Scale of UIPinchGestureRecognizer in horizontal and vertical directions separately - ios

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.