lvgl/README.md

<h1 align="center"> LittlevGL - Open-source Embedded GUI Library</h1>
<p align="center">
<a href="https://github.com/littlevgl/lvgl/blob/master/LICENCE.txt"><img src="https://img.shields.io/badge/licence-MIT-blue.svg"></a>
<a href="https://github.com/littlevgl/lvgl/releases/tag/v6.1.2"><img src="https://img.shields.io/badge/version-6.1.2-blue.svg"></a>
</p>

<p align="center">
<img src="https://littlevgl.com/github/cover_ori_reduced_2.gif">
</p>

<p align="center">
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. 
</p>

<h4 align="center">
<a href="https://littlevgl.com">Website </a> &middot; 
<a href="https://littlevgl.com/live-demo">Live demo</a> &middot; 
<a href="https://docs.littlevgl.com/en/html/get-started/pc-simulator.html">Simulator</a> &middot; 
<a href="https://forum.littlevgl.com">Forum</a> &middot; 
<a href="https://docs.littlevgl.com/">Docs</a> &middot;
<a href="https://blog.littlevgl.com/">Blog</a>
</h4>

---

- [Features](#features)
- [Supported devices](#supported-devices)
- [Quick start in a simulator](#quick-start-in-a-simulator)
- [Add LittlevGL to your project](#add-littlevgl-to-your-project)
- [Learn the basics](#learn-the-basics)
- [Examples](#examples)
- [Contributing](#contributing)
- [Donate](#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](https://blog.littlevgl.com/2019-02-20/micropython-bindings)
* **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
- &gt; 16 MHz clock speed is recommended
- Flash/ROM: &gt; 64 kB for the very essential components (&gt; 180 kB is recommended)
- RAM: 
  - Static RAM usage: ~8..16 kB depending on the used features and objects types
  - Stack: &gt; 2kB (&gt; 4 kB is recommended)
  - Dynamic data (heap): &gt; 4 KB (&gt; 16 kB is recommended if using several objects).
    Set by `LV_MEM_SIZE` in *lv_conf.h*. 
  - Display buffer:  &gt; *"Horizontal resolution"* pixels (&gt; 10 &times; *"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](https://blog.littlevgl.com/2017-07-15/stm32f429_disco_port), [STM32F7](https://github.com/littlevgl/stm32f746_disco_no_os_sw4stm32)
- Microchip dsPIC33, PIC24, PIC32MX, PIC32MZ
- NXP Kinetis, LPC, iMX
- [Linux frame buffer](https://blog.littlevgl.com/2018-01-03/linux_fb) (/dev/fb)
- [Raspberry PI](http://www.vk3erw.com/index.php/16-software/63-raspberry-pi-official-7-touchscreen-and-littlevgl)
- [Espressif ESP32](https://github.com/littlevgl/lv_port_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 |
|-------------|-------------|---------------|-----------|------------|
|  [![Eclipse](https://littlevgl.com/logo/ide/eclipse.jpg)](https://github.com/littlevgl/pc_simulator_sdl_eclipse) | [![CodeBlocks](https://littlevgl.com/logo/ide/codeblocks.jpg)](https://github.com/littlevgl/pc_simulator_win_codeblocks) | [![VisualStudio](https://littlevgl.com/logo/ide/visualstudio.jpg)](https://github.com/littlevgl/visual_studio_2017_sdl_x64)   |   [![PlatformIO](https://littlevgl.com/logo/ide/platformio.jpg)](https://github.com/littlevgl/pc_simulator_sdl_platformio) | [![QtCreator](https://littlevgl.com/logo/ide/qtcreator.jpg)](https://blog.littlevgl.com/2019-01-03/qt-creator) |
| Cross-platform<br>with SDL<br>(Recommended on<br>Linux and Mac) | Native Windows | Windows<br>with SDL | Cross-platform<br>with SDL | Cross-platform<br>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](https://docs.littlevgl.com/en/html/get-started/pc-simulator) to get ready to use projects which can be run on your PC. 

1. [Download](https://littlevgl.com/download) or [Clone](https://github.com/littlevgl/lvgl) 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
```c
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*/
```
8. 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*/
}
    
```
9. 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:
```c
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:
```c
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:
```c
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:
```c
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](https://docs.littlevgl.com/en/html/overview/style) 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: 

```c
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](https://docs.littlevgl.com/en/html/overview/event) section. 


## Examples 

### Button with label
```c
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");
    }
}
```
![LittlevGL button with label example](https://docs.littlevgl.com/en/misc/simple_button_example.gif)

### Button with styles
Add styles to the previously button from the previous example
```c
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*/
```

![Stylsd button is LittelvGL](https://docs.littlevgl.com/en/misc/button_style_example.gif)

### Slider and object alignment
```c
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*/
    }
}
```

![Slider example with LittlevGL](https://docs.littlevgl.com/en/misc/slider_example.gif)

### List and themes
```c
/*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));
    }

}
```
![List and theme example with LittlevGL](https://docs.littlevgl.com/en/misc/list_theme_example.gif)

### Use LittlevGL from Micropython
Learn more about [Micropython](https://docs.littlevgl.com/en/html/get-started/micropython).
```python
# 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](https://forum.littlevgl.com).
For development-related things (bug reports, feature suggestions) use [GitHub's Issue tracker](https://github.com/littlevgl/lvgl/issues). 

If you are interested in contributing to LittlevGL you can
- **Help others** in the [Forum](https://forum.littlevgl.com).
- **Inspire people** by speaking about your project in [My project](https://forum.littlevgl.com/c/my-projects) category in the Forum or add it to the [References](https://blog.littlevgl.com/2018-12-26/references) post
- **Improve and/or translate the documentation.** Go to the [Documentation](https://github.com/littlevgl/docs) repository to learn more
- **Write a blog post** about your experiences. See how to do it in the [Blog](https://github.com/littlevgl/blog) repository
- **Report and/or fix bugs** in [GitHub's issue tracker](https://github.com/littlevgl/lvgl/issues)
- **Help in the developement**. Check the [Open issues](https://github.com/littlevgl/lvgl/issues) especially the ones with [Help wanted](https://github.com/littlevgl/lvgl/issues?q=is%3Aissue+is%3Aopen+label%3A%22help+wanted%22) label and tell your ideas about a topic or implement a feature.

It should be useful to read the
- [Contributing guide](https://blog.littlevgl.com/2018-12-06/contributing)
- [Coding style guide](https://github.com/littlevgl/lvgl/blob/master/docs/CODING_STYLE.md)

## 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:

[![Donate](https://littlevgl.com/donate_dir/donate_btn.png)](https://littlevgl.com/donate)