Constant velocity while still being able to apply an impulse - ios

Question

I am making a game where as the main sprite/player moves constantly, he/she needs to jump through barriers.
I need help with how to set a constant velocity for my moving sprite. When I try and do this in the SpriteKit update function, I can’t apply an impulse to jump whenever the user taps the screen.
Here is my code. I commented the places where I am having trouble:
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
/* Called when a touch begins */
if (gameStarted == false) {
gameStarted = true
mainSprite.physicsBody?.affectedByGravity = true
mainSprite.physicsBody?.allowsRotation = true
let spawn = SKAction.runBlock({
() in
self.createWalls()
})
let delay = SKAction.waitForDuration(1.5)
let spawnDelay = SKAction.sequence([spawn, delay])
let spawnDelayForever = SKAction.repeatActionForever(spawnDelay)
self.runAction(spawnDelayForever)
let distance = CGFloat(self.frame.height + wallPair.frame.height)
let movePipes = SKAction.moveByX(0, y: -distance - 50, duration: NSTimeInterval(0.009 * distance)) // Speed up pipes
let removePipes = SKAction.removeFromParent()
moveAndRemove = SKAction.sequence([movePipes, removePipes])
} else {
if died == true {
}
else {
mainSprite.physicsBody?.applyImpulse(CGVectorMake(0, 20)) // TRYING TO APPLY AN IMPULSE TO MY SPRITE SO IT CAN JUMP AS IT MOVES
}
}
for touch in touches {
let location = touch.locationInNode(self)
}
}
override func update(currentTime: CFTimeInterval) {
/* Called before each frame is rendered */
updateSpritePosition()
mainSprite.physicsBody?.velocity = CGVectorMake(400, 0) // SETS A CONSTANT VELOCITY, HOWEVER I CAN NOT APPLY AN IMPULSE.
}

Answer 1

The problem is that you're overwriting the velocity in the update method. So even though you added an impulse, it gets immediately overwritten by code in the update. Try overwriting just the dx part of the velocity.
override func update(currentTime: CFTimeInterval) {
updateSpritePosition()
mainSprite.physicsBody?.velocity = CGVectorMake(400, mainSprite.physicsBody?.velocity.dy)
}