📰
NEWS
- The new latest flutter gallery commit for flutter 2.2 is
633be8a - There's now a
#custom-embedderschannel on the flutter discord which you can use if you have any questions regarding flutter-pi or generally, anything related to embedding the engine for which you don't want to open issue about or write an email.
flutter-pi
A light-weight Flutter Engine Embedder for Raspberry Pi. Inspired by https://github.com/chinmaygarde/flutter_from_scratch. Flutter-pi also runs without X11, so you don't need to boot into Raspbian Desktop & have X11 and LXDE load up; just boot into the command-line.
You can now theoretically run every flutter app you want using flutter-pi, including apps using packages & plugins, just that you'd have to build the platform side of the plugins you'd like to use yourself.
The difference between packages and plugins is that packages don't include any native code, they are just pure Dart. Plugins (like the connectivity plugin) include platform-specific code.
🖥️
Supported Platforms
Although flutter-pi is only tested on a Rasberry Pi 4 2GB, it should work fine on other linux platforms, with the following conditions:
- support for hardware 3D acceleration. more precisely support for kernel-modesetting (KMS) and the direct rendering infrastructure (DRI)
- CPU architecture is one of ARMv7, ARMv8, x86 or x86 64bit.
This means flutter-pi won't work on a Pi Zero or Pi 1. A Pi 3 works fine, even the 512MB A+ model, and a Pi 2 should work fine too.
If you encounter issues running flutter-pi on any of the supported platforms listed above, please report them to me and I'll fix them.
📑
Contents
- Building flutter-pi on the Raspberry Pi
1.1 Dependencies
1.2 Compiling - Running your App on the Raspberry Pi
2.1 Configuring your Raspberry Pi
2.2 Building the Asset bundle
2.3 Building theapp.so(for running your app in Release/Profile mode)
2.4 Running your App with flutter-pi - Performance
3.1 Graphics Performance
3.2 Touchscreen latency
🛠
Building flutter-pi on the Raspberry Pi
- If you want to update flutter-pi, you check out the latest commit using
git pull && git checkout origin/masterand continue with compiling, step 2.
Dependencies
-
Install the flutter engine binaries using the instructions in the in the flutter-engine-binaries-for-arm repo..
More Info
flutter-pi needs flutters
flutter_embedder.hto compile andicudtl.datat runtime. It also needslibflutter_engine.so.releaseat runtime when invoked with the--releaseflag andlibflutter_engine.so.debugwhen invoked without. You actually have two options here:- you build the engine yourself. takes a lot of time, and it most probably won't work on the first try. But once you have it set up, you have unlimited freedom on which engine version you want to use. You can find some rough guidelines here.
- you can use the pre-built engine binaries I am providing in the flutter-engine-binaries-for-arm repo.. I will only provide binaries for some engine versions though (most likely the stable ones).
-
Install cmake, graphics, system libraries and fonts:
sudo apt install cmake libgl1-mesa-dev libgles2-mesa-dev libegl1-mesa-dev libdrm-dev libgbm-dev ttf-mscorefonts-installer fontconfig libsystemd-dev libinput-dev libudev-dev libxkbcommon-dev
More Info
- flutter-pi needs the mesa OpenGL ES and EGL implementation and libdrm & libgbm. It may work with non-mesa implementations too, but that's untested.
- The flutter engine depends on the Arial font. Since that doesn't come included with Raspbian, you need to install it.
libsystemdis not systemd, it's just an utility library. It provides the event loop and dbus support for flutter-pi.libinput-dev,libudev-devandlibxkbcommon-devare needed for (touch, mouse, raw keyboard and text) input support.libudev-devis required, but actual udev is not. Flutter-pi will just open alleventdevices inside/dev/input(unless overwritten using-i) if udev is not present.gpiodandlibgpiod-devwhere required in the past, but aren't anymore since theflutter_gpiodplugin will directly access the kernel interface.
-
Update the system fonts.
sudo fc-cache
Compiling
- Clone flutter-pi and cd into the cloned directory:
git clone https://github.com/ardera/flutter-pi cd flutter-pi - Compile:
mkdir build && cd build cmake .. make -j`nproc`
- Install:
sudo make install
🚀
Running your App on the Raspberry Pi
Configuring your Raspberry Pi
-
Open raspi-config:
sudo raspi-config
-
Switch to console mode:
System Options -> Boot / Auto Loginand selectConsoleorConsole (Autologin). -
Enable the V3D graphics driver
Advanced Options -> GL Driver -> GL (Fake KMS) -
Configure the GPU memory
Performance Options -> GPU Memoryand enter64. -
Leave
raspi-config. -
Give the
pipermission to use 3D acceleration. (NOTE: potential security hazard. If you don't want to do this, launchflutter-piusingsudoinstead.)usermod -a -G render pi
-
Finish and reboot.
More information
- flutter-pi requires that no other process, like a X11- or wayland-server, is using the video output. So to disable the desktop environment, we boot into console instead.
- The old broadcom-proprietary GL driver was bugged and not working with flutter, so we have to use the Fake KMS driver.
- Actually, you can also configure 16MB of GPU memory if you want to. 64MB are needed when you want to use the
omxplayer_video_playerplugin. piisn't allowed to directly access the GPU because IIRC this has some privilege escalation bugs. Raspberry Pi has quite a lot of system-critical, not graphics-related stuff running on the GPU. I read somewhere it's easily possible to gain control of the GPU by writing malicious shaders. From there you can gain control of the CPU and thus the linux kernel. So basically thepiuser could escalate privileges and becomerootjust by directly accessing the GPU. But maybe this has already been fixed, I'm not sure.
Building the Asset bundle
- The asset bundle must be built on your development machine. Note that you can't use a Raspberry Pi as your development machine.
-
Make sure you've installed the flutter SDK. You must use a flutter SDK that's compatible to the installed engine binaries.
- for the flutter SDK, use flutter stable and keep it up to date.
- always use the latest available engine binaries
If you encounter error messages like
Invalid kernel binary format version,Invalid SDK hashorInvalid engine hash:- Make sure your flutter SDK is on
stableand up to date and your engine binaries are up to date. - If you made sure that's the case and the error still happens, create a new issue.
-
Open terminal or commandline and
cdinto your app directory. -
flutter build bundle -
Deploy the asset bundle to the Raspberry Pi using
rsyncorscp.- Using
rsync(available on linux and macOS or on Windows when using WSL)rsync -a --info=progress2 ./build/flutter_assets/ pi@raspberrypi:/home/pi/my_apps_flutter_assets
- Using
scp(available on linux, macOS and Windows)scp -r ./build/flutter_assets/ pi@raspberrypi:/home/pi/my_apps_flutter_assets
- Using
Example
- We'll build the asset bundle for
flutter_galleryand deploy it usingrsyncin this example.
git clone https://github.com/flutter/gallery.git flutter_gallery
cd flutter_gallery
git checkout 633be8a
flutter build bundle
rsync -a ./build/flutter_assets/ pi@raspberrypi:/home/pi/flutter_gallery/
- Done. You can now run this app in debug-mode using
flutter-pi /home/pi/flutter_gallery.
More information
- flutter_gallery is developed against flutter master.
633be8aa13799bf1215d03a155132025f42c7d07is currently the latest flutter gallery commit working with flutter stable.
Building the app.so (for running your app in Release/Profile mode)
- This is done entirely on your development machine as well.
-
Find out the path to your flutter SDK. For me it's
C:\flutter. (I'm on Windows) -
Open terminal or commandline and
cdinto your app directory. -
Build the asset bundle.
flutter build bundle -
Build the kernel snapshot. (Replace
my_app_namewith the name of your app)C:\flutter\bin\cache\dart-sdk\bin\dart.exe ^ C:\flutter\bin\cache\dart-sdk\bin\snapshots\frontend_server.dart.snapshot ^ --sdk-root C:\flutter\bin\cache\artifacts\engine\common\flutter_patched_sdk_product ^ --target=flutter ^ --aot ^ --tfa ^ -Ddart.vm.product=true ^ --packages .packages ^ --output-dill build\kernel_snapshot.dill ^ --verbose ^ --depfile build\kernel_snapshot.d ^ package:my_app_name/main.dart
-
Fetch the latest
gen_snapshot_linux_x64_releaseI provide in the engine binaries repo. -
The following steps must be executed on a linux x64 machine. If you're on windows, you can use WSL. If you're on macOS, you can use a linux VM.
-
Build the
app.so. If you're building for arm64, you need to omit the--sim-use-hardfpflag.gen_snapshot_linux_x64_release \ --deterministic \ --snapshot_kind=app-aot-elf \ --elf=build/flutter_assets/app.so \ --strip \ --sim-use-hardfp \ build/kernel_snapshot.dill
-
Now you can switch to your normal OS again.
-
Upload the asset bundle and the
app.soto your Raspberry Pi.rsync -a --info=progress2 ./build/flutter_assets/ pi@raspberrypi:/home/pi/my_app
or
scp -r ./build/flutter_assets/ pi@raspberrypi:/home/pi/my_app -
You can now launch the app in release mode using
flutter-pi --release /home/pi/my_app
Complete example on Windows
- We'll build the asset bundle for
flutter_galleryand deploy it usingrsyncin this example.git clone https://github.com/flutter/gallery.git flutter_gallery git clone --depth 1 https://github.com/ardera/flutter-engine-binaries-for-arm.git engine-binaries cd flutter_gallery git checkout 633be8a flutter build bundle C:\flutter\bin\cache\dart-sdk\bin\dart.exe ^ C:\flutter\bin\cache\dart-sdk\bin\snapshots\frontend_server.dart.snapshot ^ --sdk-root C:\flutter\bin\cache\artifacts\engine\common\flutter_patched_sdk_product ^ --target=flutter ^ --aot ^ --tfa ^ -Ddart.vm.product=true ^ --packages .packages ^ --output-dill build\kernel_snapshot.dill ^ --verbose ^ --depfile build\kernel_snapshot.d ^ package:gallery/main.dart wsl ../engine-binaries/arm/gen_snapshot_linux_x64_release \ --deterministic \ --snapshot_kind=app-aot-elf \ --elf=build/flutter_assets/app.so \ --strip \ --sim-use-hardfp \ build/kernel_snapshot.dill rsync -a --info=progress2 ./build/flutter_assets/ pi@raspberrypi:/home/pi/flutter_gallery/ exit
- Done. You can now run this app in release mode using
flutter-pi --release /home/pi/flutter_gallery.
Running your App with flutter-pi
USAGE:
flutter-pi [options] <asset bundle path> [flutter engine options]
OPTIONS:
--release Run the app in release mode. The AOT snapshot
of the app ("app.so") must be located inside the
asset bundle directory.
This also requires a libflutter_engine.so that was
built with --runtime-mode=release.
-o, --orientation <orientation> Start the app in this orientation. Valid
for <orientation> are: portrait_up, landscape_left,
portrait_down, landscape_right.
For more information about this orientation, see
the flutter docs for the "DeviceOrientation"
enum.
Only one of the --orientation and --rotation
options can be specified.
-r, --rotation <degrees> Start the app with this rotation. This is just an
alternative, more intuitive way to specify the
startup orientation. The angle is in degrees and
clock-wise.
Valid values are 0, 90, 180 and 270.
-d, --dimensions "width_mm,height_mm" The width & height of your display in
millimeters. Useful if your GPU doesn't provide
valid physical dimensions for your display.
The physical dimensions of your display are used
to calculate the flutter device-pixel-ratio, which
in turn basically "scales" the UI.
-i, --input <glob pattern> Appends all files matching this glob pattern to the
list of input (touchscreen, mouse, touchpad,
keyboard) devices. Brace and tilde expansion is
enabled.
Every file that matches this pattern, but is not
a valid touchscreen / -pad, mouse or keyboard is
silently ignored.
If no -i options are given, flutter-pi will try to
use all input devices assigned to udev seat0.
If that fails, or udev is not installed, flutter-pi
will fallback to using all devices matching
"/dev/input/event*" as inputs.
In most cases, there's no need to specify this
option.
Note that you need to properly escape each glob
pattern you use as a parameter so it isn't
implicitly expanded by your shell.
-h, --help Show this help and exit.
EXAMPLES:
flutter-pi ~/hello_world_app
flutter-pi --release ~/hello_world_app
flutter-pi -o portrait_up ./my_app
flutter-pi -r 90 ./my_app
flutter-pi -d "155, 86" ./my_app
SEE ALSO:
Author: Hannes Winkler, a.k.a ardera
Source: https://github.com/ardera/flutter-pi
License: MIT
For instructions on how to build an asset bundle or an AOT snapshot
of your app, please see the linked git repository.
For a list of options you can pass to the flutter engine, look here:
https://github.com/flutter/engine/blob/master/shell/common/switches.h
<asset bundle path> is the path of the flutter asset bundle directory (i.e. the directory containing kernel_blob.bin) of the flutter app you're trying to run.
[flutter engine options...] will be passed as commandline arguments to the flutter engine. You can find a list of commandline options for the flutter engine Here.
📊
Performance
Graphics Performance
Graphics performance is actually pretty good. With most of the apps inside the flutter SDK -> examples -> catalog directory I get smooth 50-60fps on the Pi 4 2GB and Pi 3 A+.
Touchscreen Latency
Due to the way the touchscreen driver works in raspbian, there's some delta between an actual touch of the touchscreen and a touch event arriving at userspace. The touchscreen driver in the raspbian kernel actually just repeatedly polls some buffer shared with the firmware running on the VideoCore, and the videocore repeatedly polls the touchscreen. (both at 60Hz) So on average, there's a delay of 17ms (minimum 0ms, maximum 34ms). Actually, the firmware is polling correctly at ~60Hz, but the linux driver is not because there's a bug. The linux side actually polls at 25Hz, which makes touch applications look terrible. (When you drag something in a touch application, but the application only gets new touch data at 25Hz, it'll look like the application itself is redrawing at 25Hz, making it look very laggy) The github issue for this raspberry pi kernel bug is here. Leave a like on the issue if you'd like to see this fixed in the kernel.
This is why I created my own (userspace) touchscreen driver, for improved latency & polling rate. See this repo for details. The driver is very easy to use and the difference is noticeable, flutter apps look and feel a lot better with this driver.
Any idea how to understand what's going on?
Before 1.20 and the flutter-pi update it was ok. :(
![[Unclear documentation] libflutter_engine.so: cannot open shared object file: No such file or directory](https://avatars.githubusercontent.com/u/5578017?v=4)
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