USDZ availableAnimations and collision behaviors in Entity vs ModelEntity

Question

I bought 2 USDZ models from Sketchfab. But I don't understand why the behavior is different.

The first model, I can use ModelEntity adding the object.model!.mesh.bounds.extents and storing the object.availableAnimations[0]

struct ImmrsiveView: View {

    @State var object: ModelEntity? = nil
    @State var animation: AnimationResource? = nil

    var body: some View {
        RealityView { content in
            do {
                object = try await ModelEntity(named: "speaker")

                if let object {

                    let objectBound = object.model!.mesh.bounds.extents
                    object.components.set(CollisionComponent(shapes: [.generateBox(size: objectBound)]))
                    object.components.set(InputTargetComponent())

                    animation = object.availableAnimations[0]
                    content.add(object)
                }
            }
            catch {
                print("Error loading the model")
            }
        }
    }
}

However, when I use the second USDZ file (by simply changing the entity name),

1. The model doesn't load, to fix this, I must change the object type to Entity even though the loader is ModelEntity.load(named: "object") with a warning: No 'async' operations occur within 'await' expression.
2. But then there's no .mesh.bounds.extents for Entity. The collision doesn't work
3. As an Entity, now the availableAnimations[0] works!

So now the code becomes

struct ImmrsiveView: View {

    @State var object: Entity? = nil
    @State var animation: AnimationResource? = nil

    var body: some View {
        RealityView { content in
            do {
                object = try await ModelEntity.load(named: "object2")

                if let object {

                    // This doesn't work
                    // let objectBound = object.model!.mesh.bounds.extents
                    // object.components.set(CollisionComponent(shapes: [.generateBox(size: objectBound)]))
                    // object.components.set(InputTargetComponent())

                    animation = object.availableAnimations[0]
                    content.add(object)
                }
            }
            catch {
                print("Error loading the model")
            }
        }
    }
}

The questions are ... suppose there are different ways of loading USDZ files:

1. How can I get rid of the warning?
2. How can I fix the collision for the 2nd object?

Answer 1

You can use the ModelEntity(named:) initializer to load your character as model entity to assign a collision shape to it...

import SwiftUI
import RealityKit

struct ContentView : View {
    @State var object = ModelEntity()
    @State var animation: AnimationResource? = nil

    var body: some View {
        RealityView { rvc in
            do {
                object = try await ModelEntity(named: "Man")
                object.position.z = -3.0
                object.name = "Character"    
                object.generateCollisionShapes(recursive: true)
                object.components.set(InputTargetComponent())
                animation = object.availableAnimations[0].repeat()
                object.playAnimation(animation!)
                rvc.add(object)                  
                print(object.model?.mesh.bounds.extents as Any)
            } catch {
                print("Error loading the model")
            }
        }
        .gesture(gesture)
    }       
    var gesture: some Gesture {
        TapGesture()
            .targetedToEntity(object)
            .onEnded {
                print($0.entity.name)
            }
    }
}

...however, the only "righteous" RealityKit's way is to find the ModelEntity within the hierarchical structure in your USDZ.

struct ContentView : View {
    @State var object = Entity()
    @State var animation: AnimationResource? = nil

    var body: some View {
        RealityView { rvc in
            do {
                object = try await Entity(named: "Man")
                object.position.z = -3.0                  
                // find the model entity's name in the hierarchy
                // in my case it's "skin0"
                print(object)
                
                let me = object.findEntity(named: "skin0") as! ModelEntity
                me.generateCollisionShapes(recursive: true)
                me.components.set(InputTargetComponent())
                animation = me.availableAnimations[0].repeat()
                me.playAnimation(animation!)
                rvc.add(object)
                print(me.model?.mesh.bounds.extents as Any)
            } catch {
                print("Error loading the model")
            }
        }
        .gesture(gesture)
    }        
    var gesture: some Gesture {
        TapGesture()
            .targetedToEntity(object)
            .onEnded {
                print($0.entity.name)
            }
    }
}