Apple Game Frameworks and Technologies: Changes to GameScene+PhysicsContact

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Title: Changes to GameScene+PhysicsContact

(I understand, it may be to late in your process to make such a change, but I’ll share here anyway, and would welcome feedback)

The GameScene+PhysicsContact extension was the source of one of my typos, and I also found the code to be quite “dense” to read.

I’m taking a bit of time at the end of Val’s Revenge to go in and make changes that seem good, but mainly to test that I’m getting the hang of Swift.

I added a couple of functions to factor out a lot of the common code and reduce the noise of reading the cases and then matching up the nodes. (On the plus side, my typo was accidentally having a collisionBitMask one place rather than a categoryBitMask (probably just a cursor key error with code completion, but I really don’t want to admit how long it took me to track that down). This code prevents that sort of error by placing it into the function where it’s done once, and will either be always right, or always wrong)

Anyway… as the tag says… Just a suggestion

This is my revised version of GameScene+PhysicsContact.swift:

import SpriteKit

extension GameScene: SKPhysicsContactDelegate {
    func match(_ contact: SKPhysicsContact, body: PhysicsBody) -> (match:SKNode, other:SKNode) {
        return contact.bodyA.categoryBitMask == body.categoryBitMask ?
            (contact.bodyA.node!, contact.bodyB.node!) :
            (contact.bodyB.node!, contact.bodyA.node!)
    }
    
    func collisionOf(_ bodyA :PhysicsBody, _ bodyB: PhysicsBody) -> UInt32 {
        bodyA.categoryBitMask | bodyB.categoryBitMask
    }

    func didBegin(_ contact: SKPhysicsContact) {
        let collision = contact.bodyA.categoryBitMask | contact.bodyB.categoryBitMask
        switch collision {
        // MARK: - Player | Collectible

        case collisionOf(.player,.collectible):
            let (playerNode, collectible) = match(contact, body: .player)

            if let player = playerNode as? Player {
                player.collectItem(collectible)
            }

        // MARK: - Player | Door

        case collisionOf(.player,.door):
            let (playerNode, door) = match(contact, body: .player)

            if let player = playerNode as? Player {
                player.useKeyToOpenDoor(door)
            }

        // MARK: - Projectile | Collectible

        case collisionOf(.projectile,.collectible):
            let (projectileNode, collectibleNode) = match(contact, body: .projectile)
            if let collectibleComponent = collectibleNode.entity?.component(ofType: CollectibleComponent.self) {
                collectibleComponent.destroyedItem()
            }
            projectileNode.removeFromParent()

        // MARK: - Player | Monster

        case collisionOf(.player,.monster):
            let (playerNode, _) = match(contact, body: .player)
            if let healthComponent = playerNode.entity?.component(ofType: HealthComponent.self) {
                healthComponent.updateHealth(-1, forNode: playerNode)
            }

        // MARK: - Projectile | Monster

        case collisionOf(.projectile,.monster):
            let (monsterNode, _) = match(contact, body: .monster)

            if let healthComponent = monsterNode.entity?.component(ofType: HealthComponent.self) {
                healthComponent.updateHealth(-1, forNode: monsterNode)
            }

            // MARK: - Player | Platform

        case collisionOf(.player,.exit):
            let (playerNode, _) = match(contact, body: .player)
            // update the saved stats
            if let player = playerNode as? Player {
                GameData.shared.keys = player.getStats().keys
                GameData.shared.treasure = player.getStats().treasure
            }

            GameData.shared.level += 1
            loadSceneForLevel(GameData.shared.level)
        default:
            break
        }
    }
}
2

slight improvement to avoid “evil” ! unwraps.

import SpriteKit

extension GameScene: SKPhysicsContactDelegate {
    func match(_ contact: SKPhysicsContact, body: PhysicsBody) -> (match: SKNode, other: SKNode) {
        guard let nodeA = contact.bodyA.node,
              let nodeB = contact.bodyB.node
        else {
            fatalError("Expected contact bodies to both have attached nodes")
        }
        return contact.bodyA.categoryBitMask == body.categoryBitMask ?
            (nodeA, nodeB) :
            (nodeB, nodeA)
    }

    func collisionOf(_ bodyA: PhysicsBody, _ bodyB: PhysicsBody) -> UInt32 {
        bodyA.categoryBitMask | bodyB.categoryBitMask
    }

    func didBegin(_ contact: SKPhysicsContact) {
        let collision = contact.bodyA.categoryBitMask | contact.bodyB.categoryBitMask
        switch collision {
        // MARK: - Player | Collectible

        case collisionOf(.player, .collectible):
            let (playerNode, collectible) = match(contact, body: .player)

            if let player = playerNode as? Player {
                player.collectItem(collectible)
            }

        // MARK: - Player | Door

        case collisionOf(.player, .door):
            let (playerNode, door) = match(contact, body: .player)

            if let player = playerNode as? Player {
                player.useKeyToOpenDoor(door)
            }

        // MARK: - Projectile | Collectible

        case collisionOf(.projectile, .collectible):
            let (projectileNode, collectibleNode) = match(contact, body: .projectile)
            if let collectibleComponent = collectibleNode.entity?.component(ofType: CollectibleComponent.self) {
                collectibleComponent.destroyedItem()
            }
            projectileNode.removeFromParent()

        // MARK: - Player | Monster

        case collisionOf(.player, .monster):
            let (playerNode, _) = match(contact, body: .player)
            if let healthComponent = playerNode.entity?.component(ofType: HealthComponent.self) {
                healthComponent.updateHealth(-1, forNode: playerNode)
            }

        // MARK: - Projectile | Monster

        case collisionOf(.projectile, .monster):
            let (monsterNode, _) = match(contact, body: .monster)

            if let healthComponent = monsterNode.entity?.component(ofType: HealthComponent.self) {
                healthComponent.updateHealth(-1, forNode: monsterNode)
            }

            // MARK: - Player | Platform

        case collisionOf(.player, .exit):
            let (playerNode, _) = match(contact, body: .player)
            // update the saved stats
            if let player = playerNode as? Player {
                GameData.shared.keys = player.getStats().keys
                GameData.shared.treasure = player.getStats().treasure
            }

            GameData.shared.level += 1
            loadSceneForLevel(GameData.shared.level)
        default:
            break
        }
    }
}