CALayer subLayer边界舍入错误？

Question

The image below has been constructed using CAShapeLayer . The gray layer is a sublayer of the red layer.

If you look closely at the gray layer edges you can see the red layer edges bleeding through-- it's as if the gray layer is miscalculating it's width. This should be impossible because I set the gray layer's width to be exactly the red layer's width, and the gray layer is a sublayer of the red layer. When I print their widths they are the exact same number.

Does anyone know what is going wrong and how to fix this? Code below.

It seems to be some kind of rounding error because adjusting the frame width eventually fixes the issue on certain values. But this still doesn't make sense because the rounding error should be the same for all sublayers.

class MyLayer {
     var redLayer = CAShapeLayer()
     var grayLayer = CAShapeLayer()

      init() {
         redLayer.addSublayer(graylayer)
      }

      func layoutSublayers(_ bounds: CGRect) {
          redLayer.frame = bounds
          grayLayer.frame = CGRect(x: 0, 
                                   y: 0, 
                                   width redLayer.bounds.width, 
                                   height: redLayer.bounds.height/2)
          draw()
      }

      func draw() {
        redLayer.fillColor = UIColor.red.cgColor
        redLayer.path = UIBezierPath(rect: redLayer.bounds).cgPath
        grayLayer.fillColor = UIColor.darkGray.cgColor
        grayLayer.path = UIBezierPath(rect: grayLayer.bounds).cgPath
      }

}

Answer 1

Try add gray layer inside layoutSublayers after sets the size. Like this:

override func layoutSublayers(of layer: CALayer) {
    redLayer.addSublayer(graylayer)
}