Legacy Optifabric

If you're looking for Optifabric for 1.14 to 1.15.2 for regular Fabric instead of Ornithe, check out Optifabric Origins

Optifabric for Legacy Fabric (1.3-1.13.2) and Ornithe (b1.7.3-1.13.2)

Legacy Fabric installer and official MultiMC instances: https://legacyfabric.net/downloads.html
Ornithe installer (can generate MultiMC instances): https://ornithemc.net
Legal speedrunning MultiMC instances: Minecraft-Java-Edition-Speedrunning/legacy-fabric-instance-generator/releases

based on the work of RedLime's OptiFabric-Pre1.14, a fork of hYdos's OptiFabric 1.8.9 which in turn is a derivative of modmuss' original OptiFabric

installing

this mod requires an optifine jar in the mods folder alongside optifabric. for 1.7.2 and onwards this can be sourced from OptiFine's official website, and older versions these can be retrieved either from SpeedyCube64's Pre-1.9 Optifine Archive or on the OptiFine history thread.

how it works

this mod uses Minecraft-Java-Edition-Speedrunning/fabric-asm, a minor derivative of Cat Core's Fabric-ASM/no-guava which itself is an updated version of Chocohead's fabric-asm. fabric asm allows more extreme asm modification and the fork used has no dependency on guava or apache commons, which older minecraft versions don't provide.

steps

the mod looks for an optifine installer or mod jar or zip in the current mods folder
if it finds an installer jar it runs the extract task in its own throwaway classloader
the optifine mod jar is a set of classes that need to replace the ones that minecraft provides
optifine's replacement classes change the name of some lambda methods, so it take a good guess at the old name (using the original minecraft jar)
remap optifine to intermediary
move the patched classes out as they won't do much good on the classpath twice
add optifine to the classpath
register the patching tweaker for every class that needs replacing
replace the target class with the class that was extracted, also do some more fixes to it, and make it public (due to access issues)
hope it works

notes

this does not work for any optifine releases for minecraft 1.1 except for the optifine light edition due to some method signature crash (optifabric-hd-1.1-crash.log) outside my control
this mod does not work in dev or named environments, if someone fixes that do make a pull request
the accessWideners are created based on the output of tiny remapper's checkPackageAccess option, but they cannot ever be 100% complete. if you have a crash that has to do with and invalid access, report it and it may be able to be fixed.

class excluder

this is a kind of hidden feature that is occasionally useful to remove files when remapping the jar. to do this, it reads the optifabric-excluded-classes.json file in .minecraft/config/ if it exists, and expects the file to contain a mapping of versions (field names) to an array of removable classes (or textures or anything else, it's just a filename). an example file contents to revert the removal of the profiler for 1.3.2 light is provided below. if the optifine version you are trying to make an excluder extry for has already been loaded before in your instance, delete its folder in the .optifine folder in .minecraft to force a recache.

{
  "OptiFine_1.3.2_L_B2": [
    "ik.class"
  ]
}

Legacy Optifabric