lv_obj_t *label, uint8_t type)
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

void lv_label_refr_text(lv_obj_t *label)

Refresh the label with its text stored in its extended data

Parameters

label -- pointer to a label object

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
uint32_t dot_end
uint16_t anim_speed
lv_point_t offset
lv_draw_label_hint_t hint
uint32_t sel_start
uint32_t sel_end
lv_label_long_mode_t long_mode
uint8_t static_txt
uint8_t align
uint8_t recolor
uint8_t expand
uint8_t dot_tmp_alloc