Swift Uint32 Recognizing All Even Numbers as the Same - swift

Question

I am using SpriteKit in Swift and have the following situation:
I construct a struct in the superclass level that has a list of UInt32s to represent the various bitmasks that I need to establish types of physics bodies. (This is stupid because struct properties cannot be overridden in the subclass. Considering removing.)
In the subclass I create a physics body that has collision, contact, and category bitmasks of UInt32(4), referenced by a static constant from the superclass struct.
These bodies fall through the ground that is created in the superclass with bitmasks of UInt(2) from the struct property.
When I change the static constant from UInt(4) to an unsigned int 32 of any odd number between 0 - 32, the bodies do not fall through the ground. Using any even number makes the bodies fall through the ground.
Superclass.swift
struct physicsBitMasks {
static let one = UInt32(1) //for player
static let two = UInt32(2) //for ground
static let three = UInt32(3) //for you don't need to know
static let four = UInt32(4) //for enemy
...
ground.physicsBody?.categoryBitMask = physicsBitMasks.one
ground.physicsBody?.contactTestBitMask = physicsBitMasks.one
ground.physicsBody?.collisionBitMask = physicsBitMasks.two
}
Subclass.swift
Subclass: Superclass {
//create enemy
thing.physicsBody?.categoryBitMask = physicsBitMasks.four
thing.physicsBody?.contactTestBitMask = physicsBitMasks.four
thing.physicsBody?.collisionBitMask = physicsBitMasks.four
}
Enemy falls through ground
REDEFINE
Superclass.swift
struct physicsBitMasks {
static let one = UInt32(1) //for player
static let two = UInt32(2) //for ground
static let three = UInt32(3) //for you don't need to know
static let four = UInt32(5) // or 7, 9, ...31 for enemy
}
Enemy does not fall through ground.
What is going on?

Answer 1

Wouldn't playerMask, groundMask, mysteryMask, and enemyMask be better names than one, two, three, and four?
Also, because they are bit mask components, you need each to have a single unique bit set. But 3, for example, contains the bits of 1 and 2. Let's define them this way:
struct BodyMask {
static let Player = UInt32(1)
static let Ground = UInt32(2)
static let EmbarrassingSecret = UInt32(4)
static let Enemy = UInt32(8)
}
Now you need to set the various masks on your bodies. You should set each's body's categoryBitMask to the mask for its type:
ground.physicsBody?.categoryBitMask = BodyMask.Ground
player.physicsBody?.categoryBitMask = BodyMask.Player
enemies.forEach { $0.physicsBody?.categoryBitMask = BodyMask.Enemy }
twilightNovel.physicsBody?.categoryBitMask = BodyMask.EmbarrassingSecret
You need to set each body's collisionBitMask based on what other bodies you want it to bounce off of. That is, do you want an enemy to bounce off the ground? Then the enemy's collisionBitMask must include the BodyMask.Ground bit. Do you want the ground to bounce off of an enemy? Or bounce off of anything else? Probably not. Note that this is asymmetric! The enemy can bounce of the ground without the ground bouncing. That is, Newton's third law (for every action there is an equal and opposite reaction) doesn't have to apply.
If you want a body to bounce off of multiple other body types, you can bitwise-or the masks together. Let's assume you want enemies to bounce off of the ground and each other.
ground.physicsBody?.collisionBitMask = 0
player.physicsBody?.collisionBitMask = BodyMask.Ground
enemies.forEach { $0.physicsBody?.collisionBitMask = BodyMask.Ground | BodyMask.Enemy }
twilightNovel.physicsBody?.collisionBitMask = BodyMask.Ground
Finally, if you want to be notified when two bodies collide (regardless of whether they bounce), you can use contactTestBitMask. You probably want to know when the player touches an enemy, or when the player does something embarrassing, even though you don't necessarily want the player to bounce off of enemies or trashy novels.
ground.physicsBody?.contactTestBitMask = 0
player.physicsBody?.contactTestBitMask = BodyMask.Enemy | BodyMask.EmbarrassingSecret
enemies.forEach { $0.physicsBody?.contactTestBitMask = 0 }
twilightNovel.physicsBody?.contactTestBitMask = 0