An Entity extension that supports animated changes the opacity of an entity and its descendants

Entity+Opacity.swift

//
//  Entity+Opacity.swift
//
//  Created by Drew Olbrich on 10/25/23.
//  Copyright © 2023 Lunar Skydiving LLC. All rights reserved.
//
//  MIT License
//  
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//  
//  The above copyright notice and this permission notice shall be included in all
//  copies or substantial portions of the Software.
//  
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.
//

import Foundation
import RealityKit
import Combine

private var playbackCompletedSubscriptions: Set<AnyCancellable> = .init()

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, completion: (() -> Void)? = nil) {
        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)
            let animationPlaybackController = playAnimation(animationResource)
            
            if completion != nil {
                scene?.publisher(for: AnimationEvents.PlaybackCompleted.self)
                    .filter { $0.playbackController == animationPlaybackController }
                    .sink(receiveValue: { event in
                        completion?()
                    }).store(in: &playbackCompletedSubscriptions)
            }
        } catch {
            assertionFailure("Could not generate animation: \(error.localizedDescription)")
        }
    }
    
}