Chart (lv_chart)

Overview

Charts are a basic object to visualize data points. Currently Line charts (connect points with lines and/or draw points on them) and Bar charts are supported.

Charts can have: - division lines - 2 y axis - axis ticks and texts on ticks - cursors - scrolling and zooming

Parts and Styles

• LV_PART_MAIN The background of the chart. Uses all the typical background and line (for the division lines) related style properties. Padding makes the series area smaller. For column charts pad_column sets the space between the columns of the adjacent indices.

• LV_PART_SCROLLBAR The scrollbar used if the chart is zoomed. See the Base object's documentation for details.

• LV_PART_ITEMS Refers to the line or bar series.

  • Line chart: The line properties are used by the lines. width, height, bg_color and radius is used to set the appearance of points.

  • Bar chart: The typical background properties are used to style the bars. pad_column sets the space between the columns on the same index.

• LV_PART_INDICATOR Refers to the points on line and scatter chart (small circles or squares).

• LV_PART_CURSOR Line properties are used to style the cursors. width, height, bg_color and radius are used to set the appearance of points.

Usage

Chart type

The following data display types exist:

• LV_CHART_TYPE_NONE: Do not display any data. Can be used to hide the series.

• LV_CHART_TYPE_LINE: Draw lines between the data points and/or points (rectangles or circles) on the data points.

• LV_CHART_TYPE_BAR: Draw bars.

• LV_CHART_TYPE_SCATTER: X/Y chart drawing point's and lines between the points. .

You can specify the display type with lv_chart_set_type(chart, LV_CHART_TYPE_...).

Data series

You can add any number of series to the charts by lv_chart_add_series(chart, color, axis). This allocates an lv_chart_series_t structure which contains the chosen color and an array for the data points. axis can have the following values:

• LV_CHART_AXIS_PRIMARY_Y: Left axis

• LV_CHART_AXIS_SECONDARY_Y: Right axis

• LV_CHART_AXIS_PRIMARY_X: Bottom axis

• LV_CHART_AXIS_SECONDARY_X: Top axis

axis tells which axis's range should be used to scale the values.

lv_chart_set_ext_y_array(chart, ser, value_array) makes the chart use an external array for the given series. value_array should look like this: int32_t * value_array[num_points]. The array size needs to be large enough to hold all the points of that series. The array's pointer will be saved in the chart so it needs to be global, static or dynamically allocated. Note: you should call lv_chart_refresh(chart) after the external data source has been updated to update the chart.

The value array of a series can be obtained with lv_chart_get_y_array(chart, ser), which can be used with ext_array or normal arrays.

For LV_CHART_TYPE_SCATTER type lv_chart_set_ext_x_array(chart, ser, value_array) and lv_chart_get_x_array(chart, ser) can be used as well.

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 lv_chart_set_value_by_id(chart, ser, id, value) where id is the index of the point you wish to update.

3. Use the lv_chart_set_next_value(chart, ser, value).

4. Initialize all points to a given value with lv_chart_set_all_value(chart, ser, value).

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

For LV_CHART_TYPE_SCATTER type lv_chart_set_value_by_id2(chart, ser, id, value) and lv_chart_set_next_value2(chart, ser, x_value, y_value) can be used as well.

Update modes

lv_chart_set_next_value() 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 to the right.

• LV_CHART_UPDATE_MODE_CIRCULAR: Add the new data in circular fashion, 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. Note: this also affects the number of points processed when an external buffer is assigned to a series, so you need to be sure the external array is large enough.

Handling large number of points

On line charts, if the number of points is greater than the pixels horizontally, the Chart will draw only vertical lines to make the drawing of large amount of data effective. If there are, let's say, 10 points to a pixel, LVGL searches the smallest and the largest value and draws a vertical lines between them to ensure no peaks are missed.

Vertical range

You can specify the minimum and maximum values in y-direction with lv_chart_set_range(chart, axis, min, max). axis can be LV_CHART_AXIS_PRIMARY (left axis) or LV_CHART_AXIS_SECONDARY (right axis).

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. If there is a visible border on a side and no padding on that side, the division line would be drawn on top of the border and therefore it won't be drawn.

Override default start point for series

If you want a plot to start from a point other than the default which is point[0] of the series, you can set an alternative index with the function lv_chart_set_x_start_point(chart, ser, id) where id is the new index position to start plotting from.

Note that LV_CHART_UPDATE_MODE_SHIFT also changes the start_point.

Tick marks and labels

With the help of Scale, vertical and horizontal scales can be added in a very flexible way. See the example below to learn more.

Zoom

To zoom the chart all you need to is wrapping it into a parent container and set the chart's width or height to larger value. This way the chart will be scrollable on its parent.

Cursor

A cursor can be added with lv_chart_cursor_t * c1 = lv_chart_add_cursor(chart, color, dir);. The possible values of dir LV_DIR_NONE/RIGHT/UP/LEFT/DOWN/HOR/VER/ALL or their OR-ed values to tell in which direction(s) should the cursor be drawn.

lv_chart_set_cursor_pos(chart, cursor, &point) sets the position of the cursor. pos is a pointer to an lv_point_t variable. E.g. lv_point_t point = {10, 20}. If the chart is scrolled the cursor will remain in the same place.

lv_chart_get_point_pos_by_id(chart, series, id, &point_out) gets the coordinate of a given point. It's useful to place the cursor at a given point.

lv_chart_set_cursor_point(chart, cursor, series, point_id) sticks the cursor at a point. If the point's position changes (new value or scrolling) the cursor will move with the point.

Events

• LV_EVENT_VALUE_CHANGED Sent when a new point is clicked pressed. lv_chart_get_pressed_point(chart) returns the zero-based index of the pressed point.

See the events of the Base object too.

Learn more about Events.

Keys

No Keys are processed by the object type.

Learn more about Keys.

Example

Line Chart

C code  

 View on GitHub

#include "../../lv_examples.h"
#if LV_USE_CHART && LV_BUILD_EXAMPLES

/**
 * A very basic line chart
 */
void lv_example_chart_1(void)
{
    /*Create a chart*/
    lv_obj_t * chart;
    chart = lv_chart_create(lv_screen_active());
    lv_obj_set_size(chart, 200, 150);
    lv_obj_center(chart);
    lv_chart_set_type(chart, LV_CHART_TYPE_LINE);   /*Show lines and points too*/

    /*Add two data series*/
    lv_chart_series_t * ser1 = lv_chart_add_series(chart, lv_palette_main(LV_PALETTE_GREEN), LV_CHART_AXIS_PRIMARY_Y);
    lv_chart_series_t * ser2 = lv_chart_add_series(chart, lv_palette_main(LV_PALETTE_RED), LV_CHART_AXIS_SECONDARY_Y);

    uint32_t i;
    for(i = 0; i < 10; i++) {
        /*Set the next points on 'ser1'*/
        lv_chart_set_next_value(chart, ser1, lv_rand(10, 50));

        /*Directly set points on 'ser2'*/
        ser2->y_points[i] = lv_rand(50, 90);
    }

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

#endif

---

Axis ticks and labels with scrolling

C code  

 View on GitHub

#include "../../lv_examples.h"
#if LV_USE_CHART && LV_BUILD_EXAMPLES

/**
 * Use lv_scale to add ticks to a scrollable chart
 */
void lv_example_chart_2(void)
{
    /*Create a container*/
    lv_obj_t * main_cont = lv_obj_create(lv_screen_active());
    lv_obj_set_size(main_cont, 200, 150);
    lv_obj_center(main_cont);

    /*Create a transparent wrapper for the chart and the scale.
     *Set a large width, to make it scrollable on the main container*/
    lv_obj_t * wrapper = lv_obj_create(main_cont);
    lv_obj_remove_style_all(wrapper);
    lv_obj_set_size(wrapper, lv_pct(300), lv_pct(100));
    lv_obj_set_flex_flow(wrapper, LV_FLEX_FLOW_COLUMN);

    /*Create a chart on the wrapper
     *Set it's width to 100% to fill the large wrapper*/
    lv_obj_t * chart = lv_chart_create(wrapper);
    lv_obj_set_width(chart, lv_pct(100));
    lv_obj_set_flex_grow(chart, 1);
    lv_chart_set_type(chart, LV_CHART_TYPE_BAR);
    lv_chart_set_range(chart, LV_CHART_AXIS_PRIMARY_Y, 0, 100);
    lv_chart_set_range(chart, LV_CHART_AXIS_SECONDARY_Y, 0, 400);
    lv_chart_set_point_count(chart, 12);
    lv_obj_set_style_radius(chart, 0, 0);

    /*Create a scale also with 100% width*/
    lv_obj_t * scale_bottom = lv_scale_create(wrapper);
    lv_scale_set_mode(scale_bottom, LV_SCALE_MODE_HORIZONTAL_BOTTOM);
    lv_obj_set_size(scale_bottom, lv_pct(100), 25);
    lv_scale_set_total_tick_count(scale_bottom, 12);
    lv_scale_set_major_tick_every(scale_bottom, 1);
    lv_obj_set_style_pad_hor(scale_bottom, lv_chart_get_first_point_center_offset(chart), 0);

    static const char * month[] = {"Jan", "Febr", "March", "Apr", "May", "Jun", "July", "Aug", "Sept", "Oct", "Nov", "Dec", NULL};
    lv_scale_set_text_src(scale_bottom, month);

    /*Add two data series*/
    lv_chart_series_t * ser1 = lv_chart_add_series(chart, lv_palette_lighten(LV_PALETTE_GREEN, 2), LV_CHART_AXIS_PRIMARY_Y);
    lv_chart_series_t * ser2 = lv_chart_add_series(chart, lv_palette_darken(LV_PALETTE_GREEN, 2), LV_CHART_AXIS_PRIMARY_Y);

    /*Set the next points on 'ser1'*/
    uint32_t i;
    for(i = 0; i < 12; i++) {
        lv_chart_set_next_value(chart, ser1, lv_rand(10, 60));
        lv_chart_set_next_value(chart, ser2, lv_rand(50, 90));
    }
    lv_chart_refresh(chart); /*Required after direct set*/
}

#endif

---

Show the value of the pressed points

C code  

 View on GitHub

#include "../../lv_examples.h"
#if LV_USE_CHART && LV_BUILD_EXAMPLES

static void event_cb(lv_event_t * e)
{
    lv_event_code_t code = lv_event_get_code(e);
    lv_obj_t * chart = lv_event_get_target(e);

    if(code == LV_EVENT_VALUE_CHANGED) {
        lv_obj_invalidate(chart);
    }
    if(code == LV_EVENT_REFR_EXT_DRAW_SIZE) {
        int32_t * s = lv_event_get_param(e);
        *s = LV_MAX(*s, 20);
    }
    else if(code == LV_EVENT_DRAW_POST_END) {
        int32_t id = lv_chart_get_pressed_point(chart);
        if(id == LV_CHART_POINT_NONE) return;

        LV_LOG_USER("Selected point %d", (int)id);

        lv_chart_series_t * ser = lv_chart_get_series_next(chart, NULL);
        while(ser) {
            lv_point_t p;
            lv_chart_get_point_pos_by_id(chart, ser, id, &p);

            int32_t * y_array = lv_chart_get_y_array(chart, ser);
            int32_t value = y_array[id];

            char buf[16];
            lv_snprintf(buf, sizeof(buf), LV_SYMBOL_DUMMY"$%d", value);

            lv_draw_rect_dsc_t draw_rect_dsc;
            lv_draw_rect_dsc_init(&draw_rect_dsc);
            draw_rect_dsc.bg_color = lv_color_black();
            draw_rect_dsc.bg_opa = LV_OPA_50;
            draw_rect_dsc.radius = 3;
            draw_rect_dsc.bg_image_src = buf;
            draw_rect_dsc.bg_image_recolor = lv_color_white();

            lv_area_t a;
            a.x1 = chart->coords.x1 + p.x - 20;
            a.x2 = chart->coords.x1 + p.x + 20;
            a.y1 = chart->coords.y1 + p.y - 30;
            a.y2 = chart->coords.y1 + p.y - 10;

            lv_layer_t * layer = lv_event_get_layer(e);
            lv_draw_rect(layer, &draw_rect_dsc, &a);

            ser = lv_chart_get_series_next(chart, ser);
        }
    }
    else if(code == LV_EVENT_RELEASED) {
        lv_obj_invalidate(chart);
    }
}

/**
 * Show the value of the pressed points
 */
void lv_example_chart_3(void)
{
    /*Create a chart*/
    lv_obj_t * chart;
    chart = lv_chart_create(lv_screen_active());
    lv_obj_set_size(chart, 200, 150);
    lv_obj_center(chart);

    lv_obj_add_event_cb(chart, event_cb, LV_EVENT_ALL, NULL);
    lv_obj_refresh_ext_draw_size(chart);

    /*Zoom in a little in X*/
    //    lv_chart_set_scale_x(chart, 800);

    /*Add two data series*/
    lv_chart_series_t * ser1 = lv_chart_add_series(chart, lv_palette_main(LV_PALETTE_RED), LV_CHART_AXIS_PRIMARY_Y);
    lv_chart_series_t * ser2 = lv_chart_add_series(chart, lv_palette_main(LV_PALETTE_GREEN), LV_CHART_AXIS_PRIMARY_Y);
    uint32_t i;
    for(i = 0; i < 10; i++) {
        lv_chart_set_next_value(chart, ser1, lv_rand(60, 90));
        lv_chart_set_next_value(chart, ser2, lv_rand(10, 40));
    }
}

#endif

---

Recolor bars based on their value

C code  

 View on GitHub

#include "../../lv_examples.h"

#if LV_USE_CHART && LV_DRAW_SW_COMPLEX && LV_BUILD_EXAMPLES

static void draw_event_cb(lv_event_t * e)
{
    lv_draw_task_t * draw_task = lv_event_get_draw_task(e);
    lv_draw_dsc_base_t * base_dsc = draw_task->draw_dsc;

    if(base_dsc->part == LV_PART_ITEMS && draw_task->type == LV_DRAW_TASK_TYPE_FILL) {
        lv_draw_fill_dsc_t * fill_dsc = draw_task->draw_dsc;

        lv_obj_t * chart = lv_event_get_target(e);
        int32_t * y_array = lv_chart_get_y_array(chart, lv_chart_get_series_next(chart, NULL));
        int32_t v = y_array[base_dsc->id2];

        uint32_t ratio = v * 255 / 100;
        fill_dsc->color = lv_color_mix(lv_palette_main(LV_PALETTE_GREEN), lv_palette_main(LV_PALETTE_RED), ratio);
    }
}

/**
 * Recolor the bars of a chart based on their value
 */
void lv_example_chart_4(void)
{
    /*Create a chart1*/
    lv_obj_t * chart = lv_chart_create(lv_screen_active());
    lv_chart_set_type(chart, LV_CHART_TYPE_BAR);
    lv_chart_set_point_count(chart, 24);
    lv_obj_set_style_pad_column(chart, 2, 0);
    lv_obj_set_size(chart, 260, 160);
    lv_obj_center(chart);

    lv_chart_series_t * ser = lv_chart_add_series(chart, lv_color_hex(0xff0000), LV_CHART_AXIS_PRIMARY_Y);
    lv_obj_add_event_cb(chart, draw_event_cb, LV_EVENT_DRAW_TASK_ADDED, NULL);
    lv_obj_add_flag(chart, LV_OBJ_FLAG_SEND_DRAW_TASK_EVENTS);

    uint32_t i;
    for(i = 0; i < 24; i++) {
        lv_chart_set_next_value(chart, ser, lv_rand(10, 90));
    }
}

#endif

---

Faded area line chart with custom division lines

C code  

 View on GitHub

#include "../../lv_examples.h"

#if LV_USE_CHART && LV_DRAW_SW_COMPLEX && LV_BUILD_EXAMPLES

static void hook_division_lines(lv_event_t * e);
static void add_faded_area(lv_event_t * e);
static void draw_event_cb(lv_event_t * e);

/**
 * Add a faded area effect to the line chart and make some division lines ticker
 */
void lv_example_chart_5(void)
{
    /*Create a chart*/
    lv_obj_t * chart = lv_chart_create(lv_screen_active());
    lv_chart_set_type(chart, LV_CHART_TYPE_LINE);   /*Show lines and points too*/
    lv_obj_set_size(chart, 200, 150);
    lv_obj_set_style_pad_all(chart, 0, 0);
    lv_obj_set_style_radius(chart, 0, 0);
    lv_obj_center(chart);

    lv_chart_set_div_line_count(chart, 5, 7);

    lv_obj_add_event_cb(chart, draw_event_cb, LV_EVENT_DRAW_TASK_ADDED, NULL);
    lv_obj_add_flag(chart, LV_OBJ_FLAG_SEND_DRAW_TASK_EVENTS);

    lv_chart_series_t * ser = lv_chart_add_series(chart, lv_palette_main(LV_PALETTE_RED), LV_CHART_AXIS_PRIMARY_Y);

    uint32_t i;
    for(i = 0; i < 10; i++) {
        lv_chart_set_next_value(chart, ser, lv_rand(10, 80));
    }
}

static void draw_event_cb(lv_event_t * e)
{
    lv_draw_task_t * draw_task = lv_event_get_draw_task(e);
    lv_draw_dsc_base_t * base_dsc = draw_task->draw_dsc;

    if(base_dsc->part == LV_PART_ITEMS && draw_task->type == LV_DRAW_TASK_TYPE_LINE) {
        add_faded_area(e);

    }
    /*Hook the division lines too*/
    if(base_dsc->part == LV_PART_MAIN && draw_task->type == LV_DRAW_TASK_TYPE_LINE) {
        hook_division_lines(e);
    }
}

static void add_faded_area(lv_event_t * e)
{
    lv_obj_t * obj = lv_event_get_target(e);

    lv_draw_task_t * draw_task = lv_event_get_draw_task(e);
    lv_draw_dsc_base_t * base_dsc = draw_task->draw_dsc;

    const lv_chart_series_t * ser = lv_chart_get_series_next(obj, NULL);

    /*Draw a triangle below the line witch some opacity gradient*/
    lv_draw_line_dsc_t * draw_line_dsc = draw_task->draw_dsc;
    lv_draw_triangle_dsc_t tri_dsc;

    lv_draw_triangle_dsc_init(&tri_dsc);
    tri_dsc.p[0].x = draw_line_dsc->p1.x;
    tri_dsc.p[0].y = draw_line_dsc->p1.y;
    tri_dsc.p[1].x = draw_line_dsc->p2.x;
    tri_dsc.p[1].y = draw_line_dsc->p2.y;
    tri_dsc.p[2].x = draw_line_dsc->p1.y < draw_line_dsc->p2.y ? draw_line_dsc->p1.x : draw_line_dsc->p2.x;
    tri_dsc.p[2].y = LV_MAX(draw_line_dsc->p1.y, draw_line_dsc->p2.y);
    tri_dsc.bg_grad.dir = LV_GRAD_DIR_VER;

    int32_t full_h = lv_obj_get_height(obj);
    int32_t fract_uppter = (int32_t)(LV_MIN(draw_line_dsc->p1.y, draw_line_dsc->p2.y) - obj->coords.y1) * 255 / full_h;
    int32_t fract_lower = (int32_t)(LV_MAX(draw_line_dsc->p1.y, draw_line_dsc->p2.y) - obj->coords.y1) * 255 / full_h;
    tri_dsc.bg_grad.stops[0].color = ser->color;
    tri_dsc.bg_grad.stops[0].opa = 255 - fract_uppter;
    tri_dsc.bg_grad.stops[0].frac = 0;
    tri_dsc.bg_grad.stops[1].color = ser->color;
    tri_dsc.bg_grad.stops[1].opa = 255 - fract_lower;
    tri_dsc.bg_grad.stops[1].frac = 255;

    lv_draw_triangle(base_dsc->layer, &tri_dsc);

    /*Draw rectangle below the triangle*/
    lv_draw_rect_dsc_t rect_dsc;
    lv_draw_rect_dsc_init(&rect_dsc);
    rect_dsc.bg_grad.dir = LV_GRAD_DIR_VER;
    rect_dsc.bg_grad.stops[0].color = ser->color;
    rect_dsc.bg_grad.stops[0].frac = 0;
    rect_dsc.bg_grad.stops[0].opa = 255 - fract_lower;
    rect_dsc.bg_grad.stops[1].color = ser->color;
    rect_dsc.bg_grad.stops[1].frac = 255;
    rect_dsc.bg_grad.stops[1].opa = 0;

    lv_area_t rect_area;
    rect_area.x1 = (int32_t)draw_line_dsc->p1.x;
    rect_area.x2 = (int32_t)draw_line_dsc->p2.x - 1;
    rect_area.y1 = (int32_t)LV_MAX(draw_line_dsc->p1.y, draw_line_dsc->p2.y) - 1;
    rect_area.y2 = (int32_t)obj->coords.y2;
    lv_draw_rect(base_dsc->layer, &rect_dsc, &rect_area);
}

static void hook_division_lines(lv_event_t * e)
{
    lv_draw_task_t * draw_task = lv_event_get_draw_task(e);
    lv_draw_dsc_base_t * base_dsc = draw_task->draw_dsc;
    lv_draw_line_dsc_t * line_dsc = draw_task->draw_dsc;

    /*Vertical line*/
    if(line_dsc->p1.x == line_dsc->p2.x) {
        line_dsc->color  = lv_palette_lighten(LV_PALETTE_GREY, 1);
        if(base_dsc->id1 == 3) {
            line_dsc->width = 2;
            line_dsc->dash_gap = 0;
            line_dsc->dash_width = 0;
        }
        else {
            line_dsc->width = 1;
            line_dsc->dash_gap = 6;
            line_dsc->dash_width = 6;
        }
    }
    /*Horizontal line*/
    else {
        if(base_dsc->id1 == 2) {
            line_dsc->width  = 2;
            line_dsc->dash_gap  = 0;
            line_dsc->dash_width  = 0;
        }
        else {
            line_dsc->width = 2;
            line_dsc->dash_gap  = 6;
            line_dsc->dash_width  = 6;
        }

        if(base_dsc->id1 == 1  || base_dsc->id1 == 3) {
            line_dsc->color  = lv_palette_main(LV_PALETTE_GREEN);
        }
        else {
            line_dsc->color  = lv_palette_lighten(LV_PALETTE_GREY, 1);
        }
    }
}

#endif

---

Show cursor on the clicked point

C code  

 View on GitHub

#include "../../lv_examples.h"
#if LV_USE_CHART && LV_BUILD_EXAMPLES

static lv_obj_t * chart;
static lv_chart_series_t * ser;
static lv_chart_cursor_t * cursor;

static void value_changed_event_cb(lv_event_t * e)
{
    static int32_t last_id = -1;
    lv_obj_t * obj = lv_event_get_target(e);

    last_id = lv_chart_get_pressed_point(obj);
    if(last_id != LV_CHART_POINT_NONE) {
        lv_chart_set_cursor_point(obj, cursor, NULL, last_id);
    }
}

/**
 * Show cursor on the clicked point
 */
void lv_example_chart_6(void)
{
    chart = lv_chart_create(lv_screen_active());
    lv_obj_set_size(chart, 200, 150);
    lv_obj_align(chart, LV_ALIGN_CENTER, 0, -10);

    //    lv_chart_set_axis_tick(chart, LV_CHART_AXIS_PRIMARY_Y, 10, 5, 6, 5, true, 40);
    //    lv_chart_set_axis_tick(chart, LV_CHART_AXIS_PRIMARY_X, 10, 5, 10, 1, true, 30);

    lv_obj_add_event_cb(chart, value_changed_event_cb, LV_EVENT_VALUE_CHANGED, NULL);
    lv_obj_refresh_ext_draw_size(chart);

    cursor = lv_chart_add_cursor(chart, lv_palette_main(LV_PALETTE_BLUE), LV_DIR_LEFT | LV_DIR_BOTTOM);

    ser = lv_chart_add_series(chart, lv_palette_main(LV_PALETTE_RED), LV_CHART_AXIS_PRIMARY_Y);
    uint32_t i;
    for(i = 0; i < 10; i++) {
        lv_chart_set_next_value(chart, ser, lv_rand(10, 90));
    }

    //    lv_chart_set_scale_x(chart, 500);

    lv_obj_t * label = lv_label_create(lv_screen_active());
    lv_label_set_text(label, "Click on a point");
    lv_obj_align_to(label, chart, LV_ALIGN_OUT_TOP_MID, 0, -5);
}

#endif

---

Scatter chart

C code  

 View on GitHub

#include "../../lv_examples.h"
#if LV_USE_CHART && LV_BUILD_EXAMPLES

static void draw_event_cb(lv_event_t * e)
{
    lv_draw_task_t * draw_task = lv_event_get_draw_task(e);
    lv_draw_dsc_base_t * base_dsc = draw_task->draw_dsc;
    if(base_dsc->part == LV_PART_INDICATOR) {
        lv_obj_t * obj = lv_event_get_target(e);
        lv_chart_series_t * ser = lv_chart_get_series_next(obj, NULL);
        lv_draw_rect_dsc_t * rect_draw_dsc = draw_task->draw_dsc;
        uint32_t cnt = lv_chart_get_point_count(obj);

        /*Make older value more transparent*/
        rect_draw_dsc->bg_opa = (LV_OPA_COVER *  base_dsc->id2) / (cnt - 1);

        /*Make smaller values blue, higher values red*/
        int32_t * x_array = lv_chart_get_x_array(obj, ser);
        int32_t * y_array = lv_chart_get_y_array(obj, ser);
        /*dsc->id is the tells drawing order, but we need the ID of the point being drawn.*/
        uint32_t start_point = lv_chart_get_x_start_point(obj, ser);
        uint32_t p_act = (start_point + base_dsc->id2) % cnt; /*Consider start point to get the index of the array*/
        lv_opa_t x_opa = (x_array[p_act] * LV_OPA_50) / 200;
        lv_opa_t y_opa = (y_array[p_act] * LV_OPA_50) / 1000;

        rect_draw_dsc->bg_color = lv_color_mix(lv_palette_main(LV_PALETTE_RED),
                                               lv_palette_main(LV_PALETTE_BLUE),
                                               x_opa + y_opa);
    }
}

static void add_data(lv_timer_t * timer)
{
    LV_UNUSED(timer);
    lv_obj_t * chart = timer->user_data;
    lv_chart_set_next_value2(chart, lv_chart_get_series_next(chart, NULL), lv_rand(0, 200), lv_rand(0, 1000));
}

/**
 * A scatter chart
 */
void lv_example_chart_7(void)
{
    lv_obj_t * chart = lv_chart_create(lv_screen_active());
    lv_obj_set_size(chart, 200, 150);
    lv_obj_align(chart, LV_ALIGN_CENTER, 0, 0);
    lv_obj_add_event_cb(chart, draw_event_cb, LV_EVENT_DRAW_TASK_ADDED, NULL);
    lv_obj_add_flag(chart, LV_OBJ_FLAG_SEND_DRAW_TASK_EVENTS);
    lv_obj_set_style_line_width(chart, 0, LV_PART_ITEMS);   /*Remove the lines*/

    lv_chart_set_type(chart, LV_CHART_TYPE_SCATTER);

    lv_chart_set_range(chart, LV_CHART_AXIS_PRIMARY_X, 0, 200);
    lv_chart_set_range(chart, LV_CHART_AXIS_PRIMARY_Y, 0, 1000);

    lv_chart_set_point_count(chart, 50);

    lv_chart_series_t * ser = lv_chart_add_series(chart, lv_palette_main(LV_PALETTE_RED), LV_CHART_AXIS_PRIMARY_Y);
    uint32_t i;
    for(i = 0; i < 50; i++) {
        lv_chart_set_next_value2(chart, ser, lv_rand(0, 200), lv_rand(0, 1000));
    }

    lv_timer_create(add_data, 100, chart);
}

#endif

---

API

lv_chart.h