Chart (lv_chart)

Overview

Charts consist of the following:

  • A background

  • Horizontal and vertical division lines

  • Data series, which can be represented with points, lines, columns, or filled areas.

Data series

You can add any number of series to the charts by lv_chart_add_series(chart, color). It allocates data for a lv_chart_series_t structure which contains the chosen color and an array for the data points.

Series’ type

The following data display types exist:

  • LV_CHART_TYPE_NONE - Do not display any data. It can be used to hide a series.

  • LV_CHART_TYPE_LINE - Draw lines between the points.

  • LV_CHART_TYPE_COL - Draw columns.

  • LV_CHART_TYPE_POINT - Draw points.

  • LV_CHART_TYPE_AREA - Draw areas (fill the area below the lines).

  • LV_CHART_TYPE_VERTICAL_LINE - Draw only vertical lines to connect the points. Useful if the chart width is equal to the number of points, because it can redraw much faster than the LV_CHART_TYPE_AREA.

You can specify the display type with lv_chart_set_type(chart, LV_CHART_TYPE_...). The types can be ‘OR’ed (like LV_CHART_TYPE_LINE | LV_CHART_TYPE_POINT).

Modify the data

You have several options to set the data of series:

  1. Set the values manually in the array like ser1->points[3] = 7 and refresh the chart with lv_chart_refresh(chart).

  2. Use the lv_chart_set_next(chart, ser, value).

  3. Initialize all points to a given value with: lv_chart_init_points(chart, ser, value).

  4. Set all points from an array with: lv_chart_set_points(chart, ser, value_array).

Use LV_CHART_POINT_DEF as value to make the library skip drawing that point, column, or line segment.

Update modes

lv_chart_set_next can behave in two ways depending on update mode:

  • LV_CHART_UPDATE_MODE_SHIFT - Shift old data to the left and add the new one o the right.

  • LV_CHART_UPDATE_MODE_CIRCULAR - Circularly add the new data (Like an ECG diagram).

The update mode can be changed with lv_chart_set_update_mode(chart, LV_CHART_UPDATE_MODE_...).

Number of points

The number of points in the series can be modified by lv_chart_set_point_count(chart, point_num). The default value is 10.

Vertical range

You can specify the minimum and maximum values in y-direction with lv_chart_set_range(chart, y_min, y_max). The value of the points will be scaled proportionally. The default range is: 0..100.

Division lines

The number of horizontal and vertical division lines can be modified by lv_chart_set_div_line_count(chart, hdiv_num, vdiv_num). The default settings are 3 horizontal and 5 vertical division lines.

Series’ appearance

To set the line width and point radius of the series, use the lv_chart_set_series_width(chart, size) function. The default value is 2.

The opacity of the data lines can be specified by lv_chart_set_series_opa(chart, opa). The default value is LV_OPA_COVER.

You can apply a dark color fade on the bottom of columns and points by lv_chart_set_series_darking(chart, effect) function. The default dark level is LV_OPA_50.

Tick marks and labels

Ticks and labels beside them can be added.

lv_chart_set_margin(chart, 20) needs to be used to add some extra space around the chart for the ticks and texts. Otherwise, you will not see them at all. You may need to adjust the number 20 depending on your requirements.

lv_chart_set_x_tick_text(chart, list_of_values, num_tick_marks, LV_CHART_AXIS_...) set the ticks and texts on x axis. list_of_values is a string with '\n' terminated text (expect the last) with text for the ticks. E.g. const char * list_of_values = "first\nseco\nthird". list_of_values can be NULL. If list_of_values is set then num_tick_marks tells the number of ticks between two labels. If list_of_values is NULL then it specifies the total number of ticks.

Major tick lines are drawn where text is placed, and minor tick lines are drawn elsewhere. lv_chart_set_x_tick_length(chart, major_tick_len, minor_tick_len) sets the length of tick lines on the x-axis.

The same functions exists for the y axis too: lv_chart_set_y_tick_text and lv_chart_set_y_tick_length.

Styles

You can set the styles with lv_chart_set_style(btn, LV_CHART_STYLE_MAIN, &style).

  • style.body - properties set the background’s appearance.

  • style.line - properties set the division lines’ appearance.

  • style.text - properties set the axis labels’ appearance.

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

Line Chart

Simple Chart example in LittlevGL

code

#include "lvgl/lvgl.h"

void lv_ex_chart_1(void)
{
    /*Create a chart*/
    lv_obj_t * chart;
    chart = lv_chart_create(lv_scr_act(), NULL);
    lv_obj_set_size(chart, 200, 150);
    lv_obj_align(chart, NULL, LV_ALIGN_CENTER, 0, 0);
    lv_chart_set_type(chart, LV_CHART_TYPE_POINT | LV_CHART_TYPE_LINE);   /*Show lines and points too*/
    lv_chart_set_series_opa(chart, LV_OPA_70);                            /*Opacity of the data series*/
    lv_chart_set_series_width(chart, 4);                                  /*Line width and point radious*/

    lv_chart_set_range(chart, 0, 100);

    /*Add two data series*/
    lv_chart_series_t * ser1 = lv_chart_add_series(chart, LV_COLOR_RED);
    lv_chart_series_t * ser2 = lv_chart_add_series(chart, LV_COLOR_GREEN);

    /*Set the next points on 'dl1'*/
    lv_chart_set_next(chart, ser1, 10);
    lv_chart_set_next(chart, ser1, 10);
    lv_chart_set_next(chart, ser1, 10);
    lv_chart_set_next(chart, ser1, 10);
    lv_chart_set_next(chart, ser1, 10);
    lv_chart_set_next(chart, ser1, 10);
    lv_chart_set_next(chart, ser1, 10);
    lv_chart_set_next(chart, ser1, 30);
    lv_chart_set_next(chart, ser1, 70);
    lv_chart_set_next(chart, ser1, 90);

    /*Directly set points on 'dl2'*/
    ser2->points[0] = 90;
    ser2->points[1] = 70;
    ser2->points[2] = 65;
    ser2->points[3] = 65;
    ser2->points[4] = 65;
    ser2->points[5] = 65;
    ser2->points[6] = 65;
    ser2->points[7] = 65;
    ser2->points[8] = 65;
    ser2->points[9] = 65;

    lv_chart_refresh(chart); /*Required after direct set*/
}

MicroPython

Line Chart

Simple Chart example in LittlevGL

code

# Create a chart
chart = lv.chart(lv.scr_act())
chart.set_size(200, 150)
chart.align(None, lv.ALIGN.CENTER, 0, 0)
chart.set_type(lv.chart.TYPE.POINT | lv.chart.TYPE.LINE)   # Show lines and points too
chart.set_series_opa(lv.OPA._70)                           # Opacity of the data series
chart.set_series_width(4)                                  # Line width and point radious

chart.set_range(0, 100)

# Add two data series
ser1 = chart.add_series(lv.color_make(0xFF,0,0))
ser2 = chart.add_series(lv.color_make(0,0x80,0))

# Set points on 'dl1'
chart.set_points(ser1, [10, 10, 10, 10, 10, 10, 10, 30, 70, 90])

# Set points on 'dl2'
chart.set_points(ser2, [90, 70, 65, 65, 65, 65, 65, 65, 65, 65])

API

Typedefs

typedef uint8_t lv_chart_type_t
typedef uint8_t lv_chart_update_mode_t
typedef uint8_t lv_chart_axis_options_t
typedef uint8_t lv_chart_style_t

Enums

enum [anonymous]

Chart types

Values:

LV_CHART_TYPE_NONE = 0x00

Don’t draw the series

LV_CHART_TYPE_LINE = 0x01

Connect the points with lines

LV_CHART_TYPE_COLUMN = 0x02

Draw columns

LV_CHART_TYPE_POINT = 0x04

Draw circles on the points

LV_CHART_TYPE_VERTICAL_LINE = 0x08

Draw vertical lines on points (useful when chart width == point count)

LV_CHART_TYPE_AREA = 0x10

Draw area chart

enum [anonymous]

Chart update mode for lv_chart_set_next

Values:

LV_CHART_UPDATE_MODE_SHIFT

Shift old data to the left and add the new one o the right

LV_CHART_UPDATE_MODE_CIRCULAR

Add the new data in a circular way

enum [anonymous]

Data of axis

Values:

LV_CHART_AXIS_SKIP_LAST_TICK = 0x00

don’t draw the last tick

LV_CHART_AXIS_DRAW_LAST_TICK = 0x01

draw the last tick

LV_CHART_AXIS_INVERSE_LABELS_ORDER = 0x02

draw tick labels in an inversed order

enum [anonymous]

Values:

LV_CHART_STYLE_MAIN

Functions

LV_EXPORT_CONST_INT(LV_CHART_POINT_DEF)
LV_EXPORT_CONST_INT(LV_CHART_TICK_LENGTH_AUTO)
lv_obj_t *lv_chart_create(lv_obj_t *par, const lv_obj_t *copy)

Create a chart background objects

Return

pointer to the created chart background

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

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

lv_chart_series_t *lv_chart_add_series(lv_obj_t *chart, lv_color_t color)

Allocate and add a data series to the chart

Return

pointer to the allocated data series

Parameters
  • chart: pointer to a chart object

  • color: color of the data series

void lv_chart_clear_serie(lv_obj_t *chart, lv_chart_series_t *serie)

Clear the point of a serie

Parameters
  • chart: pointer to a chart object

  • serie: pointer to the chart’s serie to clear

void lv_chart_set_div_line_count(lv_obj_t *chart, uint8_t hdiv, uint8_t vdiv)

Set the number of horizontal and vertical division lines

Parameters
  • chart: pointer to a graph background object

  • hdiv: number of horizontal division lines

  • vdiv: number of vertical division lines

void lv_chart_set_range(lv_obj_t *chart, lv_coord_t ymin, lv_coord_t ymax)

Set the minimal and maximal y values

Parameters
  • chart: pointer to a graph background object

  • ymin: y minimum value

  • ymax: y maximum value

void lv_chart_set_type(lv_obj_t *chart, lv_chart_type_t type)

Set a new type for a chart

Parameters
  • chart: pointer to a chart object

  • type: new type of the chart (from ‘lv_chart_type_t’ enum)

void lv_chart_set_point_count(lv_obj_t *chart, uint16_t point_cnt)

Set the number of points on a data line on a chart

Parameters
  • chart: pointer r to chart object

  • point_cnt: new number of points on the data lines

void lv_chart_set_series_opa(lv_obj_t *chart, lv_opa_t opa)

Set the opacity of the data series

Parameters
  • chart: pointer to a chart object

  • opa: opacity of the data series

void lv_chart_set_series_width(lv_obj_t *chart, lv_coord_t width)

Set the line width or point radius of the data series

Parameters
  • chart: pointer to a chart object

  • width: the new width

void lv_chart_set_series_darking(lv_obj_t *chart, lv_opa_t dark_eff)

Set the dark effect on the bottom of the points or columns

Parameters
  • chart: pointer to a chart object

  • dark_eff: dark effect level (LV_OPA_TRANSP to turn off)

void lv_chart_init_points(lv_obj_t *chart, lv_chart_series_t *ser, lv_coord_t y)

Initialize all data points with a value

Parameters
  • chart: pointer to chart object

  • ser: pointer to a data series on ‘chart’

  • y: the new value for all points

void lv_chart_set_points(lv_obj_t *chart, lv_chart_series_t *ser, lv_coord_t y_array[])

Set the value of points from an array

Parameters
  • chart: pointer to chart object

  • ser: pointer to a data series on ‘chart’

  • y_array: array of ‘lv_coord_t’ points (with ‘points count’ elements )

void lv_chart_set_next(lv_obj_t *chart, lv_chart_series_t *ser, lv_coord_t y)

Shift all data right and set the most right data on a data line

Parameters
  • chart: pointer to chart object

  • ser: pointer to a data series on ‘chart’

  • y: the new value of the most right data

void lv_chart_set_update_mode(lv_obj_t *chart, lv_chart_update_mode_t update_mode)

Set update mode of the chart object.

Parameters
  • chart: pointer to a chart object

  • update: mode

static void lv_chart_set_style(lv_obj_t *chart, lv_chart_style_t type, const lv_style_t *style)

Set the style of a chart

Parameters
  • chart: pointer to a chart object

  • type: which style should be set (can be only LV_CHART_STYLE_MAIN)

  • style: pointer to a style

void lv_chart_set_x_tick_length(lv_obj_t *chart, uint8_t major_tick_len, uint8_t minor_tick_len)

Set the length of the tick marks on the x axis

Parameters
  • chart: pointer to the chart

  • major_tick_len: the length of the major tick or LV_CHART_TICK_LENGTH_AUTO to set automatically (where labels are added)

  • minor_tick_len: the length of the minor tick, LV_CHART_TICK_LENGTH_AUTO to set automatically (where no labels are added)

void lv_chart_set_y_tick_length(lv_obj_t *chart, uint8_t major_tick_len, uint8_t minor_tick_len)

Set the length of the tick marks on the y axis

Parameters
  • chart: pointer to the chart

  • major_tick_len: the length of the major tick or LV_CHART_TICK_LENGTH_AUTO to set automatically (where labels are added)

  • minor_tick_len: the length of the minor tick, LV_CHART_TICK_LENGTH_AUTO to set automatically (where no labels are added)

void lv_chart_set_secondary_y_tick_length(lv_obj_t *chart, uint8_t major_tick_len, uint8_t minor_tick_len)

Set the length of the tick marks on the secondary y axis

Parameters
  • chart: pointer to the chart

  • major_tick_len: the length of the major tick or LV_CHART_TICK_LENGTH_AUTO to set automatically (where labels are added)

  • minor_tick_len: the length of the minor tick, LV_CHART_TICK_LENGTH_AUTO to set automatically (where no labels are added)

void lv_chart_set_x_tick_texts(lv_obj_t *chart, const char *list_of_values, uint8_t num_tick_marks, lv_chart_axis_options_t options)

Set the x-axis tick count and labels of a chart

Parameters
  • chart: pointer to a chart object

  • list_of_values: list of string values, terminated with

    , except the last

  • num_tick_marks: if list_of_values is NULL: total number of ticks per axis else number of ticks between two value labels

  • options: extra options

void lv_chart_set_secondary_y_tick_texts(lv_obj_t *chart, const char *list_of_values, uint8_t num_tick_marks, lv_chart_axis_options_t options)

Set the secondary y-axis tick count and labels of a chart

Parameters
  • chart: pointer to a chart object

  • list_of_values: list of string values, terminated with

    , except the last

  • num_tick_marks: if list_of_values is NULL: total number of ticks per axis else number of ticks between two value labels

  • options: extra options

void lv_chart_set_y_tick_texts(lv_obj_t *chart, const char *list_of_values, uint8_t num_tick_marks, lv_chart_axis_options_t options)

Set the y-axis tick count and labels of a chart

Parameters
  • chart: pointer to a chart object

  • list_of_values: list of string values, terminated with

    , except the last

  • num_tick_marks: if list_of_values is NULL: total number of ticks per axis else number of ticks between two value labels

  • options: extra options

void lv_chart_set_margin(lv_obj_t *chart, uint16_t margin)

Set the margin around the chart, used for axes value and ticks

Parameters
  • chart: pointer to an chart object

  • margin: value of the margin [px]

lv_chart_type_t lv_chart_get_type(const lv_obj_t *chart)

Get the type of a chart

Return

type of the chart (from ‘lv_chart_t’ enum)

Parameters
  • chart: pointer to chart object

uint16_t lv_chart_get_point_cnt(const lv_obj_t *chart)

Get the data point number per data line on chart

Return

point number on each data line

Parameters
  • chart: pointer to chart object

lv_opa_t lv_chart_get_series_opa(const lv_obj_t *chart)

Get the opacity of the data series

Return

the opacity of the data series

Parameters
  • chart: pointer to chart object

lv_coord_t lv_chart_get_series_width(const lv_obj_t *chart)

Get the data series width

Return

the width the data series (lines or points)

Parameters
  • chart: pointer to chart object

lv_opa_t lv_chart_get_series_darking(const lv_obj_t *chart)

Get the dark effect level on the bottom of the points or columns

Return

dark effect level (LV_OPA_TRANSP to turn off)

Parameters
  • chart: pointer to chart object

static const lv_style_t *lv_chart_get_style(const lv_obj_t *chart, lv_chart_style_t type)

Get the style of an chart object

Return

pointer to the chart’s style

Parameters
  • chart: pointer to an chart object

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

uint16_t lv_chart_get_margin(lv_obj_t *chart)

Get the margin around the chart, used for axes value and labels

Parameters
  • chart: pointer to an chart object

  • return: value of the margin

void lv_chart_refresh(lv_obj_t *chart)

Refresh a chart if its data line has changed

Parameters
  • chart: pointer to chart object

struct lv_chart_series_t

Public Members

lv_coord_t *points
lv_color_t color
uint16_t start_point
struct lv_chart_axis_cfg_t

Public Members

const char *list_of_values
lv_chart_axis_options_t options
uint8_t num_tick_marks
uint8_t major_tick_len
uint8_t minor_tick_len
struct lv_chart_ext_t

Public Members

lv_ll_t series_ll
lv_coord_t ymin
lv_coord_t ymax
uint8_t hdiv_cnt
uint8_t vdiv_cnt
uint16_t point_cnt
lv_chart_type_t type
lv_chart_axis_cfg_t y_axis
lv_chart_axis_cfg_t x_axis
lv_chart_axis_cfg_t secondary_y_axis
uint16_t margin
uint8_t update_mode
lv_coord_t width
uint8_t num
lv_opa_t opa
lv_opa_t dark
struct lv_chart_ext_t::[anonymous] series