Building flutter apps
Use --target-backend-type option to select display backends. Default is Wayland.
- We do not expect to use
x11in embedded products, it is just for debugging and development on Linux desktop PCs. - 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
-
gbmandeglstreamwill basically work but they are still development phase (have some issues).
| 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 |
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
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 |
See the following links.
- libflutter_engine.so: Building Flutter Engine from source
- libflutter_elinux_wayland.so: Building Embedded Linux embedding for Flutter
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, you can use the following options.
| build command options | description | default |
|---|---|---|
| --target-arch | specify arm64 targets | current host CPU architecture (self builds) |
| --target-toolchain | specify custom toolchain path | null ('/') |
$ flutter-elinux build elinux --target-arch=arm64 --target-sysroot=<path_to_target's_sysroot>There are some ways to cross-build, and are some ways to create a sysroot like Yocto, buildroot, and so on.
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.
$ sudo apt install gcc-aarch64-linux-gnu g++-aarch64-linux-gnu
$ sudo apt install libstdc++-8-dev-arm64-crossFirst, install Docker by following Install Docker Engine on Ubuntu.
S sudo apt install qemu-user-staticNote that you have to choose a docker image/OS version that matches your target machine. Here, we will use Ubuntu 18.04 as an example.
$ sudo docker run -it arm64v8/ubuntu:18.04In 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
exitCopy 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$ flutter-elinux build elinux \
--target-arch=arm64 \
--target-compiler-triple=aarch64-linux-gnu \
--target-sysroot=<Absolute_path_to>/ubuntu18-arm64-sysrootIf 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-gnuSee: Cross-building using Yocto SDK
$ source /opt/poky/3.1.15/environment-setup-aarch64-poky-linux
$ export CC=${CLANGCC}
$ export CXX=${CLANGCXX}See: https://github.com/sony/flutter-embedded-linux/issues/4#issuecomment-1090157925
$ sudo mv /opt/poky/3.1.16/sysroots/x86_64-pokysdk-linux/usr/bin/ld \
/opt/poky/3.1.16/sysroots/x86_64-pokysdk-linux/usr/bin/ld.x86_64
$ sudo cp -a /opt/poky/3.1.16/sysroots/x86_64-pokysdk-linux/usr/bin/aarch64-poky-linux/aarch64-poky-linux-ld \
/opt/poky/3.1.16/sysroots/x86_64-pokysdk-linux/usr/bin/ldUse target-compiler-triple option to set CMAKE_C_COMPILER_TARGET and CMAKE_CXX_COMPILER_TARGET in the toolchain cmake configuration file make it use the right compiler path and filename.
$ flutter-elinux build elinux --target-arch=arm64 \
--target-compiler-triple=aarch64-poky-linux \
--target-sysroot=/opt/poky/3.1.16/sysroots/aarch64-poky-linuxAs Buildroot doesn't come with clang tool, you should install it yourself. In the command below, clang will use aarch64-buildroot-linux-gnu-ld, which comes with your buildroot, as the linker.
sudo apt install clang
sudo apt install wayland-protocols libwayland-bin # host tools needed to build wayland backend
export PATH=$PATH:~/buildroot/output/host/bin # add aarch64-buildroot-linux-gnu-ld to PATH
~/flutter-elinux/bin/flutter-elinux build elinux --target-arch=arm64 \
--target-compiler-triple=aarch64-buildroot-linux-gnu \
--target-sysroot=~/buildroot/output/staging \
--target-compiler-flags=--gcc-toolchain=~/buildroot/output/host