在 Spritekit 中扩展圆形切口过渡效果

Question

我正在尝试获得类似于任天堂在 sprite kit 中的超级马里奥奔跑游戏中的过渡效果

我只想要一个圆形切口来扩展以显示下一个场景或仅显示当前场景。这不能作为标准 iOS sprite kit 转换之一使用。

我已经用一个完全黑色的图层覆盖整个场景并使用 SKCropNode 动画一个扩大的圆圈来显示场景。

以下是didMove(to view: SKView)中的代码

let fullScreen = SKSpriteNode(color: .black, size: self.size)
let mask = SKSpriteNode(color: .black, size: self.size)
let circle = SKShapeNode(circleOfRadius: self.size.height / 2)
circle.fillColor = .white
circle.blendMode = .subtract
circle.setScale(0.001)
circle.isHidden = true
circle.name = "circleShape"
mask.addChild(circle)

let crop = SKCropNode()
crop.position = CGPoint(x: self.size.width / 2, y: self.size.height / 2)
crop.maskNode = mask
crop.name = "cropNode"
crop.addChild(fullScreen)
crop.zPosition = 100

self.addChild(crop)

let waitAction = SKAction.wait(forDuration: 2.0)
let callAction = SKAction.run({
    let cropNode = self.childNode(withName: "cropNode") as! SKCropNode
    let maskNode = cropNode.maskNode as! SKSpriteNode
    let circleNode = maskNode.childNode(withName: "circleShape") as! SKShapeNode
    circleNode.isHidden = false
    let scaleAction = SKAction.scale(to: 2.0, duration: 2.0)
    scaleAction.timingFunction = scaleAction.easeInQuartic
    circleNode.run(scaleAction, completion: {
        cropNode.removeFromParent()
    })
})
let seqAction = SKAction.sequence([waitAction,callAction])
self.run(seqAction)

这在模拟器中有效，但在设备上运行时无效（iPad pro 2016 和最新的 iOS 10）。在设备上，缩放动作完成后，没有出现扩大的圆圈，黑色的覆盖层消失了。

我的问题：

1) 为什么这不能在设备上运行，只能在模拟器上运行？

2) 有没有更好更有效的方法来实现 sprite kit 中的这种过渡？

提前致谢。

Answer 1

可能有 100 种不同的方法可以实现这一目标。我的方法比你的好吗？可能不是，但这对我在模拟器和 iPad 上都有效。

只需以 0.0 的持续时间过渡到您的场景，然后从 didMove(to view:) 运行这个乐趣

你需要一个单独的圆圈图像的原因是它在放大时保持其漂亮的清晰边缘

bgOverlay 只是从一个完全黑屏开始，然后应用伪过渡

func circleTransition() {

    let bgMask = SKSpriteNode(texture: SKTexture(imageNamed: "bg_mask"), color: .clear, size: CGSize(width: self.size.width, height: self.size.height))
    bgMask.position = CGPoint(x: self.size.width / 2, y: self.size.height / 2)
    bgMask.zPosition = 5000
    self.addChild(bgMask)

    let transitionCircle = SKSpriteNode(texture: SKTexture(imageNamed: "transition_circle"), color: .clear, size: CGSize(width: 13, height: 13))
    transitionCircle.position = CGPoint.zero
    transitionCircle.zPosition = 1
    bgMask.addChild(transitionCircle)

    let bgOverlay = SKSpriteNode(texture: SKTexture(imageNamed: "bg_overlay"), color: .clear, size: CGSize(width: self.size.width, height: self.size.height))
    bgOverlay.position = CGPoint(x: self.size.width / 2, y: self.size.height / 2)
    bgOverlay.zPosition = 5001
    self.addChild(bgOverlay)

    bgMask.run(SKAction.sequence([SKAction.scale(to: 100.0, duration: 2.0), SKAction.removeFromParent()]))
    bgOverlay.run(SKAction.sequence([SKAction.fadeOut(withDuration: 0.1), SKAction.removeFromParent()]))
}

Answer 2

我最终使用了带有片段着色器的 SKSpriteNode。以下是主场景中的代码：

let fullScreen = SKSpriteNode(color: UIColor.clear, size: CGSize(width: self.size.width, height: self.size.height))
fullScreen.position = CGPoint(x: self.size.width / 2.0, y: self.size.height / 2.0)
fullScreen.zPosition = 200
self.addChild(fullScreen)
let shader = SKShader(fileNamed: "transitionShader.fsh")
shader.attributes = [SKAttribute(name: "a_sprite_size", type: .vectorFloat2),
                     SKAttribute(name:"a_duration", type: .float)]
fullScreen.shader = shader
let spriteSize = vector_float2(Float(fullScreen.frame.size.width),Float(fullScreen.frame.size.height))
fullScreen.setValue(SKAttributeValue(vectorFloat2: spriteSize),forAttribute: "a_sprite_size")
fullScreen.setValue(SKAttributeValue(float: Float(mainGameTransitionDuration)), forAttribute: "a_duration")

以下是位于transitionShader.fsh文件中的着色器代码

#define M 1000.0 // Multiplier

void main()
{
    float aspect = a_sprite_size.y / a_sprite_size.x;
    float u = v_tex_coord.x;
    float v = v_tex_coord.y * aspect;
    vec2 uv = vec2(u,v) * M;
    vec2 center = vec2(0.60,0.55 * aspect) * M;
    float t = u_time / a_duration;
    if ( t < 1.0 )
    {
        float easeIn = pow(t,5.0);
        float radius = easeIn * 2.0 * M;
        float d = length(center - uv) - radius;
        float a = clamp(d, 0.0, 1.0);
        gl_FragColor = vec4(0.0,0.0,0.0, a);
    }
    else
    {
        gl_FragColor = vec4(0.0,0.0,0.0,0.0);
    }
}

它似乎可以正常工作，并且在 CPU 或内存上似乎并不昂贵。