Embedded Linux embedding for Flutter

This project was created to develop non-official embedded Linux embeddings of Flutter. This embedder is focusing on embedded Linux system use cases. It is also implemented based on Flutter desktop for Windows and has some unique features to use it in embedded systems.

Objective & Goal

Our objective is to use Flutter in embedded systems. We're developing this embedder to use Flutter in embedded products. Ultimately we would like to propose and contribute this software to the mainline of Flutter Engine, which means we would like to add embedded systems support into Flutter officially for all embedded developers. Please note that this is just our ideal, not the official opinion of the Flutter community.

We would be grateful if you could give us feedback on bugs and new feature requests. We would like to cover specifications of general-purpose embedded systems.

Features

• Suitable for use in embedded systems
  • A few dependent libraries
  • Lightweight than Flutter desktop for Linux (Not using X11 and GTK)
  • The main target of this embedder is Arm64 devices. We haven't confirmed in Arm 32bit (ARMv7, armhf) devices
• Wayland backend support
• Direct rendering module (DRM) backend support
  • Generic Buffer Management (GBM)
  • EGLStream for NVIDIA devices (coming soon)
• Always single window fullscreen
  • You can choose always-fullscreen or flexible-screen (any size) only when you use Wayland backend
• Keyboard, mouse and touch inputs support
• Equivalent quality to Flutter desktops
• API compatibility with Flutter desktop for Windows and GLFW
  • APIs such as MethodChannel and EventChannel are completely the same with them

Supported platforms

This embedder supports x64 and Arm64 (aarch64, ARMv8) architectures on Linux which supports either Wayland backend or DRM backend.

Tested devices

Board/SoC	Vendor	OS	Display backend	Status
Desktop (x64)	Intel	Ubuntu18.04	Wayland	✔️
Desktop (x64)	Intel	Ubuntu18.04	DRM	✔️
Jetson Nano	NVIDIA	JetPack 4.3	Wayland	✔️
Jetson Nano	NVIDIA	JetPack 4.3	DRM	See: #1
Raspberry Pi 4 Model B	Raspberry Pi Foundation	Ubuntu 20.10	Wayland	✔️
Raspberry Pi 4 Model B	Raspberry Pi Foundation	Ubuntu 20.10	DRM	See: #9
i.MX 8MQuad EVK	NXP	Sumo (kernel 4.14.98)	Wayland	✔️
i.MX 8MQuad EVK	NXP	Sumo (kernel 4.14.98)	DRM	Not tested
i.MX 8M Mini EVKB	NXP	Sumo (kernel 4.14.98)	Wayland	✔️
i.MX 8M Mini EVKB	NXP	Sumo (kernel 4.14.98)	DRM	Not tested
Zynq	Xilinx	-	-	Not tested
RB5 Development Kit	Qualcomm	-	-	Not tested

Contributing

Now, we cannot accept any Pull Request (PR). Because We are building a system (e.g. CLA) to accept PRs, so please wait for a while the system is getting ready! However, we are always welcome to report bugs and request new features by creating issues.

With the assumption, our final goal of this software openly is to be merged this embedder into Flutter Engine after getting feedbacks. And Google CLA will be required when we do that in the future. Therefore, we cannot easily accept an external PR. However, you can free to create issues for reporting bugs and requesting new features.

See also: Contributing to the Flutter engine

Contents

1. Install libraries

You need to install the following dependent libraries to build and run. Here introduce how to install the libraries on Ubuntu OS and x64 hosts.

Mandatory

• clang (for building)
• cmake (for building)
• build-essential (for building)
• pkg-config (for building)
• EGL
• xkbcommon
• OpenGL ES (>=2.0)

$ sudo apt install clang build-essential pkg-config libegl1-mesa-dev libxkbcommon-dev libgles2-mesa-dev

Only when you use Wayland backend

• libwayland

$ sudo apt install libwayland-dev

Only when you use weston desktop-shell

• weston (>=6.0.1)

$ sudo apt install weston

Only when you use DRM backend

• libdrm
• libgbm
• libinput
• libudev
• libsystemd

$ sudo apt install libdrm-dev libgbm-dev libinput-dev libudev-dev libsystemd-dev

Install Flutter core embedder library

This embedder requres libflutter_engine.so (Flutter embedder library). You need to install libflutter_engine.so to /usr/lib. See: Building Flutter Engine embedder

Or you can download a specific Flutter Engine by the following steps, but it's limited to debug mode and x64 targets.

[Step1] Check the version (SHA) of the channel you want to use.

• master channel
• dev channel
• beta channel
• stable channel

[Step2] Download Flutter Engine embedder library. Note that replace FLUTTER_ENGINE with the SHA of the Flutter engine you want to use.

$ curl -O https://storage.googleapis.com/flutter_infra/flutter/FLUTTER_ENGINE/linux-x64/linux-x64-embedder

2. Examples

There are sample projects in examples directory. You can also comunicate with Dart code by using the plugin APIs with the same specifications as with Flutter desktops for Windows.

3. Building

Build for Wayland backend (Stand-alone Wayland app)

$ mkdir build
$ cd build
$ cmake -DUSER_PROJECT_PATH=examples/flutter-wayland-client ..
$ make

Build for DRM backend

$ mkdir build
$ cd build
$ cmake -DUSER_PROJECT_PATH=examples/flutter-drm-backend ..
$ make

Build for Wayland backend (weston desktop-shell)

This binary will run as a desktop-shell by setting weston.ini when Weston starts. See Settings of weston.ini file.

$ mkdir build
$ cd build
$ cmake -DUSER_PROJECT_PATH=examples/flutter-weston-desktop-shell ..
$ make

User configuration parameters (CMAKE options)

Please edit cmake/user_config.cmake file.

Option	Description
USE_DRM	Use DRM backend instead of Wayland
DESKTOP_SHELL	Work as weston desktop-shell
USE_VIRTUAL_KEYBOARD	Use Virtual Keyboard (only when you use DESKTOP_SHELL)
USE_GLES3	Use OpenGLES3 instead of OpenGLES2

4. Running your Flutter app

Install Flutter SDK

Please note that you must use the same version that you built Flutter embedder for. See also: Building Flutter Engine embedder

$ git clone https://github.com/flutter/flutter
$ sudo mv flutter /opt/
$ export PATH=$PATH:/opt/flutter/bin

Build your Flutter app

Here introduce how to build the flutter sample app.

for x64 targets on x64 hosts / for Arm64 targets on Arm64 hosts

$ flutter create sample
$ cd sample/
$ flutter build linux
$ cd ..

for Arm64 targets on x64 hosts

Comming soon. We are contributing to support this now. See: flutter/flutter#74929

Run Fluter app

Wayland compositor (weston) must be running before running the program when you use the Wayland backend.

$ ./flutter-client ./sample/build/linux/x64/release/bundle

Note

You need to run this program by a user who has the permission to access the input devices(/dev/input/xxx), if you use the DRM backend. Generally, it is a root user or a user who belongs to an input group.

5. Settings of weston.ini file (Only when you use weston desktop-shell)

Sets the following parameters when this embedder works as a desktop-shell on weston. Sample file can be found examples/config/weston.ini. See also man weston.ini.

shell section

Specifies the path to the binary file to start as the shell when weston starts.

Field	Description
client	${path to the binary}/flutter-desktop-shell

extended section

An extended section for this embedder. The entries that can appear in this section are:

Field	Description
show-cursor	Set whether to show mouse cursor (boolean)
flutter-project-path	Set an absolute path or relative path from the binary file to Flutter project path (string)