How to detect contact on different areas of a physicsbody

Question

I would like to achieve the classic \'headshot\' effect in a sprite-kit game.

My ideas and attempts:

1. Create separate \'body\' and \'head\' physicsBodies

Answer 1

Using the pinned attribute of a physicsBody makes it easy to create complex sprites with multiple contact zones. Pinning a Physics Body to the Node's Parent:

The default value is NO. If YES, then the node’s position is fixed relative to its parent. The node’s position cannot be changed by actions or physics forces. The node can freely rotate around its position in response to collisions or other forces. If the parent node has a physics body, then the two physics bodies are treated as if they are connected with a pin joint.

Here is a basic Dog class, where the dog has a main body and a head. Note that I set allowsRotation = false as well so the head cannot move around the body.

import SpriteKit

// for readability
let mainSize = CGSize(width: 300, height: 300)
let headSize = CGSize(width: 100, height: 100)

class Dog : SKSpriteNode {

    let head = SKSpriteNode(color: SKColor.greenColor(), size: headSize)

    init() {
        super.init(texture: nil, color: SKColor.redColor(), size: mainSize)

        head.position = CGPoint(x: mainSize.width - headSize.width, y: 0)
        addChild(head)
    }

    // called after Dog has been added to the scene
    func configurePhysicsBody() {

        physicsBody = SKPhysicsBody(circleOfRadius: mainSize.width / 2)
        physicsBody.dynamic = true
        physicsBody.allowsRotation = false
        // set contactBitmask for main body

        head.physicsBody = SKPhysicsBody(circleOfRadius: headSize.width / 2)
        head.physicsBody.dynamic = true
        head.physicsBody.allowsRotation = false
        // The head is pinned to the parent node, so position is fixed relative to parent
        head.physicsBody.pinned = true
        // set contactBitmask for head

    }

}