Add support for n-gons

[virtualritz]

Many geometries found in OBJs are not made out of triangles and this is a feature. If I load an OBJ to send to an high end offline renderer, the last thing I want is probably triangles (as such I also do not want the reader to convert the OBJ to triangles, on-the-fly, as tobj does).

Basically the mesh returned would then consist of:

mesh.positions
mesh.facevertices // number of vertices per each face (u32)
mesh.indices

[virtualritz]

I quickly made a file in Wings3D – this is an all quad model. Feel free to use however you want.

knotty02.zip

[Twinklebear]

Hey @virtualritz , yeah this can be added as an option telling tobj not to triangulate. Then it can just give you back the face vertex counts of the quads/polygons directly. Thanks for the test model!

[virtualritz]

Yes, this would be super useful.
I am using tobj here (have a play).

[Twinklebear]

Very cool! I'll ping you on this issue when I've added support and released and updated crate

[virtualritz]

Cheers!

[Twinklebear]

Should be done in 1ae79e6 , I'll cut a release shortly. This is a breaking change for the API since I'm just adding a bool option to load_obj which will set whether or not to triangulate the loaded faces

The number of indices used by each face are now stored in Mesh::num_face_indices, check out the print mesh example. This is the same as tinyobjloader, though I named the list of verts/indices used per-face as num_face_indices instead of num_face_vertices

[Twinklebear]

Let me know if you run into any issues!

[virtualritz]

Yeah, cool. I am trying this in a few hours. Will let you know.

[virtualritz]

Done.

A two line change. Nice one. The commit only looks big because of Rustfmt stuff.

[virtualritz]

You should update the README since your crate is actually the only one in the whole Rust universe that doesn't triangulate on import (if not asked to).

[Twinklebear]

That's a good point! I'll update it