# 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 Basically, every modern controller which is able to drive a display is suitable to run LVGL. The minimal requirements are: Note that 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 [contributing](/CONTRIBUTING) to the project. You can choose from [many different ways of contributing](/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 versions for incompatible API changes. E.g. v5.0.0, v6.0.0 - Minor version for new but backward-compatible functionalities. E.g. v6.1.0, v6.2.0 - Patch version for 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 [CHANGELOG.md](/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 | Feb 1, 2019 |Feb 1, 2020 | No | | v6.1 | Nov 26, 2019 |Nov 26, 2020 | No | | v7.11 | Mar 16, 2021 |Mar 16, 2022 | No | | v8.0 | 1 Jun, 2021 |1 Jun, 2022 | Yes | | v8.1 | 10 Nov, 2021 |10 Nov, 2022 | Yes | | v8.2 | 31 Jan, 2022 |31 Jan, 2023 | Yes | | v8.3 | 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 [Requirements](#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 and Espressif ESP32 - 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 32 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 [Porting](/porting/display) section to learn more. ### LVGL doesn't start, randomly crashes or nothing is drawn on the display. What can be the problem? - Try increasing `LV_MEM_SIZE`. - Be sure `lv_disp_drv_t`, `lv_indev_drv_t` and `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 [Logging](porting/log) - Enable asserts in `lv_conf.h` (`LV_USE_ASSERT_...`) - If you use an RTOS - increase the stack size of the task which calls `lv_timer_handler()` - Be sure you used a mutex as [described here](/porting/os) ### My display driver is not called. What have I missed? Be sure you are calling `lv_tick_inc(x)` in an interrupt and `lv_timer_handler()` in your main `while(1)`. Learn more in the [Tick](/porting/tick) and [Timer handler](/porting/timer-handler) sections. ### Why is the display driver called only once? Only the upper part of the display is refreshed. Be sure you are calling `lv_disp_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. ```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 `LV_COLOR_DEPTH` in *lv_conf.h*. If you are using 16-bit colors with SPI (or another byte-oriented interface) you probably need to set `LV_COLOR_16_SWAP  1` in *lv_conf.h*. It swaps the upper and lower bytes of the pixels. ### 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 `LV_MEM_SIZE` in *lv_conf.h*. This memory is used when you create objects like buttons, labels, etc. - To work with lower `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 [Operating system and interrupts](/porting/os) section to learn more.