I would like to position UI elements at specific positions on an image, for all iPad resolutions.
Imagine a ground plan with different icons/buttons on top. Each icon should be at a very specific position (e.g. exactly in the kitchen, floor, ...). When changing the device/resolution (iPad only) the icons should stay at the correct position, according to the background/ground plan imageView.
See the images (only quick examples): The smallest iPad (9.7") would be the correct position. The other image (12.9") shows the wrong position. (For all iPad sizes, I only chose two examples)
9.7":
12.9":
I can't get a way or idea to achieve this positioning problem.
You can do this by making your "bulb" positions relative to the size of the "floor plan" image view.
For example:
suppose your floor plan image is 1800 x 1500 and your bulb images are 96 x 96 (I'm estimating, based on the images you posted)...
and let's say the center of the top-left bulb is at 276, 486
and the imageView holding your floor plan is 900 x 750 (half the original size)
You would set:
xScale = 900 / 1800 (0.5)
yScale = 750 / 1500 (0.5)
bulb width = 96 * xScale
bulb height = 96 * yScale
bulb center = 276 * xScale, 486 * yScale
Here is some sample code that may help you get started:
class FloorPlanViewController: UIViewController {
#IBOutlet var floorPlanView: UIImageView!
var bulbs: [UIImageView] = [UIImageView]()
var centers: [CGPoint] = [
CGPoint(x: 276, y: 486),
CGPoint(x: 276, y: 648),
CGPoint(x: 640, y: 486),
CGPoint(x: 640, y: 648),
CGPoint(x: 877, y: 486),
CGPoint(x: 877, y: 648),
]
override func viewDidLoad() {
super.viewDidLoad()
for _ in centers {
let v = bulbImageView()
floorPlanView.addSubview(v)
bulbs.append(v)
}
}
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
if let fpImage = floorPlanView.image {
let xScale = floorPlanView.frame.width / fpImage.size.width
let yScale = floorPlanView.frame.height / fpImage.size.height
for i in 0..<centers.count {
let thisCenter = centers[i]
let thisBulb = bulbs[i]
thisBulb.frame.size.width = 96.0 * xScale
thisBulb.frame.size.height = 96.0 * yScale
thisBulb.center = CGPoint(x: thisCenter.x * xScale, y: thisCenter.y * yScale)
}
}
}
func bulbImageView() -> UIImageView {
let v = UIImageView()
if let img = UIImage(named: "bulb96x96") {
v.image = img
} else {
v.backgroundColor = .red
}
return v
}
}
Yes, this will be difficult because in the screenshots you added, the images look to be fitted to the screen size, meaning their content is transformed to fit within the frame. In that case, you will have have to calculate a transform ratio between the actual image size and the frame size and update your child view's positions to the new ratio.
One alternative is to embed the image view inside of a scrollview and have it match the image's full-size height and width. In this case, you would always have a 1:1 aspect ratio, and not have to reposition the child views. However, you would have to scroll within the scrollview to view the image.
Related
I made a subclass of UIImageView. I use its function setupView() to setup each DirectionView object's frame in viewDidLoad() and it works perfectly. But when I reset a DirectionView object's frame using the same function when a button is triggered, the new frame value is not what I expected.
The x, y, width, and height value shown in debug area are all correct. However, the frame value I print out using print("Original frame: \(self.frame)") shows a different set of value.
Why does this happen? And how to fix it?
class DirectionView: UIImageView {
override init(image: UIImage?) {
super.init(image: image)
}
required init?(coder: NSCoder) {
super.init(coder: coder)
}
func setupView(_ degree: Double, showSigInfo: Bool) {
let rotationAngle = degree.toRadians
var height: Double = 375 / 2
let width = height / 47 * 37
let x = 375 / 2 - width / 2
let y = 0.0
self.frame = CGRect(x: x, y: y, width: width, height: height)
print("Original frame: \(self.frame)")
self.contentMode = .scaleAspectFit
self.setAnchorPoint(CGPoint(x: 0.5, y: 1.0))
UIView.animate(withDuration: 0.0) {
self.transform = CGAffineTransform(rotationAngle: rotationAngle)
}
}
}
The problem is due to the anchor point. According to docs, "All geometric manipulations to the view occur about the specified point" (referring to the anchor point). When you rotate the image, and then resize it, the anchor point is not well located so, the final height and width aren't the ones you specified.
I avoided doing all the geometric calculations that would've led to the correct location of the anchor point (or the correct height and width). But, here's one solution:
Remove the code line self.setAnchorPoint(CGPoint(x: 0.5, y: 1.0))
Before setting the frame, that is before the line self.frame = CGRect(x: x, y: y, width: width, height: height). Add the following line: UIView.animate(withDuration: 0.0) {self.transform = CGAffineTransform(rotationAngle: 0)}
That should do the work.
Why it works? The default value of the anchor point is (0.5,0.5), which gives the correct resizing when the image is on its standard position (rotation = 0). So, the solution rotates the image to its standard position, resizes it, and then rotates it to the angle you want. The device does it fast enough so that the user doesn't notices the double rotation.
I'm trying to crop a sub-image of a image view using an overlay UIView that can be positioned anywhere in the UIImageView. I'm borrowing a solution from a similar post on how to solve this when the UIImageView content mode is 'Aspect Fit'. That proposed solution is:
func computeCropRect(for sourceFrame : CGRect) -> CGRect {
let widthScale = bounds.size.width / image!.size.width
let heightScale = bounds.size.height / image!.size.height
var x : CGFloat = 0
var y : CGFloat = 0
var width : CGFloat = 0
var height : CGFloat = 0
var offSet : CGFloat = 0
if widthScale < heightScale {
offSet = (bounds.size.height - (image!.size.height * widthScale))/2
x = sourceFrame.origin.x / widthScale
y = (sourceFrame.origin.y - offSet) / widthScale
width = sourceFrame.size.width / widthScale
height = sourceFrame.size.height / widthScale
} else {
offSet = (bounds.size.width - (image!.size.width * heightScale))/2
x = (sourceFrame.origin.x - offSet) / heightScale
y = sourceFrame.origin.y / heightScale
width = sourceFrame.size.width / heightScale
height = sourceFrame.size.height / heightScale
}
return CGRect(x: x, y: y, width: width, height: height)
}
The problem is that using this solution when the image view is aspect fill causes the cropped segment to not line up exactly with where the overlay UIView was positioned. I'm not quite sure how to adapt this code to accommodate for Aspect Fill or reposition my overlay UIView so that it lines up 1:1 with the segment I'm trying to crop.
UPDATE Solved using Matt's answer below
class ViewController: UIViewController {
#IBOutlet weak var catImageView: UIImageView!
private var cropView : CropView!
override func viewDidLoad() {
super.viewDidLoad()
cropView = CropView(frame: CGRect(x: 0, y: 0, width: 45, height: 45))
catImageView.image = UIImage(named: "cat")
catImageView.clipsToBounds = true
catImageView.layer.borderColor = UIColor.purple.cgColor
catImageView.layer.borderWidth = 2.0
catImageView.backgroundColor = UIColor.yellow
catImageView.addSubview(cropView)
let imageSize = catImageView.image!.size
let imageViewSize = catImageView.bounds.size
var scale : CGFloat = imageViewSize.width / imageSize.width
if imageSize.height * scale < imageViewSize.height {
scale = imageViewSize.height / imageSize.height
}
let croppedImageSize = CGSize(width: imageViewSize.width/scale, height: imageViewSize.height/scale)
let croppedImrect =
CGRect(origin: CGPoint(x: (imageSize.width-croppedImageSize.width)/2.0,
y: (imageSize.height-croppedImageSize.height)/2.0),
size: croppedImageSize)
let renderer = UIGraphicsImageRenderer(size:croppedImageSize)
let _ = renderer.image { _ in
catImageView.image!.draw(at: CGPoint(x:-croppedImrect.origin.x, y:-croppedImrect.origin.y))
}
}
#IBAction func performCrop(_ sender: Any) {
let cropFrame = catImageView.computeCropRect(for: cropView.frame)
if let imageRef = catImageView.image?.cgImage?.cropping(to: cropFrame) {
catImageView.image = UIImage(cgImage: imageRef)
}
}
#IBAction func resetCrop(_ sender: Any) {
catImageView.image = UIImage(named: "cat")
}
}
The Final Result
Let's divide the problem into two parts:
Given the size of a UIImageView and the size of its UIImage, if the UIImageView's content mode is Aspect Fill, what is the part of the UIImage that fits into the UIImageView? We need, in effect, to crop the original image to match what the UIImageView is actually displaying.
Given an arbitrary rect within the UIImageView, what part of the cropped image (derived in part 1) does it correspond to?
The first part is the interesting part, so let's try it. (The second part will then turn out to be trivial.)
Here's the original image I'll use:
https://static1.squarespace.com/static/54e8ba93e4b07c3f655b452e/t/56c2a04520c64707756f4267/1455596221531/
That image is 1000x611. Here's what it looks like scaled down (but keep in mind that I'm going to be using the original image throughout):
My image view, however, will be 139x182, and is set to Aspect Fill. When it displays the image, it looks like this:
The problem we want to solve is: what part of the original image is being displayed in my image view, if my image view is set to Aspect Fill?
Here we go. Assume that iv is the image view:
let imsize = iv.image!.size
let ivsize = iv.bounds.size
var scale : CGFloat = ivsize.width / imsize.width
if imsize.height * scale < ivsize.height {
scale = ivsize.height / imsize.height
}
let croppedImsize = CGSize(width:ivsize.width/scale, height:ivsize.height/scale)
let croppedImrect =
CGRect(origin: CGPoint(x: (imsize.width-croppedImsize.width)/2.0,
y: (imsize.height-croppedImsize.height)/2.0),
size: croppedImsize)
So now we have solved the problem: croppedImrect is the region of the original image that is showing in the image view. Let's proceed to use our knowledge, by actually cropping the image to a new image matching what is shown in the image view:
let r = UIGraphicsImageRenderer(size:croppedImsize)
let croppedIm = r.image { _ in
iv.image!.draw(at: CGPoint(x:-croppedImrect.origin.x, y:-croppedImrect.origin.y))
}
The result is this image (ignore the gray border):
But lo and behold, that is the correct answer! I have extracted from the original image exactly the region portrayed in the interior of the image view.
So now you have all the information you need. croppedIm is the UIImage actually displayed in the clipped area of the image view. scale is the scale between the image view and that image. Therefore, you can easily solve the problem you originally proposed! Given any rectangle imposed upon the image view, in the image view's bounds coordinates, you simply apply the scale (i.e. divide all four of its attributes by scale) — and now you have the same rectangle as a portion of croppedIm.
(Observe that we didn't really need to crop the original image to get croppedIm; it was sufficient, in reality, to know how to perform that crop. The important information is the scale along with the origin of croppedImRect; given that information, you can take the rectangle imposed upon the image view, scale it, and offset it to get the desired rectangle of the original image.)
EDIT I added a little screencast just to show that my approach works as a proof of concept:
EDIT Also created a downloadable example project here:
https://github.com/mattneub/Programming-iOS-Book-Examples/blob/39cc800d18aa484d17c26ffcbab8bbe51c614573/bk2ch02p058cropImageView/Cropper/ViewController.swift
But note that I can't guarantee that URL will last forever, so please read the discussion above to understand the approach used.
Matt answered the question perfectly. I was creating a full-screen camera and had a need to make the final output match the full-screen preview. Offering here a compact extension of Matt's overall answer in Swift 5 for easy use by others. Recommend reading Matt's answer as it explains things very well.
extension UIImage {
func cropToRect(rect: CGRect) -> UIImage? {
var scale = rect.width / self.size.width
scale = self.size.height * scale < rect.height ? rect.height/self.size.height : scale
let croppedImsize = CGSize(width:rect.width/scale, height:rect.height/scale)
let croppedImrect = CGRect(origin: CGPoint(x: (self.size.width-croppedImsize.width)/2.0,
y: (self.size.height-croppedImsize.height)/2.0),
size: croppedImsize)
UIGraphicsBeginImageContextWithOptions(croppedImsize, true, 0)
self.draw(at: CGPoint(x:-croppedImrect.origin.x, y:-croppedImrect.origin.y))
let croppedImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return croppedImage
}
}
I'm trying to crop a sub-image of a image view using an overlay UIView that can be positioned anywhere in the UIImageView. I'm borrowing a solution from a similar post on how to solve this when the UIImageView content mode is 'Aspect Fit'. That proposed solution is:
func computeCropRect(for sourceFrame : CGRect) -> CGRect {
let widthScale = bounds.size.width / image!.size.width
let heightScale = bounds.size.height / image!.size.height
var x : CGFloat = 0
var y : CGFloat = 0
var width : CGFloat = 0
var height : CGFloat = 0
var offSet : CGFloat = 0
if widthScale < heightScale {
offSet = (bounds.size.height - (image!.size.height * widthScale))/2
x = sourceFrame.origin.x / widthScale
y = (sourceFrame.origin.y - offSet) / widthScale
width = sourceFrame.size.width / widthScale
height = sourceFrame.size.height / widthScale
} else {
offSet = (bounds.size.width - (image!.size.width * heightScale))/2
x = (sourceFrame.origin.x - offSet) / heightScale
y = sourceFrame.origin.y / heightScale
width = sourceFrame.size.width / heightScale
height = sourceFrame.size.height / heightScale
}
return CGRect(x: x, y: y, width: width, height: height)
}
The problem is that using this solution when the image view is aspect fill causes the cropped segment to not line up exactly with where the overlay UIView was positioned. I'm not quite sure how to adapt this code to accommodate for Aspect Fill or reposition my overlay UIView so that it lines up 1:1 with the segment I'm trying to crop.
UPDATE Solved using Matt's answer below
class ViewController: UIViewController {
#IBOutlet weak var catImageView: UIImageView!
private var cropView : CropView!
override func viewDidLoad() {
super.viewDidLoad()
cropView = CropView(frame: CGRect(x: 0, y: 0, width: 45, height: 45))
catImageView.image = UIImage(named: "cat")
catImageView.clipsToBounds = true
catImageView.layer.borderColor = UIColor.purple.cgColor
catImageView.layer.borderWidth = 2.0
catImageView.backgroundColor = UIColor.yellow
catImageView.addSubview(cropView)
let imageSize = catImageView.image!.size
let imageViewSize = catImageView.bounds.size
var scale : CGFloat = imageViewSize.width / imageSize.width
if imageSize.height * scale < imageViewSize.height {
scale = imageViewSize.height / imageSize.height
}
let croppedImageSize = CGSize(width: imageViewSize.width/scale, height: imageViewSize.height/scale)
let croppedImrect =
CGRect(origin: CGPoint(x: (imageSize.width-croppedImageSize.width)/2.0,
y: (imageSize.height-croppedImageSize.height)/2.0),
size: croppedImageSize)
let renderer = UIGraphicsImageRenderer(size:croppedImageSize)
let _ = renderer.image { _ in
catImageView.image!.draw(at: CGPoint(x:-croppedImrect.origin.x, y:-croppedImrect.origin.y))
}
}
#IBAction func performCrop(_ sender: Any) {
let cropFrame = catImageView.computeCropRect(for: cropView.frame)
if let imageRef = catImageView.image?.cgImage?.cropping(to: cropFrame) {
catImageView.image = UIImage(cgImage: imageRef)
}
}
#IBAction func resetCrop(_ sender: Any) {
catImageView.image = UIImage(named: "cat")
}
}
The Final Result
Let's divide the problem into two parts:
Given the size of a UIImageView and the size of its UIImage, if the UIImageView's content mode is Aspect Fill, what is the part of the UIImage that fits into the UIImageView? We need, in effect, to crop the original image to match what the UIImageView is actually displaying.
Given an arbitrary rect within the UIImageView, what part of the cropped image (derived in part 1) does it correspond to?
The first part is the interesting part, so let's try it. (The second part will then turn out to be trivial.)
Here's the original image I'll use:
https://static1.squarespace.com/static/54e8ba93e4b07c3f655b452e/t/56c2a04520c64707756f4267/1455596221531/
That image is 1000x611. Here's what it looks like scaled down (but keep in mind that I'm going to be using the original image throughout):
My image view, however, will be 139x182, and is set to Aspect Fill. When it displays the image, it looks like this:
The problem we want to solve is: what part of the original image is being displayed in my image view, if my image view is set to Aspect Fill?
Here we go. Assume that iv is the image view:
let imsize = iv.image!.size
let ivsize = iv.bounds.size
var scale : CGFloat = ivsize.width / imsize.width
if imsize.height * scale < ivsize.height {
scale = ivsize.height / imsize.height
}
let croppedImsize = CGSize(width:ivsize.width/scale, height:ivsize.height/scale)
let croppedImrect =
CGRect(origin: CGPoint(x: (imsize.width-croppedImsize.width)/2.0,
y: (imsize.height-croppedImsize.height)/2.0),
size: croppedImsize)
So now we have solved the problem: croppedImrect is the region of the original image that is showing in the image view. Let's proceed to use our knowledge, by actually cropping the image to a new image matching what is shown in the image view:
let r = UIGraphicsImageRenderer(size:croppedImsize)
let croppedIm = r.image { _ in
iv.image!.draw(at: CGPoint(x:-croppedImrect.origin.x, y:-croppedImrect.origin.y))
}
The result is this image (ignore the gray border):
But lo and behold, that is the correct answer! I have extracted from the original image exactly the region portrayed in the interior of the image view.
So now you have all the information you need. croppedIm is the UIImage actually displayed in the clipped area of the image view. scale is the scale between the image view and that image. Therefore, you can easily solve the problem you originally proposed! Given any rectangle imposed upon the image view, in the image view's bounds coordinates, you simply apply the scale (i.e. divide all four of its attributes by scale) — and now you have the same rectangle as a portion of croppedIm.
(Observe that we didn't really need to crop the original image to get croppedIm; it was sufficient, in reality, to know how to perform that crop. The important information is the scale along with the origin of croppedImRect; given that information, you can take the rectangle imposed upon the image view, scale it, and offset it to get the desired rectangle of the original image.)
EDIT I added a little screencast just to show that my approach works as a proof of concept:
EDIT Also created a downloadable example project here:
https://github.com/mattneub/Programming-iOS-Book-Examples/blob/39cc800d18aa484d17c26ffcbab8bbe51c614573/bk2ch02p058cropImageView/Cropper/ViewController.swift
But note that I can't guarantee that URL will last forever, so please read the discussion above to understand the approach used.
Matt answered the question perfectly. I was creating a full-screen camera and had a need to make the final output match the full-screen preview. Offering here a compact extension of Matt's overall answer in Swift 5 for easy use by others. Recommend reading Matt's answer as it explains things very well.
extension UIImage {
func cropToRect(rect: CGRect) -> UIImage? {
var scale = rect.width / self.size.width
scale = self.size.height * scale < rect.height ? rect.height/self.size.height : scale
let croppedImsize = CGSize(width:rect.width/scale, height:rect.height/scale)
let croppedImrect = CGRect(origin: CGPoint(x: (self.size.width-croppedImsize.width)/2.0,
y: (self.size.height-croppedImsize.height)/2.0),
size: croppedImsize)
UIGraphicsBeginImageContextWithOptions(croppedImsize, true, 0)
self.draw(at: CGPoint(x:-croppedImrect.origin.x, y:-croppedImrect.origin.y))
let croppedImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return croppedImage
}
}
I have an image which is set inside a scroll view, though I have set the frame of the scrollView to fixed height and width as shown below, the image goes beyond the bounds (see below picture).
How can I limit the picture to fit inside the scrollView.
imageScrollView.frame = CGRect(x: 0, y: 0, width: viewWidth, height: viewHeight-50)
imageScrollView.clipsToBounds = true // Has no affect on the image
Do you have a reference to the UIImageView? If so, then set its content mode to aspect fit. Like this:
theImageView.contentMode = .scaleAspectFit
The clipsToBounds you set only covers up any parts of child views that are sticking out of the bounds of the parent view, so that's why it doesn't do anything for you.
OR if you're using Interface Builder, set this option:
So, what if you don't have the reference to the UIImageView?...
You could iterate through the subviews of your scroll view, and whenever it finds a UIImageView, you can set the content mode like that. Something like:
//This is off the top of my head, so my filtering may not be right...
//This is also a one and done solution if you've got a lot of images in your scroll view
for anImgVw in imageScrollView.subviews.filter({$0.isKind(of: UIImageView.self)})
{
anImgVw.contentMode = .scaleAspectFit
}
Otherwise, I'm not sure if it's possible without a reference to the UIImageView.
The library you are using is coded to match the scaling to the device orientation. So, if the image orientation doesn't match the view orientation, you end up with the image not quite fitting in your scroll view.
You'll need to edit the ImageScrollView.swift source file. Assuming you're using the same version that is currently at the link you provided ( https://github.com/huynguyencong/ImageScrollView ), change the setMaxMinZoomScalesForCurrentBounds() function as follows:
fileprivate func setMaxMinZoomScalesForCurrentBounds() {
// calculate min/max zoomscale
let xScale = bounds.width / imageSize.width // the scale needed to perfectly fit the image width-wise
let yScale = bounds.height / imageSize.height // the scale needed to perfectly fit the image height-wise
// fill width if the image and phone are both portrait or both landscape; otherwise take smaller scale
//let imagePortrait = imageSize.height > imageSize.width
//let phonePortrait = bounds.height >= bounds.width
//var minScale = (imagePortrait == phonePortrait) ? xScale : min(xScale, yScale)
//
// just take the min scale, so the image will completely fit regardless of orientation
var minScale = min(xScale, yScale)
let maxScale = maxScaleFromMinScale*minScale
// don't let minScale exceed maxScale. (If the image is smaller than the screen, we don't want to force it to be zoomed.)
if minScale > maxScale {
minScale = maxScale
}
maximumZoomScale = maxScale
minimumZoomScale = minScale * 0.999 // the multiply factor to prevent user cannot scroll page while they use this control in UIPageViewController
}
you can use the screenHeight rather than the viewHeight
let screenSize: CGRect = UIScreen.mainScreen().bounds
let screenWidth = screenSize.width
let screenHeight = screenSize.height
imageScrollView.frame = CGRect(x: 0, y: 0, width: viewWidth, height: screenHeight-50)
I'm trying to crop a sub-image of a image view using an overlay UIView that can be positioned anywhere in the UIImageView. I'm borrowing a solution from a similar post on how to solve this when the UIImageView content mode is 'Aspect Fit'. That proposed solution is:
func computeCropRect(for sourceFrame : CGRect) -> CGRect {
let widthScale = bounds.size.width / image!.size.width
let heightScale = bounds.size.height / image!.size.height
var x : CGFloat = 0
var y : CGFloat = 0
var width : CGFloat = 0
var height : CGFloat = 0
var offSet : CGFloat = 0
if widthScale < heightScale {
offSet = (bounds.size.height - (image!.size.height * widthScale))/2
x = sourceFrame.origin.x / widthScale
y = (sourceFrame.origin.y - offSet) / widthScale
width = sourceFrame.size.width / widthScale
height = sourceFrame.size.height / widthScale
} else {
offSet = (bounds.size.width - (image!.size.width * heightScale))/2
x = (sourceFrame.origin.x - offSet) / heightScale
y = sourceFrame.origin.y / heightScale
width = sourceFrame.size.width / heightScale
height = sourceFrame.size.height / heightScale
}
return CGRect(x: x, y: y, width: width, height: height)
}
The problem is that using this solution when the image view is aspect fill causes the cropped segment to not line up exactly with where the overlay UIView was positioned. I'm not quite sure how to adapt this code to accommodate for Aspect Fill or reposition my overlay UIView so that it lines up 1:1 with the segment I'm trying to crop.
UPDATE Solved using Matt's answer below
class ViewController: UIViewController {
#IBOutlet weak var catImageView: UIImageView!
private var cropView : CropView!
override func viewDidLoad() {
super.viewDidLoad()
cropView = CropView(frame: CGRect(x: 0, y: 0, width: 45, height: 45))
catImageView.image = UIImage(named: "cat")
catImageView.clipsToBounds = true
catImageView.layer.borderColor = UIColor.purple.cgColor
catImageView.layer.borderWidth = 2.0
catImageView.backgroundColor = UIColor.yellow
catImageView.addSubview(cropView)
let imageSize = catImageView.image!.size
let imageViewSize = catImageView.bounds.size
var scale : CGFloat = imageViewSize.width / imageSize.width
if imageSize.height * scale < imageViewSize.height {
scale = imageViewSize.height / imageSize.height
}
let croppedImageSize = CGSize(width: imageViewSize.width/scale, height: imageViewSize.height/scale)
let croppedImrect =
CGRect(origin: CGPoint(x: (imageSize.width-croppedImageSize.width)/2.0,
y: (imageSize.height-croppedImageSize.height)/2.0),
size: croppedImageSize)
let renderer = UIGraphicsImageRenderer(size:croppedImageSize)
let _ = renderer.image { _ in
catImageView.image!.draw(at: CGPoint(x:-croppedImrect.origin.x, y:-croppedImrect.origin.y))
}
}
#IBAction func performCrop(_ sender: Any) {
let cropFrame = catImageView.computeCropRect(for: cropView.frame)
if let imageRef = catImageView.image?.cgImage?.cropping(to: cropFrame) {
catImageView.image = UIImage(cgImage: imageRef)
}
}
#IBAction func resetCrop(_ sender: Any) {
catImageView.image = UIImage(named: "cat")
}
}
The Final Result
Let's divide the problem into two parts:
Given the size of a UIImageView and the size of its UIImage, if the UIImageView's content mode is Aspect Fill, what is the part of the UIImage that fits into the UIImageView? We need, in effect, to crop the original image to match what the UIImageView is actually displaying.
Given an arbitrary rect within the UIImageView, what part of the cropped image (derived in part 1) does it correspond to?
The first part is the interesting part, so let's try it. (The second part will then turn out to be trivial.)
Here's the original image I'll use:
https://static1.squarespace.com/static/54e8ba93e4b07c3f655b452e/t/56c2a04520c64707756f4267/1455596221531/
That image is 1000x611. Here's what it looks like scaled down (but keep in mind that I'm going to be using the original image throughout):
My image view, however, will be 139x182, and is set to Aspect Fill. When it displays the image, it looks like this:
The problem we want to solve is: what part of the original image is being displayed in my image view, if my image view is set to Aspect Fill?
Here we go. Assume that iv is the image view:
let imsize = iv.image!.size
let ivsize = iv.bounds.size
var scale : CGFloat = ivsize.width / imsize.width
if imsize.height * scale < ivsize.height {
scale = ivsize.height / imsize.height
}
let croppedImsize = CGSize(width:ivsize.width/scale, height:ivsize.height/scale)
let croppedImrect =
CGRect(origin: CGPoint(x: (imsize.width-croppedImsize.width)/2.0,
y: (imsize.height-croppedImsize.height)/2.0),
size: croppedImsize)
So now we have solved the problem: croppedImrect is the region of the original image that is showing in the image view. Let's proceed to use our knowledge, by actually cropping the image to a new image matching what is shown in the image view:
let r = UIGraphicsImageRenderer(size:croppedImsize)
let croppedIm = r.image { _ in
iv.image!.draw(at: CGPoint(x:-croppedImrect.origin.x, y:-croppedImrect.origin.y))
}
The result is this image (ignore the gray border):
But lo and behold, that is the correct answer! I have extracted from the original image exactly the region portrayed in the interior of the image view.
So now you have all the information you need. croppedIm is the UIImage actually displayed in the clipped area of the image view. scale is the scale between the image view and that image. Therefore, you can easily solve the problem you originally proposed! Given any rectangle imposed upon the image view, in the image view's bounds coordinates, you simply apply the scale (i.e. divide all four of its attributes by scale) — and now you have the same rectangle as a portion of croppedIm.
(Observe that we didn't really need to crop the original image to get croppedIm; it was sufficient, in reality, to know how to perform that crop. The important information is the scale along with the origin of croppedImRect; given that information, you can take the rectangle imposed upon the image view, scale it, and offset it to get the desired rectangle of the original image.)
EDIT I added a little screencast just to show that my approach works as a proof of concept:
EDIT Also created a downloadable example project here:
https://github.com/mattneub/Programming-iOS-Book-Examples/blob/39cc800d18aa484d17c26ffcbab8bbe51c614573/bk2ch02p058cropImageView/Cropper/ViewController.swift
But note that I can't guarantee that URL will last forever, so please read the discussion above to understand the approach used.
Matt answered the question perfectly. I was creating a full-screen camera and had a need to make the final output match the full-screen preview. Offering here a compact extension of Matt's overall answer in Swift 5 for easy use by others. Recommend reading Matt's answer as it explains things very well.
extension UIImage {
func cropToRect(rect: CGRect) -> UIImage? {
var scale = rect.width / self.size.width
scale = self.size.height * scale < rect.height ? rect.height/self.size.height : scale
let croppedImsize = CGSize(width:rect.width/scale, height:rect.height/scale)
let croppedImrect = CGRect(origin: CGPoint(x: (self.size.width-croppedImsize.width)/2.0,
y: (self.size.height-croppedImsize.height)/2.0),
size: croppedImsize)
UIGraphicsBeginImageContextWithOptions(croppedImsize, true, 0)
self.draw(at: CGPoint(x:-croppedImrect.origin.x, y:-croppedImrect.origin.y))
let croppedImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return croppedImage
}
}