Material rendered black on non-instanced object, correct if object is instanced

[Theverat]

Reported by Max from Insertcoin.tv.

LuxCore version: v2.3beta1
Scene: black_material.zip

Steps to reproduce:

• Start a viewport render. The object will be instanced by BlendLuxCore and everything works fine
• Start a final render. The object will not be instanced anymore and appear black

I have a feeling there might be NaNs involved here, possibly caused by some of these factors:

• The object has a negative scale of -0.385706 along the Z axis (when the scale is applied in Blender, the problem vanishes)
• A bump map is used on the object (when the bump map is removed, the problem vanishes)

Viewport render, object instanced:

Final render, object not instanced:

[Dade916]

The problem may be in BlendLuxCore (or in the LuxCore export process). Try to do this test:

1. use FILESAVER to export the scene with +Z scale

2. use FILESAVER to export the scene with -Z scale

3. now import the 2 mesh .ply files inside Blender and check the normals: they point in the same direction (while they should be flipped in one case).

So the problem may be in the process of exporting normals when Z scale is negative (?)

[Theverat]

You mean somewhere in here?

LuxCore/src/luxcore/pyluxcoreforblender.cpp

Line 673 in ab1c6c6

static bool Scene_DefineBlenderMesh(luxcore::detail::SceneImpl *scene, const string &name,

Or maybe in

LuxCore/src/luxrays/core/exttrianglemesh.cpp

Line 249 in 09fc105

void ExtTriangleMesh::ApplyTransform(const Transform &trans) {

However, even with normals pointing to the wrong side, why would the mesh be black? Wouldn't that be like looking at it from the other side?

[Dade916]

I should have fixed the problem: the transformation was swapping the handiness of reference system.

[Theverat]

Confirmed, thanks!