How to prevent Sprite Nodes from pushing each other? - swift

Question

3 Sprite Nodes are moving up at different speed levels. You see that the gorilla likes to rest, but the lobster is pushing it slowly upwards. Expected behaviour would be, that the lobster would rest also and continue going upwards when the gorilla starts moving again. Using .isDynamic = false did not work — the Sprite Nodes were overlaying and lobster ignored the physical body of the hedgehog and the gorilla totally.
Recording of my Playground Scene: https://youtu.be/l47kaJiJvkM
Screenshot of the video:
Code:
import SpriteKit
public class WalkingScene: SKScene {
public override func didMove(to view: SKView) {
backgroundColor = .white
view.showsPhysics = true
let hedgehog = SKSpriteNode(imageNamed: "hedgehog")
hedgehog.size = CGSize(width: 64, height: 64)
hedgehog.position = CGPoint(x: size.width/2, y: 400)
hedgehog.physicsBody = SKPhysicsBody(rectangleOf: CGSize(width: 80, height: 80))
hedgehog.physicsBody?.affectedByGravity = false
hedgehog.physicsBody?.allowsRotation = false
let gorilla = SKSpriteNode(imageNamed: "gorilla")
gorilla.size = CGSize(width: 64, height: 64)
gorilla.position = CGPoint(x: size.width/2, y: 140)
gorilla.physicsBody = SKPhysicsBody(rectangleOf: CGSize(width: 80, height: 80))
gorilla.physicsBody?.affectedByGravity = false
gorilla.physicsBody?.allowsRotation = false
let lobster = SKSpriteNode(imageNamed: "lobster")
lobster.size = CGSize(width: 64, height: 64)
lobster.position = CGPoint(x: size.width/2, y: 20)
lobster.physicsBody = SKPhysicsBody(rectangleOf: CGSize(width: 80, height: 80))
lobster.physicsBody?.affectedByGravity = false
lobster.physicsBody?.allowsRotation = false
// hedgehog.physicsBody?.isDynamic = false
// gorilla.physicsBody?.isDynamic = false
// lobster.physicsBody?.isDynamic = false
// hedgehog.physicsBody?.usesPreciseCollisionDetection = true
// hedgehog.physicsBody?.collisionBitMask = 0
// gorilla.physicsBody?.usesPreciseCollisionDetection = true
// gorilla.physicsBody?.collisionBitMask = 0
// lobster.physicsBody?.usesPreciseCollisionDetection = true
// lobster.physicsBody?.collisionBitMask = 0
self.addChild(lobster)
self.addChild(hedgehog)
self.addChild(gorilla)
self.moveGorilla(gorilla)
self.moveLobster(lobster)
self.moveHedgeHog(hedgehog)
}
func moveGorilla(_ passenger: SKSpriteNode) {
let moveLeft = CGVector(dx: 0, dy: 200)
let aYYY = CGVector(dx: 200, dy: 0)
let moving = SKAction.move(by: moveLeft, duration: 1)
let turnAYY = SKAction.move(by: aYYY, duration: 1)
let chill = SKAction.wait(forDuration: 3)
passenger.run(SKAction.sequence([moving, chill, moving, chill, turnAYY])) {
print("Gorilla arrived")
}
}
func moveLobster(_ passenger: SKSpriteNode) {
let moveLeft = CGVector(dx: 0, dy: 200)
let moving = SKAction.move(by: moveLeft, duration: 1.2)
passenger.run(SKAction.sequence([moving, moving, moving, moving, moving, moving, moving, moving, moving])) {
print("Lobster arrived")
}
}
func moveHedgeHog(_ passenger: SKSpriteNode) {
let moveLeft = CGVector(dx: 0, dy: 200)
let moving = SKAction.move(by: moveLeft, duration: 1)
let chill = SKAction.wait(forDuration: 2)
passenger.run(SKAction.sequence([chill, moving, moving, moving])) {
print("Hedgehog arrived")
}
}
}

Answer 1

You can set those dynamics this way:
hedgehog.physicsBody?.isDynamic = true
gorilla.physicsBody?.isDynamic = false
lobster.physicsBody?.isDynamic = true
By this strategy, you can extend this example to other situations.
If isDynamic = true is treated as 0 , and the isDynamic = false, ie static, treated as infinity,
there is something between which can be controlled by the mass of a physics body.
hedgehog.physicsBody?.isDynamic = false. (mass = Infinity)
gorilla.physicsBody?.isDynamic = true. (mass = big)
lobster.physicsBody?.isDynamic = true (mass = 0)
gorilla.physicsBody?.mass = 1000