An entity that supports animated changes in opacity

OpacityEntity.swift

import Foundation
import RealityKit

// ***********************************************************************
// Important: You may want to use this newer `Entity` extension instead,
// which includes a completion handler for the `Entity/setOpacity` method:
// https://gist.github.com/drewolbrich/1e9d3da074c8a1d5ca93721124b97596
// ***********************************************************************

extension Entity {
    
    /// The opacity value applied to the entity and its descendants.
    ///
    /// `OpacityComponent` is assigned to the entity if it doesn't already exist.
    var opacity: Float {
        get {
            return components[OpacityComponent.self]?.opacity ?? 1
        }
        set {
            if !components.has(OpacityComponent.self) {
                components[OpacityComponent.self] = OpacityComponent(opacity: newValue)
            } else {
                components[OpacityComponent.self]?.opacity = newValue
            }
        }
    }
    
    /// Sets the opacity value applied to the entity and its descendants with optional animation.
    ///
    /// `OpacityComponent` is assigned to the entity if it doesn't already exist.
    func setOpacity(_ opacity: Float, animated: Bool, duration: TimeInterval = 0.2, delay: TimeInterval = 0) {
        guard animated else {
            self.opacity = opacity
            return
        }

        if !components.has(OpacityComponent.self) {
            components[OpacityComponent.self] = OpacityComponent(opacity: 1)
        }

        let animation = FromToByAnimation(name: "Entity/setOpacity", to: opacity, duration: duration, timing: .linear, isAdditive: false, bindTarget: .opacity, delay: delay)
        
        do {
            let animationResource: AnimationResource = try .generate(with: animation)
            playAnimation(animationResource)
        } catch {
            assertionFailure("Could not generate animation: \(error.localizedDescription)")
        }
    }
    
}