Billboarding Anchor's Child Entity in RealityKit

Question

utahwithak OP

Created Mar ’24

Replies 1

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Participants 2

Trying to find some answers on why billboarding isn't working when attaching to an entity that is a child of an anchor.

I'm trying to billboard an attachment so that it remains pointed at the user wherever they're viewing the content from. For example, showing some context information over dynamic 3d model on the table top. Not baked into a Reality Composer pro scene. I pulled the component and system used in the various Apple example projects (Diorama) that have the billboarding system.

Playing around with the system and component I can add a simple model entity to the scene, tag it with the component and it works perfectly, all the time. As the camera moves it tracks it perfectly. Even when nested under other empty entities or off center or oddly rotated.

Great! Then I wanted to apply this to an attachment that is shown from a model entity that is anchored to a horizontal plane and all of the sudden it doesn't work at all.

I create the anchor:

let anchor = AnchorEntity(.plane(.horizontal, classification: .table, minimumBounds: [0.01, 0.01]))

if let lookAtText = attachments.entity(for: "LookAtMe") {
    lookAtText.position = [0,0.5,0]
    lookAtText.components.set(BillboardComponent())
    lookAtText.name = "Look At Me"
    anchor.addChild(lookAtText)
}
content.add(anchor)

The attachment shows correctly above the anchor, as expected, and does rotate some, just totally wrong or stops, It does not billboard correctly, or even remotely correctly.

if I switch the anchor.addChild to be a content.add it isn't in the correct place, but billboarding works.

I don't understand why adding it as a child to the anchor entity suddenly breaks completely unrelated systems.

Am I doing something wrong or is this some sort of privacy issue? I can't find any documentation that using the look at api from an anchored entity is somehow forbidden.

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Answer 1

DTS Engineer OP

Apple

Mar ’24

Hello @utahwithak,

I believe that the reason this doesn't work as you'd expect when the entity you are billboarding is a child of an AnchorEntity, is because AnchorEntity exists in an independent coordinate space, your app has no access to the AnchorEntity's relationship to your ImmersiveSpace's coordinate system.

One alternative you can consider is using ARKit directly for plane detection (you would have to coordinate the PlaneAnchor-to-Entity relationship yourself). This approach does require the user to grant world sensing permission to your app. See Placing content on detected planes for more on this topic.

Otherwise, I recommend that you file an enhancement request for AnchorEntity to support the functionality you are trying to build via Feedback Assistant.

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