The requirements for recompiling Celeste into a web browser runnable version are a bit tedious. Due to the nature of the ahead of time compilation, you'll need Windows Subsystem for Linux. According to the docs it does not matter that much whether you use WSL 1 or 2, however 1 might be faster for this use case. However I ended up setting mine with WSL 2 before reading that bit of documentation.

Also for audio, only FMOD 2 has a webassembly version but Celeste's bank files are on an earlier version so we'll need to regenerate the bank files from the public Celeste FMOD project. Simply download the project and open it with fmod studio 2 and it should automatically upgrade it. Then rebuild the bank files as needed. Instead of putting them in the Desktop folder, we'll be putting them in the Web folder later on.

If you've already gotten a setup suitable for making Everest mods then GOOD JOB! If not you should probaly get one. In addition since the packaging runs on .NET 5 you should get .NET 5 installed.

Throughout this "DIY" tutorial I will be referencing a couple of things.

Resources (for when you are stuck) #

• Google and other search engines
• The FNA to WASM gist
• Massive Uno Wasm Bootstrap 2.1 README
• XNA Reference

Remeber, FNA aims to be a better reimplementation of XNA!

• FNA Source
• Everest Wiki for Modding

A few other things we might need #

• Visual Studio (code might work as an editor, I used VS 2022 for this though), make sure you're able to do a msbuild
• FMOD for HTML5 as a zip file
• FMOD Studio (only if you want to rebuild the banks yourself)
• Git, in case you break stuff. Also helps apply patchfiles I'll be putting out for this.
• WSL as said above. I recommend Ubuntu 18.04 LTS as a distro for this.
• Chromium-based browser for testing. They seem to be the fastest at executing WASM.
• NET 5 as said above. Make sure to download for developers so not just the runtime.
• ILSpy (I'm sorry dnspy lovers I decompiled Celeste for this project with this first and then discovered dnspy existed, so unless it produces identical code then you'll need to temporarily use ILSpy).
• The Vanilla game, obviously! I used the itch.io FNA version. Patching may have issues when basing off an XNA or Steam version.

(TODO: Yea I think this is good enough to be in another post)

Extract the unmodified source code. #

Simply open up ILSpy, open the Celeste.exe assembly, and then select everything and hit export code so it makes a project openable by Visual Studio. Keep in mind at this point the project still uses .NET 4.5.2, while our target project uses .NET 5. I'll be providing another csproj for the web build. By the way, making the game run off .NET 5 actually requires absolutely no code modifacation.

• Next Up: Intro

Have questions? Contact smashmaster in the Celeste discord :)