How to properly convert UIView scale to UIScrollView motion
To have a similar effect for the Snapchat HUD movement, I created the movement of the HUD based elements UIScollView's
contentOffset
. Edit: Link to Github project
func scrollViewDidScroll(_ scrollView: UIScrollView) {
self.view.layoutIfNeeded()
let factor = scrollView.contentOffset.y / self.view.frame.height
self.transformElements(self.playButton,
0.45 + 0.55 * factor, // 0.45 = desired scale + 0.55 = 1.0 == original scale
Roots.screenSize.height - 280, // 280 == original Y
Roots.screenSize.height - 84, // 84 == minimum desired Y
factor)
}
func transformElements(_ element: UIView?,
_ scale: CGFloat,
_ originY: CGFloat,
_ desiredY: CGFloat,
_ factor: CGFloat) {
if let e = element {
e.transform = CGAffineTransform(scaleX: scale, y: scale) // this line lagging
let resultY = desiredY + (originY - desiredY) * factor
var frame = e.frame
frame.origin.y = resultY
e.frame = frame
}
}
When using this code, the scrolling as well as the transition turned out to be "laggy" / nonsmooth. (Physical iPhone 6S + and 7 +).
Removing next line: e.transform = CGAffineTransform(scaleX: scale, y: scale)
removed the problem. The scrolling as well as the Y-movement
object UIView
will again be smooth.
What's the best approach for transforming the scale of an object?
No layout restrictions.
func setupPlayButton() {
let rect = CGRect(x: Roots.screenSize.width / 2 - 60,
y: Roots.screenSize.height - 280,
width: 120,
height: 120)
self.playButton = UIButton(frame: rect)
self.playButton.setImage(UIImage(named: "playBtn")?.withRenderingMode(.alwaysTemplate), for: .normal)
self.playButton.tintColor = #colorLiteral(red: 1, green: 1, blue: 1, alpha: 1)
self.view.addSubview(playButton)
}
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This is because you are using both transform
and frame
. It will be smoother if you apply only transform
. Update the function transformElements
as shown below:
func transformElements(_ element: UIView?,
_ scale: CGFloat,
_ originY: CGFloat,
_ desiredY: CGFloat,
_ factor: CGFloat) {
if let e = element {
e.transform = CGAffineTransform(scaleX: scale, y: scale).translatedBy(x: 0, y: desiredY * (1 - factor))
}
}
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You can make these kinds of animations smoother by creating an animation, then setting the layer speed to 0 and then changing the layer's timeOffset value.
first add animation to the method setupPlayButton
let animation = CABasicAnimation.init(keyPath: "transform.scale")
animation.fromValue = 1.0
animation.toValue = 0.45
animation.duration = 1.0
//Set the speed of the layer to 0 so it doesn't animate until we tell it to
self.playButton.layer.speed = 0.0;
self.playButton.layer.add(animation, forKey: "transform");
Next, scrollViewDidScroll
change the timeOffset value of the layer and move the center of the button.
if let btn = self.playButton{
var factor:CGFloat = 1.0
if isVertically {
factor = scrollView.contentOffset.y / self.view.frame.height
} else {
factor = scrollView.contentOffset.x / Roots.screenSize.width
var transformedFractionalPage: CGFloat = 0
if factor > 1 {
transformedFractionalPage = 2 - factor
} else {
transformedFractionalPage = factor
}
factor = transformedFractionalPage;
}
//This will change the size
let timeOffset = CFTimeInterval(1-factor)
btn.layer.timeOffset = timeOffset
//now change the positions. only use center - not frame - so you don't mess up the animation. These numbers aren't right I don't know why
let desiredY = Roots.screenSize.height - (280-60);
let originY = Roots.screenSize.height - (84-60);
let resultY = desiredY + (originY - desiredY) * (1-factor)
btn.center = CGPoint.init(x: btn.center.x, y: resultY);
}
I couldn't figure out the position of the button correctly - so there is something wrong with my math, but I hope you can fix it.
If you would like more information on this technique see here: http://ronnqvi.st/controlling-animation-timing/
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