CSG Lighting changes

[captainleighwalker]

Dear friends

I am pulling my hair out with a model imported from 3Ds max. When I use csg subtract the lighting on the new mesh looks different as if the vertices are in a different position to the original mesh. Or is it the normals.

I have reproduced it here https://www.babylonjs-playground.com/#EFXZ8U

The difference is a lot worse on the mesh I am working with. It is a lot darker after the operation.

Any help?

Thanks in advance

[Pryme8]

https://www.babylonjs-playground.com/#EFXZ8U#1

I do not see anything noticeable.

[captainleighwalker]

On my playground you can easily compare the original mesh and subtracted mesh and the lighting is looking different

[Arte]

Hi from me,

After 2 sec... https://www.babylonjs-playground.com/#EFXZ8U#2

[captainleighwalker]

The problem is something to do with normal are different after subtract.

If I do convertToFlatShadedMesh then it looks like same. The problem is my mesh has curved surfaces.

How can I get around this problem?

[Guest]

Can you try to recreate the normals with mesh.createNormals(true) ?

[captainleighwalker]

Hi @Deltakosh

It does sort the lighting out but its making the curves faceted (the bottom is the original mesh)

This is how it looks after using subtract 

I don't get how this works or if it would have any affect but when drawing normal positions they seem to be in different position and rotation on https://www.babylonjs-playground.com/#EFXZ8U#3

[Guest]

Unfortunately this is not an easy one and the CSG algorithm does not help a lot. 

 

can you share a repro on the playground with only your mesh? I'll try to see how we can make sure the createNormals does not lose the smoothing

[captainleighwalker]

Hi @Deltakosh

 

Please see https://www.babylonjs-playground.com/#EFXZ8U#5

You have to replace var data with below as the file was too big. Thanks.

_________________________

 

I've realised you get a different set of normals if you are using intersect depending on which mesh you intersect from.

See https://www.babylonjs-playground.com/#EFXZ8U#4

If you swap  bCSG.intersect(aCSG);for  aCSG.intersect(bCSG); The normal are ok

[Guest]

Ok unfortunately this is because of the CSG it will separate the face and thus losing the smoothness

I have no solution for you this time (unless than digging into CSG to try to fix this behavior)

[captainleighwalker]

Could there be a way to recalculate normals and join vertices back together based on a threshold angle between the faces?

[Guest]

There is an hope here:

http://doc.babylonjs.com/snippets/minimise_vertices

If you do that and then run createNormals again it could work (not tested but worth the try)

[captainleighwalker]

nope! haha

[Guest]

Erf:(