Adding linear and radial gradients to SKScene.

GameScene.swift

final class GameScene: SKScene
{
  override func didMove(to view: SKView)
  {
    let linearGradientSize = size
    let linearGradientColors = [UIColor(red: 53.0 / 255.0, green: 92.0 / 255.0, blue: 125.0 / 255.0, alpha: 1.0),
                                UIColor(red: 108.0 / 255.0, green: 91.0 / 255.0, blue: 123.0 / 255.0, alpha: 1.0),
                                UIColor(red: 192.0 / 255.0, green: 108.0 / 255.0, blue: 132.0 / 255.0, alpha: 1.0)]
    let linearGradientLocations: [CGFloat] = [0, 0.5, 1]
    let textureCount = 8
    let textures = (0..<textureCount).map { (index) -> SKTexture in
      let angle = 2.0 * CGFloat.pi / CGFloat(textureCount) * CGFloat(index)
      return SKTexture(linearGradientWithAngle: angle, colors: linearGradientColors, locations: linearGradientLocations, size: linearGradientSize)
    }
        
    let linearGradientNode = SKSpriteNode(texture: textures.first)
    linearGradientNode.zPosition = 1
    addChild(linearGradientNode)
        
    let action = SKAction.animate(with: textures, timePerFrame: 0.5)
    linearGradientNode.run(SKAction.repeatForever(action))
        
    let radialGradientSize = CGSize(width: min(size.width, size.height), height: min(size.width, size.height))
    let radialGradientColors = [UIColor.yellow, UIColor.orange]
    let radialGradientLocations: [CGFloat] = [0, 1]
    let radialGradientTexture = SKTexture(radialGradientWithColors: radialGradientColors, locations: radialGradientLocations, size: radialGradientSize)
    let radialGradientNode = SKSpriteNode(texture: radialGradientTexture)
    radialGradientNode.zPosition = 2
    addChild(radialGradientNode)
        
    let pulse = SKAction.sequence([SKAction.fadeIn(withDuration: 3.0), SKAction.fadeOut(withDuration: 1.0)])
    radialGradientNode.run(SKAction.repeatForever(pulse))
  }
}