How can I use CGRect() dynamically?

Question

I have the following scene example where I can crop an image based on the selection (red square).

That square has dynamic Height and Width - base on this fact I want to use the selected Height and Width to crop what is inside of the Red square.

The function that I am using for cropping is from Apple developer and looks like this:

func cropImage(_ inputImage: UIImage, toRect cropRect: CGRect, viewWidth: CGFloat, viewHeight: CGFloat) -> UIImage? 
{    
    let imageViewScale = max(inputImage.size.width / viewWidth,
                             inputImage.size.height / viewHeight)

    // Scale cropRect to handle images larger than shown-on-screen size
    let cropZone = CGRect(x:cropRect.origin.x * imageViewScale,
                          y:cropRect.origin.y * imageViewScale,
                          width:cropRect.size.width * imageViewScale,
                          height:cropRect.size.height * imageViewScale)

    // Perform cropping in Core Graphics
    guard let cutImageRef: CGImage = inputImage.cgImage?.cropping(to:cropZone)
    else {
        return nil
    }

    // Return image to UIImage
    let croppedImage: UIImage = UIImage(cgImage: cutImageRef)
    return croppedImage
}

Now. I want to use the given Height and Width to crop that selection.

 let croppedImage =  cropImage(image!, toRect: CGRect(x:?? , y:?? , width: ??, height: ??), viewWidth: ??, viewHeight: ??)

What should I fill in these parameters in order to crop the image based on the above dynamic selection?

There's something else missing in this question, where's the code related to the cropping tool? And how are you doing the crop right now? — Jan Cássio, Dec 14 '21 at 18:36
That crop tool comes on top of a Camera View - when I am doing the picture I want to save only the selected part. The selection tool (red square) is returning only the Height and Width variables which I suppose to use them in the crop function. Now I am doing the function like I said in the original question, using the cropImage function. — Laur, Dec 14 '21 at 18:48
If the selection tool is only returning hight and width it won't really work. If you're selecting a rectangle, you need to return a rectangle. Without the origin height and width doesn't give you enough information to know what to crop. — Duncan C, Dec 14 '21 at 18:59
Do you mean like https://stackoverflow.com/questions/43720720/how-to-crop-a-uiimageview-to-a-new-uiimage-in-aspect-fill-mode/43720791?r=SearchResults&s=5|34.9765#43720791 ? — matt, Dec 14 '21 at 21:20
@matt yes, actually that is the case. Now, I have to adapt that solution to SwiftUI approach :) Until now I have the following info: The image, the rectangle thinghy which returns only the height and width and the crop function. — Laur, Dec 15 '21 at 03:47

Alexander Naumenko · Answer 1 · 2021-12-14T21:09:29.327

0

Ok, let's assume that your image is in imageView, wich is located somewhere in your screen. The rect is a variable where your selected frame (related to the imageView.frame) is stored. So the result is:

let croppedImage =  cropImage(image!, toRect: rect, viewWidth: imageView.width, viewHeight: imageView.height)

edited Dec 14 '21 at 21:09

answered Dec 14 '21 at 18:37

Alexander Naumenko

56
5

Basically, the crop tool comes on top of a full-screen Camera View. When I am doing the picture I want to save only the selected area. – Laur Dec 14 '21 at 18:44
ok, try this: let croppedImage = cropImage(image!, toRect: CGRect(x: rect.x , y: rect.y , width: rect.width, height: rect.heigh), viewWidth: UIScreen.main.bounds.width, viewHeight: UIScreen.main.bounds.height) – Alexander Naumenko Dec 14 '21 at 18:54
what is the point of the construct `toRect: CGRect(x: rect.x , y: rect.y , width: rect.width, height: rect.height)`? Why not just use `toRect: rect` since you're creating a new CGRect with all the same values as rect? – Duncan C Dec 14 '21 at 20:32
Ahah, really! I tried to answer quickly and just replaced the author's "??" in the question :-) – Alexander Naumenko Dec 14 '21 at 21:08

score 0 · Answer 2 · answered Dec 14 '21 at 19:06

Ok, since you just have info of width and height of the cropping shape. You'll need to calculate the x and y by yourself.

First, let's consider these information:

// let's pretend this is a sample of size that your crop tool provides to you
let cropSize = CGSize(width: 120, height: 260)

Next, you'll need to obtain the display size (width and height) of your image. Display size here is the frame's size of your image, not the size of the image itself.

// again, lets pretend it's just a frame size of your image
let imageSize = CGSize(width: 320, height: 480)

With this info, you can obtain the x and y necessary to compose a CGRect and then, provide to a cropping function you desire.

let x = (imageSize.width - cropSize.width) / 2
let y = (imageSize.height - cropSize.height) / 2

So now, you can create a rectangle to crop your image like this:

let cropRect = CGRect(x: x, y: y, width: cropSize.width, height: cropSize.height)

With cropRect you can use on both cropping or cropImage functions mentioned in your question.

score 0 · Accepted Answer · answered Dec 16 '21 at 16:39

I've used the info from all of your answers and especially @matt's comment and this is the final solution.

Using the input values that my red square returned, I've adapted the original Crop function to this one:

    func cropImage(_ inputImage: UIImage, width: Double, height: Double) -> UIImage?
    {

        let imsize = inputImage.size
        let ivsize = UIScreen.main.bounds.size
        
        var scale : CGFloat = ivsize.width / imsize.width
        if imsize.height * scale < ivsize.height {
            scale = ivsize.height / imsize.height
        }

        let croppedImsize = CGSize(width:height/scale, height:width/scale)

        
        let croppedImrect =
            CGRect(origin: CGPoint(x: (imsize.width-croppedImsize.width)/2.0,
                                   y: (imsize.height-croppedImsize.height)/2.4),
                   size: croppedImsize)
        
        let r = UIGraphicsImageRenderer(size:croppedImsize)
        let croppedIm = r.image { _ in
            inputImage.draw(at: CGPoint(x:-croppedImrect.origin.x, y:-croppedImrect.origin.y))
        }
        
        return croppedIm
        
    }

How can I use CGRect() dynamically?

3 Answers3