I needed a Pinch Recognizer that would scale in x, or y, or both directions depending on the direction of the pinch. I looked through many of the of the other questions here and they only had parts of the answer. Here's my complete solution that uses a custom UIPinchGestureRecognizer.
Use UIPinchGestureRecognizer to scale view in direction of pinch
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This alternative solution determines the direction of scaling based on bearing angle rather than slope. I find it a bit easier to adjust the different zones using angle measurements.
@objc func viewPinched(sender: UIPinchGestureRecognizer) {
// Scale the view either vertically, horizontally, or diagonally based on the axis of the initial pinch
let locationOne = sender.location(ofTouch: 0, in: sender.view)
let locationTwo = sender.location(ofTouch: 1, in: sender.view)
let diffX = locationOne.x - locationTwo.x
let diffY = locationOne.y - locationTwo.y
// Break the plane into 3 equal segments
// Inverse tangent will return between π/2 and -π/2. Absolute value can be used to only consider 0 to π/2 - don't forget to handle divide by 0 case
// Breaking π/2 into three equal pieces, we get regions of 0 to π/6, π/6 to 2π/6, and 2π/6 to π/2 (note 2π/6 = π/3)
// Radian reminder - π/2 is 90 degreees :)
let bearingAngle = diffY == 0 ? CGFloat.pi / 2.0 : abs(atan(diffX/diffY))
if sender.state == .began {
// Determine type of pan based on bearing angle formed by the two touch points.
// Only do this when the pan begins - don't change type as the user rotates their fingers. Require a new gesture to change pan type
if bearingAngle < CGFloat.pi / 6.0 {
panType = .vertical
} else if bearingAngle < CGFloat.pi / 3.0 {
panType = .diagonal
} else if bearingAngle <= CGFloat.pi / 2.0 {
panType = .horizontal
}
}
// Scale the view based on the pan type
switch panType {
case .diagonal: transform = CGAffineTransform(scaleX: sender.scale, y: sender.scale)
case .horizontal: transform = CGAffineTransform(scaleX: sender.scale, y: 1.0)
case .vertical: transform = CGAffineTransform(scaleX: 1.0, y: sender.scale)
}
}
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Here's a solution in Swift:
extension UIPinchGestureRecognizer {
func scale(view: UIView) -> (x: CGFloat, y: CGFloat)? {
if numberOfTouches() > 1 {
let touch1 = self.locationOfTouch(0, inView: view)
let touch2 = self.locationOfTouch(1, inView: view)
let deltaX = abs(touch1.x - touch2.x)
let deltaY = abs(touch1.y - touch2.y)
let sum = deltaX + deltaY
if sum > 0 {
let scale = self.scale
return (1.0 + (scale - 1.0) * (deltaX / sum), 1.0 + (scale - 1.0) * (deltaY / sum))
}
}
return nil
}
}
I created a custom version of a UIPinchGestureRecognizer. It uses the slope of line between the two fingers to determine the direction of the scale. It does 3 types: Vertical; Horizontal; and Combined(diagonal). Please see my notes at the bottom.
Remember to add the protocol to the view controller header file:
And add the recognizer in the viewDidLoad:
This is set up to use the main view to capture the pinch; and manipulate a second view. This way you can still scale it as the view gets small. You can change it to react directly to the scalable view.
LIMITS: I arbitrarily chose the starting size of my view so a scale limit of 2.0 would equal full screen. My lower scale is set at 0.1.
USER INTERACTION: I mess around with a lot of user interaction things like changing the view's background color and adding/changing arrows over the view to show direction. It's important to give them feedback during the scaling process, especially when changing directions like this codes allows.
BUG: There is a bug in Apple's UIPinchGestureRecognizer. It registers UIGestureRecognizerStateBegan with the touch of 2 fingers as you would expect. But once it is in StateBegan or StateChanged you can lift one finger and the state remains. It doesn't move to StateEnded or StateCancelled until BOTH fingers are lifted. This created a bug in my code and many headaches! The if numberOfTouches > 1 fixes it.
FUTURE: You can change the slope settings to scale in just one direction, or just 2. If you add the arrows images, you can see them change as you rotate your fingers.