EC600G/components/ql-application/lvgl_lib/lvgl

LittlevGL - Open-source Embedded GUI Library

LittlevGL provides everything you need to create a Graphical User Interface (GUI) on embedded systems with easy-to-use graphical elements, beautiful visual effects and low memory footprint.

Website · Live demo · Simulator · Forum · Docs · Blog

---

• Features
• Supported devices
• Quick start in a simulator
• Add LittlevGL to your project
• Learn the basics
• Examples
• Contributing
• Donate

Features

• Powerful building blocks buttons, charts, lists, sliders, images, etc.
• Advanced graphics with animations, anti-aliasing, opacity, smooth scrolling
• Simultaneously use various input devices touchscreen, mouse, keyboard, encoder, buttons, etc.
• Simultaneously use multiple displays i.e. monochrome and color display
• Multi-language support with UTF-8 encoding
• Fully customizable graphical elements
• Hardware independent to use with any microcontroller or display
• Scalable to operate with little memory (64 kB Flash, 10 kB RAM)
• OS, External memory and GPU supported but not required
• Single frame buffer operation even with advances graphical effects
• Written in C for maximal compatibility
• Micropython Binding exposes LittlevGL API in Micropython
• Simulator to develop on PC without embedded hardware
• Tutorials, examples, themes for rapid development
• Documentation and API references

Supported devices

Basically, every modern controller - which is able to drive a display - is suitable to run LittlevGL. The minimal requirements:

• 16, 32 or 64 bit microcontroller or processor
• > 16 MHz clock speed is recommended
• Flash/ROM: > 64 kB for the very essential components (> 180 kB is recommended)
• RAM:
  • Static RAM usage: ~8..16 kB depending on the used features and objects types
  • Stack: > 2kB (> 4 kB is recommended)
  • Dynamic data (heap): > 4 KB (> 16 kB is recommended if using several objects). Set by LV_MEM_SIZE in lv_conf.h.
  • Display buffer: > "Horizontal resolution" pixels (> 10 × "Horizontal resolution" is recommended)
• C99 or newer compiler

Note that the memory usage might vary depending on the architecture, compiler and build options.

Just to mention some platforms:

• STM32F1, STM32F3, STM32F4, STM32F7
• Microchip dsPIC33, PIC24, PIC32MX, PIC32MZ
• NXP Kinetis, LPC, iMX
• Linux frame buffer (/dev/fb)
• Raspberry PI
• Espressif ESP32
• Nordic nrf52
• Quectell M66

Quick start in a simulator

The easiest way to get started with LittlevGL is to run it in a simulator on your PC without any embedded hardware.

Choose a project with your favourite IDE:

Eclipse	CodeBlocks	Visual Studio	PlatformIO	Qt Creator
Cross-platform with SDL (Recommended on Linux and Mac)	Native Windows	Windows with SDL	Cross-platform with SDL	Cross-platform with SDL

Add LittlevGL to your project

The steps below show how to setup LittlevGL on an embedded system with a display and a touchpad. You can use the Simulators to get ready to use projects which can be run on your PC.

1. Download or Clone the library
2. Copy the lvgl folder into your project
3. Copy lvgl/lv_conf_template.h as lv_conf.h next to the lvgl folder and set at least LV_HOR_RES_MAX, LV_VER_RES_MAX and LV_COLOR_DEPTH.
4. Include lvgl/lvgl.h where you need to use LittlevGL related functions.
5. Call lv_tick_inc(x) every x milliseconds in a Timer or Task (x should be between 1 and 10). It is required for the internal timing of LittlevGL.
6. Call lv_init()

7. Create a display buffer for LittlevGL

   static lv_disp_buf_t disp_buf;
   static lv_color_t buf[LV_HOR_RES_MAX * 10];                     /*Declare a buffer for 10 lines*/
   lv_disp_buf_init(&disp_buf, buf, NULL, LV_HOR_RES_MAX * 10);    /*Initialize the display buffer*/
   

   1. Implement and register a function which can copy a pixel array to an area of your display: ```c lv_disp_drv_t disp_drv; /Descriptor of a display driver/ lv_disp_drv_init(&disp_drv); /Basic initialization/ disp_drv.flush_cb = my_disp_flush; /Set your driver function/ disp_drv.buffer = &disp_buf; /Assign the buffer to the display/ lv_disp_drv_register(&disp_drv); /Finally register the driver/
      

   void my_disp_flush(lv_disp_t * disp, const lv_area_t * area, lv_color_t * color_p) { int32_t x, y; for(y = area->y1; y <= area->y2; y++) {

   for(x = area->x1; x <= area->x2; x++) {
       set_pixel(x, y, *color_p);  /* Put a pixel to the display.*/
       color_p++;
   }
   

   }

   lv_disp_flush_ready(disp); /* Indicate you are ready with the flushing*/ }

   ```

8. Implement and register a function which can read an input device. E.g. for a touch pad: ```c lv_indev_drv_init(&indev_drv); /Descriptor of a input device driver/ indev_drv.type = LV_INDEV_TYPE_POINTER; /Touch pad is a pointer-like device/ indev_drv.read_cb = my_touchpad_read; /Set your driver function/ lv_indev_drv_register(&indev_drv); /Finally register the driver/

bool my_touchpad_read(lv_indev_drv_t * indev_driver, lv_indev_data_t * data) {

static lv_coord_t last_x = 0;
static lv_coord_t last_y = 0;

/*Save the state and save the pressed coordinate*/
data->state = touchpad_is_pressed() ? LV_INDEV_STATE_PR : LV_INDEV_STATE_REL; 
if(data->state == LV_INDEV_STATE_PR) touchpad_get_xy(&last_x, &last_y);

/*Set the coordinates (if released use the last pressed coordinates)*/
data->point.x = last_x;
data->point.y = last_y;

return false; /*Return `false` because we are not buffering and no more data to read*/

}

10. Call `lv_task_handler()` periodically every few milliseconds in the main `while(1)` loop, in Timer interrupt or in an Operation system task. 
It will redraw the screen if required, handle input devices etc. 


## Learn the basics

### Objects (Widgets)

The graphical elements like Buttons, Labels, Sliders, Charts etc are called objects in LittelvGL. Go to [Object types](https://docs.littlevgl.com/en/html/object-types/index) to see the full list of available types.

Every object has a parent object. The child object moves with the parent and if you delete the parent the children will be deleted too. Children can be visible only on their parent.

The *screen* are the "root" parents. To get the current screen call `lv_scr_act()`.

You can create a new object with `lv_<type>_create(parent, obj_to_copy)`. It will return an `lv_obj_t *` variable which should be used as a reference to the object to set its parameters. 
The first parameter is the desired *parent*, te second parameters can be an object to copy (`NULL` is unused). 
For example:
```c
lv_obj_t * slider1 = lv_slider_create(lv_scr_act(), NULL);

To set some basic attribute lv_obj_set_<paramters_name>(obj, <value>) function can be used. For example:

lv_obj_set_x(btn1, 30);
lv_obj_set_y(btn1, 10);
lv_obj_set_size(btn1, 200, 50);

The objects has type specific parameters too which can be set by lv_<type>_set_<paramters_name>(obj, <value>) functions. For example:

lv_slider_set_value(slider1, 70, LV_ANIM_ON);

To see the full API visit the documentation of the object types or the related header file (e.g. lvgl/src/lv_objx/lv_slider.h).

Styles

Styles can be assigned to the objects to changed their appearance. A style describes the appearance of rectangle-like objects (like a button or slider), texts, images and lines at once.

You can create a new style like this:

static lv_style_t style1;                       /*Declare a new style. Should be `static`*/
lv_style_copy(&style1, &lv_style_plain);        /*Copy a built-in style*/
style1.body.main_color = LV_COLOR_RED;          /*Main color*/
style1.body.grad_color = lv_color_hex(0xffd83c) /*Gradient color (orange)*/
style1.body.radius = 3;
style1.text.color = lv_color_hex3(0x0F0)        /*Label color (green)*/
style1.text.font = &lv_font_dejavu_22;          /*Change font*/
...

To set a new style for an object use the lv_<type>set_style(obj, LV_<TYPE>_STYLE_<NAME>, &my_style) functions. For example:

lv_slider_set_style(slider1, LV_SLIDER_STYLE_BG, &slider_bg_style);
lv_slider_set_style(slider1, LV_SLIDER_STYLE_INDIC, &slider_indic_style);
lv_slider_set_style(slider1, LV_SLIDER_STYLE_KNOB, &slider_knob_style);

If an object's style is NULL then it will inherit its parent's style. For example, the labels' style are NULL by default. If you place them on a button then they will use the style.text properties from the button's style.

Learn more in Style overview section.

Events

Events are used to inform the user if something has happened with an object. You can assign a callback to an object which will be called if the object is clicked, released, dragged, being deleted etc. It should look like this:

lv_obj_set_event_cb(btn, btn_event_cb);                 /*Assign a callback to the button*/

...

void btn_event_cb(lv_obj_t * btn, lv_event_t event)
{
    if(event == LV_EVENT_CLICKED) {
        printf("Clicked\n");
    }
}

Learn more about the events in the Event overview section.

Examples

Button with label

lv_obj_t * btn = lv_btn_create(lv_scr_act(), NULL);     /*Add a button the current screen*/
lv_obj_set_pos(btn, 10, 10);                            /*Set its position*/
lv_obj_set_size(btn, 100, 50);                          /*Set its size*/
lv_obj_set_event_cb(btn, btn_event_cb);                 /*Assign a callback to the button*/

lv_obj_t * label = lv_label_create(btn, NULL);          /*Add a label to the button*/
lv_label_set_text(label, "Button");                     /*Set the labels text*/

...

void btn_event_cb(lv_obj_t * btn, lv_event_t event)
{
    if(event == LV_EVENT_CLICKED) {
        printf("Clicked\n");
    }
}

Button with styles

Add styles to the previously button from the previous example

static lv_style_t style_btn_rel;                        /*A variable to store the released style*/
lv_style_copy(&style_btn_rel, &lv_style_plain);         /*Initialize from a built-in style*/
style_btn_rel.body.border.color = lv_color_hex3(0x269);
style_btn_rel.body.border.width = 1;
style_btn_rel.body.main_color = lv_color_hex3(0xADF);
style_btn_rel.body.grad_color = lv_color_hex3(0x46B);
style_btn_rel.body.shadow.width = 4;
style_btn_rel.body.shadow.type = LV_SHADOW_BOTTOM;
style_btn_rel.body.radius = LV_RADIUS_CIRCLE;
style_btn_rel.text.color = lv_color_hex3(0xDEF);

static lv_style_t style_btn_pr;                         /*A variable to store the pressed style*/
lv_style_copy(&style_btn_pr, &style_btn_rel);           /*Initialize from the released style*/
style_btn_pr.body.border.color = lv_color_hex3(0x46B);
style_btn_pr.body.main_color = lv_color_hex3(0x8BD);
style_btn_pr.body.grad_color = lv_color_hex3(0x24A);
style_btn_pr.body.shadow.width = 2;
style_btn_pr.text.color = lv_color_hex3(0xBCD);

lv_btn_set_style(btn, LV_BTN_STYLE_REL, &style_btn_rel);    /*Set the button's released style*/
lv_btn_set_style(btn, LV_BTN_STYLE_PR, &style_btn_pr);      /*Set the button's pressed style*/

Slider and object alignment

lv_obj_t * label;

...

/* Create a slider in the center of the display */
lv_obj_t * slider = lv_slider_create(lv_scr_act(), NULL);
lv_obj_set_width(slider, 200);                        /*Set the width*/
lv_obj_align(slider, NULL, LV_ALIGN_CENTER, 0, 0);    /*Align to the center of the parent (screen)*/
lv_obj_set_event_cb(slider, slider_event_cb);         /*Assign an event function*/

/* Create a label below the slider */
label = lv_label_create(lv_scr_act(), NULL);
lv_label_set_text(label, "0");
lv_obj_set_auto_realign(slider, true);
lv_obj_align(label, slider, LV_ALIGN_OUT_BOTTOM_MID, 0, 10);

...

void slider_event_cb(lv_obj_t * slider, lv_event_t event)
{
    if(event == LV_EVENT_VALUE_CHANGED) {
        static char buf[4];                                 /* max 3 bytes  for number plus 1 null terminating byte */
        snprintf(buf, 4, "%u", lv_slider_get_value(slider));
        lv_label_set_text(slider_label, buf);               /*Refresh the text*/
    }
}

List and themes

/*Texts of the list elements*/
const char * txts[] = {"First", "Second", "Third", "Forth", "Fifth", "Sixth", NULL};

/* Initialize and set a theme. `LV_THEME_NIGHT` needs to enabled in lv_conf.h. */
lv_theme_t * th = lv_theme_night_init(20, NULL);
lv_theme_set_current(th);

/*Create a list*/
lv_obj_t* list = lv_list_create(lv_scr_act(), NULL);
lv_obj_set_size(list, 120, 180);
lv_obj_set_pos(list, 10, 10);

/*Add buttons*/
uint8_t i;
for(i = 0; txts[i]; i++) {
    lv_obj_t * btn = lv_list_add_btn(list, LV_SYMBOL_FILE, txts[i]);
    lv_obj_set_event_cb(btn, list_event);       /*Assign event function*/
    lv_btn_set_toggle(btn, true);               /*Enable on/off states*/
}

/* Initialize and set an other theme. `LV_THEME_MATERIAL` needs to enabled in lv_conf.h.
 * If `LV_TEHE_LIVE_UPDATE  1` then the previous list's style will be updated too.*/
th = lv_theme_material_init(210, NULL);
lv_theme_set_current(th);

/*Create an other list*/
list = lv_list_create(lv_scr_act(), NULL);
lv_obj_set_size(list, 120, 180);
lv_obj_set_pos(list, 150, 10);

/*Add buttons with the same texts*/
for(i = 0; txts[i]; i++) {
    lv_obj_t * btn = lv_list_add_btn(list, LV_SYMBOL_FILE, txts[i]);
    lv_obj_set_event_cb(btn, list_event);
    lv_btn_set_toggle(btn, true);
}

...

static void list_event(lv_obj_t * btn, lv_event_t e)
{
    if(e == LV_EVENT_CLICKED) {
        printf("%s\n", lv_list_get_btn_text(btn));
    }

}

Use LittlevGL from Micropython

Learn more about Micropython.

# Create a Button and a Label
scr = lv.obj()
btn = lv.btn(scr)
btn.align(lv.scr_act(), lv.ALIGN.CENTER, 0, 0)
label = lv.label(btn)
label.set_text("Button")

# Load the screen
lv.scr_load(scr)

Contributing

To ask questions please use the Forum. For development-related things (bug reports, feature suggestions) use GitHub's Issue tracker.

If you are interested in contributing to LittlevGL you can

• Help others in the Forum.
• Inspire people by speaking about your project in My project category in the Forum or add it to the References post
• Improve and/or translate the documentation. Go to the Documentation repository to learn more
• Write a blog post about your experiences. See how to do it in the Blog repository
• Report and/or fix bugs in GitHub's issue tracker
• Help in the developement. Check the Open issues especially the ones with Help wanted label and tell your ideas about a topic or implement a feature.

It should be useful to read the

• Contributing guide
• Coding style guide

Donate

If you are pleased with the library, found it useful, or you are happy with the support you got, please help its further development: