Learn how to create invisible collision meshes in Houdini using the collision_geo primitive group for use in game engines.

In Houdini

  1. Install, instantiate, and unlock the Collisions_InvisibleCollisionMeshes_Start.hda example in Houdini.
  2. Go inside the Collisions_InvisibleCollisionMeshes1 node in the network editor.
  3. Here we have a OBJ node, planet, with a fairly dense mesh. We want to create a lighter mesh that approximates the planet for its collision geometry.
  4. Create Sphere OBJ node by hitting Tab, typing sphere, and pressing Enter.
  5. Go inside the newly created Sphere OBJ, sphere, and select the Sphere SOP, sphere1.
  6. In its parameters, change Primitive Type to Polygon.
  7. Hit Tab, type group, and press Enter to create a Group SOP.
  8. Connect sphere1 to the first input of the newly created group1 node and move the blue display flag from sphere1 to group1.
  9. In group1 node's parameters, set its Group Name parameter to collision_geo, Entity to Primitives, and Number > Pattern to *.
  10. In Houdini's top-menu, click on Assets > Save Asset > Collisions_InvisibleCollisionMeshes.

In Unity

  1. Go to Houdini Engine > Load Houdini Asset... and find your Collisions_InvisibleCollisionMeshes_Start.hda asset.
  2. In the Inspector, make sure Asset Settings > Auto Select Asset Root Node is disabled.
  3. In the Hierarchy window dive down to and select Collisions_InvisibleCollisionMeshes1 > sphere > group1 > collision_geo_0.
  4. Notice the Mesh Collider component.
  5. Instantiate in Unity the HoudiniAsteroid prefab from HoudiniAsteroid.unitypackage somewhere above the planet.
  6. Press Play in Unity and watch the asteroid hit the planet's collider.


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