Sprite subclass detecting touches despite actually touching empty space - swift

Question

I'm subclassing nodes to use for touch detection. I have a box parent which has a line child directly next to it, with the gray space being just empty space:
The problem is when I click the gray space, it registers as a touch on the box, which is quite far away.
Here's the code where I show the problem, and my crappy workaround... I make two sets of boxes, the first being the one showing the problem, and the second being the one with the workaround:
import SpriteKit
class GameScene: SKScene {
enum sizez {
static let
box = CGSize(width: 50, height: 35),
line = CGSize(width: 200, height: 10)
}
class Box: SKSpriteNode {
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
print("touched box")
}
}
class Line: SKSpriteNode {
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
print("touched line")
}
}
override func didMove(to view: SKView) {
// The problem sprites that register touch despite empty space:
let box = Box(color: .red, size: sizez.box)
box.isUserInteractionEnabled = true
addChild(box)
let line = Line(color: .purple, size: sizez.line)
line.isUserInteractionEnabled = true
line.anchorPoint = CGPoint.zero
line.position = CGPoint(x: box.frame.maxX + 10, y: box.frame.minY)
///////////////////
box.addChild(line)
///////////////////
// These sprites detect touches properly (no detection in empty space)
let box2 = Box(color: .red, size: sizez.box)
box2.isUserInteractionEnabled = true
box2.position.y -= 100
addChild(box2)
let line2 = Line(color: .purple, size: sizez.line)
line2.isUserInteractionEnabled = true
line2.anchorPoint = CGPoint.zero
line2.position = CGPoint(x: box2.frame.maxX + 10, y: box2.frame.minY)
////////////////
addChild(line2)
////////////////
}
}
When you click directly above (or even farther out from) the top line, you get this:
When you do the same for the bottom line, you get this:
It will be a huge hassle to forgo SK's built in parent / child system, and then for me to keep track of them on my own manually... as well as it being a big performance hit for my app.
Any reasonable workaround or solution that lets me click in the gray space while using code similar to the first box would be greatly appreciated.
UPDATE:
By making an invisible background node and setting its zPositon 1 less, I can now click in the gray space and it registers as the background node, not the box.
let bkgSize = CGSize(width: 1000, height: 1000)
let bkg = Bkg(color: .gray, size: bkgSize)
bkg.isUserInteractionEnabled = true
bkg.zPosition -= 1
addChild(bkg)
But still, why is this empty space touch being registered as a box touch in the absence of a background node?

Answer 1

You're absolutely correct with a background node it works as expected, without a background sprite it gives the results as described by #Confused. I was able to get it to work as expected without a background by just fine tuning the TouchesBegan function like so...
class Box: SKSpriteNode {
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
if let touch = touches.first as UITouch! {
let touchLocation = touch.location(in: parent!)
if frame.contains(touchLocation) {
print("touched box")
}
}
}
}
class Line: SKSpriteNode {
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
if let touch = touches.first as UITouch! {
let touchLocation = touch.location(in: parent!)
if frame.contains(touchLocation) {
print("touched line")
}
}
}
}

Answer 2

From my understanding of how bounds work for parented objects, I think this is what's going on...
Addendum
This is slightly related, and may help in understanding why this is happening, and why Apple considers this to be how a parent and its children should use an accumulated (combined) rectangle/quad for touch response: