NovumCoder NovumCoder - 2 months ago 46
Swift Question

SpriteKit: Howto make holes in layer with blendMode

I have a simple scene with some elements added to it.

Now i want focus on a specific element with a mask a cut a whole at the same position as the element I want to focus on. Very similar to what we can see on some games when they are started first time showing some kind of tutorial.

Basically I am adding a fullscreen layer with

(so user still see all the content) but then add a circle at a specific position as this layers child and set
. Subtract so it "cuts" out a circle from this fullscreen layer so within this circle you have a clear view.

I have the following code after I have added all the elements onto the screen.

// before this code i added some basic elements like circles and backgrounds
let mask = SKSpriteNode(color: .blackColor(), size: self._screenSize)
mask.anchorPoint =
mask.position =
mask.zPosition = 100
mask.alpha = 0.7

let circle = SKShapeNode(circleOfRadius: Constants.Config.playersize*2)
circle.fillColor = .blackColor()
circle.lineWidth = 0
let circle_mask = SKSpriteNode(texture: SKView().textureFromNode(circle, crop: circle.frame))
circle_mask.blendMode = .Subtract
circle_mask.zPosition = 101

// now show the layer with alpha=0.7 and the circle mask being at the same position as my player element i want to focus on
circle_mask.position = player.position

But this simply adds the fullscreen layer, no circle holes. Looks like it is ignoring the circle_mask node. What am I doing wrong?

My plan is also to keep moving the circle mask to focus on other elements on this scene. As I understand. Subtract it should subtract only from its parent node, which is the fullscreen layer with
, right?

I just tried with SKCropNode. Added the fullscreen layer as a child into the crop node, then assigned the circle as mask. But now its cutting out nearly everything but just showing a circle of my fullscreen layer, i actually need the inverted result of this crop node.

The problem with blendMode is that is runs it on the final framebuffer, but what i need is to run it on the parent node only, so it does not cut everything behind the node when using .Subtract


Here is an example on how to create a translucent layer with a hole punched into it:

-(NOTE: .subtract blend mode does not take alpha of the sprite into consideration, so you need to use a crop node)

self.backgroundColor = .red

//Our transparent overlay
let fullScreen = SKSpriteNode(color: .black, size: self.size)
fullScreen.position =
fullScreen.zPosition = 100
fullScreen.alpha = 0.7

//let's make a mask to punch circles in our shape
let mask = SKSpriteNode(color: .white, size: self.size)
mask.position =
mask.zPosition = 100
mask.alpha = 1

let circle = SKShapeNode(circleOfRadius: 20*2)
circle.fillColor = .white
circle.lineWidth = 0
circle.alpha = 1

//let circle_mask = SKSpriteNode()
circle.blendMode = .subtract

//let's create the node to place on screen
let crop = SKCropNode()
crop.maskNode = mask