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[Ludovic Marcé]

Hi again,

I've a problem loading OBJ objects with Xith in my application.
Better than an inexact explication, i show you my problem in attached image.
I think this is a problem about normals, but i don't know how to resolve it.

Do you know what happened and how to resolve this appearance problem ?

[Marvin Fröhlich]

Well, what did you expect the model to look like? I guess, you used a 3d modeler (blender?) to create the model. So you could attach a screenshot of blender showing the model.

Marvin

[Ludovic Marcé]

The attached file show what i can see when loading and rendering it with Blender.

[Marvin Fröhlich]

Hmm... This looks indeed strange.

Could you maybe attach the .blend file and the .obj file?

Marvin

[Ludovic Marcé]

Sure.

[Ludovic Marcé]

Up !

Any idea ?

[Mathias 'cylab' Henze]

I would say either the .obj does not specify the all triangles in the same order (clockwise/anticlockwise) or the importer does not correctly set up the triangles regarding this aspect from that file. And since your .obj file seems to not contain normals your get the wrong autogenerated ones. Try to add normals to your .obj export and see, if it makes any difference.

[Ludovic Marcé]

Thanks for your answer. So, i suppose my OBJs aren't correct.
In fact, i create this OBJ file from a list of points on the fly.
See here why : http://xith.org/forum/index.php/topic,530.msg4566.html#msg4566

I think i should add normals (how?) when creating the OBJ file, or calculate them after loading the OBJ file.

[Marvin Fröhlich]

You could use calculateFaceNormals() to get some good normals.

Marvin

[Ludovic Marcé]

Something like that?

Code:

            OBJModel model = new OBJLoader().loadModel( fileName );
            for (Shape3D shape : model.getShapeNodes())
            {
            ((TriangleArray)shape.getGeometry()).calculateFaceNormals();           
            System.out.println("getTriangleCount(): " + ((TriangleArray)shape.getGeometry()).getTriangleCount());
            }

But i know what is my problem now, the obj file i create is not good. Some faces are duplicated... 
Is there any way to detect and remove duplicated triangles ?
Or you suggest me to create correct OBJ files instead ?

['n ddrylliog]

I'd use something like epsilonEquals() from Point3f to test all the triangles' points.

[Marvin Fröhlich]

I guess, the simplest and most high performance way would be to search blender for a function like that.

Marvin

[Ludovic Marcé]

I'd use something like epsilonEquals() from Point3f to test all the triangles' points.

I know this very useful fonction but i don't know exactly how to use it in this case.

I guess, the simplest and most high performance way would be to search blender for a function like that.

Marvin

The problem is that i don't create these OBJ files from blender, but in the code when i want to convert on the fly the format used at my work.

So the best solution probably is to fix my converter.

[Marvin Fröhlich]

I know this very useful fonction but i don't know exactly how to use it in this case.

Just loop over all triangles ( @see: getTriangle() ) in your model's shapes and compare each with each {O(n²)} using the Point3f.epsilonEquals() method.

Marvin

[Ludovic Marcé]

In fact, i don't think this is a problem with duplicated faces.
I've tested with a small OBJ file with only 2 triangles, and i've the same problem as you can see.
The first screenshot shows the "front" side of my shape and the second shows the back side.
I also include the OBJ file.

Should i triangulate the shapes to avoid this phenomenon? If yes, how to do that?