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Rhino to UE4 via Datasmith - displacement map driven tessellation not working

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    Rhino to UE4 via Datasmith - displacement map driven tessellation not working

    Full disclaimer, I'm brand new to UE4 so maybe the answer to this question should be obvious.

    As an architecture student, my 3D workflow has only involved Rhino. So far importing from Rhino to UE4 via Datasmith is smooth and easy, making it simple to turn my projects into a more interactive experience.

    However, I can't get texture tessellation to work. I am using Megascans materials, imported directly from Quixel Bridge, and they come preset with tessellation parameters and displacement maps. Enabling tessellation and applying the materials to a BSP works fine. I can parametrically control them no problem. The problem arises when I try to apply those same materials to meshes imported from Rhino. The mesh shows only the default grey grid texture even after rebuilding the lighting. Interestingly enough, the tessellation works fine in the static mesh editor, just not in the scene itself. The material editor also does not give me any errors. Turning off tessellation applies the material and all its other properties correctly. The meshes in question are simple planes (walls) showing as static mesh actors in UE4. In Rhino, they are NURB surfaces. I did not do any conversion beforehand, Datasmith covered that.

    Troubleshooting this, I imported the same 3D model as an obj, bypassing Datasmith, and the tessellation works just fine on the static meshes there. So what gives? Am I missing something obvious here? I would much prefer to use Datasmith, especially as it seems to make the auto-generate Lightmaps process much easier. For some reason, Datasmith imports two UVs when importing from Rhino. The UV that I've mapped (custom mapping for things like arches, mapping for proper texture tiling, etc) and another that mysteriously appears, even though I've only mapped one channel in Rhino (Rhino supports multichannel UVs but you can't actually edit the second channel in any meaningful way, other than the basic planar/box/etc, not helpful for Lightmapping and also tends to override the texture mapping). Even though I'm a bit stumped by this behavior, UE4 generates the Lightmap from the second, mysterious UV channel and this produces (so far) clean Lightmaps so I'm absolutely not complaining on this part. Importing as obj or fbx, however, almost always results in overlapping Lightmaps because there is only one, often custom mapped channel, for UE4 to choose from.

    To summarize: I'm having trouble with material-driven tessellation on meshes imported with Datasmith from Rhino, and for the purposes of better auto-generated Lightmaps, I'd like to continue using Datasmith to import Rhino files.

    Thank you in advance!

    #2
    From my experimentation, a material will not show on Rhino Datasmith meshes unless you have Flat Tessellation selected in the Tessellation Mode, not PN Triangles, and Crack Free Displacement cannot be checked. But without the crack free option the planes of all your meshes split at the seams and leave you with sizable gaps when trying to apply a visible amount of displacement.

    FBX and OBJ imports don't have this problem with the same Rhino meshes. I don't understand why the seamless crack free option would be unavailable with Datasmith content as displacement is a pretty important thing to make your scenes look more realistic. Can we add this to a wishlist somewhere with the UE4 devs?

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