A floating bubble (morphing transparent sphere) RealityView created from a LowLevelMesh

BubbleRealityView.swift

import RealityKit
import SwiftUI

struct BubbleRealityView: View {
    @State private var currentEntity: Entity?
    @State private var morphFactor: Float = 0.0
    @State private var frameDuration: TimeInterval = 0.0
    @State private var lastUpdateTime = CACurrentMediaTime()
    
    static let animationFrameDuration: TimeInterval = 1.0 / 120.0
    private let timer = Timer.publish(every: animationFrameDuration, on: .main, in: .common).autoconnect()
    
    var body: some View {
        GeometryReader3D { proxy in
            RealityView { content in
                let size = content.convert(proxy.frame(in: .local), from: .local, to: .scene).extents
                let radius = Float(0.5 * size.x)
                currentEntity = try! createSphereEntity(morphFactor: 0, radius: radius)
                if let entity = currentEntity {
                    content.add(entity)
                }
            } update: { content in
                let size = content.convert(proxy.frame(in: .local), from: .local, to: .scene).extents
                let radius = Float(0.5 * size.x)
                if let modelComponent = try? getModelComponent(morphFactor: morphFactor, radius: radius) {
                    currentEntity?.components.set(modelComponent)
                }
            }
            .onReceive(timer) { _ in
                let currentTime = CACurrentMediaTime()
                frameDuration = currentTime - lastUpdateTime
                lastUpdateTime = currentTime
                let morphAmount = Float(frameDuration)
                morphFactor = morphFactor + morphAmount*1.125
            }
        }
    }
    
    func createSphereEntity(morphFactor: Float, radius: Float = 0.5) throws -> Entity {
        let modelComponent = try getModelComponent(morphFactor: morphFactor, radius: radius)
        
        let entity = Entity()
        entity.name = "Sphere"
        entity.components.set(modelComponent)
        entity.scale *= 0.25
        return entity
    }
    
    func getModelComponent(morphFactor: Float, radius: Float = 0.5) throws -> ModelComponent {
        let lowLevelMesh = try sphereMesh(morphFactor: morphFactor, radius: radius)
        let resource = try MeshResource(from: lowLevelMesh)
        
        var material = PhysicallyBasedMaterial()
        material.baseColor.tint = .init(red: 1.0, green: 1.0, blue: 1.0, alpha: 1.0)
        material.roughness.scale = 0.0
        material.faceCulling = .front
        material.blending = .transparent(opacity: 0.1)

        return ModelComponent(mesh: resource, materials: [material])
    }
    
    func sphereMesh(morphFactor: Float, radius: Float = 0.5) throws -> LowLevelMesh {
        let latitudeBands = 30
        let longitudeBands = 50
        
        let vertexCount = (latitudeBands + 1) * (longitudeBands + 1)
        let indexCount = latitudeBands * longitudeBands * 6
        
        var desc = MyVertex.descriptor
        desc.vertexCapacity = vertexCount
        desc.indexCapacity = indexCount
        
        let mesh = try LowLevelMesh(descriptor: desc)
        
        mesh.withUnsafeMutableBytes(bufferIndex: 0) { rawBytes in
            let vertices = rawBytes.bindMemory(to: MyVertex.self)
            var vertexIndex = 0
            
            for latNumber in 0...latitudeBands {
                let theta = Float(latNumber) * Float.pi / Float(latitudeBands)
                let sinTheta = sin(theta)
                let cosTheta = cos(theta)
                
                for longNumber in 0...longitudeBands {
                    let phi = Float(longNumber) * 2 * Float.pi / Float(longitudeBands)
                    let sinPhi = sin(phi)
                    let cosPhi = cos(phi)
                    
                    var x = cosPhi * sinTheta
                    var y = cosTheta
                    var z = sinPhi * sinTheta
                    
                    let scaleFactorX: Float = 1.0 + 0.04 * sin(morphFactor * 1.0)
                    let scaleFactorY: Float = 1.0 + 0.08 * cos(morphFactor * 1.5)
                    let scaleFactorZ: Float = 1.0 + 0.12 * sin(morphFactor * 2.0)
                    
                    x *= scaleFactorX
                    y *= scaleFactorY
                    z *= scaleFactorZ
                    
                    let noiseScale: Float = 0.0375
                    let noiseValueX = smoothNoise(x: morphFactor + theta, y: phi) * noiseScale
                    let noiseValueY = smoothNoise(x: morphFactor + phi, y: theta) * noiseScale
                    let noiseValueZ = smoothNoise(x: morphFactor + theta + phi, y: theta) * noiseScale
                    
                    x += noiseValueX
                    y += noiseValueY
                    z += noiseValueZ

                    let position = SIMD3<Float>(x, y, z) * radius
                    let color = 0xFFFFFFFF
                    vertices[vertexIndex] = MyVertex(position: position, color: UInt32(color))
                    vertexIndex += 1
                }
            }
        }
        
        mesh.withUnsafeMutableIndices { rawIndices in
            let indices = rawIndices.bindMemory(to: UInt32.self)
            var index = 0
            
            for latNumber in 0..<latitudeBands {
                for longNumber in 0..<longitudeBands {
                    let first = (latNumber * (longitudeBands + 1)) + longNumber
                    let second = first + longitudeBands + 1
                    
                    indices[index] = UInt32(first)
                    indices[index + 1] = UInt32(second)
                    indices[index + 2] = UInt32(first + 1)
                    indices[index + 3] = UInt32(second)
                    indices[index + 4] = UInt32(second + 1)
                    indices[index + 5] = UInt32(first + 1)
                    
                    index += 6
                }
            }
        }
        
        let meshBounds = BoundingBox(min: [-radius, -radius, -radius], max: [radius, radius, radius])
        mesh.parts.replaceAll([
            LowLevelMesh.Part(
                indexCount: indexCount,
                topology: .triangle,
                bounds: meshBounds
            )
        ])
        
        return mesh
    }
    
    func smoothNoise(x: Float, y: Float) -> Float {
        return 0.2 * sin(x * 2.0) + 0.2 * cos(y * 2.0)
    }
    
    struct MyVertex {
        var position: SIMD3<Float> = .zero
        var color: UInt32 = .zero
        
        static var vertexAttributes: [LowLevelMesh.Attribute] = [
            .init(semantic: .position, format: .float3, offset: MemoryLayout<Self>.offset(of: \.position)!),
            .init(semantic: .color, format: .uchar4Normalized_bgra, offset: MemoryLayout<Self>.offset(of: \.color)!)
        ]


        static var vertexLayouts: [LowLevelMesh.Layout] = [
            .init(bufferIndex: 0, bufferStride: MemoryLayout<Self>.stride)
        ]


        static var descriptor: LowLevelMesh.Descriptor {
            var desc = LowLevelMesh.Descriptor()
            desc.vertexAttributes = MyVertex.vertexAttributes
            desc.vertexLayouts = MyVertex.vertexLayouts
            desc.indexType = .uint32
            return desc
        }
    }
}

#Preview {
    BubbleRealityView()
}