Node is slowing down in Sprite Kit

Question

I'm trying to create an arcade game, where a ball moves at a constant speed and is unaffected by gravity or friction. So I created the ball as an SKShapeNode and set its linearDamping and friction to 0. I also set the game scene to have no gravity. But when playing, if the ball hits another shape node (a circle) at a low angle, it can slow down. The ball's restitution is 1, and allowsRotation is false.

I am keeping the ball moving by applying one impulse at the beginning of the game, that is a random direction.

Answer 1

This might not be the most ideal fix but you could set the fixed speed of the object every update to a specific value which is your constant speed.

The other alternative way to solve this would be to set the fixed speed of the object under the collision delegate functions.

Answer 2

I had a similar problem that was resolved by setting physicsBody?.isDynamic = false on the node that the ball makes contact with.

For example if you have a ball and a brick:

ball.physicsBody = SKPhysicsBody(circleOfRadius: ball.frame.width / 2) // (diameter / 2) = radius
ball.physicsBody?.categoryBitMask = ballCategoryBitMask
// Detect contact with the bottom of the screen or a brick
//
ball.physicsBody?.contactTestBitMask = bottomCategoryBitMask | brickCategoryBitMask
ball.physicsBody?.friction = 0
ball.physicsBody?.allowsRotation = false
ball.physicsBody?.linearDamping = 0
ball.physicsBody?.restitution = 1
ball.physicsBody?.applyImpulse(CGVector(dx: 10, dy: -10))

brick.physicsBody = SKPhysicsBody(rectangleOf: brick.frame.size)
brick.physicsBody?.linearDamping = 0
brick.physicsBody?.allowsRotation = false
brick.physicsBody?.isDynamic = false // Prevents the ball slowing down when it gets hit
brick.physicsBody?.affectedByGravity = false
brick.physicsBody?.friction = 0.0