(caption: A screenshot of Marvelous, with the 3D viewport showing a garment ‘optimized’ for cloth sim in Unreal)

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Exporting

Once you have an outfit put together in Marvelous, export everything as an FBX. For export settings, choose 'thin’, ‘single object’, and ‘unweld’. And don’t export the textures.

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Old problems:

In previous iterations of the pipeline, I chose ‘welded’ on the export. Welding merges edges where there’s stitching between two patterns, which results in non-manifold geometry. It’s actually not bad, Unreal and Maya’s rigging tools aren’t bothered by non-manifold geometry. But non-manifold geometry is entirely incompatible with Maya’s UV editing tools. It’s best to layout the UVs and then weld verts and then rig.

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Marvelous’ UV editing tools are… limited. Exporting a garment as a .OBJ and fixing the UVs in Maya seems like a good idea but MD is a one-way street. Too much data is lost exporting it to reimport it. I asked the Marvelous Designer discord forum and nobody had a solution for getting a garment back into Marvelous once exported.

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When discarding Marvelous’ textures in favor of good UV layouts, some details are lost. In my project, the most notable example was buttonholes. The reason for this is that the buttonholes are textures on loose pieces of geometry, not actual geometry (like the topstitching is). This is no great loss, because Marvelous doesn’t handle hardware well in simulations (because it is not optimized for rigid body simulations, the buttons take a long time to settle down). It is better to place the buttons on a single layer of fabric and then to create the buttonholes in Substance Painter.

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UV Editing, Merging, Skin Weights, and Texturing

 

Then UV layout the garments. I just do the auto layout. The default layout tool shouldn’t rotate your UV shells, which is good because they should already be rotated correctly because Marvelous matches the UV rotation to the 2D pattern window, and the 2D pattern window is how cloth would actually be cut.

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I also deleted faces that were hidden by layering. As long as the area is fitted to the body, this has no effects.

Once the UVs were good, I selected all the verts and merged to a distance of .001, which is the lowest. This distance is good because the verts along the sewn edges have no distance between them.

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For the piping, I used the target weld tool to clean it up.

Topstitching, which looks really cool, isn’t compatible with UE cloth sim tools. So it’s best to save off a ‘high poly’ version, remove the topstitching (it’s easy with mesh -> separate) and then use Substance to add the ‘high poly’ stitching to the normal map.

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Old problems:

I used to export ‘welded’ from Marvelous. Box pleats cause nonmanifold geometry.  Fixing this (prompt occurs when trying to layout UVs) causes a ton of single-face loose pieces. To prevent this, export the garments ‘unwelded’, layout the UVs, then merge verts at a low distance.

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With 'welded' exports, I had a workflow like this: Select the geometry around the loose triangles. The default distance threshold is too high, so reduce it to .001. Then select the edges of loose triangles that resulted from cleaning up the nonmanifold geometry. These, so far in my experience, have been the result of pleating and piping in Marvelous. Use Shift+> and the stitch together tool to get multi stitching. (Multi-stitching is great but takes a lot of RAM.) When stitching, it’s best not to include a UV shell that already has a lot of geometry. The reason for this is that the stitching tool needs to think through the entire shell, not just the edges selected. The sewing tool doesn’t have this problem, and can be used with any size of shell.

 

Skin Weighting

Unreal Engine needs clothing to be skinned to the Metahuman base skeleton. To do this quickly, I just added the ‘_preview’ FBX to my maya scene, bound the garment to the skeleton, and then used the copy skin weights tool to get the weights from the ‘_preview’ mesh.

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The resulting weights would be good enough for a fitted outfit, but my outfit is fairly loose, so I had to clean up the skin weighting.

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Since the culottes are very long, the fronts were skin weighted to the tops of the feet, which resulted in the clothes appearing to be caught on the feet, even after cloth sim was applied. This could be fixed by hammering skin weights.

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Another problem area was under the sleeves, near the ribs. Since the clothing here was closer to body preview’s ribs than its arms, the underside of the sleeves were weighted to the spine. Even enabling UE5’s geodesic [image name] setting in the cloth configs, it looked odd. This couldn’t be fixed by just hammering verts, I needed to actually open Maya’s paint skin weights tool and flood weight the verts to the correct bone. Same process with the inner thighs.

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I also used the paint skin weights tool on the collar. Since the shirtwaist has a high collar, it extends higher than the body preview mesh that I copied skin weights from.  Unfortunately, because Metahuman necks have odd bones, this gave me imperfect results. The shirtwaist’s collar clipped into the neck until I made some extreme adjustments to the physics asset. (I tried combining the face skeletal mesh with the body and then copying the shirtwaist’s skin weights from that, but it didn’t work.)

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For hardware (ex: buttons), I just selected a vertex near where the item connects to the fabric (ex: the middle of a button), copied skin weights and then selected the whole item and pasted skin weights. This prevents the solid pieces from stretching when the bones move.

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The cleanup looks like it would be time consuming, but once I got it working correctly once, I could instantly copy skin weights from the cleaned up version to any new iterations of the garment. In the entire project, I probably only spent three hours skin weighting.

 

Old Problems:

A something that repeatedly tripped me up was that UE can’t handle groups within FBXs. The reason is that UE interprets groups as bones in skeletal meshes (which makes sense. They’re both just positions and places in the hierarchy). Since importing an FBX into Maya (such as the ‘_preview’ skeletal mesh that I was copying weights from) results in the FBX’s contents being automatically grouped, the resulting skeletal mesh didn’t match the default skeleton anymore and couldn’t be imported. It’s an easy fix.

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Top stitching needs to be baked to texture, not persist as geometry. This is because they’re loose pieces, they don’t actually share any geometry with the main garment. By default, they’re exported in a single object with the garment, with the same material applied. Trying to create cloth from a mesh that has multiple loose pieces results in Unreal hanging. Even applying cloth data created on another piece of geometry won’t work.

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Cloth Sim on Metahumans

Since my metahuman came with a default shirt and pants, I was able to replace those nodes in the Metahuman blueprint with my own assets. Doing this early in the process gave me a way to quickly see the cloth simulation in context.

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Creating Clothing Data

My final cloth assets (the best results I had) were actually created from ‘low poly’ versions. I took the finished FBXs of the skinned and textured clothes, put them in Blender, and decimated the vertices by around half (the default Blender decimate tool doesn’t cause ‘shrinking’, so it’s better for preventing clipping). Then I put the decimated version in Unreal and created clothing data from selection. I stayed on the decimated version while I did the first pass cloth painting and parameters, and then added the clothing data to my original (not decimated) clothing. Using decimated versions for the first pass cloth simulation is better because it loads faster and almost never crashes. It’s best for quick feedback while making large changes, but it’s not useful for fine-tuning.

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Physics asset

In my experience, about 30% of what I thought at first were cloth parameter problems were easily fixed by adjusting the physics asset. The cuffs of the sleeve look lumpy? Scale down the Y axis on the forearms. The neck is clipping with the shirt? Scale up and adjust the positions of the physics bodies for the neck, head, and clavicles.