Move a circular UIView inside another circular UIView

I'm trying to do a joystick swift, and I'm almost there.

But I have a problem, the movement of the joystick is smooth when I move it "in the middle", but when the joystick touches the edges of "its container" it becomes laggy.

But I know why, it's because I allow the joystick to move only if it doesn't touch the edges, and I don't know how to correct this problem (what code to put in the else).

Here's my code and a GIF so you can see better.

import UIKit
import SnapKit

class ViewController: UIViewController {

    let joystickSize = 150
    let substractSize = 200
    let joystickOffset = 10

    let joystickSubstractView = UIView()
    let joystickView = UIView()

    override func viewDidLoad() {
        super.viewDidLoad()

        joystickSubstractView.backgroundColor = .gray
        joystickSubstractView.layer.cornerRadius = CGFloat(substractSize / 2)
        self.view.addSubview(joystickSubstractView)

        let panGesture = UIPanGestureRecognizer(target: self, action: #selector(dragJoystick))
        joystickView.isUserInteractionEnabled = true
        joystickView.addGestureRecognizer(panGesture)
        joystickView.backgroundColor = .white
        joystickView.layer.cornerRadius = CGFloat(joystickSize / 2)
        joystickSubstractView.addSubview(joystickView)

        joystickSubstractView.snp.makeConstraints {
            $0.width.height.equalTo(substractSize)
            $0.centerX.equalToSuperview()
            $0.bottom.equalToSuperview().inset(150)
        }

        joystickView.snp.makeConstraints {
            $0.width.height.equalTo(joystickSize)
            $0.center.equalToSuperview()
        }
    }

    @objc func dragJoystick(_ sender: UIPanGestureRecognizer) {
        self.view.bringSubviewToFront(joystickView)
        let translation = sender.translation(in: self.view)

        let joystickCenter = joystickView.convert(joystickView.center, to: self.view)
        let futureJoystickCenter =  CGPoint(x: joystickCenter.x - joystickView.frame.minX + translation.x,
                                            y: joystickCenter.y - joystickView.frame.minY + translation.y)
        let distanceBetweenCenters = hypot(futureJoystickCenter.x - joystickSubstractView.center.x,
                                           futureJoystickCenter.y - joystickSubstractView.center.y)

        if CGFloat(substractSize / 2 + joystickOffset) >= (distanceBetweenCenters + CGFloat(joystickSize / 2)) {
            joystickView.center = CGPoint(x: joystickView.center.x + translation.x,
                                          y: joystickView.center.y + translation.y)
        } else {
            // I don't know what to put here to make the joystick "smoother"
        }

        sender.setTranslation(CGPoint.zero, in: self.view)
    }
}

Thank you for your help

Here is one approach...

• calculate the maximum available distance from the center of the outer circle to the center of the inner circle, as a radius
• track the touch / pan gesture's location relative to the center of the outer circle
• if the new distance from the center of the inner circle (the touch point) to the center of the outer circle is greater than the max radius, move the inner circle center to the intersection of the touch-to-center line and the edge of the radius circle

Here's how it would look, with the center of the "joystick" view identified with a green dot, and the radius circle shown as a red outline:

You can give it a try with this code:

class JoyStickViewController: UIViewController {
let joystickSize: CGFloat = 150
let substractSize: CGFloat = 200
var innerRadius: CGFloat = 0.0
let joystickSubstractView = UIView()
let joystickView = UIView()
override func viewDidLoad() {
super.viewDidLoad()
joystickSubstractView.backgroundColor = .gray
joystickSubstractView.layer.cornerRadius = CGFloat(substractSize / 2)
self.view.addSubview(joystickSubstractView)
let panGesture = UIPanGestureRecognizer(target: self, action: #selector(dragJoystick(_:)))
joystickView.isUserInteractionEnabled = true
joystickView.addGestureRecognizer(panGesture)
joystickView.backgroundColor = .yellow
joystickView.layer.cornerRadius = CGFloat(joystickSize / 2)
joystickSubstractView.addSubview(joystickView)
joystickSubstractView.snp.makeConstraints {
$0.width.height.equalTo(substractSize)
$0.centerX.equalToSuperview()
$0.bottom.equalToSuperview().inset(150)
}
joystickView.snp.makeConstraints {
$0.width.height.equalTo(joystickSize)
$0.center.equalToSuperview()
}
// if you want the "joystick" circle to overlap the "outer circle" a bit, adjust this value
innerRadius = (substractSize - joystickSize) * 0.5
// start debugging / clarification...
// add a center "dot" to the joystick view
// add a red circle showing the inner radius - where we want to restrict the center of the joystick view
let jsCenterView = UIView()
jsCenterView.backgroundColor = .green
jsCenterView.layer.cornerRadius = 2.0
joystickView.addSubview(jsCenterView)
jsCenterView.snp.makeConstraints {
$0.width.height.equalTo(4.0)
$0.center.equalToSuperview()
}
let v = UIView()
v.backgroundColor = .clear
v.layer.borderColor = UIColor.red.cgColor
v.layer.borderWidth = 2
v.layer.cornerRadius = innerRadius
v.isUserInteractionEnabled = false
joystickSubstractView.addSubview(v)
v.snp.makeConstraints {
$0.width.height.equalTo(innerRadius * 2.0)
$0.center.equalToSuperview()
}
// end debugging / clarification
}
func lineLength(from pt1: CGPoint, to pt2: CGPoint) -> CGFloat {
return hypot(pt2.x - pt1.x, pt2.y - pt1.y)
}
func pointOnLine(from startPt: CGPoint, to endPt: CGPoint, distance: CGFloat) -> CGPoint {
let totalDistance = lineLength(from: startPt, to: endPt)
let totalDelta = CGPoint(x: endPt.x - startPt.x, y: endPt.y - startPt.y)
let pct = distance / totalDistance;
let delta = CGPoint(x: totalDelta.x * pct, y: totalDelta.y * pct)
return CGPoint(x: startPt.x + delta.x, y: startPt.y + delta.y)
}
@objc func dragJoystick(_ sender: UIPanGestureRecognizer) {
let touchLocation = sender.location(in: joystickSubstractView)
let outerCircleViewCenter = CGPoint(x: joystickSubstractView.bounds.width * 0.5, y: joystickSubstractView.bounds.height * 0.5)
var newCenter = touchLocation
let distance = lineLength(from: touchLocation, to: outerCircleViewCenter)
// if the touch would put the "joystick circle" outside the "outer circle"
// find the point on the line from center to touch, at innerRadius distance
if distance > innerRadius {
newCenter = pointOnLine(from: outerCircleViewCenter, to: touchLocation, distance: innerRadius)
}
joystickView.center = newCenter
}
}

Note: you can delete (or comment-out) the lines of code in viewDidLoad() between the // start debugging and // end debugging comments to remove the green center-dot and the red circle.