UV coordinates possibly incorrect when importing FBX for baking

gxcode

Hello all. I recently started learning 3D modelling for game art. I am currently modelling in Blender 2.83.5 and then attempting to bake in Marmoset 4.01. I am encountering a weird issue while baking in Marmoset. It may be a bug, but it could be that I am also doing something stupid. I am hoping somebody can confirm this is a known issue or set me on the correct path if I am at fault.

I have this rather basic trunk lid which I created in blender:

 
I also have a high-poly version of it which is just the low-poly version, plus some sub-surf modifiers. The low-poly is UV unwrapped like this:


I realize my unwrapping may be spatially suboptimal (new to this), but I have confirmed that there are no overlapping islands (blender can check for this). My procedure is as follows:

1) Export the high and low poly to FBX (after triangulating w/ the Blender modifier).
2) Import high and low poly into Marmoset toolbag and bake w/ the following settings:


The issue I observed is that the resulting AO map is not arranged spatially in a way that matches the UV unwrapping above. It has islands in the wrong place (see the red circle pieces here):


If I re-export the low poly as OBJ from Blender, and then re-bake using that file (leaving high poly as the FBX) it does not do this. The map looks fine as far as I can tell. Superficially, it seems like some of the UV coordinates are incorrect when importing as FBX? Or maybe there is something wrong with my model. I'm interested in any thoughts on the matter.

Another unrelated question I have: I noticed the "material ID" output does not agree with my material assignments from the low-poly mesh. Are these IDs being resampled from the high poly mesh?

EarthQuake

Generally speaking, Toolbag reads the UV data in the file that you import, so if this is incorrect, that would tend to mean that something is happening at export time from your 3D application that is causing the problem. You can verify this by importing the FBX file back into your 3D app, or into a different 3D app.

Material IDs are based on the materials assigned to the high poly mesh(es), not the low.

gxcode

Hi @EarthQuake, thank you for your reply. To verify the UVs I imported the FBX into unreal engine:

They match what I see in Blender.

I also tried doing the Bake in Substance Painter. It did not have the same issue as Marmoset. Both seem to produce really ugly results (particularly on the small details), although I suspect somehow that is my mesh being badly arranged:

This is unrelated to my original question, but any thoughts on what could cause that?

Thanks for your assistance. 

EarthQuake

Yes, there are a couple of general issues with your UV layout:

• It looks like you're using hard edges but not splitting the UVs along these edges, you'll need to make sure you're splitting your UVs to avoid artifacts along the edges
• The UV layout in general has a lot of slanted edges for areas that should be straight, this will generally look worse as it takes more resolution to represent a slant than a straight line