Model JSONs

A “model” is simply a shape. It can be a simple cube, it can be several cubes, it can be a truncated icosidodecahedron, or anything in between. Most models you’ll see will be in the vanilla JSON format. Models in other formats are loaded into an IModelGeometry by an IModelLoader at runtime. Forge provides default implementations for WaveFront OBJ files, buckets, composite models, models in different render layers, and a reimplementation of Vanilla's builtin/generated item model. Most things do not care about what loaded the model or what format it’s in as they all "bake" into an BakedModel.

When ResourceLocation refers to a model, the path is normally relative to models (e.g. examplemod:block/block → assets/examplemod/models/block/block).

Block and item models differ in a few ways, the major one being item property overrides.

Textures

Textures, like models, are contained within resource packs and are referred to with ResourceLocations. When ResourceLocations refer to textures in models, the paths are taken to be relative to textures/ (e.g. examplemod:blocks/test → assets/examplemod/textures/blocks/test.png). Additionally, in Minecraft, the UV coordinates (0,0) are taken to mean the top-left corner. UVs are always from 0 to 16. If a texture is larger or smaller, the coordinates are scaled to fit. A texture should also be square, and the side length of a texture should be a power of two, as doing otherwise breaks mipmapping. (E.g. 1x1, 2x2, 8x8, 16x16, and 128x128 are good. 5x5 and 30x30 are not recommended because they are not powers of 2. 5x10 and 4x8 are completely broken as they are not square.) If there is an mcmeta file associated with the texture, and an animation is defined, the image can be rectangular and is interpreted as a vertical sequence of square regions from top to bottom, where each square is a frame of the animation.

JSON Models

Vanilla Minecraft’s JSON model format is rather simple. It defines cuboid (cube/rectangular prism) elements, and assigns textures to their faces. On the wiki, there is a definition of its format.

Tip

JSON models only support cuboid elements; there is no way to express a triangular wedge or anything like it. To have more complicated models, another format must be used.

When a ResourceLocation refers to the location of a JSON model, it is not suffixed with .json, unlike OBJ (e.g. minecraft:block/cube_all, not minecraft:block/cube_all.json).

WaveFront OBJ Models

Forge adds a loader for the .obj file format. To use these models, the JSON must reference the forge:obj loader. This loader accepts any model location that is in a registered namespace and whose path ends in .obj. The .mtl file should be placed in the same location with the same name as the .obj to be used automatically. The .mtl file will probably have to be manually edited to change the paths pointing to textures defined within the JSON. Additionally, the V axis for textures may be flipped depending on the external program that created the model (i.e. V = 0 may be the bottom edge, not the top). This may be rectified in the modelling program itself or done in the model JSON like so:

{
  "__comment": "Add the following line on the same level as a 'model' declaration.",
  "loader": "forge:obj",
  "flip-v": true,
  "model": "examplemod:models/block/model.obj",
  "textures": {
    "_comment": "Can refer to in .mtl using #texture0",
    "texture0": "minecraft:block/dirt",
    "particle": "minecraft:block/dirt"
  }
}