Parsing Wavefront OBJ files in C#

28 Apr

I have recently been doing significant work with processing 3D meshes and associated textures.  Today I have extracted the Wavefront OBJ parser I’m using into a seperate library and posted the code for others to use.

https://github.com/stefangordon/ObjParser

If you are not familiar with the Obj spec, this is a great reference:

http://www.martinreddy.net/gfx/3d/OBJ.spec

Usage

The main entry point to the library is via the Obj class.  Parsing and writing files is very simple.

// Initialize
var obj = new Obj();

// Read Wavefront OBJ file
obj.LoadObj([input path]);

// Write OBJ file
obj.WriteObjFile([output path]);

 

When an OBJ file is loaded all of its faces, vertices, and UV’s are accessible to you in IEnumerables of types Face, Vertex, and TextureVertex.  All of these elemental types are based on IType, so adding support for additional parts of the OBJ format is quite simple.

You can use this library as a start to basic mesh manipulation.  For example, cropping a mesh is as simple as removing all vertices and faces outside of a specific boundary, and updating indexes appropriately, then writing the file back out.

 

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5 thoughts on “Parsing Wavefront OBJ files in C#

  1. I had to change source to
    success = double.TryParse(data[1], NumberStyles.Any, culture, out x);
    coz I’m from another notation system 😉

  2. I have OBJ definition like the following one. I got exception “Could not parse parameter as int” in Face.LoadFromStringArray(). I’m not using any textures, so I think it must be omitted, right?

    v -0.5 -0.5 0.5
    v 0.5 -0.5 0.5
    v 0.5 -0.5 -0.5
    v -0.5 -0.5 -0.5
    v -0.5 0.5 0.5
    v 0.5 0.5 0.5
    v 0.5 0.5 -0.5
    v -0.5 0.5 -0.5

    f 4//1 3//2 2//3 1//4
    f 2//5 6//6 5//7 1//8
    f 3//9 7//10 6//11 2//12
    f 8//13 7//14 3//15 4//16
    f 5//17 8//18 4//19 1//20
    f 6//21 7//22 8//23 5//24

    • Yes the face parser needs a small upgrade I think. The “for” loop around line 32 of types\face.cs is designed to parse the individual components of the face, but it is only designed to handle V/VT or V, where as you have V//VN.

      The spec is V/VT/VN so probably we should look at position 1 and 2 of the resulting split array and if 1 parses we store it in VT. We can optionally add a normals array and start storing VN also.

      Feel free to file an issue on the github repo (this will remind me to fix it) or submit a pull request if you fix it. Thanks!

  3. Dear Stefan,

    First, thanks for your code.
    I noticed all the texture vertices (“vt” s) are 0 0 when I write out the OBJ file.
    I’m trying to fix this in the TextureVertex.cs file but not making any head way.

    Any ideas?

    Many thanks,
    Ghetz

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