将阴影与投射它的SKSpriteNode一起淡化

Question

这是我的设置,使用Sprite Kit.首先,我在SKScene中创建一个简单的精灵节点,如下所示:

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

然后向场景添加一个灯光节点:

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

果然,块现在投下一个漂亮的小阴影:

现在我通过操纵其alpha值来淡化块,例如通过运行一个动作:

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

这是一个尴尬的情况:当块变得越来越半透明时,阴影保持完全相同.这就是它在行动结束前的一刻:

一旦alpha完全降至0.0,阴影就会从一帧到下一帧突然消失.

这将是多漂亮,但有阴影慢慢的越来越弱,作为对象铸造它变得越来越透明.

题:

使用Sprite Kit可以达到这样的效果吗？如果是这样,你会怎么做呢？

Answer 1

这有点棘手，因为 an 投射的阴影SKLightNode不受节点alpha属性的影响。您需要做的是shadowColor在SKLightNode淡出block.

基本步骤是：

1. 存储灯光shadowColor和该颜色的 Alpha 通道以供参考。
2. 创建SKAction.customActionWithDuration一个：
   1. 根据原始值以及操作到目前为止已过去的时间重新计算 Alpha 通道的值。
   2. 将灯光设置shadowColor为其原始颜色，但使用新的 Alpha 通道。
3. 并行运行块的淡入淡出操作和阴影的淡入淡出操作。

例子：

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]))