Dynamically crop image using SwiftUI and contentMode = .aspectFit - ios

Question

I want a view in which the user is shown an image. By dragging the corner points I want him to be capable of choosing the crop rectangle.
Because the input image can be of bigger dimensions than the screen, I want to use aspect fit as content mode of the image.
The problem I have is that I don't know how to take the displacement caused by the content mode into account when determining the measurements of the crop rectangle relative to the original size of the image.
This might be easier to explain in a video:
As you can see, the context for the positions of the circles is the whole view. I want to use the coordinate system of the resized image instead. For this transformation I would need the difference between the size of the outer view and the resized image.
So the question is: How can I get the correct measurements of the user-chosen rectangle with respect to the resized image?
import SwiftUI
struct CropImageViewTest: View {
var currentImage: Image
#State private var currentPositionTopLeft: CGPoint = .zero
#State private var newPositionTopLeft: CGPoint = .zero
#State private var currentPositionTopRight: CGPoint = .zero
#State private var newPositionTopRight: CGPoint = .zero
#State private var currentPositionBottomLeft: CGPoint = .zero
#State private var newPositionBottomLeft: CGPoint = .zero
#State private var currentPositionBottomRight: CGPoint = .zero
#State private var newPositionBottomRight: CGPoint = .zero
var body: some View {
ZStack {
VStack {
Text("Top left: \(currentPositionTopLeft.x) | \(currentPositionTopLeft.y)")
Text("Top right: \(currentPositionTopRight.x) | \(currentPositionTopRight.y)")
Text("Bottom left: \(currentPositionBottomLeft.x) | \(currentPositionBottomLeft.y)")
Text("Bottom right: \(currentPositionBottomRight.x) | \(currentPositionBottomRight.y)")
Spacer()
currentImage
.resizable()
.aspectRatio(1 , contentMode: .fit)
.background(Color.red)
Spacer()
Group {
Button(action: {
// TODO: Crop it
}) {
Image(systemName: "checkmark").resizable().frame(width: 24, height: 24)
.padding(20)
.background(Color(Colors.getColor(Colors.colorSboBlue)))
.foregroundColor(Color.white)
}.clipShape(Circle())
.shadow(radius: 4)
}
}
getCorners()
}
}
private func getCorners() -> some View{
return
HStack {
VStack {
ZStack {
GeometryReader { geometry in
Path { path in
path.move(to: self.currentPositionTopLeft)
path.addLine(
to: .init(
x: self.currentPositionTopRight.x + geometry.size.width,
y: self.currentPositionTopRight.y
)
)
path.addLine(
to: .init(
x: self.currentPositionBottomRight.x + geometry.size.width,
y: self.currentPositionBottomRight.y + geometry.size.height
)
)
path.addLine(
to: .init(
x: self.currentPositionBottomLeft.x,
y: self.currentPositionBottomLeft.y + geometry.size.height
)
)
path.addLine(
to: .init(
x: self.currentPositionTopLeft.x,
y: self.currentPositionTopLeft.y
)
)
}
.stroke(Color.blue, lineWidth: CGFloat(1))
}
Circle().foregroundColor(Color.blue).frame(width: 24, height: 24)
.offset(x: self.currentPositionTopLeft.x, y: self.currentPositionTopLeft.y)
.gesture(DragGesture()
.onChanged { value in
self.currentPositionTopLeft = CGPoint(x: value.translation.width + self.newPositionTopLeft.x, y: value.translation.height + self.newPositionTopLeft.y)
}
.onEnded { value in
self.currentPositionTopLeft = CGPoint(x: value.translation.width + self.newPositionTopLeft.x, y: value.translation.height + self.newPositionTopLeft.y)
self.newPositionTopLeft = self.currentPositionTopLeft
print(self.currentPositionTopLeft)
print(self.newPositionTopLeft)
}
)
.opacity(0.5)
.position(CGPoint(x: 0, y: 0))
GeometryReader { geometry in
Circle().foregroundColor(Color.blue).frame(width: 24, height: 24)
.offset(x: self.currentPositionTopRight.x, y: self.currentPositionTopRight.y)
.gesture(DragGesture()
.onChanged { value in
self.currentPositionTopRight = CGPoint(x: value.translation.width + self.newPositionTopRight.x, y: value.translation.height + self.newPositionTopRight.y)
}
.onEnded { value in
self.currentPositionTopRight = CGPoint(x: value.translation.width + self.newPositionTopRight.x, y: value.translation.height + self.newPositionTopRight.y)
self.newPositionTopRight = self.currentPositionTopRight
print(self.currentPositionTopRight)
print(self.newPositionTopRight)
}
)
.opacity(0.5)
.position(CGPoint(x: geometry.size.width, y: 0))
}
GeometryReader { geometry in
Circle().foregroundColor(Color.blue).frame(width: 24, height: 24)
.offset(x: self.currentPositionBottomLeft.x, y: self.currentPositionBottomLeft.y)
.gesture(DragGesture()
.onChanged { value in
self.currentPositionBottomLeft = CGPoint(x: value.translation.width + self.newPositionBottomLeft.x, y: value.translation.height + self.newPositionBottomLeft.y)
}
.onEnded { value in
self.currentPositionBottomLeft = CGPoint(x: value.translation.width + self.newPositionBottomLeft.x, y: value.translation.height + self.newPositionBottomLeft.y)
self.newPositionBottomLeft = self.currentPositionBottomLeft
print(self.currentPositionBottomLeft)
print(self.newPositionBottomLeft)
}
)
.opacity(0.5)
.position(CGPoint(x: 0, y: geometry.size.height))
}
GeometryReader { geometry in
Circle().foregroundColor(Color.blue).frame(width: 24, height: 24)
.offset(x: self.currentPositionBottomRight.x, y: self.currentPositionBottomRight.y)
.gesture(DragGesture()
.onChanged { value in
self.currentPositionBottomRight = CGPoint(x: value.translation.width + self.newPositionBottomRight.x, y: value.translation.height + self.newPositionBottomRight.y)
}
.onEnded { value in
self.currentPositionBottomRight = CGPoint(x: value.translation.width + self.newPositionBottomRight.x, y: value.translation.height + self.newPositionBottomRight.y)
self.newPositionBottomRight = self.currentPositionBottomRight
print(self.currentPositionBottomRight)
print(self.newPositionBottomRight)
}
)
.opacity(0.5)
.position(CGPoint(x: geometry.size.width, y: geometry.size.height))
}
}
Spacer()
}
Spacer()
}
}
}
If you don't have a sample image with you, you can just call the View this way:
CropImageViewTest(currentImage: Image(systemName: "camera.fill"))
I added a red background so that you can see the constraints of the image.
I am also open to completely different approaches if the current way is not the "swiftiest" way to go.
Thank you in advance!
Edit:
I have the UIImage available the (SwiftUI) Image originates from. If this is of any help in determining the correct measurements.
Update:
If I use the crop rectangle as an overlay of the image like so:
currentImage
.resizable()
.aspectRatio(1 , contentMode: .fit)
.overlay(getCorners())
it's actually working. Still, there is the problem that every corner defines its starting position is (0|0). I would like the position to be defined relative to the upper left corner of the image.

Answer 1

Okay, finally solved it.
1.) I used the view with the rectangle and the draggable corners as an overlay of the Image. This way, the origin of the rectangle and the corners is the image, not the surrounding view. Got the inspiration for that from here: https://swiftui-lab.com/geometryreader-to-the-rescue/
2.) There was still the problem that every corner defined it origin (0|0) as where it was initially positioned. I got around that by using
.position(CGPoint(x: 0, y: 0))
and using onAppear to place displace the coordinates.
This leads to the application correctly calculating the coordinates relative to the resized image:
I also encapsulated the rectangle and the corners in custom views resulting in this code:
The root view:
import SwiftUI
struct CropImageViewTest: View {
var currentImage: Image
#State private var currentPositionTopLeft: CGPoint = .zero
#State private var newPositionTopLeft: CGPoint = .zero
#State private var currentPositionTopRight: CGPoint = .zero
#State private var newPositionTopRight: CGPoint = .zero
#State private var currentPositionBottomLeft: CGPoint = .zero
#State private var newPositionBottomLeft: CGPoint = .zero
#State private var currentPositionBottomRight: CGPoint = .zero
#State private var newPositionBottomRight: CGPoint = .zero
var body: some View {
ZStack {
VStack {
Text("Top left: \(currentPositionTopLeft.x) | \(currentPositionTopLeft.y)")
Text("Top right: \(currentPositionTopRight.x) | \(currentPositionTopRight.y)")
Text("Bottom left: \(currentPositionBottomLeft.x) | \(currentPositionBottomLeft.y)")
Text("Bottom right: \(currentPositionBottomRight.x) | \(currentPositionBottomRight.y)")
Spacer()
currentImage
.resizable()
.aspectRatio(1 , contentMode: .fit)
.overlay(getCorners())
Spacer()
Group {
Button(action: {
// TODO: Crop it
}) {
Image(systemName: "checkmark").resizable().frame(width: 24, height: 24)
.padding(20)
.background(Color(Colors.getColor(Colors.colorSboBlue)))
.foregroundColor(Color.white)
}.clipShape(Circle())
.shadow(radius: 4)
}
}
}
}
private func getCorners() -> some View{
return
HStack {
VStack {
ZStack {
CropImageViewRectangle(
currentPositionTopLeft: self.$currentPositionTopLeft,
currentPositionTopRight: self.$currentPositionTopRight,
currentPositionBottomLeft: self.$currentPositionBottomLeft,
currentPositionBottomRight: self.$currentPositionBottomRight
)
GeometryReader { geometry in
CropImageViewRectangleCorner(
currentPosition: self.$currentPositionTopLeft,
newPosition: self.$newPositionTopLeft,
displacementX: 0,
displacementY: 0
)
CropImageViewRectangleCorner(
currentPosition: self.$currentPositionTopRight,
newPosition: self.$newPositionTopRight,
displacementX: geometry.size.width,
displacementY: 0
)
CropImageViewRectangleCorner(
currentPosition: self.$currentPositionBottomLeft,
newPosition: self.$newPositionBottomLeft,
displacementX: 0,
displacementY: geometry.size.height
)
CropImageViewRectangleCorner(
currentPosition: self.$currentPositionBottomRight,
newPosition: self.$newPositionBottomRight,
displacementX: geometry.size.width,
displacementY: geometry.size.height
)
}
}
Spacer()
}
Spacer()
}
}
}
The rectangle:
import SwiftUI
struct CropImageViewRectangle: View {
#Binding var currentPositionTopLeft: CGPoint
#Binding var currentPositionTopRight: CGPoint
#Binding var currentPositionBottomLeft: CGPoint
#Binding var currentPositionBottomRight: CGPoint
var body: some View {
GeometryReader { geometry in
Path { path in
path.move(to: self.currentPositionTopLeft)
path.addLine(
to: .init(
x: self.currentPositionTopRight.x,
y: self.currentPositionTopRight.y
)
)
path.addLine(
to: .init(
x: self.currentPositionBottomRight.x,
y: self.currentPositionBottomRight.y
)
)
path.addLine(
to: .init(
x: self.currentPositionBottomLeft.x,
y: self.currentPositionBottomLeft.y
)
)
path.addLine(
to: .init(
x: self.currentPositionTopLeft.x,
y: self.currentPositionTopLeft.y
)
)
}
.stroke(Color.blue, lineWidth: CGFloat(1))
}
}
}
The corner:
import SwiftUI
struct CropImageViewRectangleCorner: View {
#Binding var currentPosition: CGPoint
#Binding var newPosition: CGPoint
var displacementX: CGFloat
var displacementY: CGFloat
var body: some View {
Circle().foregroundColor(Color.blue).frame(width: 24, height: 24)
.offset(x: self.currentPosition.x, y: self.currentPosition.y)
.gesture(DragGesture()
.onChanged { value in
self.currentPosition = CGPoint(x: value.translation.width + self.newPosition.x, y: value.translation.height + self.newPosition.y)
}
.onEnded { value in
self.currentPosition = CGPoint(x: value.translation.width + self.newPosition.x, y: value.translation.height + self.newPosition.y)
self.newPosition = self.currentPosition
}
)
.opacity(0.5)
.position(CGPoint(x: 0, y: 0))
.onAppear() {
if self.displacementX > 0 || self.displacementY > 0 {
self.currentPosition = CGPoint(x: self.displacementX, y: self.displacementY)
self.newPosition = self.currentPosition
}
}
}
}