Model files

Model files

loaders/obj.mojo. read_obj reads a Wavefront OBJ file into named objects, each with a BufferGeometry. parse_obj reads the text of one.

three.js: OBJLoader.

Read a file

var model = read_obj("assets/cube.obj")
for index in range(model.count()):
    print(model.objects[index].name, model.objects[index].material)
var shape = assets.geometries.add(model.objects[0].take_geometry())

Function	Meaning
read_obj(path) -> ObjModel	Read a file.
parse_obj(text) -> ObjModel	Read the text of one.

ObjModel and ObjObject

ObjModel.objects holds one ObjObject per object, in file order. count() says how many.

Field	Meaning
name	From o or g. Empty when the file has neither. Faces read before the first o or g belong to it, as three.js has it.
material	The name from usemtl. Empty before one. The material library is not read.
geometry	A non-indexed BufferGeometry with position, and with normal and uv when the faces name them.

take_geometry() swaps the geometry out for an empty one, so it can go into a store. A BufferGeometry moves and does not copy.

What is read

Line	Meaning
v x y z	A position. A fourth number is ignored.
vt u v	A texture coordinate.
vn x y z	A normal.
f a b c ...	A face of three or more corners, cut into a fan of triangles. A polygon must be convex. Each corner is v, v/vt, v//vn or v/vt/vn.
o name, g name	A new object. One with no faces is dropped.
usemtl name	A new object under that material, with the same name.
#	A comment, to the end of the line.

An index counts from one. A negative index counts back from the last entry so far. mtllib, s, l, p and unknown lines are skipped.

Every face of one object must agree about normals and texture coordinates. A geometry without normals shades flat. See Renderer.

Errors

The parser raises, naming the line, for:

• A v, vt or vn line with too few coordinates. A coordinate that is not a number, or is not finite as a Float32.
• A face with fewer than three corners, or a corner with more than three parts.
• A face of four or more corners that is not convex, or has no area. A fan covers a convex polygon and only that.
• An index that is not a whole number, is zero, or names an entry the file does not have.
• A face that names a normal or a texture coordinate where an earlier face of the object did not, or the other way round.

read_obj raises for a file it cannot read.

Example

assets/cube.obj is a unit cube with normals and texture coordinates. tests/test_obj.mojo reads it and draws it.