Making the components interact

Although the app is colorful and seeing the bird fly is fun, we need to create a scene like the real world, where collision with an obstacle typically brings you to a halt.

Setting up the collision detection engine

The SpriteKit physics engine provides us with a really simple mechanism to detect collisions between objects. Basically, we need to set a bitmask for each component, and then a collision detection delegate. Let start defining the bitmask; for it, we define an enumeration in GameScene:

enum BodyType : UInt32 {
    case bird   = 1  // 0b0001
    case ground = 2  // 0b0010
    case pipe   = 4  // 0b0100
    case gap    = 8  // 0b1000
}

Pay attention to two things: the first is that we must define the bitmask as a power of 2; so that we can detect what touches what, using a bitwise or operation. The second is that we've added a gap identifier, a component we haven't defined yet.

The gap is the hole between two pipes, and we need to detect the moment when...