Unreal Open USD

This repository contains an Unreal content plugin (OpenUSDGames) that demonstrates USD content building in Unreal.

- primal_cube

Notes

A collection of notes on the Unreal USD asset process.

Importing

• Reimporting a USD asset through the content browser uses the first imported USD asset during the editor session. This can reproduce as:

  1. Import a.usd
  2. Import b.usd
  3. Reimport b.uasset from the content browser.
  4. Reimport window shows contents from a.usd instead of b.usd.

• UAssets need to be manually reimported into Unreal.

  • Possible option to have automatic caching / update mechanism similar to mesh builds?

• Edits made to the UAsset in Unreal need to be manually exported back into the source USD file.

Materials

• Unreal material assignment can be done through the USD Stage View but can't be assigned from DCC (Maya, 3DSMax, etc.).
• Materials can be assigned in Unreal via the USD Stage View but only as a manually input string.
• Materials are bound via a custom string unrealMaterial = "/Game/foo" line.
• MaterialX workflows seem hindered by having the custom string attribute for both import and export, needs to be cleaner.

Collision

• PhysicsCollisionAPI and PhysicsMeshCollisionAPI can't be assigned from DCC.
• PhysicsCollisionAPI and PhysicsMeshCollisionAPI can be assigned through the USD Stage View, but not normal to user workflows.

LOD's

• LOD's can be created from DCC but must have a specific prim structure.
• No control on LOD switch distances or custom vs generated.