Houdini HDA breaks FBXs normals into Unreal Engine

Dantexagc

Hi everybody, I have a problem regarding normal maps and shading in Houdini and in Unreal Engine when I bring my HDA. I will try to be as concise and to the point to explain the issue

CONTEXT
I am making a building generator tool for Unreal Engine, I have created a Houdini HDA and brought that into UE. I modeled some windows, doors and balconies in Blender, just traditional modelling, high poly to low poly baking and texturing.

To maximize texture resolution I mirrored some parts of the models. The mirrored UVs are offset to the next UV tile, this is common practice and has nothing to do with UDIMS. The normal map looks correct in Marmoset toolbag, where i baked the high to low poly, and it also looks correct in Substance Painter where I textured.

The problem is that when the HDA is brought into unreal, the normals of these parts are broken and the normal map no longer looks correct, showing sharp edges where it shouldn't.

WHAT I HAVE TRIED SO FAR

1. Disable the option "Recompute normals" in Project Settings > Houdini Engine Plugin (This in Unreal Engine)

2. Bipassed all the other nodes in my node network in houdini. Meaning the File node that brings the fbx into houdini is directly connected to the final output after being assigned an unreal material attribute.

3. I tried to create a material and visualize my window prop inside houdini. I brought the FBX into solaris (Completely separated from the procedural building tool) and created a material to visualize the prop as I have done in Blender and unreal and Substance painter. It looks broken. I think houdini does not understand the mirrored UVs. I have tried using both and Open GL and Direct X normal map and also flipping the green channel but that did not work.

At this point I am out of ideas so that is why I am posting, thank you so much for your time and brain power.


UPDATE

I created an HDA in a new Houdini file with just the FBX and the unreal material attribute, the issue is still there. Is this a bug from Houdini perhaps?

poopipe

you need simpler examples to diagnose this.  like a plane with some simple primitives baked into your normals 

Benjammin

I have learnt in the past two weeks that HDA bugs are highly dependent on houdini/unreal version combo. I'd advise against being on the latest versions of either - Houdini 20.5 and Unreal 5.3 seem solid. 

Dantexagc

I ended up changing the logic of the tool and instead of importing FBXs into houdini I now instantiate the unreal engine actors on points where my windows, doors and balconies are supposed to be. It was a bit painful and i still do not understand why the previous method broke but now things are working