Scale of UIPinchGestureRecognizer in horizontal and vertical directions separately

Question

When using UIPinchGestureRecognizer what is the best way to detect/read the pinch scale in horizontal and vertical directions individually? I saw this post

UIPinchGestureRecognizer Scale view in different x and y directions

but I noticed there were so many going back and forth for such a seemingly routine task that I am not sure that is the best answer/way.

If not using UIPinchGestureRecognizer altogether for this purpose is the answer, what's the best way to detect pinch scale in two different directions?

Answer 1

Basically do this,

func _mode(_ sender: UIPinchGestureRecognizer)->String {

    // very important:
    if sender.numberOfTouches < 2 {
        print("avoided an obscure crash!!")
        return ""
    }

    let A = sender.location(ofTouch: 0, in: self.view)
    let B = sender.location(ofTouch: 1, in: self.view)

    let xD = fabs( A.x - B.x )
    let yD = fabs( A.y - B.y )
    if (xD == 0) { return "V" }
    if (yD == 0) { return "H" }
    let ratio = xD / yD
    // print(ratio)
    if (ratio > 2) { return "H" }
    if (ratio < 0.5) { return "V" }
    return "D"
}

That function will return H, V, D for you .. horizontal, vertical, diagonal.

You would use it something like this ...

func yourSelector(_ sender: UIPinchGestureRecognizer) {

    // your usual code such as ..
    // if sender.state == .ended { return } .. etc

    let mode = _mode(sender)
    print("the mode is \(mode) !!!")

    // in this example, we only care about horizontal pinches...
    if mode != "H" { return }

    let vel = sender.velocity
    if vel < 0 {
        print("you're squeezing the screen!")
    }
}

Answer 2

In my C# I do the following

    private double _firstDistance = 0;
    private int _firstScaling = 0;
    private void PinchHandler(UIPinchGestureRecognizer pinchRecognizer)
    {
        nfloat x1, y1, x2, y2 = 0;
        var t1 = pinchRecognizer.LocationOfTouch(0, _previewView);
        x1 = t1.X;
        y1 = t1.Y;
        var t2 = pinchRecognizer.LocationOfTouch(1, _previewView);
        x2 = t2.X;
        y2 = t2.Y;

        if (pinchRecognizer.State == UIGestureRecognizerState.Began)
        {
            _firstDistance = Math.Sqrt(Math.Pow((x2 - x1), 2) + Math.Pow((y2 - y1), 2));
            _firstScaling = _task.TextTemplates[_selectedTextTemplate].FontScaling;
        }
        if (pinchRecognizer.State == UIGestureRecognizerState.Changed)
        {
            var distance = Math.Sqrt(Math.Pow((x2 - x1), 2) + Math.Pow((y2 - y1), 2));
            var fontScaling = Convert.ToInt32((distance - _firstDistance) / _previewView.Frame.Height * 100);
            fontScaling += _firstScaling;
            _task.TextTemplates[_selectedTextTemplate].FontScaling = fontScaling;
            UpdateBitmapPreview();
        }
    }

I calculate the distance between the two points when pinch "began" and hold that value in two privates. Then I calculate a scaling (fontScaling) based on the first measured distance and the second one (in "changed"). I use my own view (_previewView) to set as base (100%), but you can use View.Bounds.height instead or the width for that matter. in my case, I always have a square view, so height == width in my app.

Answer 3

Use this extension (based on the pervious answer).

extension UIPinchGestureRecognizer {

enum Direction {
    case horizontal, vertical, diagonal, undefined
}

var direction: Direction {

    if numberOfTouches < 2 {
        return .undefined
    }

    let A = location(ofTouch: 0, in: self.view)
    let B = location(ofTouch: 1, in: self.view)

    let xD = abs( A.x - B.x )
    let yD = abs( A.y - B.y )
    if (xD == 0) { return .vertical }
    if (yD == 0) { return .horizontal }
    let ratio = xD / yD

    if (ratio > 2) { return .horizontal }
    if (ratio < 0.5) { return .vertical }
    return .diagonal
}
}