moving platform with gameplay kit - ios

Question

Creating a 2d game, and want to add moving platforms where I can control the pattern and rotation of the platform.
Example:
I want this platform to move in a clockwise motion, also when it reaches the top and bottom I want it to rotate accordingly as if it is facing the direction it is going (so the platform would essentially rotate 180 degrees as it arches at the top and bottom).
I can't use SKActions because I need the physics to work properly.
My idea is that I can use an Agent with behaviors and goals to do this. Not sure if I will need path finding as well.
I'm researching how to use these features, but the documentation and lack of tutorials is hard to decipher. I'm hoping someone could save my some time of trial and error by providing an example of how this would work.
Thanks in advance!

Answer 1

Using SKActions or adjusting the position manually will be sucky to get working the way you want, BUT it's always worth a shot to give it a go, since it would take 2 minutes to mock it up and see...
I'd suggest doing something like a Path class that sends velocity commands to the platform every frame ...
Actually, this could be a good exercise in learning the state machine..
MOVE RIGHT STATE: if X position > starting position X + 200, enter state "move down"
MOVE DOWN STATE: if Y position < starting position Y - 200, enter state "move left"
MOVE LEFT STATE: if X position < starting position X, enter state "move up"
MOVE UP STATE: if Y position > starting position Y, enter state "move right"
.. there are ways you could figure out to give it more curvature instead of just straight angle (when changing direction)
Otherwise you would have to translate that into a class / struct / component and give each platform it's own instance of it.
///
Another option is to take the physics out of the equation, and create a playerIsOnPlatform property... then you manually adjust the position of the player each frame... (or maybe a SKConstraint)
This would then require more code on jumping and such, and turns things to spaghetti pretty quickly (last time I tried it)
But, I was able to successfully clone this, using proper hit detection going that route:
https://www.youtube.com/watch?v=cnhlFZeIR7Q
UPDATE:
Here is a working project:
https://github.com/fluidityt/exo2/tree/master
Boilerplate swift stuff:
import SpriteKit
import GameplayKit
// Workaround to not having any references to the scene off top my head..
// Simply add `gScene = self` in your didMoveToViews... or add a base scene and `super.didMoveToView()`
var gScene = GameScene()
class GameScene: SKScene {
override func didMove(to view: SKView) {
gScene = self
}
var entities = [GKEntity]()
var graphs = [String : GKGraph]()
private var lastUpdateTime : TimeInterval = 0
func gkUpdate(_ currentTime: TimeInterval) -> TimeInterval {
if (self.lastUpdateTime == 0) {
self.lastUpdateTime = currentTime
}
let dt = currentTime - self.lastUpdateTime
for entity in self.entities {
entity.update(deltaTime: dt)
}
return currentTime
}
override func update(_ currentTime: TimeInterval) {
self.lastUpdateTime = gkUpdate(currentTime)
}
}
Here is the very basic component:
class Platforms_BoxPathComponent: GKComponent {
private enum MovingDirection: String { case up, down, left, right }
private var node: SKSpriteNode!
private var state: MovingDirection = .right
private lazy var startingPos: CGPoint = { self.node.position }()
#GKInspectable var startingDirection: String = "down"
#GKInspectable var uniqueName: String = "platform"
#GKInspectable var xPathSize: CGFloat = 400
#GKInspectable var yPathSize: CGFloat = 400
// Moves in clockwise:
private var isTooFarRight: Bool { return self.node.position.x > (self.startingPos.x + self.xPathSize) }
private var isTooFarDown: Bool { return self.node.position.y < (self.startingPos.y - self.yPathSize) }
private var isTooFarLeft: Bool { return self.node.position.x < self.startingPos.x }
private var isTooFarUp: Bool { return self.node.position.y > self.startingPos.y }
override func didAddToEntity() {
print("adding component")
// can't add node here because nodes aren't part of scene yet :(
// possibly do a thread?
}
override func update(deltaTime seconds: TimeInterval) {
if node == nil {
node = gScene.childNode(withName: uniqueName) as! SKSpriteNode
// for some reason this is glitching out and needed to be redeclared..
// showing 0 despite clearly not being 0, both here and in the SKS editor:
xPathSize = 300
}
let amount: CGFloat = 2 // Amount to move platform (could also be for for velocity)
// Moves in clockwise:
switch state {
case .up:
if isTooFarUp {
state = .right
fallthrough
} else { node.position.y += amount }
case .right:
if isTooFarRight {
state = .down
fallthrough
} else { node.position.x += amount }
case .down:
if isTooFarDown {
state = .left
fallthrough
} else { node.position.y -= amount }
case .left:
if isTooFarLeft {
state = .up
fallthrough
} else { node.position.x -= amount }
default:
print("this is not really a default, just a restarting of the loop :)")
node.position.y += amount
}
}
}
And here is what you do in the sks editor: