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77 lines
2.4 KiB
Markdown
77 lines
2.4 KiB
Markdown
# Minetest Wavefront `.obj` file format specification
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Minetest Wavefront `.obj` is a subset of [Wavefront `.obj`](http://paulbourke.net/dataformats/obj/).
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It is inferred from the [Minetest Irrlicht `.obj` reader](https://github.com/minetest/irrlicht/blob/master/source/Irrlicht/COBJMeshFileLoader.cpp).
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`.mtl` files are not supported since Minetest's media loading process ignores them due to the extension.
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## Lines / "Commands"
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Irrlicht only looks at the first characters needed to tell commands apart (imagine a prefix tree of commands).
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Superfluous parameters are ignored.
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Numbers are formatted as either:
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* Float: An optional minus sign (`-`), one or more decimal digits, followed by the decimal dot (`.`) then again one or more digits
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* Integer: An optional minus sign (`-`) followed by one or more decimal digits
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Indexing starts at one. Indices are formatted as integers. Negative indices relative to the end of a buffer are supported.
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* Comments: `# ...`; unsupported commands are silently ignored as well
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* Groups: `g <name>` or `usemtl <name>`
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* Subsequent faces belong to a new group / material, no matter the supplied names
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* Each group gets their own material (texture); indices are determined by order of appearance
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* Empty groups (groups without faces) are ignored
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* Vertices (all numbers): `v <x> <y> <z>`, global to the model
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* Texture Coordinates (all numbers): `vt <x> <y>`, global to the model
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* Normals (all numbers): `vn <x> <y> <z>`, global to the model
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* Faces (all vertex/texcoord/normal indices); always local to the current group:
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* `f <v1> <v2> <v3>`
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* `f <v1>/<t1> <v2>/<t2> ... <vn>/<tn>`
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* `f <v1>//<n1> <v2>/<n2> ... <vn>/<nn>`
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* `f <v1>/<t1>/<n1> <v2>/<t2>/<n2> ... <vn>/<tn>/<nn>`
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## Coordinate system orientation ("handedness")
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Vertex & normal X-coordinates are inverted ($x' = -x$);
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texture Y-coordinates are inverted as well ($y' = 1 - y$).
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## Example
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```obj
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# A simple 2³ cube centered at the origin; each face receives a separate texture / tile
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# no care was taken to ensure "proper" texture orientation
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v -1 -1 -1
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v -1 -1 1
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v -1 1 -1
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v -1 1 1
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v 1 -1 -1
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v 1 -1 1
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v 1 1 -1
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v 1 1 1
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vn -1 0 0
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vn 0 -1 0
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vn 0 0 -1
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vn 1 0 0
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vn 0 1 0
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vn 0 0 1
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vt 0 0
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vt 1 0
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vt 0 1
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vt 1 1
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g negative_x
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f 1/1/1 3/3/1 2/2/1 4/4/1
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g negative_y
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f 1/1/2 5/3/2 2/2/2 6/4/2
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g negative_z
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f 1/1/3 5/3/3 3/2/3 7/4/3
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g positive_x
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f 5/1/4 7/3/4 2/2/4 8/4/4
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g positive_y
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f 3/1/5 7/3/5 4/2/5 8/4/5
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g positive_z
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f 2/1/6 6/3/6 4/2/6 8/4/6
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```
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