Hemi-light differences between generated and imported block

BrianW · May 7, 2019, 6:16pm

I have the following playground with an imported chair and generated box.
The hemi-light effects each differently. I can’t see any shading on the chair.

We are having the same issue with imported obj blocks in our application.
What are we missing?

Playground:
https://www.babylonjs-playground.com/#KJV35B#6

Deltakosh · May 7, 2019, 6:32pm

Ok this is because there is no back face on your mesh:

using the vertex normal:

BrianW · May 7, 2019, 7:12pm

What about these two boxes? One is imported and one is generated. The imported one has had it’s normal’s computed.

https://www.babylonjs-playground.com/#95MJI8#27

Deltakosh · May 7, 2019, 8:34pm

The imported one has normals: yes but they are per faces as vertices are shared by faces (look the generated one has 36 vertices)

BrianW · May 8, 2019, 1:19pm

Okay I think I narrowed down my problem. I’m sorry I was not clear in my previous posts.

The .obj file I provided does not contain any normals.
BABYLON import loads the block and initialized a default normal array? A bunch of normals in the y-direction?
BABYLON.OBJFileLoader.COMPUTE_NORMALS = true;
^ This line of code is equivalent to smooth shading?

I want to be able to know if there were no normals supplied. So then I can let the user decide on
smooth/flat shading.

Deltakosh · May 8, 2019, 3:04pm

In this case the best option is to set COMPUTE_NORMALS to false and then check after loading the mesh if there are normals with:

mesh.isVerticesDataPresent(BABYLON.VertexBuffer.NormalKind)

BrianW · May 8, 2019, 3:14pm

I tried that and I’m getting true back. https://www.babylonjs-playground.com/#95MJI8#29

I know the obj file does not have any normals. The normals I get back are all y-up (0,1,0).

Exported from 3D Builder

mtllib box.mtl

o Object.1
v -506.154510 -506.180054 1012.309021
v 506.154510 -506.180054 1012.309021
v -506.154510 506.179688 1012.309021
v 506.154510 506.179688 0.000000
v -506.154510 -506.180054 0.000000
v -506.154510 506.179688 0.000000
v 506.154510 -506.180054 0.000000
v 506.154510 506.179688 1012.309021

usemtl Regular_0
f 1 2 3
f 4 5 6
f 5 4 7
f 8 3 2
f 5 7 2
f 5 3 6
f 8 2 7
f 6 3 8
f 5 1 3
f 7 4 8
f 2 1 5
f 8 4 6

Deltakosh · May 8, 2019, 3:29pm

Oh yeah you are right! By default the normals will be filled with Vector3.up

github.com

BabylonJS/Babylon.js/blob/master/loaders/src/OBJ/objFileLoader.ts#L704


    //For each element in the triangles array.
    //This var could contains 1 to an infinity of triangles
    for (var k = 0; k < triangles.length; k++) {
        // Set position indice
        var indicePositionFromObj = parseInt(triangles[k]) - 1;


        setData(
            indicePositionFromObj,
            0, 0,                                           //In the pattern 1, normals and uvs are not defined
            positions[indicePositionFromObj],               //Get the vectors data
            Vector2.Zero(), Vector3.Up(),    //Create default vectors
            this._meshLoadOptions.ImportVertexColors === true ? colors[indicePositionFromObj] : undefined
        );
    }
    //Reset variable for the next line
    triangles = [];
};


/**
 * Create triangles and push the data for each polygon for the pattern 2
 * In this pattern we get vertice positions and uvsu

BrianW · May 8, 2019, 3:34pm

We were going to use that as our check to see if normals were not supplied. Wondering if there is a better way.

Deltakosh · May 8, 2019, 3:51pm

Not now but maybe we can add an observable or an option to disable populating by default

BrianW · May 8, 2019, 3:54pm

Alright, Thanks Deltakosh!

Deltakosh · May 8, 2019, 4:04pm

If you want to try, I will be happy to merge a PR

Topic		Replies	Views
Imported mesh, how to "shade" sides Questions	4	210	September 14, 2023
Problem with lighting after importing OBJ file Questions lighting	6	1555	April 17, 2019
"Flat look" of a particular imported model; doesn't respond to scene lights Questions	5	508	February 19, 2020
Is there a way to generate normals in Babylon Sandbox? Questions	1	419	November 4, 2020
Imported GLB model won't light up Questions	11	3336	May 29, 2022

Hemi-light differences between generated and imported block

Exported from 3D Builder

Related Topics