RetopoGEN User Guide

Turn a detailed mesh into a lighter mesh, check it beside the original, and save the result as a new Unreal asset.

RetopoGEN works with Static Meshes such as props and scenery, and Skeletal Meshes such as animated characters and creatures. Its workspace is called Retopo LAB.

Retopology means changing the small faces that make up a model. Reducing those faces can make a model less expensive to render. The aim is to use fewer faces while keeping the shape and appearance you need.

Your original mesh stays unchanged. You work on a preview and choose when to export a new asset. Processing happens locally on your computer.

Contents

• Your first retopology: start here
• Enable the plugin and open a mesh
• Find your way around Retopo LAB
• Choose a retopology tool
• Adjust the settings
• Check the result
• Edit UVs and keep textures looking right
• Export and use your new mesh
• Work with characters and creatures
• Save settings for another session
• Troubleshooting

Your first retopology: start here

For your first attempt, choose a mesh that already looks correct in Unreal.

1. Find the mesh in the Content Browser or Content Drawer.
2. Right-click that one mesh and choose Edit in Retopo LAB....
3. Wait for the model to appear. It loads automatically; you do not need to click Load Source.
4. Leave the settings at their defaults. The triangle target starts at half of the loaded mesh's triangle count.
5. Click AutoRemesh Quads on the left.
6. Wait for processing to finish, then click COMPARE above the preview.
7. Compare the shape of the original and the result. Turn off Result wireframe to check the materials and textures.
8. If the result looks good, click Export Result Mesh.
9. Open Content > HKH > RetopoGEN in the Content Browser. Your new mesh is saved there. Double-click it to inspect it in Unreal's mesh editor.

Example: a source with 40,000 triangles starts with a target of 20,000. This is a starting goal, not a guaranteed final count. Check the actual result in Topology Health.

If the result loses too much detail, increase Auto Remesher > Target Triangles and click AutoRemesh Quads again. Try a few counts before choosing the version you want to keep.

Enable the plugin and open a mesh

Enable RetopoGEN

With the plugin installed in your Unreal project, open Edit > Plugins, search for RetopoGEN, and enable [HKH] RetopoGEN. Restart the Editor if prompted. This version targets Unreal Engine 5.8 on Windows.

You do not need VellForge to use RetopoGEN.

Open from the Content Browser

Select one Static Mesh or Skeletal Mesh asset, right-click it, and choose Edit in Retopo LAB.... Use the mesh asset itself, rather than a material, Skeleton asset, Blueprint or object selected in the level.

Opening the same mesh again brings its existing Retopo LAB session forward.

Open an empty workspace

Choose Window > Retopo LAB. In the Inspector, expand Source:

1. Set Source Type to Static Mesh or Skeletal Mesh.
2. Choose the asset in Source Mesh or Source Skeletal Mesh.
3. Leave Source LOD at 0 for the first attempt.

An LOD is a version of a mesh with a different level of detail. LOD 0 is normally the most detailed version. Choose another LOD only if your source asset already has it.

Selecting a source or changing its LOD loads it automatically. Load Source reloads the current selection. Every successful load resets both triangle targets to half of that source LOD's triangle count, so set your preferred target after loading.

What can I load?

The selected source LOD must contain 1 to 2,000,000 triangles and editable mesh data. Targets can be set from 1 to 1,000,000 triangles.

Import external model files into Unreal first. Retopo LAB opens Unreal mesh assets; it does not open an FBX or OBJ file directly. For a Nanite asset, it uses the editable source LOD, not Nanite's internal rendering geometry.

Meshes with open edges or holes are supported. RetopoGEN can automatically repair some connectivity problems on its working copy. It does not fill the model's holes.

Find your way around Retopo LAB

Changing settings means you must run the tool again before exporting. A mesh may still be visible from a previous attempt, but it is not a current result for the new settings.

Each retopology tool starts from the loaded source, rather than repeatedly reducing the previous result. Finish retopology before editing UVs. Running another retopology operation replaces the working result and its UV edits; export a version first if you want to keep it.

Choose a retopology tool

You only need to run one of these tools for an attempt. They are alternatives, not three required steps.

A quad is a face with four sides. Unreal still renders it as two triangles. For example, 5,000 quads use 10,000 render triangles if there are no additional triangle faces. Target Triangles always means triangles, not quads.

AutoRemesh Quads may keep some triangle faces in difficult regions. It will not increase the output above the loaded source triangle count, but it may keep more triangles than your requested target to retain a usable shape. It does not guarantee an all-quad result or the carefully arranged joint loops of a manually retopologized character.

Adjust the settings

AutoRemesh Quads settings

Expand Auto Remesher in the Inspector.

A small object may need a smaller deviation goal than a large statue. Setting Max Deviation to 0 disables its distance warning; it does not improve the mesh.

Optimize and Remesh + Optimize settings

For these two tools, use Target Triangles under Retopology, not the one under Auto Remesher.

Leave the four Constraints checkboxes enabled at first:

These checkboxes affect Optimize and Remesh + Optimize. AutoRemesh Quads uses its own shape and texture-transfer behavior.

If reduction is very limited, you can try turning off one protection at a time and inspect the change. For example, relaxing hard-normal protection may help a smooth organic model, but may soften the appearance of a mechanical part.

Check the result

Click COMPARE and inspect the model from several angles. Check the outer shape, small openings, thin pieces and material borders. With Result wireframe off, look for stretched textures or unusual shading. With it on, look at the arrangement of faces.

Understand Topology Health

The UV counts do not detect every overlap or texture problem. A warning is a reason to inspect the result, rather than an automatic instruction to discard it.

If the shape looks poor, raise the triangle target and rerun. If the result still has nearly as many triangles as the source, try Optimize, or use a less aggressive target on a mesh with many small separate parts.

Edit UVs and keep textures looking right

UVs tell Unreal which part of a texture belongs on each face. RetopoGEN transfers the source UVs and material assignments to the new mesh. This helps retain the existing look, but a larger new face may cover several old texture or material regions, so the transfer may need adjustment.

You can skip UV editing if the result already looks correct. RetopoGEN does not repaint or rebake your textures. Moving, repacking or unwrapping UVs can change where an existing texture appears on the model.

Apply a UV edit

1. Finish your retopology attempt, then click UV Editor on the Tool Shelf.
2. Choose the UV channel you want to edit. Channel 0 is commonly used for surface textures; other channels may serve different purposes in your materials.
3. Select the faces, edges or UV islands you want to work on. An island is a connected patch of the flattened texture layout.
4. Choose a tool and adjust its settings. Use Transform to move, rotate or scale an existing layout. Seam, Split and Sew change where patches separate or join. Unwrap creates a new flattening; Layout packs existing islands; AutoUV unwraps and packs automatically.
5. Click Accept to finish a tool that has an Accept button. Then click Apply to send the accepted UV changes back to the RetopoGEN result.
6. Close the UV Editor tab to return to retopology and make the Inspector settings editable again.
7. Check the textured result, then click Export Result Mesh to save it.

Accept finishes the current UV tool. Apply updates the working result. Export Result Mesh saves the mesh asset. They are separate steps.

UV Apply supports undo and redo while the UV session is open. If a close or export prompt offers Apply / Discard / Cancel, choose Apply to keep pending UV edits, Discard to leave them out, or Cancel to return to editing.

You can also use Retopo LAB just for UV editing: load a source and open UV Editor without running a retopology tool. It creates a working copy for you to edit and export.

Export and use your new mesh

1. Check that processing has finished and the displayed result is the version you want.
2. Apply any UV changes you want to keep.
3. Click Export Result Mesh on the left.
4. Wait for the Processing message to confirm that the mesh was saved. The message includes its asset path.
5. In the Content Browser, open Content > HKH > RetopoGEN. The path shown in messages as /Game/HKH/RetopoGEN refers to this same folder.
6. Find the new mesh. Static Mesh names begin with SM_; Skeletal Mesh names begin with SK_. Names include _Retopo, with a unique suffix when needed. You can rename the exported asset in the Content Browser.
7. Double-click the asset to inspect it in Unreal's mesh editor. For a prop, drag the new Static Mesh into a level to try it. For a character, check the Skeletal Mesh with its intended animations before assigning it to your character.

Export saves a new Unreal mesh asset. It does not overwrite your original or automatically replace meshes already used in a level or Blueprint. The Output section also shows the latest asset in Last Export or Last Skeletal Export.

This button is not an FBX/OBJ file export dialog. If you need an external file, use Unreal's available asset export options on the newly saved mesh.

What carries into the exported asset?

The new mesh keeps its source type, material slots and assignments, UV channels and original size and position relative to its origin. The preview's side-by-side spacing does not become part of the exported geometry.

Only the selected source LOD is processed. It becomes LOD 0 of the new asset. Additional LODs, mesh sockets and source Nanite settings are not copied. Set up those features on the new asset if your project needs them.

For Static Meshes, export uses the mesh surface for collision and does not copy the source's simple collision shapes. Review collision in the Static Mesh Editor before using the result in gameplay, especially for objects that need physics simulation.

Work with characters and creatures

Open a Skeletal Mesh using the same right-click shortcut. It appears in its reference pose, the resting pose used by its skeleton, rather than playing an animation.

RetopoGEN transfers UVs, materials and skin weights, including named weight profiles. Skin weights determine how strongly each bone moves each part of the mesh. The exported mesh uses the original Skeleton asset.

After export, test poses that bend the elbows, knees, shoulders, fingers and any other important joints. If bending looks worse, try a higher triangle target. A mesh can look good while standing still and still need more detail around moving joints.

Morph targets, clothing bindings and physics assets are not copied. For example, facial morph expressions or cloth simulation will need separate setup on the new mesh. Retopo LAB does not provide animation editing or skin-weight painting.

Save settings for another session

Opening a mesh from its shortcut creates a temporary session. Export any result you want to keep before closing it.

To keep a reusable set of settings:

1. Right-click an empty area in the Content Browser.
2. Choose HKH > HKH RetopoGEN Asset.
3. Give it a useful name, such as Retopo_StoneStatue.
4. Open it, choose your source, run a tool and export the result.
5. Use the Editor's Save command to save this settings asset.

This asset remembers source/settings and last-export references. It does not store the working preview or UV editing session. When reopened, it loads the source automatically; loading resets the triangle targets to half the source count. Set a different target again if needed, then rerun the tool. Previously exported mesh assets remain saved independently.

Troubleshooting