Some things to note:
Netty is screwy so currently can't join single player. @cpw
Crafting has been MAJORY reworked. The current GameRegistry functions are nooped, this is IN THE WORKS.
Just need to move the recipe list to a full class registry, and then re implement the in-code recipe registration.
Also, it IS advised that modders move to JSON, because ideally we'll see a S->C recipe syncing system in 1.13
which would allow servers to have custom recipes.
OreDictionary currently 1/2 works, need to write a better algorithm for replacing ingredients.
Please be patient
Rendering:
A lot of functions got a new float parameter, this is similar to partial ticks, needs more research
Major things to note:
Class renames: https://gist.github.com/LexManos/44dd211f90f498ad4015279b103dff86
Tile Entities are now packed in the ChunkData packet.
Forge intends to work around this to better support large moded worlds, but for the time being modders should implement the new function carefully and only send what data they need to!
Minecraft's codebase now has annotations, these are directly from Mojang and should be adheared to!
Added support for package-info.java's containing @Nullable information for all MC code base.
LexManos