Imported Mesh comes apart at the seams when using displacement

[RyanJPat]

Hi I'm trying to texture a custom mesh but it's coming apart at the seams at the slightest amount of displacement, what am i doing wrong here? It's fully UV'd

[Luca Giarrizzo]

Hello @RyanJPat,

There are two concepts to consider to understand what is happening:

• A vertex joining polygons together is often not processed as a unique vertex if the vertices of each polygon do not share exaclty the same attributes.
  Thus, at the geometry evaluation level what appears to be a single vertex can actually be multiple vertices at the same location. which are merged into what appears to be a single vertex. More on that here.
  In this case, since the mesh has hard edge, this means the normals of continuguous faces at these edges are not aligned. This means there are actually separate vertices at these hard edges.
• Tessellation displacement moves vertices along their normal vector.

When combining these concepts, we now know that the mesh is coming apart because the separate vertices along the hard edges are simply moved in the direction of their normals, which are the direction each side of the mesh is facing.

There are more sophisticated seam-aware implementations of tessellation displacement which prevent geometry from breaking apart like this, but these are still under research and development.

In the meantime, the way to prevent that break is smoothing out the normals at the hard edges so these vertices are displaced in the same direction, and recapturing the hardness using a normal map. Alternatively, you may model the required detail directly onto the base geometry.

Displacement is a tricky technique to use in cases like this. This is one of the reasons it is used either on organic models (terrain, skin, etc...) where the base mesh is smooth, or only on the interior areas of hard surfaces rather than its edges.

I hope this is informative!

Best regards.

[matibuc4eva]

Hi Luca,

thanks for the exhaustive answer, but considered that i double checked all the steps that you pointed in your reply, at the end i suppose that there is not a solution to this problem already ?

I'm in a similar situation tryng to using displacement but having issues with the mesh.

The mesh it gets ripped along the seam lines when the displacement it comes harder:

However i found an artist that looks like his main workflow is based on this displacement technique and his mesh doesn't preset any issue:

https://s-keiyu.com/texturingideationdemo/

So i was wondering about how he solved this problem, and if someone has any clou.

Thanks!

[Lee Probert]

I also have this issue, but it is when the model is rigged and then stretched. The seams break and cause holes to show. These seams are exported from Painter. Here in Blender you can see the highlighted seams that are not joined. How do we fix this? I also have an issue with Painter showing these seams visibly when you paint the model.

[Cyril Dellenbach]

As Luca mentioned, Displacement can be a tricky technique. I'd first advise you to hide seams as much as possible, but that's obviously not always an option.

In addition, depending on how important the height is on the model, you could try to gradually decrease the height value in seams' areas. The same way Wes showcased in this tutorial for Painter.

That being said, the fact that the seams are already visible in Substance 3D Painter is probably the source of the issue. Could you share the .SPP file at cdellenbach@adobe.com with a link to this thread, so I can take a closer look?

Let me know.