MainMenuScene.swift

//
//  MainMenuScene.swift
//  Color-Pong
//
//  Created by Blake Ehrenbeck on 3/25/17.
//  Copyright © 2017  huangzhen. All rights reserved.
//

import UIKit
import SpriteKit

class MainMenuScene: SKScene {

    func starfieldEmitter(color: SKColor, starSpeedY: CGFloat, starsPerSecond: CGFloat, starScaleFactor: CGFloat) -> SKEmitterNode {
        
        // Determine the time a star is visible on screen
        let lifetime =  frame.size.height * UIScreen.main.scale / starSpeedY
        
        // Create the emitter node
        let emitterNode = SKEmitterNode()
        emitterNode.particleTexture = SKTexture(imageNamed: "Star")
        emitterNode.particleBirthRate = starsPerSecond
        emitterNode.particleColor = SKColor.lightGray
        emitterNode.particleSpeed = starSpeedY * -1
        emitterNode.particleScale = starScaleFactor
        emitterNode.particleColorBlendFactor = 1
        emitterNode.particleLifetime = lifetime
        
        // Position in the middle at top of the screen
        emitterNode.position = CGPoint(x: frame.size.width/2, y: frame.size.height)
        emitterNode.particlePositionRange = CGVector(dx: frame.size.width, dy: 0)
        
        // Fast forward the effect to start with a filled screen
        emitterNode.advanceSimulationTime(TimeInterval(lifetime))
        
        return emitterNode
    }
    
    override func didMove(to view: SKView) {
        // Add Starfield with 3 emitterNodes for a parallax effect
        // - Stars in top layer: light, fast, big
        // - ...
        // - Stars in back layer: dark, slow, small
        var emitterNode = starfieldEmitter(color: SKColor.lightGray, starSpeedY: 50, starsPerSecond: 1, starScaleFactor: 0.2)
        emitterNode.zPosition = -10
        self.addChild(emitterNode)
        
        emitterNode = starfieldEmitter(color: SKColor.gray, starSpeedY: 30, starsPerSecond: 2, starScaleFactor: 0.1)
        emitterNode.zPosition = -11
        self.addChild(emitterNode)
        
        emitterNode = starfieldEmitter(color: SKColor.darkGray, starSpeedY: 15, starsPerSecond: 4, starScaleFactor: 0.05)
        emitterNode.zPosition = -12
        self.addChild(emitterNode)
        
        self.backgroundColor = .black
        
    }
    
}