Retrofit runs a real Minecraft 1.7.10 with Forge 10.13.4 inside your 1.20.1 game and connects it to the 1.20.1 world. Your 1.7.10 mods run their own code, so their blocks, items, machines, GUIs, creatures, recipes, world generation, and sounds work as they were made, alongside your 1.20.1 mods.

**This mod is still in Alpha. A lot works; a lot is untested. Read the compatibility list below before building a world around it, and keep backups.

My goal is to build a compatibility bridge between modern Minecraft and past versions to help revive dead mods. 1.7.10 is only the beginning.

Getting started

1. Install Forge 1.20.1 (47.x) and put Retrofit in your `mods` folder.
2. Start the game once. Retrofit creates a `retrofit/mods` folder in your game directory.
3. Put your 1.7.10 Forge mod JARs in `retrofit/mods` and start again.

On first start, Retrofit downloads Minecraft 1.7.10 and Forge 10.13.4.1614 from Mojang and Forge (skipped if your launcher already has them). Retrofit itself contains no Mojang code and no mods. Every start spends about 5-10 seconds booting 1.7.10 while mods load.

Servers work the same way: install it on a Forge 1.20.1 server and put the 1.7.10 mods in the server's `retrofit/mods`. Players need the same 1.7.10 mods.

What works

- Blocks: textures, custom models and tile entity renderers, collision, tools and tiers, redstone, right-click, placing, breaking and the mods' own drops
- Machines and storage: ticking tile entities, saving, client sync, 1.20.1 hoppers and pipes moving items in and out, and legacy pipes and machines using vanilla chests and furnaces
- Items, tools, weapons, food and armor, with the mods' own behaviour
- GUIs: the mods' own screens and containers, buttons, progress bars, shift-click
- Creatures: the mods' mobs with their own AI and models, spawn eggs, natural spawning and riding (brooms, mounts, sleds)
- Dimensions: the mods' own dimensions, generated by the mods (Thaumcraft's Outer Lands, Witchery's Spirit World, Mo' Creatures' Wyvern Lair)
- Players: mod potions, flight, the mods' saved player data, living events, tooltips
- Chunk loading through the mods' chunk loading tickets
- Recipes: all crafting recipes, furnace recipes, fuels
- World generation: mod ores, plants and structures in new chunks
- Commands, key bindings, HUD overlays, sounds, mod packets
- Multiplayer: dedicated servers (LAN not tested yet)

Tested mods (not included)

Each of these was tested in a new world (every block, machine, creature, and item, plus world generation), and all of them together in singleplayer and on a dedicated server:

- Works: Thaumcraft, Witchery, Ars Magica 2, BuildCraft, BiblioCraft, IronChests, OreSpawn, Mo'Creatures, RotaryCraft (with DragonAPI), Tinkers' Construct, Pam's HarvestCraft, Carpenter's Blocks, Chisel, IndustrialCraft 2, Lycanite's Mobs
- Loads: CodeChickenCore and NEI (NEI's panel only on 1.7.10 screens; use JEI)

Libraries they need (Baubles, DragonAPI, AnimationAPI, Mantle, Custom Mob Spawner) go in `retrofit/mods` too. Other mods are untested; reports are very welcome.

None of the mods mentioned here are included with this project. All 1.7.10 mods must be downloaded separately and manually put into the proper folder.

Not yet

- Mods' own sky renderers in their dimensions (the colours are used)
- Leashes on legacy creatures
- Some Forge events (block highlight, player rendering)
- Legacy crafting recipes in the recipe book and JEI (they still craft)
- 1.7.10 code expects the world to start at y=0: creatures below y=0 can't find paths

Known issues

- Connecting to a server right after the game starts can occasionally hang at "Logging in...". Cancel and connect again.
- RotaryCraft/DragonAPI on a dedicated server: add the JVM argument `DragonAPI_silence_ASM_POTIONPACKETID1`.
- 1.7.10 configs are in `retrofit/config`; ID clashes between mods (e.g., Witchery and RotaryCraft potion IDs) are fixed there, as in a 1.7.10 pack.

Requirements

Forge 1.20.1 (47.x), Java 17 or newer (tested with 17, 21 and 26). Internet on first start, unless the Minecraft launcher already has 1.7.10 and Forge 10.13.4.1614 installed.

Credits

Built on Minecraft Forge and FML for both versions, and on everyone who wrote the 1.7.10 mods this is for.