Cleanroom

The cleanroom plugin, from @opys/minecraft.

Cleanroom: Forge 1.12.2 mods on a modern Java.

// opys.config.mjs
export default defineConfig({
  plugins: [
    cleanroom({ version: '1.12.2' }),
    java({ version: '25' }),
  ],
  manifest: {
    command: '@cleanroom.command',
    args: [
      '@cleanroom.jvmArgs',
      '@cleanroom.mainClass',
      '@cleanroom.gameArgs',
    ],
    workdir: '${game_directory}',
  },
});

Use it instead of minecraft. A loader brings the game with it.

Options

Option	What it does
version	Which build. See below.
source	A mirror of the build index.
libraries	Libraries to add or replace.

version

You write	You get
'1.12.2'	The recommended release, or the newest if none is recommended.
'1.12.2-latest'	The newest release.
'1.12.2-recommended'	The recommended release.
'0.6.13-alpha'	Exactly that release.

The version is resolved when you build. '1.12.2' today and in six months can be different releases. For a pack that never moves, write the exact one.

What it adds

Everything Vanilla Minecraft adds, with these differences.

Kind	What
Files	The 1.12.2 game with Cleanroom's libraries.
Launch	command, jvmArgs, mainClass, gameArgs.
Variables	The same as vanilla.
Environment	None.

Each one below: what it is, and how it ends up in the manifest.

Files · the game and Cleanroom libraries

The 1.12.2 game, with the old graphics library (LWJGL 2) swapped for the current one (LWJGL 3). The old one is not installed at all.

// opys.config.mjs
export default defineConfig({
  plugins: [
    cleanroom({ version: '1.12.2' }),
    java({ version: '25' }),
  ],
  manifest: {
    command: '@cleanroom.command',
    args: [
      '@cleanroom.jvmArgs',
      '@cleanroom.mainClass',
      '@cleanroom.gameArgs',
    ],
    workdir: '${game_directory}',
  },
});

// in the manifest
{
  "path": "${library_directory}/com/cleanroommc/cleanroom/0.6.13-alpha/cleanroom-0.6.13-alpha.jar",
  "source": { "url": "https://github.com/CleanroomMC/Cleanroom/releases/download/0.6.13-alpha/cleanroom-0.6.13-alpha-universal.jar" },
  "size": 6505649,
  "integrity": { "sha1": "8d59eda7065f26fc0c1bbd3a9fa9f272ff89917f" }
}

Launch

A short one. 1.12.2 needs little, and Cleanroom starts through its own main class.

// opys.config.mjs
export default defineConfig({
  plugins: [
    cleanroom({ version: '1.12.2' }),
    java({ version: '25' }),
  ],
  manifest: {
    command: '@cleanroom.command',
    args: [
      '@cleanroom.jvmArgs',
      '@cleanroom.mainClass',
      '@cleanroom.gameArgs',
    ],
    workdir: '${game_directory}',
  },
});

// in the manifest
"launch": {
  // '@cleanroom.command'
  "command": "${java_bin}",
  "args": [
    // '@cleanroom.jvmArgs'
    "-Djava.library.path=${natives_directory}",
    "-cp",
    "${classpath}",
    // '@cleanroom.mainClass'
    "top.outlands.foundation.boot.Foundation",
    // '@cleanroom.gameArgs'
    "--username", "${auth_player_name}",
    // … the rest of the 1.12.2 game arguments, then:
    "--tweakClass", "net.minecraftforge.fml.common.launcher.FMLTweaker",
    "--versionType", "Forge"
  ],
  "workdir": "${game_directory}"
}

You write	Becomes
'@cleanroom.command'	The program to run: whatever Java the pack has.
'@cleanroom.jvmArgs'	Arguments for Java itself, ending with the classpath.
'@cleanroom.mainClass'	The class to start. One argument.
'@cleanroom.gameArgs'	Arguments for the game: who is playing, and where things are.

Variables

The same names as vanilla. classpath now has this loader's libraries ahead of the game's.

// opys.config.mjs
export default defineConfig({
  plugins: [
    cleanroom({ version: '1.12.2' }),
    java({ version: '25' }),
  ],
  manifest: {
    command: '@cleanroom.command',
    args: [
      '@cleanroom.jvmArgs',
      '@cleanroom.mainClass',
      '@cleanroom.gameArgs',
    ],
    workdir: '${game_directory}',
  },
});

// in the manifest
"vars": {
  "game_directory": "${root}/",
  "library_directory": "${root}/libraries",
  // … the rest, as in vanilla
}

Nothing runs on the player's machine before the game.

Good to know

• It replaces both minecraft and forge.
• Use Java 25 whatever the Minecraft version says. opys does not check.
• Pair it with java({ version: '25' }).