SpriteKit - Bouncing node constant speed/velocity?

Question

Simple setup - I have bouncing ball nodes (blue) and static ball nodes (green). The grey box has Physics body SKPhysicsBody(edgeLoopFrom: box.frame), so it limits the bouncing ball from moving outside. I set the bouncing balls node (blue) velocity to a random CGVector upon creation and it starts moving. It bounces off the static ball node (green), and off the edges of the grey box.

My general SKPhysicsBody setup with all nodes is:

node.physicsBody?.restitution = 1
node.physicsBody?.friction = 0.0
node.physicsBody?.linearDamping = 0.0
node.physicsBody?.angularDamping = 0.0

My question is: How do I make sure the bouncing ball does move at a constant speed? After a couple of bounces, the node is either speeding up, or slowing down.

Set the value to a constant number, you may use contact delegate and set the value as same as they began contacting. — E.Coms, Apr 02 '19 at 11:42
I notice its a CGVector. You need to normalize the value with hypot() to get the vector length and keep this length same all the time. It's a simple calculation and you can find anywhere. — E.Coms, Apr 02 '19 at 13:42
That was actually the right clue, thanks a lot. Do you want to write a response so I can accept it, or should I answer this question myself? — schnabler, Apr 02 '19 at 14:46

score 3 · Accepted Answer · answered Apr 09 '19 at 08:50

In order to achieve this, I normalized the vector whenever the physics engine detects a collision. So in func didBegin(_ contact: SKPhysicsContact), the following happens:

let length = hypotf(Float(node.velocity.dx), Float(node.velocity.dy)) 
let multiplier = (290.0 / length)
firstBody.velocity.dx *= CGFloat(multiplier)
firstBody.velocity.dy *= CGFloat(multiplier)

290.0 is an arbitrary value that determines the speed of ball.

For reference, check this answer.

SpriteKit - Bouncing node constant speed/velocity?

1 Answers1