Houdini 20.5 Unreal Meshes

Setup collision for an asset

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There are multiple ways to setup collision with Houdini Engine for Unreal.

You can generate complex, convex, simple, or create your own custom collision.

To create these collisions, you assign your geometry or parts of it to the Group SOP node. The colliders are generated based on your Group Name in the Group SOP node parameter.

Note

If you use your original static mesh to generate a collision, you must use the rendered prefix attributes for the collision and your static mesh to appear.

See Collision types for further explanations and its attributes for your Group Name.

Generate collision from your asset

This is the basic method to generate a collision using the collision attributes, a single group, and your existing asset.

Example: Node network example to create a collision using your existing asset

  1. In the node network, go into the geometry level for your asset.

  2. Create a Group SOP node.

  3. Connect your object output to the input of Group SOP node.

  4. Select the Group SOP node, and open the Parameter Editor.

  5. In the Group Name, enter rendered_collision_geo_ucx.

  6. In the Base Group category, turn on Enable.

  7. Create an Ouput SOP node.

  8. Connect your Group SOP node output to the input of the Output SOP node.

  9. Create an HDA and import it to your Unreal project.

Example: Collision in Unreal Engine using the rendered_collision_geo_ucx attribute

Collision from multiple geometries

Example: Arch doorframe using a single collider and multiple colliders

This method generates collision from multiple geometries on a single asset.

This can be useful if you have areas like a doorframe or fence that a player can walk through without colliding with a single collision.

For multiple geometries, make sure the name group has a sequential suffix after the collision attributes. For example, the first collision is collision_geo_simple_1 and second is collision_geo_simple_2.

Warning

DO NOT use the rendered_collision_geo attribute for your custom collision. This results in Unreal generating a collision based on your original asset and not your custom collision.

Example: Node network to create multiple colliders for an asset

  1. In the node network, go into the geometry level for your asset.

  2. Create a Group SOP node.

  3. Connect your first collision geometry output to the input of Group SOP node.

  4. Select the Group SOP node, and open the Parameter Editor.

  5. In the Group Name, enter collision_geo_simple_1.

  6. In the Base Group category, turn on Enable.

  7. Repeat steps 2-6 for the rest of your collision geometry.

    • Make sure to change the end numerical value after the collision attribute prefix. For example, the first collision is collision_geo_simple_1, second is collision_geo_simple_2.

  8. Create a Merge SOP node.

  9. Connect the output of your multiple collisions and original asset to the input of the Merge SOP node.

  10. Create an Ouput SOP node.

  11. Connect your Group SOP node output to the input of the Output SOP node.

  12. Create an HDA and import it to your Unreal project.

Example: Using multiple geometries to generate collision for a single object

Collision from LOD

If your HDA has multiple LODs, you can use one of the LOD levels for your collision. LOD collisions uses complex collisions.

You need to use unreal_uproperty_LODForCollision as a detail attribute and set its value to the LOD level you want for your collision.

Example: Node network to create collision from an LOD

  1. In the node network, go into the geometry level for your asset.

  2. Create a Group SOP node.

  3. Connect your LOD0 geometry output to the input of Group SOP node.

  4. Select the Group SOP node, and open the Parameter Editor.

  5. In the Group Name, enter lod_0.

  6. In the Base Group category, turn on Enable.

  7. Repeat steps 2-6 for the rest of your LODs.

    • Make sure to change the end numerical value after the collision attribute prefix. For example, LOD0 is lod_0, LOD1 is lod_1.

  8. Create a Merge SOP node.

  9. Connect the output of all of your LODs the input of the Merge SOP node.

  10. Create an Attribute Wrangle SOP node.

  11. Select the Attribute Wrangle SOP node, and open the Parameter Editor.

  12. In the VEXpression, enter i@unreal_uproperty_LODForCollision = 1;

  13. Create an Ouput SOP node.

  14. Connect your Group SOP node output to the input of the Output SOP node.

  15. Create an HDA and import it to your Unreal project.

Meshes