Houdini 20.5 Unreal Meshes

Collision types

On this page

The collision system in Unreal Engine refers to the detection of a physical interaction between objects in the level.

Houdini Engine for Unreal can generate collision from many types and sources:

To create collision, assign your geometry to the Group SOP node and use the proper attribute prefix as the group name.

See Setup collision for an asset for different methods to create collisions in Houdini.

If you use your original static mesh to generate a collision, you must use the rendered (visible) prefix attributes for both the collision and your static mesh to appear in Unreal Engine.

If you create a custom collision, you can use the without rendered (invisble) prefixes.

Complex collision

This is the default collision behavior for Houdini Engine.

Complex collisions generates colliders using the exact model of your static mesh. This results in an accurate collision but is more expensive than simple or convex collisions if your static mesh has high triangle count.

Complex collisions can be useful for objects that have irregular or complex shapes such as rocks, trees, or characters.

Note

Complex collisions DO NOT work for physical simulations.

Example: Collision in Unreal Engine using the rendered_collision_geo attribute

Convex collision

Convex collisions are simplified geometries made from a set of convex polygons. These can be generated as simple colliders in Unreal. You can use convex collisions for both collision and phyiscal simulation.

Simplified collision geometries help optimize collision detection in-game.

Example: Collision in Unreal Engine using the rendered_collision_geo_ucx attribute

Simple collision

A simple collision is a basic shapes such as a box, sphere, capsule or K-DOP. You can use simple collisions for both collision and phyiscal simulation.

See Unreal’s K-DOP Documentation for more information.

Simple collisions can be useful for simple objects such as walls, floors, or basic shapes.

Example: From left to right - rendered_collision_geo_simple_box, rendered_collision_geo_simple_sphere, rendered_collision_geo_simple_capsule
Example: From left to right - rendered_collision_geo_simple_kdop10×, rendered_collision_geo_simple_kdop10y, rendered_collision_geo_simple_kdop10z
Example: From left to right - rendered_collision_geo_simple_kdop18, rendered_collision_geo_simple_kdop26

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.

Level of detail (LOD) collisions

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

See Level of Details to setup your mesh for LODs.

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

See Setup collision for an asset to create a collision from an LOD.

Groups

Some special group names have naming schemes which specify generation behavior when marshalling data from Houdini to Unreal.

Collisions

Complex collision

Group name

Description

collision_geo

Creates a complex collision (invisible)

rendered_collision_geo

Creates a complex collision (visible)

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.

Convex collision

Group name

Description

collision_geo_ucx

Creates a convex hull collision (invisble)

rendered_collision_geo_ucx

Creates a convex hull collision (visible)

Simple collision

Group name

Description

collision_geo_simple

Creates a default simple collision (invisible)

rendered_collision_geo_simple

Creates a default simple collision (visible)

collision_geo_simple_box

Creates a simple box collision (invisible)

rendered_collision_geo_simple_box

Creates a simple box collision (visible)

collision_geo_simple_sphere

Creates a simple sphere collision (invisible)

rendered_collision_geo_simple_sphere

Creates a simple sphere collision (visible)

collision_geo_simple_capsule

Creates a simple capsule collision (invisible)

rendered_collision_geo_simple_capsule

Creates a simple capsule collision (visible)

collision_geo_simple_kdop10x

Creates a simple 10DOP-X collision (invisible)

rendered_collision_geo_simple_kdop10x

Creates a simple 10DOP-X collision (visible)

collision_geo_simple_kdop10y

Creates a simple 10DOP-Y collision (invisible)

rendered_collision_geo_simple_kdop10y

Creates a simple 10DOP-Y collision (visible)

collision_geo_simple_kdop10z

Creates a simple 10DOP-Z collision (invisible)

rendered_collision_geo_simple_kdop10z

Creates a simple 10DOP-Z collision (visible)

collision_geo_simple_kdop18

Creates a simple 18DOP collision (invisible)

rendered_collision_geo_simple_kdop18

Creates a simple 18DOP collision (visible)

collision_geo_simple_kdop26

Creates a simple 26DOP collision (invisible)

rendered_collision_geo_simple_kdop26

Creates a simple 26DOP collision (visible)

Meshes