for visionOS gestures, generate a box with its surfaces facing inward

Inwardbox.swift

import RealityKit

extension ShapeResource {
    /// generate a box with its surfaces facing inward.
    /// NOTE: size 30 works with interactions, 50 does not work with interactions
    static func generateInwardBox(size: Float) async throws -> ShapeResource {
        // An array of vertex positions containing discrete points on the mesh.
        let meshPositions: [SIMD3<Float>] = [
            .init(-1, -1, -1), // 0 LBF
            .init(+1, -1, -1), // 1 RBF
            .init(+1, +1, -1), // 2 RTF
            .init(-1, +1, -1), // 3 LTF
            .init(-1, -1, +1), // 4 LBB
            .init(+1, -1, +1), // 5 RBB
            .init(+1, +1, +1), // 6 RTB
            .init(-1, +1, +1), // 7 LTB
        ].map { $0 * size / 2 }
        // An array of integers used to index into the position array. 3 indices per polygon are used to define a polygon in the mesh.
        // left turn only
        let meshFaceIndices: [UInt16] = [
            0, 1, 2, // front
            0, 2, 3, // front
            0, 3, 7, // left
            0, 7, 4, // left
            1, 6, 2, // right
            1, 5, 6, // right
            4, 7, 6, // back
            4, 6, 5, // back
            3, 6, 7, // top
            3, 2, 6, // top
            0, 4, 5, // bottom
            0, 5, 1 // bottom
        ]
        return try await ShapeResource.generateStaticMesh(positions: meshPositions, faceIndices: meshFaceIndices)
    }
}