CODEWITHSUNDEEP
swiftsprite-kit
ymulki
ymulki

Reputation: 432

Random Downwards Motion of SKSpriteNode with Constraints in Swift

I am making a small SpriteKit game in Swift playgrounds and it is an asteroid defence type of game. Basically,the player is defending the spacecraft with a cannon and has to destroy approaching rocks. The image link below is my scene without the gun added yet, but basically I want the rocks to move slowly down from the top towards the spacecraft at the bottom (Sorry, it's too big to add in here).

https://www.dropbox.com/s/pisgazar4jaxra0/Screenshot%202017-03-18%2011.23.17.png?dl=0

The rocks will be SKSpriteNodes and I want to speed them up for each successive rock to increase difficulty over time.

How would I be able to implement this. I have seen some answers elsewhere about using UIBezierPaths but how do I make it random but with the constraint that the rocks only fall from above?

Thanks in advance!

Upvotes: 0

Views: 45

Answers (1)

Stoyan
Stoyan

Reputation: 330

If you only need them to go from top to bottom without any special curvy trajectory then you don't need to deal with splines.

Let's address the gradual acceleration first. You want them to fall slowly in the beginning and speed up during game progress. One approach would be to do track level time and do some duration math based on elapsed level time. An easier one would be to decrease the duration of time taken by the asteroid to reach the bottom. In your scene declaration section, declare those:

fileprivate let startingDuration: TimeInterval = 6.0  // Put here whatever value you feel fit for the level start falling speed
fileprivate let difficultyIncrease: TimeInterval = 0.05  // Put here whatever value you feel fit for how much should each next asteroid accelerate
fileprivate let collisionPosition = CGPoint(x: 300, y: 200)  // Put here the onscreen location where the asteroids should be heading to
fileprivate var asteroidCounter = 0  // Increase this counter every time you spawn a new asteroid

Now, let's get down to the actual asteroid movement. There are different ways to approach it. The easiest one and recommended by Apple is to use an action for that. Add this code to your asteroid spawn method:

// Implement here your spawning code ...
// It's best to choose random starting points (X axis) a bit higher than the upper screen boundary

let fallingDuration: TimeInterval = startingDuration - difficultyIncrease * TimeInterval(asteroidCounter)
let fallingAction = SKAction.move(to: collisionPosition, duration: fallingDuration)
asteroid.runAction(fallingAction)

If you need a function for random integer generation, try this:

func RandomInt(min: Int, max: Int) -> Int {
    return Int(arc4random_uniform(UInt32(max-(min-1)))) + min
}

Upvotes: 1

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