TouchesMoved is lagged in swift - swift

Question

I am writing the code in Xcode 6 Beta 6 using Swift in SpriteKit. In the code I need a picture to follow the finger when the user moves it. touchesMoved works but with glitches. If I move the finger slowly everything is fine. If I the move the finger fast going right to left then everything is fine. If I move the finger fast going left to right, then the picture follows the finger only for a fraction of a second. If I tap and hold the picture in its current position for about half a second then everything is fine when I move it fast going both from right to left or left to right. In summary I cannot move the picture fast going left to right unless I tap and hold the picture for about half a second. Anybody has a clue why this is happening? Thanks for your time. Below is the code. I am moving SKSPriteNode follow2
override func touchesMoved(touches: NSSet, withEvent event: UIEvent) {
for touch: AnyObject in touches {
let angle_area_location = touch.locationInNode(self)
if self.nodeAtPoint(angle_area_location) == self.angle_area {
if (angle_area_location.x <= 21) {
angle = 1.55681122463001
distance12 = sqrt((angle_area_location.y - 30) * (angle_area_location.y - 30) + 1)
}
if (angle_area_location.y <= 31) {
angle = 0.0102037274939542
distance12 = sqrt((31 - 30) * (31 - 30) + (angle_area_location.x - 20) * (angle_area_location.x - 20))
}
if (angle_area_location.x > 21) && (angle_area_location.y > 31) {
angle = atan((angle_area_location.y - 30) / (angle_area_location.x - 20))
distance12 = sqrt((angle_area_location.y - 30) * (angle_area_location.y - 30) + (angle_area_location.x - 20) * (angle_area_location.x - 20))
}
if (distance12 <= maxFollow2) && (distance12 >= minFollow2) {
self.cannon.zRotation = angle
self.arc.zRotation = angle
if (angle_area_location.x > 21) || (angle_area_location.y > 31) {
follow2.position = CGPointMake(angle_area_location.x , angle_area_location.y)
}
if(angle_area_location.x <= 21) {
follow2.position = CGPointMake(21 , angle_area_location.y)
}
if (angle_area_location.y <= 31) {
follow2.position = CGPointMake(angle_area_location.x , 31)
}
}
if(distance12 > maxFollow2) {
self.cannon.zRotation = angle
self.arc.zRotation = angle
delta = 290/3
arc.size = CGSizeMake(160 * (1 + delta/20) , 35)
arc.position = CGPointMake(20 - 3 * (delta) * cos(angle) , 30 - 3 * (delta) * sin(angle))
followdist = 360
follow2.position = CGPointMake(angle_area_location.x , angle_area_location.y)
velocity = vmin + (followdist - minFollow2) * (300/(maxFollow2 - minFollow2))
}
if (distance12 < minFollow2) {
self.cannon.zRotation = angle
self.arc.zRotation = angle
arc.size = CGSizeMake(160 , 6.8)
arc.position = CGPointMake(20 , 30)
follow2.position = CGPointMake( minFollow2 * cos(angle) + 20 , minFollow2 * sin(angle) + 30)
followdist = sqrt((follow2.position.y - 30) * (follow2.position.y - 30) + (follow2.position.x - 20) * (follow2.position.x - 20))
velocity = vmin + (followdist - minFollow2) * (300/(maxFollow2 - minFollow2))
}
}
}
}

Answer 1

Ok I figured the glitch. I had a UISwipeGestureRecognizer that calls a method when I right swipe. I deactivated that and everything works fine. I guess swiping right and moving left to right on touchesMoved are interfering with each other.

Answer 2

A common trick when working with distances is to avoid taking the square root and only compare the squared values. This saves quite a bit of processor resources.
Example:
let maxfollow2sqr = maxFollow2 * maxFollow2
distance12 = (angle_area_location.y - 30) * (angle_area_location.y - 30) + (angle_area_location.x - 20) * (angle_area_location.x - 20)
if (distance12 <= maxFollow2sqr) {
// do something here
}
Since all you care about is if the calculated distance is between the min and the max you can deal just with the squares. This may speed up the function quite a bit but there are probably other optimizations that can be done.