220 lines
11 KiB
Markdown
220 lines
11 KiB
Markdown
```eval_rst
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.. include:: /header.rst
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:github_url: |github_link_base|/intro/index.md
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```
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# Introduction
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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.
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## Key features
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- Powerful building blocks such as buttons, charts, lists, sliders, images, etc.
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- Advanced graphics with animations, anti-aliasing, opacity, smooth scrolling
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- Various input devices such as touchpad, mouse, keyboard, encoder, etc.
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- Multi-language support with UTF-8 encoding
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- Multi-display support, i.e. use multiple TFT, monochrome displays simultaneously
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- Fully customizable graphic elements with CSS-like styles
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- Hardware independent: use with any microcontroller or display
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- Scalable: able to operate with little memory (64 kB Flash, 16 kB RAM)
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- OS, external memory and GPU are supported but not required
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- Single frame buffer operation even with advanced graphic effects
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- Written in C for maximal compatibility (C++ compatible)
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- Simulator to start embedded GUI design on a PC without embedded hardware
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- Binding to MicroPython
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- Tutorials, examples, themes for rapid GUI design
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- Documentation is available online and as PDF
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- Free and open-source under MIT license
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## Requirements
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Basically, every modern controller which is able to drive a display is suitable to run LVGL. The minimal requirements are:
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<ul>
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<li> 16, 32 or 64 bit microcontroller or processor</li>
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<li>> 16 MHz clock speed is recommended</li>
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<li> Flash/ROM: > 64 kB for the very essential components (> 180 kB is recommended)</li>
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<li> RAM:
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<ul>
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<li> Static RAM usage: ~2 kB depending on the used features and object types</li>
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<li> Stack: > 2kB (> 8 kB is recommended)</li>
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<li> Dynamic data (heap): > 4 KB (> 32 kB is recommended if using several objects).
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Set by <em>LV_MEM_SIZE</em> in <em>lv_conf.h</em>. </li>
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<li> Display buffer: > <em>"Horizontal resolution"</em> pixels (> 10 × <em>"Horizontal resolution"</em> is recommended) </li>
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<li> One frame buffer in the MCU or in an external display controller</li>
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</ul>
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</li>
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<li> C99 or newer compiler</li>
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<li> Basic C (or C++) knowledge:
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<a href="https://www.tutorialspoint.com/cprogramming/c_pointers.htm">pointers</a>,
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<a href="https://www.tutorialspoint.com/cprogramming/c_structures.htm">structs</a>,
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<a href="https://www.geeksforgeeks.org/callbacks-in-c/">callbacks</a>.</li>
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</ul>
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<em>Note that memory usage may vary depending on architecture, compiler and build options.</em>
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## License
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The LVGL project (including all repositories) is licensed under [MIT license](https://github.com/lvgl/lvgl/blob/master/LICENCE.txt).
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This means you can use it even in commercial projects.
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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).
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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.
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To make the LVGL project sustainable, please consider [contributing](/CONTRIBUTING) to the project.
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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.
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## Repository layout
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All repositories of the LVGL project are hosted on GitHub: https://github.com/lvgl
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You will find these repositories there:
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- [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/).
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- [lv_drivers](https://github.com/lvgl/lv_drivers) Display and input device drivers
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- [blog](https://github.com/lvgl/blog) Source of the blog's site (https://blog.lvgl.io)
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- [sim](https://github.com/lvgl/sim) Source of the online simulator's site (https://sim.lvgl.io)
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- [lv_port_...](https://github.com/lvgl?q=lv_port&type=&language=) LVGL ports to development boards or environments
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- [lv_binding_..](https://github.com/lvgl?q=lv_binding&type=&language=l) Bindings to other languages
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## Release policy
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The core repositories follow the rules of [Semantic versioning](https://semver.org/):
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- Major versions for incompatible API changes. E.g. v5.0.0, v6.0.0
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- Minor version for new but backward-compatible functionalities. E.g. v6.1.0, v6.2.0
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- Patch version for backward-compatible bug fixes. E.g. v6.1.1, v6.1.2
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Tags like `vX.Y.Z` are created for every release.
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### Release cycle
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- Bug fixes: Released on demand even weekly
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- Minor releases: Every 3-4 months
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- Major releases: Approximately yearly
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### Branches
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The core repositories have at least the following branches:
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- `master` latest version, patches are merged directly here.
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- `release/vX.Y` stable versions of the minor releases
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- `fix/some-description` temporary branches for bug fixes
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- `feat/some-description` temporary branches for features
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### Changelog
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The changes are recorded in [CHANGELOG.md](/CHANGELOG).
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### Version support
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Before v8 the last minor release of each major series was supported for 1 year.
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Starting from v8, every minor release is supported for 1 year.
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| Version | Release date | Support end | Active |
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|---------|--------------|-------------|--------|
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| v5.3 | Feb 1, 2019 |Feb 1, 2020 | No |
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| v6.1 | Nov 26, 2019 |Nov 26, 2020 | No |
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| v7.11 | Mar 16, 2021 |Mar 16, 2022 | No |
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| v8.0 | 1 Jun, 2021 |1 Jun, 2022 | Yes |
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| v8.1 | 10 Nov, 2021 |10 Nov, 2022 | Yes |
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| v8.2 | In progress | | |
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## FAQ
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### Where can I ask questions?
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You can ask questions in the forum: [https://forum.lvgl.io/](https://forum.lvgl.io/).
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We use [GitHub issues](https://github.com/lvgl/lvgl/issues) for development related discussion.
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You should use them only if your question or issue is tightly related to the development of the library.
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Before posting a question, please ready this FAQ section as you might find answer to your issue here too.
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### Is my MCU/hardware supported?
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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.
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This includes:
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- "Common" MCUs like STM32F, STM32H, NXP Kinetis, LPC, iMX, dsPIC33, PIC32 etc.
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- Bluetooth, GSM, Wi-Fi modules like Nordic NRF and Espressif ESP32
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- Linux with frame buffer device such as /dev/fb0. This includes Single-board computers like the Raspberry Pi
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- Anything else with a strong enough MCU and a peripheral to drive a display
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### Is my display supported?
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LVGL needs just one simple driver function to copy an array of pixels into a given area of the display.
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If you can do this with your display then you can use it with LVGL.
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Some examples of the supported display types:
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- TFTs with 16 or 24 bit color depth
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- Monitors with an HDMI port
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- Small monochrome displays
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- Gray-scale displays
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- even LED matrices
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- or any other display where you can control the color/state of the pixels
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See the [Porting](/porting/display) section to learn more.
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### LVGL doesn't start, randomly crashes or nothing is drawn on the display. What can be the problem?
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- Try increasing `LV_MEM_SIZE`.
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- Be sure `lv_disp_drv_t`, `lv_indev_drv_t` and `lv_fs_drv_t` are global or `static`.
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- Be sure your display works without LVGL. E.g. paint it to red on start up.
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- Enable [Logging](porting/log)
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- Enable asserts in `lv_conf.h` (`LV_USE_ASSERT_...`)
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- If you use an RTOS
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- increase the stack size of the task which calls `lv_timer_handler()`
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- Be sure you used a mutex as [described here](/porting/os)
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### My display driver is not called. What have I missed?
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Be sure you are calling `lv_tick_inc(x)` in an interrupt and `lv_timer_handler()` in your main `while(1)`.
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Learn more in the [Tick](/porting/tick) and [Timer handler](/porting/timer-handler) sections.
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### Why is the display driver called only once? Only the upper part of the display is refreshed.
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Be sure you are calling `lv_disp_flush_ready(drv)` at the end of your "*display flush callback*".
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### Why do I see only garbage on the screen?
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Probably there a bug in your display driver. Try the following code without using LVGL. You should see a square with red-blue gradient.
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```c
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#define BUF_W 20
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#define BUF_H 10
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lv_color_t buf[BUF_W * BUF_H];
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lv_color_t * buf_p = buf;
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uint16_t x, y;
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for(y = 0; y < BUF_H; y++) {
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lv_color_t c = lv_color_mix(LV_COLOR_BLUE, LV_COLOR_RED, (y * 255) / BUF_H);
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for(x = 0; x < BUF_W; x++){
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(*buf_p) = c;
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buf_p++;
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}
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}
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lv_area_t a;
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a.x1 = 10;
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a.y1 = 40;
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a.x2 = a.x1 + BUF_W - 1;
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a.y2 = a.y1 + BUF_H - 1;
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my_flush_cb(NULL, &a, buf);
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```
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### Why do I see nonsense colors on the screen?
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Probably LVGL's color format is not compatible with your display's color format. Check `LV_COLOR_DEPTH` in *lv_conf.h*.
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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*.
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It swaps the upper and lower bytes of the pixels.
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### How to speed up my UI?
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- Turn on compiler optimization and enable cache if your MCU has it
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- Increase the size of the display buffer
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- Use two display buffers and flush the buffer with DMA (or similar peripheral) in the background
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- Increase the clock speed of the SPI or parallel port if you use them to drive the display
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- If your display has an SPI port consider changing to a model with a parallel interface because it has much higher throughput
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- 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
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### How to reduce flash/ROM usage?
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You can disable all the unused features (such as animations, file system, GPU etc.) and object types in *lv_conf.h*.
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If you are using GCC you can add `-fdata-sections -ffunction-sections` compiler flags and `--gc-sections` linker flag to remove unused functions and variables from the final binary.
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### How to reduce the RAM usage
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- Lower the size of the *Display buffer*
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- Reduce `LV_MEM_SIZE` in *lv_conf.h*. This memory is used when you create objects like buttons, labels, etc.
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- To work with lower `LV_MEM_SIZE` you can create objects only when required and delete them when they are not needed anymore
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### How to work with an operating system?
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To work with an operating system where tasks can interrupt each other (preemptively) you should protect LVGL related function calls with a mutex.
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See the [Operating system and interrupts](/porting/os) section to learn more.
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