RealityKit Material add blend mode example

AddBlendModeView.swift

import RealityKit
import SwiftUI

struct AddBlendModeView: View {
    var isSphereOnTop: Bool = true
    @State var rootEntity: Entity?
    
    var body: some View {
        RealityView { content in
        } update: { content in
            if let rootEntity {
                content.add(rootEntity)
            }
        }
        .task {
            rootEntity = await AddBlendModeView.createRootEntity(isSphereOnTop: isSphereOnTop)
        }
    }
    
    static func createRootEntity(isSphereOnTop: Bool = true) async -> Entity {
        let sphereResource = MeshResource.generateSphere(radius: 0.3)
        let sphereMaterial = await generateAddMaterial(color: .red)
        let sphereModelComponent = ModelComponent(mesh: sphereResource, materials: [sphereMaterial])
        
        let coneResource = MeshResource.generateCone(height: 1.0, radius: 0.5)
        let coneMaterial = await generateAddMaterial(color: .green)
        let coneModelComponent = ModelComponent(mesh: coneResource, materials: [coneMaterial])

        let root = Entity()
        
        let topEntity = Entity()
        topEntity.components.set(isSphereOnTop ? sphereModelComponent : coneModelComponent)
        root.addChild(topEntity)
        
        let bottomEntity = Entity()
        bottomEntity.components.set(!isSphereOnTop ? sphereModelComponent : coneModelComponent)
        root.addChild(bottomEntity)
        
        root.scale *= scalePreviewFactor
        return root
    }
    
    static func generateAddMaterial(color: UIColor) async -> UnlitMaterial {
        var descriptor = UnlitMaterial.Program.Descriptor()
        descriptor.blendMode = .add
        let prog = await UnlitMaterial.Program(descriptor: descriptor)
        var material = UnlitMaterial(program: prog)
        material.color = UnlitMaterial.BaseColor(tint: color)
        return material
    }
}

#Preview("Sphere on top") {
    AddBlendModeView()
}

#Preview("Cone on top") {
    AddBlendModeView(isSphereOnTop: false)
}

var isPreview: Bool {
    return ProcessInfo.processInfo.environment["XCODE_RUNNING_FOR_PREVIEWS"] == "1"
}

var scalePreviewFactor: Float = isPreview ? 0.3 : 1.0