How to use Raycast methods in RealityKit? - swift

Question

There are three ways about Detecting Intersections in RealityKit framework, but I don't know how to use it in my project.
1.
func raycast(origin: SIMD3<Float>,
direction: SIMD3<Float>,
length: Float,
query: CollisionCastQueryType,
mask: CollisionGroup,
relativeTo: Entity?) -> [CollisionCastHit]
2.
func raycast(from: SIMD3<Float>,
to: SIMD3<Float>,
query: CollisionCastQueryType,
mask: CollisionGroup,
relativeTo: Entity?) -> [CollisionCastHit]
3.
func convexCast(convexShape: ShapeResource,
fromPosition: SIMD3<Float>,
fromOrientation: simd_quatf,
toPosition: SIMD3<Float>,
toOrientation: simd_quatf,
query: CollisionCastQueryType,
mask: CollisionGroup,
relativeTo: Entity?) -> [CollisionCastHit]

Answer 1

Simple Ray-Casting
If you want to find out how to position a model made in Reality Composer into a RealityKit scene (that has a detected horizontal plane) using Ray-Casting method, use the following code:
import RealityKit
import ARKit
class ViewController: UIViewController {
#IBOutlet var arView: ARView!
let scene = try! Experience.loadScene()
#IBAction func onTap(_ sender: UITapGestureRecognizer) {
scene.steelBox!.name = "Parcel"
let tapLocation: CGPoint = sender.location(in: arView)
let estimatedPlane: ARRaycastQuery.Target = .estimatedPlane
let alignment: ARRaycastQuery.TargetAlignment = .horizontal
let result: [ARRaycastResult] = arView.raycast(from: tapLocation,
allowing: estimatedPlane,
alignment: alignment)
guard let rayCast: ARRaycastResult = result.first
else { return }
let anchor = AnchorEntity(world: rayCast.worldTransform)
anchor.addChild(scene)
arView.scene.anchors.append(anchor)
print(rayCast)
}
}
Pay attention to a class ARRaycastQuery. This class comes from ARKit, not from RealityKit.
Convex-Ray-Casting
A Convex-Ray-Casting methods like raycast(from:to:query:mask:relativeTo:) is the op of swiping a convex shapes along a straight line and stopping at the very first intersection with any of the collision shape in the scene. Scene raycast() method performs a hit-tests against all entities with collision shapes in the scene. Entities without a collision shape are ignored.
You can use the following code to perform a convex-ray-cast from start position to end:
import RealityKit
let startPosition: SIMD3<Float> = [0, 0, 0]
let endPosition: SIMD3<Float> = [5, 5, 5]
let query: CollisionCastQueryType = .all
let mask: CollisionGroup = .all
let raycasts: [CollisionCastHit] = arView.scene.raycast(from: startPosition,
to: endPosition,
query: query,
mask: mask,
relativeTo: nil)
guard let rayCast: CollisionCastHit = raycasts.first
else { return }
print(rayCast.distance) /* The distance from the ray origin to the hit */
print(rayCast.entity.name) /* The entity's name that was hit */
A CollisionCastHit structure is a hit result of a collision cast and it lives in RealityKit's scene.
P.S.
When you use raycast(from:to:query:mask:relativeTo:) method for measuring a distance from camera to entity it doesn't matter what an orientation of ARCamera is, it only matters what its position is in world coordinates.