Add README.md

Author: swift-kim

README.md

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+# embedder
+
+[![Build](https://github.com/flutter-tizen/embedder/workflows/Build/badge.svg)](https://github.com/flutter-tizen/embedder/actions)
+
+The Flutter embedder for Tizen.
+
+## Build
+
+### Prerequisites
+
+- Linux (x64)
+- [depot_tools](https://commondatastorage.googleapis.com/chrome-infra-docs/flat/depot_tools/docs/html/depot_tools_tutorial.html#_setting_up)
+- [LLVM](https://apt.llvm.org) (10 or later)
+  - `sudo apt install clang-12`
+- Additional dependencies
+  - `sudo apt install git python3 python3-pip rpm2cpio cpio`
+  - `sudo apt install binutils-arm-linux-gnueabi binutils-aarch64-linux-gnu binutils-i686-linux-gnu`
+  - `pip3 install requests`
+
+### Environment setup
+
+1. Create an empty directory called `embedder` and `cd` into it.
+
+1. Create a `.gclient` file by running:
+
+   ```sh
+   gclient config --name=src --unmanaged https://github.com/flutter-tizen/embedder
+   ```
+
+1. Run `gclient sync` to fetch all the source code and dependencies.
+
+   Note: `gclient sync` must be run every time the `DEPS` file (or the `generate_sysroot.py` script) is updated.
+
+### Compile
+
+`cd` into the generated `src` directory and run the following commands.
+
+Note: The toolchain path (`/usr/lib/llvm-12`) can be replaced as you want. For example, you can use `~/tizen-studio/tools/llvm-10` if you have [Tizen Studio](https://developer.tizen.org/development/tizen-studio/download) and the `NativeToolchain-Gcc-9.2` package installed.
+
+- **For arm**
+
+  ```sh
+  tools/gn --target-cpu arm --target-toolchain /usr/lib/llvm-12
+  ninja -C out/tizen_arm
+  ```
+
+- **For arm64**
+
+  ```sh
+  tools/gn --target-cpu arm64 --target-toolchain /usr/lib/llvm-12
+  ninja -C out/tizen_arm64
+  ```
+
+- **For x86**
+
+  ```sh
+  tools/gn --target-cpu x86 --target-toolchain /usr/lib/llvm-12
+  ninja -C out/tizen_x86
+  ```
+
+### Notes
+
+- To build an app (TPK) with the embedder generated in the above, copy the output artifacts (`libflutter_tizen*.so`) into the [flutter-tizen](https://github.com/flutter-tizen/flutter-tizen) tool's cached artifacts directory (`flutter/bin/cache/artifacts/engine`) and run `flutter-tizen run` or `flutter-tizen build tpk`.
+- To use the target device's `libstdc++.so` instead of the embedder's built-in libc++ (`third_party/libcxx`), provide the `--system-cxx` option to `tools/gn`. Tizen 5.5's `libstdc++.so` is not compatible with C++17 so you must use a sysroot for Tizen 6.0 or above.
+- Building NUI-related code requires a sysroot for Tizen 6.5 or above and the `--api-version 6.5` option.
+
+## Repository structure
+
+This repository contains the following files and directories.
+
+- `//build`
+  - `config`: Contains GN configs for setting up the build environment for the toolchain.
+  - `secondary`: The secondary source tree to find input files for build. See the `.gn` file for details.
+- `//flutter`
+  - `fml`: A subset of the Flutter engine's [fml](https://github.com/flutter/engine/tree/main/fml) library.
+  - `shell/platform/common`: Contains C++ client wrapper and other common code used by the embedder implementation. Copied from [flutter/engine](https://github.com/flutter/engine/tree/main/shell/platform/common).
+  - `shell/platform/embedder`: Contains `embedder.h` which defines a low-level API for interacting with the Flutter engine. Copied from [flutter/engine](https://github.com/flutter/engine/tree/main/shell/platform/embedder).
+  - `shell/platform/tizen`: The Tizen embedder implementation.
+    - `channels`: Internal plugins based on platform channels.
+    - `public`: The public API of the embedder.
+  - `third_party/accessibility`: A fork of the chromium accessibility library. Copied from [flutter/engine](https://github.com/flutter/engine/tree/main/third_party/accessibility).
+- `//tools`
+  - `check_symbols.py`: A script to check whether the build artifacts contain symbols not defined in the allowlist. Used by continuous integration.
+  - `download_engine.py`: A script to download engine artifacts required for linking. Executed as a hook by `gclient sync`. The downloaded artifacts can be found in `//engine`.
+  - `generate_sysroot.py`: A script to generate Tizen sysroots for arm/arm64/x86. Executed as a hook by `gclient sync`. The sysroots are by default generated in `//sysroot`.
+  - `gn`: A script to automate running `gn gen`.
+- `.gn`: The top-level `.gn` file referenced by `gn`.
+- `DEPS`: The DEPS file used by `gclient sync` to install dependencies and execute hooks.