layer.center()

Center this layer in its parent. If there is no parent, it will be centered relative to the screen.
译：这层在超级层的中心。如果没有超级层，它将以屏幕为中心。

layerA = new Layer
    width: 500
    height: 500

layerB = new Layer
    parent: layerA
    width: 100
    height: 100

layerB.center()

print layerB.x, layerB.y
# Output: 200, 200