ios – 将阴影与投射它的SKSpriteNode一起淡化

let block = SKSpriteNode(color: UIColor.redColor(),size: CGSizeMake(90,160))
block.zPosition = 2
block.shadowCastBitMask = 1
addChild(block)

let light = SKLightNode()
light.categoryBitMask = 1
light.falloff = 1
addChild(light)

let fadeOut = SKAction.fadeAlphaTo(0.0,duration: 5.0)
block.runAction(fadeOut)

这有点棘手,因为SKLightNode投射的阴影不受节点的alpha属性的影响.您需要做的是在淡出块的同时淡出SKLightNode的shadowColor属性的alpha通道.

基本步骤是：

>存储灯光的shadowColor和该颜色的alpha通道以供参考.
>创建一个SKAction.customActionWithDuration：

>根据原始动作以及动作到目前为止的时间重新计算Alpha通道的值.
>将灯光的shadowColor设置为其原始颜色,但使用新的Alpha通道.

>并行运行块的淡入淡出动作和阴影的淡入淡出动作.

例：

let fadeDuration = 5.0 // We're going to use this a lot

// Grab the light's original shadowColor so we can use it later
let shadowColor = light.shadowColor

// Also grab its alpha channel so we don't have to do it each time
let shadowAlpha = CGColorGetAlpha(shadowColor.CGColor)

let fadeShadow = SKAction.customActionWithDuration(fadeDuration) {
    // The first parameter here is the node this is running on.
    // Ideally you'd use that to get the light,but I'm taking
    // a shortcut and accessing it directly.
    (_,time) -> Void in

    // This is the original alpha channel of the shadow,adjusted
    // for how much time has past while running the action so far
    // It will go from shadowAlpha to 0.0 over fadeDuration
    let alpha = shadowAlpha - (shadowAlpha * time / CGFloat(fadeDuration))

    // Set the light's shadowColor to the original color,but replace
    // its alpha channel our newly calculated one
    light.shadowColor = shadowColor.colorWithAlphaComponent(alpha)
}

// Make the action to fade the block too; easy!
let fadeBlock = SKAction.fadeAlphaTo(0.0,duration: fadeDuration)

// Run the fadeBlock action and fadeShadow action in parallel
block.runAction(SKAction.group([fadeBlock,fadeShadow]))