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How to advance time in an SKEmitterNode using advanceSimulationTime()

Paul Hudson       @twostraws

When you create a particle system in SpriteKit, the particles start at their creation point and move outwards from there. That’s fine for things like explosions and fire, but if you’re using the particles to simulate something that has no real start or end – space dust, for example – then having your particles start from a particular location looks wrong.

To fix this, you should use the advanceSimulationTime() method of SKEmitterNode: give it a number of seconds, and it effectively fast forwards the particle system by that amount. For a space dust particle system, this would fill the screen with particles, so the game screen doesn’t start empty.

Here’s some code:

if let starfield = SKEmitterNode(fileNamed: "Starfield") {
    starfield.position = CGPoint(x: 1024, y: 384)
    starfield.advanceSimulationTime(10)
    addChild(starfield)
}

Available from iOS 7.0

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