SwiftUI: Convert from a CGPoint on screen to a CGPoint in a view

Question

I have a view placed somewhere in my ContentView. I want to be able to drop images onto it. So I've added and .onDrop to it. In UIKit, I would use universeView.convert(point, to: targetView). How do I do this in SwiftUI?

Example utility could be to draw the thumbnail of the dropped image where it was dropped on the orange square

struct ContentView: View {
    @State var isTargeted: Bool = false
    
    var body: some View {
        VStack {
            
            Spacer()
                .frame(width: 600, height: 200)
                .background(Color.yellow.opacity(0.3))

            HStack {
                Spacer()
                    .frame(width: 200, height: 200)
                    .background(Color.yellow.opacity(0.3))

                Spacer()
                    .frame(width: 200, height: 200)
                    .background(Color.orange)
                    .onDrop(of: [ "public.image"], isTargeted: $isTargeted, perform: { (providers, point) -> Bool in
                        
                        print(point) // i.e. (x:336.0, y:486.5)
                                     // but I want it in the context of this views frame
                        // let bodyView: View
                        // let targetView: View
                        // let thePoint = bodyView.convert(point, to: targetView)
                        return true
                        
                    })

                Spacer()
                    .frame(width: 200, height: 200)
                    .background(Color.yellow.opacity(0.3))

            }
            .frame(width: 600, height: 200)

            Spacer()
                .frame(width: 600, height: 200)
                .background(Color.yellow.opacity(0.3))
        }
        .frame(width: 600, height: 600)
    }
}

Jadian · Accepted Answer · 2021-05-07T06:19:49.493

1

extension GeometryProxy {
    // converts from some other coordinate space to the proxy's own
    func convert(_ point: CGPoint, from coordinateSpace: CoordinateSpace) -> CGPoint {
        let frame = self.frame(in: coordinateSpace)
        let localViewPoint = CGPoint(x: point.x-frame.origin.x, y: point.y-frame.origin.y)
        
        // Some system bug? Test in iOS 13.4, 13.5, 14.1, 14.5
        if coordinateSpace == .global {
            switch (UIDevice.current.systemVersion as NSString).floatValue {
            case 13.5:
                return CGPoint(x: localViewPoint.x, y: point.y)
            case 14.5:
                return point
            default: break
            }
        }
        
        return localViewPoint
    }
}

Use like: geometry.convert(location, from: .global)

edited May 07 '21 at 06:19

answered May 06 '21 at 09:29

Jadian

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Thanks for the answer! Consider adding some context to the code or a short explanation of what it does / why it fixes the problem. – ZGski May 06 '21 at 16:09
Copy from CS193p - https://cs193p.sites.stanford.edu/, but it still has some problem in 14.5, and I don't know why. – Jadian May 07 '21 at 01:07

SwiftUI: Convert from a CGPoint on screen to a CGPoint in a view

1 Answers1