.. _introduction:

============
Introduction
============

LVGL (Light and Versatile Graphics Library) is a free and open-source graphics library providing everything you need to create an embedded GUI with easy-to-use graphical elements, beautiful visual effects and a low memory footprint.


Key features
------------

- Powerful building blocks such as buttons, charts, lists, sliders, images, etc.
- Advanced graphics with animations, anti-aliasing, opacity, smooth scrolling
- Various input devices such as touchpad, mouse, keyboard, encoder, etc.
- Multi-language support with UTF-8 encoding
- Multi-display support, i.e. use multiple TFT, monochrome displays simultaneously
- Fully customizable graphic elements with CSS-like styles
- Hardware independent: use with any microcontroller or display
- Scalable: able to operate with little memory (64 kB Flash, 16 kB RAM)
- OS, external memory and GPU are supported but not required
- Single frame buffer operation even with advanced graphic effects
- Written in C for maximal compatibility (C++ compatible)
- Simulator to start embedded GUI design on a PC without embedded hardware
- Binding to MicroPython
- Tutorials, examples, themes for rapid GUI design
- Documentation is available online and as PDF
- Free and open-source under MIT license

.. _requirements:

Requirements
------------

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

* 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: ~2 kB depending on the used features and object types
    * stack: > 2kB (> 8 kB is recommended)
    * Dynamic data (heap): > 2 KB (> 48 kB is recommended if using several objects).
        Set by :c:macro:`LV_MEM_SIZE` in ``lv_conf.h``.
    * Display buffer:  > *"Horizontal resolution"* pixels (> 10 *"Horizontal resolution"* is recommended)
    * One frame buffer in the MCU or in an external display controller
* C99 or newer compiler
* Basic C (or C++) knowledge:
    * `pointers <https://www.tutorialspoint.com/cprogramming/c_pointers.htm>`_.
    * `structs <https://www.tutorialspoint.com/cprogramming/c_structures.htm>`_.
    * `callbacks <https://www.geeksforgeeks.org/callbacks-in-c/>`_.



:Note: *memory usage may vary depending on architecture, compiler and build options.*

License
-------

The LVGL project (including all repositories) is licensed under `MIT license <https://github.com/lvgl/lvgl/blob/master/LICENCE.txt>`_.
This means you can use it even in commercial projects.

It's not mandatory, but we highly appreciate it if you write a few words about your project in the `My projects <https://forum.lvgl.io/c/my-projects/10>`_ category of the forum or a private message to `lvgl.io <https://lvgl.io/#contact>`_.

Although you can get LVGL for free there is a massive amount of work behind it. It's created by a group of volunteers who made it available for you in their free time.

To make the LVGL project sustainable, please consider :ref:`contributing` to the project.
You can choose from many different ways of contributing See :ref:`contributing` such as simply writing a tweet about you using LVGL, fixing bugs, translating the documentation, or even becoming a maintainer.

Repository layout
-----------------

All repositories of the LVGL project are hosted on `GitHub <https://github.com/lvgl>`_

You will find these repositories there:

* `lvgl <https://github.com/lvgl/lvgl>`_: The library itself with many `examples <https://github.com/lvgl/lvgl/blob/master/examples/>`_ and `demos <https://github.com/lvgl/lvgl/blob/master/demos/>`_.
* `lv_drivers <https://github.com/lvgl/lv_drivers>`_: Display and input device drivers
* `blog <https://github.com/lvgl/blog>`_: Source of the `blog's site <https://blog.lvgl.io>`_
* `sim <https://github.com/lvgl/sim>`_: Source of the `online simulator's site <https://sim.lvgl.io>`_
* `lv_port_* <https://github.com/lvgl?q=lv_port&type=&language=>`_: LVGL ports to development boards or environments
* `lv_binding_* <https://github.com/lvgl?q=lv_binding&type=&language=l>`_: Bindings to other languages

Release policy
--------------

The core repositories follow the rules of `Semantic versioning <https://semver.org/>`_:

* Major version: incompatible API changes. E.g. v5.0.0, v6.0.0
* Minor version: new but backward-compatible functionalities. E.g. v6.1.0, v6.2.0
* Patch version: backward-compatible bug fixes. E.g. v6.1.1, v6.1.2

Tags like `vX.Y.Z` are created for every release.


Release cycle
^^^^^^^^^^^^^

* Bug fixes: Released on demand even weekly
* Minor releases: Every 3-4 months
* Major releases: Approximately yearly

Branches
^^^^^^^^

The core repositories have at least the following branches:

* `master`: latest version, patches are merged directly here.
* `release/vX.Y`: stable versions of the minor releases
* `fix/some-description`: temporary branches for bug fixes
* `feat/some-description`: temporary branches for features


Changelog
^^^^^^^^^

The changes are recorded in :ref:`changelog`.

Version support
^^^^^^^^^^^^^^^

Before v8 the last minor release of each major series was supported for 1 year.
Starting from v8, every minor release is supported for 1 year.


+---------+--------------+--------------+--------+
| Version | Release date | Support end  | Active |
+=========+==============+==============+========+
|v5.3     | 1 Feb, 2019  | 1 Feb, 2020  | No     |
+---------+--------------+--------------+--------+
|v6.1     | 26 Nov, 2019 | 26 Nov, 2020 | No     |
+---------+--------------+--------------+--------+
|v7.11    | 16 Mar, 2021 | 16 Mar, 2022 | No     |
+---------+--------------+--------------+--------+
|v8.0     | 1 Jun, 2021  | 1 Jun, 2022  | No     |
+---------+--------------+--------------+--------+
|v8.1     | 10 Nov, 2021 | 10 Nov, 2022 | No     |
+---------+--------------+--------------+--------+
|v8.2     | 31 Jan, 2022 | 31 Jan, 2023 | No     |
+---------+--------------+--------------+--------+
|v8.3     | 6 July, 2022 | 1 Jan, 2025  | Yes    |
+---------+--------------+--------------+--------+
|v9.0     |In progress                           |
+---------+--------------------------------------+


FAQ
---

Where can I ask questions?
^^^^^^^^^^^^^^^^^^^^^^^^^^

You can ask questions in the forum: `https://forum.lvgl.io/ <https://forum.lvgl.io/>`_.

We use `GitHub issues <https://github.com/lvgl/lvgl/issues>`_ for development related discussion.
You should use them only if your question or issue is tightly related to the development of the library.

Before posting a question, please ready this FAQ section as you might find answer to your issue here too.


Is my MCU/hardware supported?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Every MCU which is capable of driving a display via parallel port, SPI, RGB interface or anything else and fulfills the :ref:`requirements` is supported by LVGL.

This includes:

* "Common" MCUs like STM32F, STM32H, NXP Kinetis, LPC, iMX, dsPIC33, PIC32, SWM341 etc.
* Bluetooth, GSM, Wi-Fi modules like Nordic NRF, Espressif ESP32 and Raspberry Pi Pico W
* Linux with frame buffer device such as /dev/fb0. This includes Single-board computers like the Raspberry Pi
* Anything else with a strong enough MCU and a peripheral to drive a display


Is my display supported?
^^^^^^^^^^^^^^^^^^^^^^^^

LVGL needs just one simple driver function to copy an array of pixels into a given area of the display.
If you can do this with your display then you can use it with LVGL.

Some examples of the supported display types:

* TFTs with 16 or 24 bit color depth
* Monitors with an HDMI port
* Small monochrome displays
* Gray-scale displays
* even LED matrices
* or any other display where you can control the color/state of the pixels

See the :ref:`display_interface` section to learn more.


LVGL doesn't start, randomly crashes or nothing is drawn on the display. What can be the problem?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

* Try increasing :c:macro:`LV_MEM_SIZE`.
* Be sure :cpp:type:`lv_display_t`, :cpp:type:`lv_indev_t` and :cpp:type:`lv_fs_drv_t` are global or `static`.
* Be sure your display works without LVGL. E.g. paint it to red on start up.
* Enable :ref:`logging`
* Enable asserts in ``lv_conf.h`` (`LV_USE_ASSERT_...`)
* If you use an RTOS
   * increase the stack size of the task which calls :cpp:func:`lv_timer_handler`
   * Be sure you used a mutex as described here: :ref:`os_interrupt`


My display driver is not called. What have I missed?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Be sure you are calling :cpp:expr:`lv_tick_inc(x)` in an interrupt and :cpp:func:`lv_timer_handler` in your main ``while(1)``.

Learn more in the :ref:`tick` and :ref:`timer` sections.


Why is the display driver called only once? Only the upper part of the display is refreshed.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Be sure you are calling :cpp:expr:`lv_display_flush_ready(drv)` at the end of your "*display flush callback*".


Why do I see only garbage on the screen?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Probably there a bug in your display driver. Try the following code without using LVGL. You should see a square with red-blue gradient.

.. code-block:: c

    #define BUF_W 20
    #define BUF_H 10

    lv_color_t buf[BUF_W * BUF_H];
    lv_color_t * buf_p = buf;
    uint16_t x, y;
    for(y = 0; y < BUF_H; y++) {
        lv_color_t c = lv_color_mix(LV_COLOR_BLUE, LV_COLOR_RED, (y * 255) / BUF_H);
        for(x = 0; x < BUF_W; x++){
            (*buf_p) =  c;
            buf_p++;
        }
    }

    lv_area_t a;
    a.x1 = 10;
    a.y1 = 40;
    a.x2 = a.x1 + BUF_W - 1;
    a.y2 = a.y1 + BUF_H - 1;
    my_flush_cb(NULL, &a, buf);


Why do I see nonsense colors on the screen?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Probably LVGL's color format is not compatible with your display's color format. Check :c:macro:`LV_COLOR_DEPTH` in *lv_conf.h*.


How to speed up my UI?
^^^^^^^^^^^^^^^^^^^^^^

- Turn on compiler optimization and enable cache if your MCU has it
- Increase the size of the display buffer
- Use two display buffers and flush the buffer with DMA (or similar peripheral) in the background
- Increase the clock speed of the SPI or parallel port if you use them to drive the display
- If your display has an SPI port consider changing to a model with a parallel interface because it has much higher throughput
- Keep the display buffer in internal RAM (not in external SRAM) because LVGL uses it a lot and it should have a fast access time


How to reduce flash/ROM usage?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

You can disable all the unused features (such as animations, file system, GPU etc.) and object types in *lv_conf.h*.

If you are using GCC/CLANG you can add `-fdata-sections -ffunction-sections` compiler flags and `--gc-sections` linker flag to remove unused functions and variables from the final binary. If possible, add the `-flto` compiler flag to enable link-time-optimisation together with `-Os` for GCC or `-Oz` for CLANG.


How to reduce the RAM usage
^^^^^^^^^^^^^^^^^^^^^^^^^^^

* Lower the size of the *Display buffer*
* Reduce :c:macro:`LV_MEM_SIZE` in *lv_conf.h*. This memory is used when you create objects like buttons, labels, etc.
* To work with lower :c:macro:`LV_MEM_SIZE` you can create objects only when required and delete them when they are not needed anymore


How to work with an operating system?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

To work with an operating system where tasks can interrupt each other (preemptively) you should protect LVGL related function calls with a mutex.
See the :ref:`os_interrupt` section to learn more.
