Moving SpriteNode Texture but not PhysicBody - swift

Question

Working on a game right now, I've faced a problem regarding management of SkSpriteNodes. I have a SpriteNode whose texture size is lower than physicsBody size assigned to it. It is possible to move, thanks to something similar to an SKAction, only the texture of a node and not its physicsBody?
To explain the problem in other terms, I will give you a graphic example:
As you can see, what I want to achieve is not to modify physicsBody proprieties(in order to not affect collision or having problems with continuos reassigning of PhysicsBody entities), but changing its texture length and adjusting its position. How can I achieve this programmatically?
A bit of code for context, which is just illustrative of the problem:
let node = SKSpriteNode(color: .red, size: CGSize(width: 8, height: 60)
node.physicsBody = SKPhysicsBody(rectangleOf: CGSize(width: 8, height: 60)
self.addChild(node)
//what I've tried is something like that
//It causes glitches in visualisation... and I need to move the object since resizing is towards the center.
let resize = SKAction.scaleY(to: 0.5, duration: 5)
let move = SKAction.move(to: node.position - CGPoint(x:0, y:node.size.height*0.5), duration: 5)
let group = SKAction.group([resize, move])
node.run(group)
//And this is even worse if I add, in this specific example, another point fixed to the previous node
let node2 = SKSpriteNode(color: .blue, size: CGSize(width: 8, length: 8)
node2.physicsBody = SKPhysicsBody(rectangleOf: CGSize(width: 8, height: 8))
node2.position = CGPoint(x: 0, y: -node.height)
self.addChild(node2)
self.physicsWorld.add(SKPhysicsJointFixed.joint(withBodyA: node.physicsBody! , bodyB: node2.physicsBody!, anchor: CGPoint(x: 0, y: -node.size.height)))

Answer 1

I get your problem.
let resize = SKAction.scaleY(to: 0.5, duration: 5)
This line will cause the physicsBody to scale the x and y axis uniformly. While your texture will just scale the y axis.
Its not so straight forward changing physicsBody shapes to match actions
One way to do it though would be to call a method from
override func didEvaluateActions()
Something like this:
var group1: SKAction? = nil
var group2: SKAction? = nil
var touchCnt = 0
var test = SKSpriteNode(texture: SKTexture(imageNamed: "circle"), color: .blue, size: CGSize(width: 100, height: 100))
func setActions() {
let newPosition = CGPoint(x: -200, y: 300)
let resize1 = SKAction.scaleY(to: 0.5, duration: 5)
let move1 = SKAction.move(to: newPosition, duration: 5)
group1 = SKAction.group([resize1, move1])
let resize2 = SKAction.scaleY(to: 1, duration: 5)
let move2 = SKAction.move(to: position, duration: 5)
group2 = SKAction.group([resize2, move2])
}
func newPhysics(node: SKSpriteNode) {
node.physicsBody = SKPhysicsBody(texture: node.texture!, size: node.size)
node.physicsBody?.affectedByGravity = false
node.physicsBody?.allowsRotation = false
node.physicsBody?.usesPreciseCollisionDetection = false
}
override func sceneDidLoad() {
physicsWorld.contactDelegate = self
test.position = CGPoint(x: 0, y: 300)
setActions()
newPhysics(node: test)
addChild(test)
}
override func didEvaluateActions() {
newPhysics(node: test)
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
if touchCnt == 0 {
if !test.hasActions() {
test.run(group1!)
touchCnt += 1
}
} else {
if !test.hasActions() {
test.run(group2!)
touchCnt -= 1
}
}
}
if you put the above code in your gameScene, taking care to replace any duplicated methods and replacing the test node texture. then when you tap the screen the sprite should animate as you want while keeping the physics body is resized at the same time. There are a few performance issues with this though. As it changes the physics body on each game loop iteration.