Datasmith is broken with Rhino 8

Development Pipeline & Plugins
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Hello,

currently the following features are not exporting correctly in Rhino 8:

  1. Per-face materials

  2. Render mesh modifiers (edge softening, curve piping, shut lining, etc.)

There are three main ways to bring a Rhino model into Unreal Engine:

  1. Exporting a Datasmith file and importing it into Unreal.

  2. Importing the .3dm file directly, with import meshes with UVs option.

  3. Importing the .3dm file directly, with import NURBS and tessellating them inside Unreal option

Render mesh modifiers have never exported correctly using methods 2 or 3 (direct .3dm import). However, both render mesh modifiers and per-face materials did export properly when using Datasmith files from Rhino 6 and 7. In Rhino 8 they no longer do.

I tested this using Rhino 8 SR23 and SR25 (Windows 10), along with Unreal Engine 5.5.4 and 5.7.0 (each with their corresponding Datasmith version) and the features above failed to export while they still export correctly from Rhino 7.

My workaround:

  • You can still export per-face materials from Rhino 8 using the direct .3dm import (method 2).

  • You can bake render mesh modifiers by using the ExtractRenderMesh command. This will include edge softening, curve piping, etc., and the resulting mesh will import correctly via method 2.

However, this comes with significant drawbacks, You must import the entire file contant and also Rhino meshes can only have one material, so if the original NURBS object had multiple materials, ExtractRenderMesh forces you to keep only one and you can not really edit render meshes afterwards plus you have to manage to sets of objects now. This really needs to get fixed in the future specially since it used to work flawless before.