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Merge pull request #14849 from s-hadinger/lv_berry_readme
Add README for lv_berry
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# LVGL + Berry
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This repo contains a full binding of LVGL to the Berry language. This project is similar to the Micropython+lvgl project in its spirit, and provides easy to use scripting for lvgl on embedded devices. It is used by the Tasmota open-source project for ESP32 based devices.
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**Supported version**: LVGL 8.2.0
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## Why use LVGL + Berry
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LVGL + Berry mapping provides an easy-to-use programming language on top of LVGL powerful APIs. This is ideal for rapid scripting as well as production applications. The Berry mapping comes from the open-source [Tasmota](https://tasmota.github.io/docs/) project for ESP32 based devices, and leverages a vivid ecosystem.
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Quickstart with this short tutorial [LVGL in less than 10 minutes with Tasmota](https://tasmota.github.io/docs/LVGL_in_10_minutes/).
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[Berry](https://github.com/berry-lang/berry) is an ultra-lightweight dynamically typed embedded scripting language. It is designed for lower-performance embedded devices. The interpreter of Berry includes a one-pass compiler and register-based VM, all the code is written in ANSI C99. Berry offers a syntax very similar to Python, and is inspired from LUA VM.
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## Quickstart
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Let's start with a simple example:
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```
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#- start LVGL and init environment (can be called multiple times) -#
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lv.start()
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hres = lv.get_hor_res() # horizontal resolution of default display
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vres = lv.get_ver_res() # vertical resolution of default display
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scr = lv.scr_act() # default screen object
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#- Background with a gradient from black #000000 (bottom) to dark blue #0000A0 (top) -#
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scr.set_style_bg_color(lv.color(0x0000A0), lv.PART_MAIN | lv.STATE_DEFAULT)
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scr.set_style_bg_grad_color(lv.color(0x000000), lv.PART_MAIN | lv.STATE_DEFAULT)
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scr.set_style_bg_grad_dir(lv.GRAD_DIR_VER, lv.PART_MAIN | lv.STATE_DEFAULT)
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```
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Let's add a label:
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```
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t = lv.label(scr)
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t.set_style_text_color(lv.color(0xFFFFFF), lv.PART_MAIN | lv.STATE_DEFAULT)
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t.set_text("Hello LVGL + Berry!")
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t.set_align(lv.ALIGN_TOP_MID)
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```
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Let's add a style for buttons:
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```
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#- create a style for the buttons -#
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btn_style = lv.style()
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btn_style.set_radius(10) # radius of rounded corners
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btn_style.set_bg_opa(lv.OPA_COVER) # 100% background opacity
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btn_style.set_bg_color(lv.color(0x1fa3ec)) # background color #1FA3EC (Tasmota Blue)
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btn_style.set_border_color(lv.color(0x0000FF)) # border color #0000FF
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btn_style.set_text_color(lv.color(0xFFFFFF)) # text color white #FFFFFF
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```
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Let's add a single button with using a symbol:
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```
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home_btn = lv.btn(scr) # center button
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home_btn.set_size(80, 30)
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home_btn.add_style(btn_style, lv.PART_MAIN | lv.STATE_DEFAULT)
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home_btn.set_align(lv.ALIGN_BOTTOM_MID)
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home_label = lv.label(home_btn)
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home_label.set_text(lv.SYMBOL_HOME) # set text as Home icon
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home_label.center()
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```
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Let's now add a colorwheel widget:
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```
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colw = lv.colorwheel(scr, false)
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colw.set_size(100, 100)
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colw.set_pos(20,30)
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```
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As a general rule:
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- calls to general APIs are mapped to module `lv`. E.g. `lv_get_hor_res()` translates to
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- enums are also mapped to module `lv`
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- widgets constructors are classes in module `lv`
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- calls to widgets are object methods (skip the first argument which is implicit)
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C call|Berry call
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:---|:---
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`lv_get_hor_res()`|`lv.get_hor_res()`
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`LV_ALIGN_BOTTOM_MID`|`lv.ALIGN_BOTTOM_MID`
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`lv_colorwheel_create(scr, false)`|`lv.colorwheel(scr, false)` or `lv.lv_colorwheel(scr, false)`
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`lv_obj_set_size(colw, 100, 100)`|`colw.set_size(100, 100)`
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## Supported features
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lv_berry provides an object-oriented interface for LVGL, and covers over 99% of LVGL's APIs, noticeably:
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- access to almost all LVGL APIs (over 1000+ calls)
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- automatic type checking and type conversion based on `C` headers
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- access to all `C` ENUMs constants (500+)
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- full support for C callbacks in Berry
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- full support for LVGL internal memory structures
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- ability to create pure Berry custom widgets and custom classes
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- supports only 16 bits display (swapped or not)
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What is currently not supported (but could be if there is demand):
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- multi-screen devices (no support in Tasmota anyways)
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- bidirectional text support
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- LVGL tasks (Berry has its own task system)
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- non-16 bits display
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## Type system
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### Widgets classes
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Although LVGL is C code and is not formally object oriented, LVGL widget follow an inheritance model. Each widget is a virtual subclass of `lv_obj` structure.
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Berry builds an actual Object Oriented class system, with a base class `lv_obj` and subclasses.
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The class names supported are defined in `convert.py` and are currently standard widgets:
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```
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'lv_arc', 'lv_bar', 'lv_btn', 'lv_btnmatrix', 'lv_canvas', 'lv_checkbox', 'lv_dropdown', 'lv_img', 'lv_label', 'lv_line', 'lv_roller', 'lv_slider', 'lv_switch', 'lv_table', 'lv_textarea'
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```
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And extra widgets:
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```
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'lv_chart', 'lv_colorwheel', 'lv_imgbtn', 'lv_led', 'lv_meter', 'lv_msgbox', 'lv_spinbox', 'lv_spinner'
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```
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Additional 'special' classes are (they do not inherit from `lv_obj`):
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```
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'lv_obj', 'lv_group', 'lv_style', 'lv_indev', 'lv_disp'
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```
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### Colors
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An exception for LVGL colors, they are defined as 32 bits RGB values as follows, and not based on their C representation:
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```C
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COLOR_WHITE=0xFFFFFF
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COLOR_SILVER=0xC0C0C0
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COLOR_GRAY=0x808080
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COLOR_BLACK=0x000000
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COLOR_RED=0xFF0000
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COLOR_MAROON=0x800000
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COLOR_YELLOW=0xFFFF00
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COLOR_OLIVE=0x808000
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COLOR_LIME=0x00FF00
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COLOR_GREEN=0x008000
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COLOR_CYAN=0x00FFFF
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COLOR_AQUA=0x00FFFF
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COLOR_TEAL=0x008080
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COLOR_BLUE=0x0000FF
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COLOR_NAVY=0x000080
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COLOR_MAGENTA=0xFF00FF
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COLOR_PURPLE=0x800080
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```
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Example: `lv.COLOR_RED`
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`lv_color` is a simple class that maps RGB 32 bits colors (as 32 bits int) to the internal representation of colors (usually 16 bits).
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Don't be surprised that getting back a value is the 16 bits color converted to 32 bits - rounding errors may occur:
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```
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[Berry Console]
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> c = lv_color(0x808080)
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> c
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lv_color(0xff838183 - native:0x1084)
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```
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Note:
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- 0xff838183 - is the 32 bits color, with alpha channel (opaque)
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- 0x1084 - is the native internal representation as 16 bits color with swapped bytes
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## Build system
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More details about the mapping are provided in [Tasmota LVGL Internals](https://tasmota.github.io/docs/LVGL_Internals/)
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`lv_berry` uses a semi-automated parsing of lvgl's `C` headers to generate the Berry mapping. The process is automated, but may require small parser adjustments with new versions.
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This module relies on [berry_mapping](https://github.com/berry-lang/berry_mapping) module to automate the mapping of C functions.
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**Phase 1: Parse LVGL source**
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This first phase parses most C headers from the LVGL source tree and generates two files:
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- `mapping/lv_enum.h` containing all the `enum` values from LVGL (constants)
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- `mapping/lv_funcs.h` containing all the functions of the LVGL API normalized to 1 function per line, and with cleaned argument signature.
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```
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(`cd` in folder tools)
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❯ python3 preprocessor.py
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(no output)
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```
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**Phase 2: Generate automatic Berry mapping**
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From the two files created in the previous step, all the requires C files are created for the Berry mapping.
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```
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(`cd`in folder tools)
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> python3 convert.py
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| callback types['lv_group_focus_cb', 'lv_event_cb', 'lv_constructor_cb', 'lv_layout_update_cb', 'lv_obj_tree_walk_cb', 'lv_theme_apply_cb', 'lv_color_filter_cb', 'lv_anim_path_cb']
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```
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The output should look as above, and indicates the C function that have been ignored (if any) if their return type is listed above. It also lists the callback types supported.
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**Phase 3: Generate the Berry pre-compiled stubs**
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This phase is specific to Berry pre-compiled modules and classes.
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```
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(berry)
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> python3 tools/pycoc/main.py -o generate src default ../berry_mapping/src ../lv_berry/src ../lv_berry/generate -c default/berry_conf.h
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(no output)
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```
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**Phase 4: compile Tasmota using platform.io as usual**
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## Future projects
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There is an on-going project to provide [OpenHASP](https://openhasp.haswitchplate.com/) emulation using LVGL+Berry. This will provide a super-easy to use JSON graphical description of UI interfaces, with no or very low knowledge of LVGL APIs.
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Stay tuned!
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@ -1,7 +1,7 @@
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{
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"name": "Berry mapping to LVGL",
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"version": "1.0",
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"description": "Mapping of LVGL functions to Berry. Currently supporting LVGL 8.0.2",
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"description": "Mapping of LVGL functions to Berry. Currently supporting LVGL 8.2.0",
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"license": "MIT",
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"homepage": "https://github.com/lvgl/lv_berry",
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"frameworks": "arduino",
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