README.md

flutter-embedder.git
=======================================

The Flutter Embedder for Fuchsia is a new in-progress runtime for Flutter apps
on Fuchsia. This runtime is built on top of Flutter's
[embedder platform](https://github.com/flutter/flutter/wiki/Custom-Flutter-Engine-Embedders).

This repository is a work in progress and should be considered
experimental.

## Requirements

If you're using WSL2 (Windows Subsystem for Linux), see
[SETUP_WINDOWS.md](https://fuchsia.googlesource.com/flutter-embedder/+/refs/heads/main/SETUP_WINDOWS.md)
first.

1. Set `$FUCHSIA_EMBEDDER_DIR` to your flutter-embedder.git checkout location,
   for example `~/flutter-embedder`.

   ```sh
   export FUCHSIA_EMBEDDER_DIR=$HOME/flutter-embedder
   ```

2. Bootstrap the repository's dependencies:

   ```sh
   $FUCHSIA_EMBEDDER_DIR/scripts/bootstrap.sh
   ```

   This script initializes tools (including `bazel` and `ffx`), installs some Git
   hooks and downloads the `workstation_eng.qemu-x64` product bundle, which you can
   use to run the examples below.

## Run an example app

1. Start the emulator.

   If running in a graphical environment:

   ```sh
   $FUCHSIA_EMBEDDER_DIR/tools/ffx emu start workstation_eng.qemu-x64
   ```

   If running in a terminal environment:

   ```sh
   $FUCHSIA_EMBEDDER_DIR/tools/ffx emu start --headless workstation_eng.qemu-x64
   ```

2. Set the default target in ffx to be `fuchsia-emulator`:

   ```sh
   $FUCHSIA_EMBEDDER_DIR/tools/ffx target default set fuchsia-emulator
   ```

3. (optional) Watch the device log in a separate window:

   ```sh
   $FUCHSIA_EMBEDDER_DIR/tools/ffx log
   ```

4. Run an example app:

   ```sh
   $FUCHSIA_EMBEDDER_DIR/scripts/build_and_run_example.sh hello_flutter
   ```

**TODO(akbiggs): The app occasionally gets stuck on a loading screen
instead of rendering. Re-running the app usually fixes it. We need to
fix this.**

## Syncing engine artifacts

Occasionally you will need to update the Flutter Engine artifacts (`embedder.h` and
`libengine_flutter.so`) that are used by the embedder to run Flutter apps. A script
is provided for this workflow.

### Requirements

1. You will
   [need to get the Flutter Engine source code](https://github.com/flutter/flutter/wiki/Setting-up-the-Engine-development-environment).
   **Note that this is not just cloning https://github.com/flutter/engine.**

2. Set `$ENGINE_DIR` to the `src` folder of your Flutter Engine checkout location,
   for example `~/engine/src`.

3. `$DEPOT_TOOLS` should be set to your
    [`depot_tools`](https://commondatastorage.googleapis.com/chrome-infra-docs/flat/depot_tools/docs/html/depot_tools_tutorial.html#_setting_up)
    location, for example `~/depot_tools`.

4. For `sync_engine_artifacts_to_revision.sh`, you will need to `git stash` or `git commit` any local
   changes to the Flutter Engine. This is not necesssary for `build_and_copy_engine_artifacts.sh`.

### Running the script

You can run the script with a `flutter/engine` Git commit to sync the Engine artifacts to
that revision.

```sh
$FUCHSIA_EMBEDDER_DIR/scripts/sync_engine_artifacts_to_revision.sh <ENGINE_COMMIT_SHA>
```

A common workflow is to sync your Engine commit to the Flutter tool in this repository,
for example when updating the Flutter tool to a new version. To do this:

```sh
$FUCHSIA_EMBEDDER_DIR/scripts/sync_engine_artifacts_to_revision.sh $(cat $FUCHSIA_EMBEDDER_DIR/third_party/dart-pkg/internal/flutter/flutter/bin/internal/engine.version)
```

If you want to test local changes to the Engine, you can run `build_and_copy_engine_artifacts.sh`
instead, which simply builds and copies your Engine into `$FUCHSIA_EMBEDDER_DIR`.

```sh
$FUCHSIA_EMBEDDER_DIR/scripts/build_and_copy_engine_artifacts.sh
```

## Uploading changes for review

flutter-embedder reviews are handled using Gerrit at https://fuchsia-review.googlesource.com, which uses a single commit per
code review. See
[this guide](https://fuchsia.dev/fuchsia-src/development/source_code/contribute_changes)
for an intro to Gerrit.

An alternative Gerrit workflow is a branchless workflow where you do all your work
from `origin/main` without creating new branches. We describe such a workflow below,
but it's not mandatory, it's just provided as an example.

An example branchless workflow for creating a new change is:

```sh
# Start work from an up-to-date main branch.
git fetch origin
git checkout origin/main
# Modify some files...
...
# Stage and commit your changes.
git add file1.cc file2.h
git commit -m "[embedder] My cool new feature."
# Upload for review.
git push origin HEAD:refs/for/main
```

An example branchless workflow to apply feedback during a code review is:

1. Visit https://fuchsia-review.googlesource.com and find your change.
2. Select `... > Download patch > Checkout` and copy the command.
3. Run the following commands:

   ```sh
   # Start from main with your change on top.
   <paste the command you copied above>
   # Make some changes to some files to apply the feedback...
   ...
   # Stage and amend your changes to your commit.
   git add file1.cc file2.h
   git commit --amend
   # Upload your updated change for review.
   git push origin HEAD:refs/for/main
   ```

An example branchless workflow to create a chain of changes is:

```sh
# Start work from an up-to-date main branch.
git fetch origin
git checkout origin/main
# Modify some files...
...
# Stage and commit your changes.
git add file1.cc file2.h
git commit -m "[embedder] My cool new feature 1."
# Upload for review.
git push origin HEAD:refs/for/main
# Do some more work on top of your cool new feature.
git add file3.cc file4.h
git commit -m "[embedder] My cool new feature 2."
# Create a second code review for your second feature.
# The second code review will only show changes for
# your second feature and it will indicate that it is based on
# top of the first feature.
git push origin HEAD:refs/for/main
```

A branchless workflow comes with some benefits:

1. It reduces the amount of local branches you have to track.
2. It reduces the amount of local branches you have to clean up after submission.
3. It reduces the amount of overhead to starting new work (just `git checkout origin/main`).

However a branchless workflow also prevents you from storing multiple
chains of commits locally. Uploading your changes to https://fuchsia-review.googlesource.com
frequently can help address that problem, as https://fuchsia-review.googlesource.com then
acts as the storage for each of your ongoing changes. This also keeps your changes in a
state where they're easy to share and hand off to other people.