Moving SKSpriteNode in a downward loop using Swift
Using Swift and SpriteKit, I'd like to move SKSpritenode in a spiral pattern, but haven't found the right resources to get me started. To be more precise, I would like to move the sprite node in a downward loop. I checked the sequence of SKActions, but since they are not executed in parallel, circular motion combined with movement will not work. I would love any hints, tutorials or snippets to set me up on the right track.
Thanx in advance, Marcus
source to share
I have put together a sample code that you can adapt for your own purposes. I based the code on the equation for the Archimedean spiral :
r = a + bθ
Where a
is the radius of the beginning; b
is the radius along which the spiral will increase per revolution, and t23 is the current angle.
A spiral is basically a glorified circle (IMO), so in order to move your node in a spiral, you need to compute a point on the circle using the angle, radius and center point:
func pointOnCircle(#angle: CGFloat, #radius: CGFloat, #center: CGPoint) -> CGPoint {
return CGPoint(x: center.x + radius * cos(angle),
y: center.y + radius * sin(angle))
}
Then stretch SKAction
so you can easily create a spiral action:
extension SKAction {
static func spiral(#startRadius: CGFloat, endRadius: CGFloat, angle
totalAngle: CGFloat, centerPoint: CGPoint, duration: NSTimeInterval) -> SKAction {
// The distance the node will travel away from/towards the
// center point, per revolution.
let radiusPerRevolution = (endRadius - startRadius) / totalAngle
let action = SKAction.customActionWithDuration(duration) { node, time in
// The current angle the node is at.
let θ = totalAngle * time / CGFloat(duration)
// The equation, r = a + bθ
let radius = startRadius + radiusPerRevolution * θ
node.position = pointOnCircle(angle: θ, radius: radius, center: centerPoint)
}
return action
}
}
Finally, a usage example. In didMoveToView
:
let node = SKSpriteNode(color: UIColor.redColor(), size: CGSize(width: 10, height: 10))
node.position = CGPoint(x: size.width / 2, y: size.height / 2)
addChild(node)
let spiral = SKAction.spiral(startRadius: size.width / 2,
endRadius: 0,
angle: CGFloat(M_PI) * 2,
centerPoint: node.position,
duration: 5.0)
node.runAction(spiral)
source to share
While the above solution is brilliantly thought, there is a much easier way.
- Add a spinnerNode and re-rotate it using rotateBy
- Add your sprite as a child to spinnerNode (your sprite will by default rotate with spinnerNode)
- Move your spriteNode (with moveTo) to the center of the wheelNode (your sprite will move in a spiral path towards the center).
source to share