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Example of native interface between EEZ Studio and LVGL when EEZ Flow is used

User actions

In LVGL project with EEZ Flow you can define user actions that can be attached to the event handlers. You are doing this in 4 steps:

  • Step 1: Add user actions

    Go to User Actions tab, press + button, enter the name of user action and press OK:

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  • Step 2: Set the "Implementation type" property of user action to "Native"

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    Note: You can still provide flow implementation of native function. This implemenentation will be used when running project inside EEZ Studio with the Run button.

  • Step 3: Create event handler and attach it to the user action

    Select widget, for example Button, and in properties find Events section and press + button:

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    Now, select event and user action and press OK:

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  • Step 4: Implement user action in C or C++

    You need to implement in C or C++ a function called void action_<user action name>(lv_event_t * e). For example, if user action is called inc_counter you need to implement void action_inc_counter(lv_event_t * e);. Declaration of all user actions can be found in generated file actions.h. You can implement user actions in any existing C or C++ file (or even INO file if you are on Arduino) or you can add actions.cpp file template in your project like this:

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Variables

In LVGL project with EEZ Flow you can define native global variables with the get/set functions that you must implement in C++. You are doing this in 3 steps:

  • Step 1: Add global variable

    Go to Variables tab, select Global, press + button, enter the name and type of variable and press OK:

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  • Step 2: Use variable inside widget

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  • Step 3: Implement get and set functions in C++

    You need to implement in C++, for each variable, functions called <variable type> get_var_<variable name>() and void set_var_<variable name>(<variable_type> value). For example, if variable is called selected_item and type is integer you need to implement int32_t get_var_selected_item(); and void set_var_selected_item(int32_t value). Function declarations for all variables can be found in generated file vars.h. You can implement these functions in any C++ file or you can add vars.cpp file template in your project like this:

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Accessing flow variables from the native code

Chech the vars.cpp file to see how can you set flow variable value from native code (check function init_vars from vars.cpp), or how can you get flow variable value from natiave code (check function get_var_greeting_str from vars.cpp).

How to build project

Install SDL

Downlad SDL (a graphics library to open a window and handle the mouse). On Linux:

  1. Find the current version of SDL2: apt-cache search libsdl2 (e.g. libsdl2-2.0-0)
  2. Install SDL2: sudo apt-get install libsdl2-2.0-0 (replace with the found version)
  3. Install SDL2 development package: sudo apt-get install libsdl2-dev
  4. If build essentials are not installed yet: sudo apt-get install build-essential

Install Emscripten SDK

Download the Emscripten SDK and make sure it is in your PATH.

  1. git clone https://github.com/emscripten-core/emsdk.git
  2. cd <path-to-emsdk>
  3. git pull
  4. ./emsdk install latest
  5. ./emsdk activate latest
  6. source ./emsdk_env.sh

More info here: https://kripken.github.io/emscripten-site/docs/getting_started/downloads.html

Build the project

  1. cd C:\work\eez\native-interface-lvgl-no-flow
  2. mkdir build
  3. cd build
  4. emcmake cmake ..
  5. emmake make -j4
  6. A file called index.html will be generated. Run this in your browser.