Make sprite move with velocity - swift

Question

I am trying to make a sprite follow my finger using velocity so it doesn't phase through other sprite nodes, or push them around. I just want the sprite node, aka the ball, to simply hit the other sprite node and either bounce off or just simply hit it and sit there until its moved again.
At the moment I am using location based movement:
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
for touch in touches {
let location = touch.location(in: self)
ball.position.x = location.x
ball.position.y = location.y
print("x: \(ball.position.x), y: \(ball.position.y)")
}
}
how can I make it so it doesn't move around other sprite nodes and actually reacts with categoryBitMask elements?
I'm new to this whole thing. Hopefully you understand :)
REST OF MY CODE:
import SpriteKit
import GameplayKit
class GameScene: SKScene {
var ball = SKSpriteNode()
var danger1 = SKSpriteNode()
var danger2 = SKSpriteNode()
var goal = SKSpriteNode()
override func didMove(to view: SKView) {
ball = self.childNode(withName: "ball") as! SKSpriteNode
danger1 = self.childNode(withName: "danger1") as! SKSpriteNode
danger2 = self.childNode(withName: "danger2") as! SKSpriteNode
goal = self.childNode(withName: "goal") as! SKSpriteNode
let border = SKPhysicsBody(edgeLoopFrom: self.frame)
border.friction = 0
border.restitution = 0
danger1.physicsBody = SKPhysicsBody()
danger1.physicsBody?.categoryBitMask = PhysicsCategories.dangerCategory
danger2.physicsBody = SKPhysicsBody()
danger2.physicsBody?.categoryBitMask = PhysicsCategories.dangerCategory
ball.physicsBody = SKPhysicsBody()
ball.physicsBody?.categoryBitMask = PhysicsCategories.ballCategory
ball.physicsBody?.contactTestBitMask = PhysicsCategories.dangerCategory
ball.physicsBody?.collisionBitMask = PhysicsCategories.none
goal.physicsBody = SKPhysicsBody(circleOfRadius: goal.size.width/2)
goal.physicsBody?.categoryBitMask = PhysicsCategories.goalCategory
danger1.physicsBody?.isDynamic = true
ball.physicsBody?.isDynamic = true
goal.physicsBody?.isDynamic = true
danger2.physicsBody?.isDynamic = true
danger2.physicsBody!.affectedByGravity = false
danger1.physicsBody!.affectedByGravity = false
goal.physicsBody!.affectedByGravity = false
ball.physicsBody!.affectedByGravity = false
setupPhysics()
}
func setupPhysics() {
physicsWorld.gravity = CGVector(dx: 0.0, dy: 0.0)
physicsWorld.contactDelegate = self
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
for touch in touches {
}
}
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
for touch in touches {
let location = touch.location(in: self)
ball.position.x = location.x
ball.position.y = location.y
print("x: \(ball.position.x), y: \(ball.position.y)")
}
}
override func update(_ currentTime: TimeInterval) {
// Called before each frame is rendered
}
}
extension GameScene: SKPhysicsContactDelegate {
func didBegin(_ contact: SKPhysicsContact) {
let contactMask = contact.bodyA.categoryBitMask | contact.bodyB.categoryBitMask
if contactMask == PhysicsCategories.ballCategory | PhysicsCategories.dangerCategory {
ball.position = CGPoint(x: 0, y: 550)
} else if contactMask == PhysicsCategories.ballCategory | PhysicsCategories.goalCategory {
print("Goal!")
}
}
}

Answer 1

Try commenting out this line:
ball.physicsBody?.collisionBitMask = PhysicsCategories.none
which prevents the ball from colliding with anything, i.e. it is unaffected by collisions with any object. Note - this does NOT mean that other objects are unaffected by collision with the ball. collision are 2-way - given 2 node A and B, you have to define if A collides with B and if B collides with A. This isn;t necessary for contact - it's enough to define that A contacts B. If it's actually b that moves into A, didBegin() will still get called. you don't have to define that B contact A also.
You haven't appeared to set the collisionBitMask on any other physics body, which means those will collide with everything.
this explains why the ball moves through the wall - because it isn't colliding with it, although every other object should get pushed around by the ball.
Try putting a:
print("Contact")
as the first line of your didBegin() to see if any contacts are being registered.
If you want to drag sprites with your finger then making them bounce off (collide with) other sprites can be tricky, because dragging implies that you want to set their position manually and bouncing off implies that your want the sprites to be moved by the Sprite-Kit engine and the 2 are not really compatible.
It's probably worth pointing our that 'collisions' are sprites bouncing off each other and are handled by the SK engine. The collisionBitMask controls what objects bounce off each other.
'Contacts' are just a way to get notified when 2 objects touch. They are controlled by the contactTestBitMask.
Both contact and collisions rely on the categoryBitMAsk
My step-by-step guide for collisions and contacts:
https://stackoverflow.com/a/51041474/1430420
And a guide to collision and contactTest bit masks:
https://stackoverflow.com/a/40596890/1430420
Manipulating bit masks to turn individual collision and contacts off and on. https://stackoverflow.com/a/46495864/1430420