How can I transition a UIImage slowly from top to bottom for applying filter to the image? - ios

Question

I want to make it appear as if my image is slowly getting filtered from top to bottom. I am adding two image views. My processed image is in the background and non-processed in the front. I am making the height of non-processed image 0. Here is my code.
imageView.frame = CGRect(x: 0, y: 100, width: self.view.bounds.size.width, height: 400)
imageView.image = processedImage
let nonProcessedImageView = UIImageView()
nonProcessedImageView.frame = CGRect(x: 0, y: 100, width: self.view.bounds.size.width, height: 400)
nonProcessedImageView.image = nonProcessedImage
view.addSubview(nonProcessedImageView)
UIView.transition(with: nonProcessedImageView,
duration: 5.0,
animations: {
nonProcessedImageView.frame = CGRect(x: 0, y: 500, width: self.view.bounds.size.width, height: 0)
},
completion: {_ in
})
The non processed image does not even appear on top of the processed.

Answer 1

The issue seems to be that changing the y coordinate of the frame in the animation block leads to issues when using the UIView.Animate function.
See this answer
To quote the most essential part:
You should change the center property (to move the view) and bounds
property (to change its size) instead. Those properties behave as
expected.
Since you want to just reduce the height, you don't need to do anything to the y coordinate
let nonProcessedImageView = UIImageView()
var newImageFrame = imageView.frame
nonProcessedImageView.frame = newImageFrame
nonProcessedImageView.clipsToBounds = true
nonProcessedImageView.contentMode = .scaleAspectFit
nonProcessedImageView.image = imageView.image
view.addSubview(nonProcessedImageView)
// I set this to 1 instead of 0 as 0 does not show the image
// for some reason
newImageFrame.size.height = 1
// Update your processed image
imageView.image = processedImage
UIView.animate(withDuration: 5.0) {
nonProcessedImageView.frame = newImageFrame
}
completion: { (isComplete) in
if isComplete {
nonProcessedImageView.removeFromSuperview()
}
}
This gives some results but as you can see, the animation is not so good because as you reduce the height, the image view's contentMode kicks in and gives the seen effect.
For best results, add the new image view to a UIView and reduce the height of the UIView instead of the UIImageView
var newImageFrame = imageView.frame
let containerView = UIView(frame: newImageFrame)
containerView.clipsToBounds = true
let nonProcessedImageView = UIImageView()
nonProcessedImageView.frame = containerView.bounds
nonProcessedImageView.clipsToBounds = true
nonProcessedImageView.contentMode = .scaleAspectFit // same as original
nonProcessedImageView.image = imageView.image
containerView.addSubview(nonProcessedImageView)
view.addSubview(containerView)
newImageFrame.size.height = 1
imageView.image = processedImage
UIView.animate(withDuration: 3.0) {
containerView.frame = newImageFrame
}
completion: { (isComplete) in
if isComplete {
containerView.removeFromSuperview()
}
}
This should give you what you want:

Answer 2

This works for top to bottom transition.
imageView.frame = CGRect(x: 0, y: 100, width: self.view.bounds.width, height: 400)
imageView.image = nonProcessedImage
view.addSubview(imageView)
let frontView = UIView(frame: CGRect(x: 0, y: 100, width: self.view.frame.width, height: 0))
frontView.clipsToBounds = true
view.addSubview(frontView)
let nonProcessedImageView = UIImageView(frame: CGRect(x: 0, y: 0, width: self.view.bounds.size.width, height: 400))
nonProcessedImageView.image = processedImage
nonProcessedImageView.clipsToBounds = true
frontView.addSubview(nonProcessedImageView)
UIView.transition(with: frontView, duration: 5, options: [.allowAnimatedContent], animations: {
frontView.frame = CGRect(x: 0, y: 100, width: self.view.frame.width, height: 400)
}, completion: nil)