Building flutter apps

1. Self-building

Use --target-backend-type option to select display backends. Default is Wayland.

Note:

• We do not expect to use x11 in embedded products, it is just for debugging on Linux desktops.
• In general, few devices support EGLStream (NVIDIA only?). Check it is supported or not before using it on your target devices.
  • See also: Tested devices
• gbm and eglstream will basically work but they are still development phase (have some issues).
  • See: sony/flutter-embedded-linux/issues for DRM

Build mode	Target backend	Command
release	wayland	flutter-elinux build elinux
	x11	flutter-elinux build elinux --target-backend-type=x11
	gbm	flutter-elinux build elinux --target-backend-type=gbm
	eglstream	flutter-elinux build elinux --target-backend-type=eglstream
debug	wayland	flutter-elinux build elinux --debug
	x11	flutter-elinux build elinux --debug --target-backend-type=x11
	gbm	flutter-elinux build elinux --debug --target-backend-type=gbm
	eglstream	flutter-elinux build elinux --debug --target-backend-type=eglstream
profile	wayland	flutter-elinux build elinux --profile
	x11	flutter-elinux build elinux --profile --target-backend-type=x11
	gbm	flutter-elinux build elinux --profile --target-backend-type=gbm
	eglstream	flutter-elinux build elinux --profile --target-backend-type=eglstream

2. Build artifacts

The artifacts will be put in your project under ./build/<target_arch>/<build_mode>/bundle. Alongside your executable binary in the bundle directory there are two directories:

• lib/ contains the required .so library files
• data/ contains the application’s data assets, such as fonts or images

Pre-built images

flutter-elinux download the Flutter engine artifacts such as libflutter_engine.so and libflutter_elinux_wayland.so to <flutter-elinux_install_path>/flutter/bin/cache/artifacts/engine directory automatically when you build your Flutter app. These .so files are download from sony/flutter-embedded-linux/releases built with a specific toolchain. Therefore, if you want to use your toolchain, you need to build it yourself.

For reference, the toolchain that the current .so files are built is below.

.so file	toolchain	sysroot	glibc
libflutter_engine.so	clang/llvm (Google Chromium)	Google Chromium	2.29
libflutter_elinux_*.so	clang/llvm (Ubuntu 18.04)	Ubuntu 18.04 for arm64	2.27

How to build libflutter_engine.so and libflutter_elinux_*.so

See the following links.

• libflutter_engine.so: Building Flutter Engine from source
• libflutter_elinux_wayland.so: Building Embedded Linux embedding for Flutter

3. Cross-building from x64 to arm64

Cross-building requires knowledge (Not easy, you might get build errors). You need to prepare your sysroot which is for cross-building for your target device by using --target-sysroot. Also, use --target-arch option to specify arm64 targets. Default is current host CPU architecture.

$ flutter-elinux build elinux --target-arch=arm64 --target-sysroot=<path_to_target's_sysroot>

Use cases

There are some ways to cross-build, and are some ways to create a sysroot like Yocto, buildroot, and so on.

1. Use Docker + QEMU
2. Use buildroot
3. Use Yocto SDK

Case 1: Use Docker + QEMU

Here, we show an example using a sysroot for arm64v8/ubuntu:18.04 docker image and a host's toolchain, but using sysroot and toolchain for your target device is better.

Install cross-build tools

$ sudo apt install gcc-aarch64-linux-gnu g++-aarch64-linux-gnu
$ sudo apt install libstdc++-8-dev-arm64-cross

Create sysroot for arm64

First, install Docker by following Install Docker Engine on Ubuntu.

S sudo apt install qemu-user-static

$ sudo docker run -it arm64v8/ubuntu:18.04

In docker:

apt update
apt install clang cmake build-essential \
            pkg-config libegl1-mesa-dev \
            libxkbcommon-dev libgles2-mesa-dev
apt install libwayland-dev wayland-protocols
apt install libdrm-dev libgbm-dev libinput-dev libudev-dev libsystemd-dev
exit

Copy sysroot from the container to host:

$ sudo docker ps -a
CONTAINER ID   IMAGE                 COMMAND   CREATED       STATUS                   PORTS     NAMES
f367a6b0316f   arm64v8/ubuntu:18.04  "bash"    4 hours ago   Exited (0) 4 hours ago   interesting_knuth
$ mkdir ubuntu18-arm64-sysroot
$ sudo docker cp f367a6b0316f:/ ubuntu18-arm64-sysroot

Build flutter apps

$ flutter-elinux build elinux --target-arch=arm64 \
     --target-sysroot=<Absolute_path_to>/ubuntu18-arm64-sysroot

Troubleshooting

If you get the following error, use --system-include-directories option.

/usr/bin/../lib/gcc-cross/aarch64-linux-gnu/9/../../../../include/c++/9/casse
rt:43:10: fatal error: 'bits/c++config.h' file not found
#include <bits/c++config.h>
         ^~~~~~~~~~~~~~~~~~

$ flutter-elinux build elinux --target-arch=arm64 \
     --target-sysroot=<Absolute_path_to>/ubuntu18-arm64-sysroot \
     --system-include-directories=/usr/aarch64-linux-gnu/include/c++/${version}/aarch64-linux-gnu