Glossary

LVGL and display jargon, in one place.

The terms used across these pages and in LVGL's own documentation, in one place. Where a term has its own page, the link is there.

Alignment anchor: One of the seventeen LV_ALIGN_* positions on a parent that a widget's X and Y offsets are measured from.
Automation: An event raised by hardware or time - startup, interval, digital edge, held input, analog threshold, variable change - with a list of actions.
Backlight: The LED behind an LCD, driven by a GPIO, optionally with PWM. An AMOLED has none.
BGR: Blue-green-red pixel order. If red and blue are swapped on the panel, switch the colour order.
Binding: A link between a variable (or another control) and one property of a widget. May run one way or both.
Board preset: A known-good hardware description - MCU, panel, bus, pins, touch, library - for a specific product, with a verify note.
Bus: A set of shared lines devices talk over: SPI, QSPI, 8- or 16-bit parallel, RGB, MIPI-DSI, I2C.
Capacitive touch: A touch panel read over I2C that senses a finger's capacitance. Precise, multi-touch, no calibration. GT911, FT6236, CST816S and the like.
C array: An image compiled into the firmware as a constant byte array, rather than a file on the filesystem.
Channel: One named reading (or writable value) on a peripheral: the BME280's Temperature, the ADS1115's Channel 0.
Clone: Taking an editable copy of a gallery design.
Colour depth: Bits per pixel the panel and LVGL work in - 16 for RGB565, the norm on these boards.
Constant: A variable source that holds a fixed value every refresh: a setpoint or a threshold.
Credit: One purchased generation, spent after the free allowance.
DC / RS: The data/command line on a serial or parallel panel bus, telling the controller whether a byte is a command or pixel data.
Draw buffer: The RAM LVGL renders into before flushing to the panel, sized in lines. Partial rendering means it is a fraction of the screen.
esp_lcd: Espressif's own panel driver component, bundled with the ESP32 Arduino core. Lowest overhead; ESP32 family only; the only backend for MIPI-DSI.
Event: A trigger on a widget and its list of actions.
Fade mode: The animation used when changing screen: over, move, fade, out, in a direction.
FFat: The FAT filesystem on ESP32 flash.
Flag: An LV_OBJ_FLAG_* switch on an object: Hidden, Clickable, Scrollable, Checkable and so on.
Flex: LVGL's flexbox-style layout for a container's children.
Flush: Copying a rendered draw buffer to the panel. The generated sketch's disp_flush().
Formula: An expression over raw and other variables, parsed by the designer and compiled to C.
FQBN: Fully qualified board name, the identifier the Arduino CLI uses: esp32:esp32:esp32s3.
Generation: One build of a project's source on the server. The metered unit.
GFX Library for Arduino: Moshi Liu's display library, with the widest QSPI, AMOLED and RGB coverage. Configured in code.
Graphics library: The library between LVGL and the panel: TFT_eSPI, LovyanGFX, GFX Library for Arduino or esp_lcd.
Guest: A visitor using the designer without an account, metered by a cookie and their address.
Hysteresis: The dead band around a threshold that stops a trigger firing repeatedly as a value hovers.
I/O extender: A port expander - PCF8574, PCF8575, MCP23017, MCP23S17 - adding digital pins over I2C or SPI.
I2C: A two-wire bus (SDA, SCL) with addressed devices. Most sensors and capacitive touch controllers.
Indev: LVGL's input device: a touch panel, an encoder, a keypad or a button pad.
Input-only pin: A GPIO that cannot be an output - 34 to 39 on the ESP32.
Inspector: The right-hand panel editing the selected widget or, with nothing selected, the screen and project.
L8: An 8-bit greyscale image format.
LEDC: The ESP32 PWM peripheral used for backlight dimming.
LittleFS: A wear-levelled flash filesystem; the better default for assets on a new project.
LovyanGFX: A display library with wide panel and bus coverage and DMA on ESP32, configured through a C++ device class.
LTDC: The LCD-TFT display controller on STM32F7/H7 that drives RGB panels directly.
lv_conf.h: LVGL's configuration header. The generated one enables only the fonts and widgets the design uses.
LVGL: Light and Versatile Graphics Library, the embedded GUI library everything here targets. Versions 8.3 and 9.
MIPI-DSI: A high-speed serial display interface; on these boards, ESP32-P4 only.
Montserrat: The font bundled with LVGL, available in sizes 8 to 48.
Part: A styleable component of a widget: Main, Indicator, Knob, Scrollbar, Items, Selected, Ticks, Cursor, Placeholder, Arc.
Partial rendering: Drawing the screen in horizontal strips the size of the draw buffer. What lets LVGL run on a chip without a framebuffer's worth of RAM.
Partition scheme: How an ESP32's flash is divided between the app, OTA and the filesystem. Huge APP gives LVGL builds room.
Peripheral: A sensor or output device on a bus, with named channels and configuration.
Poll interval: How often the firmware reads a device or input, set per device.
PSRAM: External RAM on some ESP32 modules. Required for RGB panels; optional home for draw buffers.
Push onto chart: The binding property that appends a variable's value to a chart series each refresh.
QSPI: Quad SPI, four data lines - used by AMOLED and some round panels.
Resistive touch: A touch panel read as an analog voltage divider, usually over SPI (XPT2046). Needs calibration, works with a stylus or glove.
RGB565: Sixteen bits per pixel, 5 red, 6 green, 5 blue. The native format of these panels.
RGB565A8: RGB565 plus an 8-bit alpha channel - transparency without going to 32 bits.
RGB panel: A display driven pixel by pixel over parallel RGB lines with sync signals, needing a framebuffer in PSRAM. Sunton and Waveshare 4.3" and 7" boards.
Rolling window: What a chart keeps: the last N points, or a span of time.
Screen: A top-level LVGL object the size of the panel. A project has one or more.
Series: One line, bar set or point set on a chart, with its own colour and axis.
Setpoint: A target value, typically a constant variable bound both ways to a control.
Share: A published gallery entry - a frozen copy of a project with its previews and hardware summary.
Smoothing: An exponential filter on an analog input, 0 (raw) to 1.
SPI: A four-wire serial bus (SCK, MOSI, MISO, CS). Most small panels, resistive touch, thermocouple amplifiers.
SPIFFS: The older ESP32 flash filesystem, still the Arduino core default.
State: A condition an object can be in for styling: Default, Pressed, Checked, Focused, Edited, Disabled.
Strapping pin: A GPIO sampled at reset to choose the boot mode. Usable, but a level held on it at boot can stop the chip starting.
TFT_eSPI: Bodmer's display library, fastest for SPI panels on ESP32, configured by User_Setup.h defines.
Theme: LVGL's default look, initialised with a primary colour, a secondary colour, light or dark, and a font.
Trigger: What fires an event or automation: Clicked, Value changed, every interval, and so on.
Two-way binding: A binding that both shows a variable and writes it when the widget is operated.
ui_events.c: The one generated file that is yours: stubs for Call function actions, never overwritten once edited.
Variable: A named Float, Integer or Boolean the firmware holds, refreshed from a source through a formula.
Verify note: The one-line warning on every board preset saying what to check against your revision.
Widget: An LVGL object on a screen: a button, a slider, a chart.
Z-order: Which widgets draw on top of which; later siblings are on top.