meta-flutter

Yocto Layer for Google Flutter related projects.

Discord Server https://discord.gg/cBkecwT65Q

Recommended development flow

• Create a flutter workspace using flutter_workspace.py
• Debug and validate application running on your host machine using ivi-homescreen, flutter-auto, AGL QEMU, or Linux GTK.
• Create Yocto Recipe for your Flutter application using one of the pre-existing recipes as your template.
• Add your apps recipe and your selected embedder to IMAGE_INSTALL in your conf/local.conf file.
• Image device

Supported Flutter Application types

• Flutter Application
• Flutter Web Application

Flutter Application recipe variables

Variable	Description
FLUTTER_APPLICATION_PATH	This is the path relative to the root of the repository. Override in your application recipe.
FLUTTER_PREBUILD_CMD	If set will run before Flutter build step.
PUB_CACHE_EXTRA_ARCHIVE_CMD	Command that is run prior to archive step of pub cache fetch. e.g. melos bootstrap.
PUB_CACHE_EXTRA_ARCHIVE_PATH	Appends a path to $PATH which affects PUB_CACHE_EXTRA_ARCHIVE_CMD
APP_AOT_EXTRA	Allows passing dart defines to AOT step. e.g. -DFLUTTER_APP_FLAVOR=prod.
APP_AOT_ENTRY_FILE	Allows overriding the entry file. Default is main.dart.
APP_GEN_SNAPSHOT_FLAGS	Additional flags to pass to gen_snapshot. Default is --obfuscate.
FLUTTER_APP_RUNTIME_MODES	Allows overriding modes that install app. Default is release.
FLUTTER_APPLICATION_INSTALL_PREFIX	Install prefix for flutter application install. Overriding enables installing into user directory. Default is ${datadir}/flutter.
FLUTTER_APPLICATION_INSTALL_SUFFIX	Install suffix for flutter application install. Default is "${PUBSPEC_APPNAME}".
PUBSPEC_IGNORE_LOCKFILE	Deletes pubspec.lock file if present. Used in case where lock file does not build.
APP_CONFIG	toml file to install into bundle folder. File will be installed as config.toml in the bundle root.

Supported Engine Variants

• debug
• profile
• release
• jit_release

Required Layers

• core
• meta-python
• openembedded-layer

Recommended Layers

• clang-layer

Dynamic Layers

• clang-layer

• gnome-layer

Zenity is used for fileselector plugin on ivi-homescreen. To enable this add meta-gnome to your layers.

Overview

Target BSP is expected to have a GPU with OpenGLES v2.0+ support.
If you are selecting a part go with v3.0+, ideally one with Vulkan support.

Notes

• There are no OSS Linux embedders (that I am aware of that currently support software rendering). The engine does support it.

• flutter-auto is the agl branch of https://github.com/toyota-connected/ivi-homescreen the main branch has moved to quarterly releases, the agl branch is directly supporting AGL development work.

General

Targets flutter-engine-* is known to work on

• AGL QEMU images - aarch64/x86_64
• Intel icore7-64
• NVIDIA Nano, Xavier Dev Kits - aarch64
• NXP iMX7, iMX8; imx-weston requires patch for ivi-homescreen + flutter-auto
• Qualcomm DragonBoard DB410c, DB820, SA6155P, SA8xxx - aarch64
• Raspberry Pi 3 / Compute - aarch64 / armv7hf
• Raspberry Pi 4 / Compute - aarch64
• Raspberry Pi ZeroW / Zero2W - aarch64
• Renesas R-Car M3/H3 - aarch64
• STM32MP157x - cortexa7t2hf
• etc

Include the Flutter SDK into Yocto SDK

Add to local.conf file:

TOOLCHAIN_HOST_TASK:append = " nativesdk-flutter-sdk"

Then run:

bitbake <image name> -c populate_sdk

Note: when using SDK you may need to add the following after installation:

$ export SDK_ROOT=<install folder>/sysroots/x86_64-nodistrosdk-linux/usr/share/flutter/sdk
$ git config --global --add safe.directory $SDK_ROOT

General Yocto Notes

• When building on systems with GCC version > than uninative in Yocto distro add the following to conf/local.conf

  INHERIT:remove = "uninative"

• The initial fetch with Flutter build will download over 14GB of source code. Running bitbake -C cleanall flutter-engine will clear the download cache. However, if an error occurs, the download cache remains intact, allowing you to resume the fetch later.

Flutter Workspace Automation

Please visit here.

Using Flutter SDK on target

Append this to your conf/local.conf

IMAGE_INSTALL:append = " packagegroup-flutter-sdk-deps"

You will also need to add dev packages to your platform that include libegl.so and libGLESv2.so. If the GPU driver for your platform is Mesa (such as Raspberry Pi 3/4/5), add these recipes to IMAGE_INSTALL in your conf/local.conf:

libegl-mesa-dev
libgles3-mesa-dev

From target terminal

cd ~
git clone https://github.com/flutter/flutter
cd flutter/bin
export PATH=$PATH:`pwd`
export GDK_GL=gles
flutter config --no-enable-android
flutter config --no-enable-web
flutter channel stable
flutter doctor -v

Test gallery app

cd ~
git clone https://github.com/flutter/gallery
cd gallery
flutter run -d linux

Process to Auto Roll Flutter Applications, Flutter SDK version, and Dart-SDK recipe

git clone https://github.com/meta-flutter/meta-flutter
cd meta-flutter

channel stable

tools/roll_meta_flutter.py

channel beta

tools/roll_meta_flutter.py --channel=beta

channel dev

tools/roll_meta_flutter.py --channel=dev

specific version

tools/roll_meta_flutter.py --version=2.40.0

conf/include/flutter-apps.json

This file is the origin of truth for all of the Flutter Applications present, and is used by tools/roll_meta_flutter.py.

roll_meta_flutter.py autogenerates all of the flutter application recipes.

Process used to update a Rust recipe

• Update recipe SRCREV to desired version, rename recipe name to match
• Run bitbake on the recipe, it will likely fail
• Open terminal to path of src
• delete Cargo.lock
• delete toolchain file if present
• add the toolchain version used in yocto to your path ahead of any others
• Manually build the crate using this toolchain. This will create a new Cargo.lock against the toolchain version. This is a critical step.
• Run root-pkg-ws --manifest-path=/Cargo.toml
• Copy the output from this tool to the recipe file
• Rebuild and confirm it passes
• Submit PR with updated recipe

If you need a more recent Rust toolchain for Kirkstone, you can use

https://git.yoctoproject.org/git/meta-lts-mixins

The takeaway should be that Cargo.lock and toolchain versions are tightly coupled in Yocto. If you don't follow this in theory you could set network enable for compile, and set the cargo bbclass to auto-vend. This would break all LTS scenarios.