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Problems with interaction of 3D objects. I've found some beta-functions of RealityKit such as PhysicsBodyComponent, applyImpulse, addForce, applyAngularImpulse and etc.

I was trying to add physics characteristics to object 'vase' and making an impulse to object on event a tap or something like that.

It's really strange, after execution the commands, the physics characteristics are added normal and at same time impulses and force aren't added into object(see below at debugging output).

enter image description here

Output of debugging print:

Something 1 Optional(RealityKit.PhysicsBodyComponent(mode: RealityKit.PhysicsBodyMode.dynamic, massProperties: RealityKit.PhysicsMassProperties(mass: 0.2, inertia: SIMD3(0.1, 0.1, 0.1), centerOfMass: (position: SIMD3(0.0, 0.0, 0.0), orientation: simd_quatf(real: 1.0, imag: SIMD3(0.0, 0.0, 0.0)))), material: RealityKit.PhysicsMaterialResource, isTranslationLocked: (x: false, y: false, z: false), isRotationLocked: (x: false, y: false, z: false), isContinuousCollisionDetectionEnabled: false, teleport: false, userForce: SIMD3(0.0, 0.0, 0.0), userTorque: SIMD3(0.0, 0.0, 0.0), userLinearImpulse: SIMD3(0.0, 0.0, 0.0), userAngularImpulse: SIMD3(0.0, 0.0, 0.0)))

Something 5 Optional(RealityKit.PhysicsBodyComponent(mode: RealityKit.PhysicsBodyMode.dynamic, massProperties: RealityKit.PhysicsMassProperties(mass: 0.2, inertia: SIMD3(0.1, 0.1, 0.1), centerOfMass: (position: SIMD3(0.0, 0.0, 0.0), orientation: simd_quatf(real: 1.0, imag: SIMD3(0.0, 0.0, >0.0)))), material: RealityKit.PhysicsMaterialResource, isTranslationLocked: (x: false, y: false, z: false), isRotationLocked: (x: false, y: false, z: false), isContinuousCollisionDetectionEnabled: false, teleport: false, userForce: SIMD3(0.0, 0.0, 0.0), userTorque: SIMD3(0.0, 0.0, 0.0), userLinearImpulse: SIMD3(0.0, 0.0, 0.0), userAngularImpulse: SIMD3(0.0, 0.0, 0.0)))

As we can see, functions doesn't add impulses and force to the object 'vase'. Maybe I make something wrong.

Andy Jazz
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coolpolus
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    I don’t get why this is downvoted. The documentation is indeed quite sparse. And the API everything but self-explanatory. – HelloTimo Jul 09 '19 at 08:04

1 Answers1

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I don't think you're supposed to create instances of ModelEntity directly. I think that is an internal component of the Entity class representing just the mesh. You augment the interactions/animations directly with components in RealityKit. These apply to the entire entity object. I think it's similar to how if you create a Metal view, you need it to be backed by a Core Animation layer in order to get access to user interactions.

If you look at the SwiftStrike sample application they do not directly instantiate ModelEntity which leads me to believe that it's not best practice to create those outside of an Entity object.

I believe you would add your vase to the project through Reality Composer. You can apply materials and collisions to it there. You can also add behaviors like responding to touch. Then you can access the vase through the reality composer file in Xcode and add components to the vase entity that will transform its position. All entities have a transform component, which is documented here.

RealityKit feels like it was designed to abstract as much code away from the programmer as possible, so a lot of the underlying architecture isn't really exposed or documented. It's also not organized the way that I would organize it, but I don't have a lot of familiarity with the Entity-Component design pattern.

If you don't like how RealityKit is laid out you also have the option to use SceneKit as a renderer. That does not abstract away as much of the functionality and allows you to use Core Animation commands directly on objects.

Janie Larson
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    Are you not able to create meshes at runtime then? For example, if every frame I wanted to modify some vertices, can I do that? —or instancing? The main thing that I like about RealityKit is the network and object synchronization, but I’d need to be able to make objects dynamically in the program – synchronizer Aug 08 '19 at 14:54
  • Yes you can, but you have to make it a RealityKit entity and not just a ModelObject. The mesh/ModelObject is just one property on RealityKit entities. – Janie Larson Aug 09 '19 at 15:06