Set up your environment - Windows

These instructions explain how Windows users can set up their Cobalt development environment, clone a copy of the Cobalt code repository, and build a Cobalt binary. Note that the binary has a graphical client and must be run locally on the machine that you are using to view the client. For example, you cannot SSH into another machine and run the binary on that machine.

Set up your workstation

  1. Install the following required packages:

    • git (see the Installing on Windows instructions)
    • ninja (see the Getting Ninja instructions)
    • nodejs
    • python3
    • The following VS2022 components:
      • Microsoft.VisualStudio.Component.VC.
      • Microsoft.VisualStudio.Component.VC.Llvm.Clang
      • Microsoft.VisualStudio.Component.VC.Llvm.ClangToolset
      • Microsoft.VisualStudio.Component.Windows10SDK.18362
      • Microsoft.VisualStudio.Workload.NativeDesktop
    • winflexbison
  2. Install GN, which we use for our build system code. There are a few ways to get the binary, follow the instructions for whichever way you prefer here.

  3. (Optional) Install Sccache to support build acceleration.

  4. Make sure all of the above installed packages are on your Path environment variable.

    "C:\Program Files\Git"
    "C:\Program Files\Ninja"
    "C:\Program Files\nodejs"
    "C:\python_38" # Python 3.8 is the oldest supported python version. You may have a newer version installed.
    "C:\winflexbison" # Or wherever you chose to unpack the zip file
  5. Clone the Cobalt code repository. The following git command creates a cobalt directory that contains the repository:

    $ git clone
  6. Set the PYTHONPATH environment variable to include the full path to the top-level cobalt directory from the previous step.

Set up Developer Tools

  1. Enter your new cobalt directory:

    $ cd cobalt
  2. Create a virtual evnrionment by running the following in cmd:

    py -3 -m venv "%HOME%/.virtualenvs/cobalt_dev"
    pip install -r requirements.txt

    Or the following in Powershell:

    py -3 -m venv $env:HOME/.virtualenvs/cobalt_dev
    pip install -r requirements.txt

    Or the following in Git Bash:

    py -3 -m venv ~/.virtualenvs/cobalt_dev
    source ~/.virtualenvs/cobalt_dev/Scripts/activate
    pip install -r requirements.txt
  3. Install the pre-commit hooks:

    $ pre-commit install -t post-checkout -t pre-commit -t pre-push --allow-missing-config
    $ git checkout -b <my-branch-name> origin/main

Build and Run Cobalt

  1. Build the code running the following command in the top-level cobalt directory. You must specify a platform when running this command. On Windows the canonical platform is win-win32.

    You can also use the -c command-line flag to specify a build_type. Valid build types are debug, devel, qa, and gold. If you specify a build type, the command finishes sooner. Otherwise, all types are built.

    $ python cobalt/build/ [-c <build_type>] -p <platform>
  2. Compile the code from the cobalt/ directory:

    $ ninja -C out/<platform>_<build_type> <target_name>

    The previous command contains three variables:

    1. <platform> is the platform configuration that identifies the platform. As described in the Starboard porting guide, it contains a family name (like linux) and a binary variant (like x64x11), separated by a hyphen. For Windows builds use win-win32.
    2. <build_type> is the build you are compiling. Possible values are debug, devel, qa, and gold.
    3. <target_name> is the name assigned to the compiled code and it is used to run the code compiled in this step. The most common names are cobalt, nplb, and all:
      • cobalt builds the Cobalt app.
      • nplb builds Starboard's platform verification test suite to ensure that your platform's code passes all tests for running Cobalt.
      • all builds all targets.

    For example:

    ninja -C out/win-win32_debug cobalt

    This command compiles the Cobalt debug configuration for the win-win32 platform and creates a target named cobalt that you can then use to run the compiled code.

  3. Run the compiled code to launch the Cobalt client:

    # Note that 'cobalt' was the <target_name> from the previous step.
    $ out/win-win32_debug/cobalt [--url=<url>]

    The flags in the following table are frequently used, and the full set of flags that this command supports are in cobalt/browser/

    allow_http Indicates that you want to use http instead of https.
    ignore_certificate_errors Indicates that you want to connect to an https host that doesn't have a certificate that can be validated by our set of root CAs.
    url Defines the startup URL that Cobalt will use. If no value is set, then Cobalt uses a default URL. This option lets you point at a different app than the YouTube app.

Debugging Cobalt

debug, devel, and qa configs of Cobalt expose a feature enabling developers to trace Cobalt's callstacks per-thread. This is not only a great way to debug application performance, but also a great way to debug issues and better understand Cobalt's execution flow in general.

Simply build and run one of these configs and observe the terminal output.

Cobalt on Xbox One

In order to build Cobalt for Xbox One, you will need access to Microsoft's XDK. In order to sideload and run custom apps on Xbox you will need either an Xbox devkit or the ability to put an Xbox into developer mode. Those steps are outside the scope of this document.

AppxManifest Settings

Cobalt makes use of several template files and a settings file to generate an AppxManifest.xml during the ninja step. The settings can be found in starboard/xb1/ Most of the default values are stubs and intended to be overwritten by developers creating their own app with Cobalt, but they should work for local testing.

Build Cobalt

To build Cobalt for the Xbox One, set the platform to xb1 in the gn step:

$ python cobalt/build/ [-c <build_type>] -p xb1

Then specify the cobalt_install build target in the ninja step:

ninja -C out/xb1_devel cobalt_install

Package an Appx

There's a convenience script at starboard/xb1/tools/ for packaging the compiled code into an appx and then signing the appx with the pfx file located at starboard/xb1/cert/cobalt.pfx. The source, output, and product flags must be specified, and the only valid product for an external build is cobalt. Here's an example usage:

python starboard/xb1/tools/ -s out/xb1_devel/ -o out/xb1_devel/package -p cobalt

Alternatively, you can use the MakeAppx and SignTool PowerShell commands to manually perform those steps.

Once the appx has been created and signed, it can be deployed to an Xbox using the WinAppDeployCmd PowerShell command.