Rotate group of UIViews together from common center

问题

This is a follow up to this question. I have a similar setup with n number of views, and I want to rotate them together with the rotation gesture.

I know how to apply a rotation to a single view, but here I want to rotate all of them from common center instead of their own.

So I tried this approach

Calculated a common center point of all selected views
Set the view translation pointing to this common center
And rotated the view

So this is what I got

CGPoint newCenter =CGPointZero;
for(UIView *node in self.selectedNodes){
    newCenter = CGPointMake(newCenter.x + node.center.x, newCenter.y + node.center.y);
}

newCenter = CGPointMake(newCenter.x/self.selectedNodes.count, newCenter.y/self.selectedNodes.count);
for(UIview *node in self.selectedNodes){
     CGAffineTransform newTransform = CGAffineTransformMakeTranslation(groupCenter.x,groupCenter.y);
    newTransform = CGAffineTransformRotate( node.transform,recognizer.rotation);
    newTransform = CGAffineTransformTranslate(newTransform,-groupCenter.x, -groupCenter.y);
     node.transform = newTransform;
}

But this isn't working as expected. any help is much appreciated..

回答1:

it's me again. Here's how I did rotation:

let rotation = recognizer.rotation
recognizer.rotation = 0
let center = views.map { $0.center }.reduce(CGPoint.zero, +) / CGFloat(views.count)
views.forEach {
    $0.transform = $0.transform.rotated(by: rotation)
    let distance = $0.center - center
    $0.center = center + CGPoint(
        x: distance.x * cos(rotation) - distance.y * sin(rotation),
        y: distance.y * cos(rotation) + distance.x * sin(rotation)
    )
}

It's very similar to the scale, you get the center of all views, for each view you get the distance to that center, rotate it using the formula to rotate a point, and add that rotated distance to the center of all views.

来源：https://stackoverflow.com/questions/52052198/rotate-group-of-uiviews-together-from-common-center

标签

ios

objective-c

uiview

rotation

transform