Forge Blockstate V1 specs

<blockstate> == {
  "forge_marker": 1,
  "defaults": <variant>, // optional, added to all variants
  "variants": {
    "<property>": {
    "<value>": <variant> // variant definition for the specified value of this property; variants for multiple values can be specified.
  },
    "<variant name>": <variant>, // variant definition for the full variant string
    "<variant name>": [<variant1>, ...], // array of definitions for the full variant - result will be the random variant
  }
}

<variant> == {
  "model": "<model location>",
  "textures": {  // remaps the <from> texture in the model to <to>; multiple remappings can be specified
    "<from>": "<to>"
  },
  "x": <angle-90>, // vanilla rotation compatibility; only multiples of 90 degrees are supported, see vanilla specification
  "y": <angle-90>,
  "transform": <root-transform>, // transformations
  "uvlock": <bool>, // see vanilla specification
  "weight": <int>, // random weight, see vanilla specification
  // submodels: all stuff specified will be merged into the base model. If this is the root variant without the model - base will be chosen from one of the submodels.
  "submodel": "<model location>",
  "submodel": <variant>,
  "submodel": [<variant>, ...],
  "custom": { "<key>": <value> } // custom data that models can use
}

<root-transform> == <transform>

<root-transform> == {
  "thirdperson": <transform>,
  "firstperson": <transform>,
  "gui": <transform>,
  "head": <transform>,
  // or any of the <transform> keys
}

<transform> == "<builtin string>"
currently supported builtin strings:
  "identity" - identity transformation
  "forge:default-block" - default block transformation (example: stone)
  "forge:default-item" - default 2d item transformation (example: bucket)
  "forge:default-tool" - default 2d tool transformation (example: pickaxe)
This may be expanded to something more generic in the future.

<transform> == <matrix>
<transform> == { "matrix": <matrix> }

<matrix> == [
  [<number>, <number>, <number>, <number>],
  [<number>, <number>, <number>, <number>],
  [<number>, <number>, <number>, <number>]
]
4x3 matrix (3x3 affine part + translation column)

<transform> == {
  // all keys are optional
  "translation": [<number>, <number>, <number>],
  "rotation": <rotation>,
  "scale": [<number>, <number>, <number>], // per-axis scale
  "scale": <number>, // uniform scale
  "post-rotation": <rotation>
}

<rotation> == [<number>, <number>, <number>, <number>]
Quaternion(x, y, z, w)

<rotation> == {"<axis>": <number>}
Rotation around the coordinate axis, in degrees. Value is unrestricted

<rotation> == [{"<axis1>": <number>}, ...]
Composition of rotations around multiple axes, in the specified order

It would be great to have a tutorial explain how to properly create custom transforms for inventory rendering.

This is awesome information however one thing remains unclear to me. If i have a block that has 6 Properties that are correctly synced between the block and tile entity, How do i properly implement the blockstate where each of those Properties represents a different model within the block. I've tried separate Properties and i've tried nesting them. Each of the 6 properties can be true or false meaning there are 64 possible states (although in practice 2 of those states are impossible to place in world) Thanks in advance! :D

The <variant> object can also have the property "gui3d": <bool> (same effect as IBakedModel::isGui3D) and the property "smooth_lighting": <bool> (that replaces "ambientocclusion" in vanilla models)