Introduction¶

LVGL (Light and Versatile Graphics Library) is a free and open-source graphics library providing everything you need to create 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 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 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:

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 objects types
- Stack: > 2kB (> 8 kB is recommended)
- Dynamic data (heap): > 4 KB (> 32 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)
- One frame buffer in the MCU or in external display controller
C99 or newer compiler
Basic C (or C++) knowledge: pointers, structs, callbacks.

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. It 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 category of the forum or a private message to lvgl.io.

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 to the project. You can choose from many different ways of contributing such as simply writing a tweet about you are 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 The library itself with many examples.
lv_demos Demos created with LVGL.
lv_drivers Display and input device drivers
blog Source of the blog's site (https://blog.lvgl.io)
sim Source of the online simulator's site (https://sim.lvgl.io)
lv_sim_... Simulator projects for various IDEs and platforms
lv_port_... LVGL ports to development boards
lv_binding_.. Bindings to other languages
lv_... Ports to other platforms

Release policy¶

The core repositories follow the rules of Semantic versioning:

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¶

Bugfixes: Released on demand even weekly
Minor releases: Every 3-4 months
Major releases: Approximatelly 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 temporal branches for bug fixes
feat/some-description temporal branches for features

Changelog¶

The changes are recorded in CHANGELOG.md.

Version support¶

Before v8 every minor release of major releases is supported for 1 year. 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	Yes
v8.0	In progress

FAQ¶

Where can I ask questions?¶

You can ask questions in the forum: https://forum.lvgl.io/.

We use GitHub issues for development related discussion. So you should use them only if your question or issue is tightly related to the development of the library.

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 is supported by LLVGL.

This includes:

"Common" MCUs like STM32F, STM32H, NXP Kinetis, LPC, iMX, dsPIC33, PIC32 etc.
Bluetooth, GSM, WiFi 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
And anything else with a strong enough MCU and a periphery 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 that display with LVGL.

Some examples of the supported display types:

TFTs with 16 or 24 bit color depth
Monitors with 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 section to learn more.

Nothing happens, 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 and Task handler section.

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.

#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 &lt; BUF_H; y++) {
    lv_color_t c = lv_color_mix(LV_COLOR_BLUE, LV_COLOR_RED, (y * 255) / BUF_H);
    for(x = 0; x &lt; 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 I see nonsense colors on the screen?¶

Probably LVGL's color format is not compatible with your displays color format. Check LV_COLOR_DEPTH in lv_conf.h.

If you are using 16 bit colors with SPI (or other byte-oriented interface) probably you 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
Increase the size of the display buffer
Use 2 display buffers and flush the buffer with DMA (or similar periphery) 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 SPI port consider changing to a model with parallel because it has much higher throughput
Keep the display buffer in the internal RAM (not in external SRAM) because LVGL uses it a lot and it should have a small 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 you can add

-fdata-sections -ffunction-sections compiler flags
--gc-sections linker flag

to remove unused functions and variables from the final binary

How to reduce the RAM usage¶

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

How to work with an operating system?¶

To work with an operating system where tasks can interrupt each other (preemptive) you should protect LVGL related function calls with a mutex. See the Operating system and interrupts section to learn more.