SwiftUI UnitPoint for Angle

UnitSquareIntersectionPoint.swift

//
//  ContentView.swift
//  GradientComponenet
//
//  Created by David Smith on 2/21/23.
//

import SwiftUI

struct ContentView: View {
    
    @State var rotationAngle:CGFloat = 0.0
    
    func unitSquareIntersectionPoint(_ angle:Angle) -> UnitPoint {
        var normalizedDegree = angle.degrees
        while normalizedDegree > 360.0 {
            normalizedDegree -= 360.0
        }
        while normalizedDegree < 0.0 {
            normalizedDegree += 360.0
        }
        if normalizedDegree < 45.0 || normalizedDegree >= 315 {
            //Right Edge, x = 1.0
            var degreeToConsider = normalizedDegree
            if degreeToConsider < 45.0 {
                degreeToConsider = normalizedDegree +  360.0
                //angle now between 315 & 405
            }
            let degreeProportion = (degreeToConsider - 315.0) / 90.0
            return UnitPoint(x: 1.0, y: 1.0 - degreeProportion)
        } else if normalizedDegree < 135.0 {
            //Top Edge, y = 0.0
            let degreeProportion = (normalizedDegree - 45.0) / 90.0
            return UnitPoint(x: 1.0 - degreeProportion, y: 0.0)
        } else if normalizedDegree < 225.0 {
            //left Edge, x = 0.0
            let degreeProportion = (normalizedDegree - 135) / 90.0
            return UnitPoint(x: 0.0, y: degreeProportion)
        } else if normalizedDegree < 315.0 {
            //Bottom Edge, y = 1.0
            let degreeProportion = (normalizedDegree - 225) / 90.0
            return UnitPoint(x: degreeProportion, y: 1.0)
        }
        return .zero
    }
    
    
    var startPoint:UnitPoint {
        return unitSquareIntersectionPoint(Angle(degrees: 360.0 * rotationAngle))
    }
    
    var endPoint:UnitPoint {
        return unitSquareIntersectionPoint(Angle(degrees: 360.0 * rotationAngle + 180.0))
    }
    
    
    var body: some View {
        VStack {
            let start = startPoint
            let end = endPoint
            ZStack {
                LinearGradient(colors: [Color.red, Color.blue], startPoint: startPoint, endPoint: endPoint)
                    .border(.black)
                
                Circle()
                    .fill(.red)
                    .frame(width:15, height:15)
                    .overlay(Circle().stroke(.black))
                    .position(x:start.x * 200, y:start.y * 200)
                
                Rectangle()
                    .fill(.blue)
                    .frame(width:15, height:15)
                    .border(.black)
                    .position(x:end.x * 200, y:end.y * 200)
                
            }
            .frame(width:200, height:200)
            
            Text("\(Int(rotationAngle * 360.0))°")
            
            HStack {
                Circle().fill(.red).frame(width:10, height:10)
                Text("Start: \(String(format:"%0.1f", start.x)),\(String(format:"%0.1f", start.y))")
            }
            
            HStack {
                Rectangle().fill(.blue).frame(width:10, height:10)
                Text("End: \(String(format:"%0.1f", end.x)),\(String(format:"%0.1f", end.y))")
            }
            
            
            GeometryReader { proxy in
                ZStack {
                    Color(white:0.9)
                    
                    RoundedRectangle(cornerRadius: 8)
                        .fill(Color.green)
                        .frame(width:32, height:32)
                        .overlay(
                            HStack(spacing:3) {
                                RoundedRectangle(cornerRadius: 4)
                                    .fill(.white)
                                    .frame(width: 2, height:24)
                                RoundedRectangle(cornerRadius: 4)
                                    .fill(.white)
                                    .frame(width: 2, height:24)
                                RoundedRectangle(cornerRadius: 4)
                                    .fill(.white)
                                    .frame(width: 2, height:24)
                            }
                        )
                        .position(x:22 + ((proxy.size.width - 44) * rotationAngle), y:proxy.size.height * 0.5)
                        .highPriorityGesture(DragGesture().onChanged { dragValue in
                            var dragLocation = dragValue.location.x
                            
                            dragLocation = max(22, dragLocation)
                            dragLocation = min(proxy.size.width - 22, dragLocation)
                            
                            rotationAngle = (dragLocation - 22) / (proxy.size.width - 44)
                        })
                    
                }
            }
            .frame(height:44)
            
            Text("Rotation")
                .frame(minWidth:0, maxWidth:.infinity)
        }
        .padding()
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

Quick SwiftUI file for calculating arbitrary LinearGradient angles.

Thanks for the great article! I updated the geometry calculation to be an angle-based interpolation vs the linear interpolation you used! The linear solution is very close so I included a reference line to show the input angle.

https://gist.github.com/DrewFitz/9447d8ccbc2b89cac7b5d41ebfbb2a79

This:

var normalizedDegree = angle.degrees
while normalizedDegree > 360.0 {
    normalizedDegree -= 360.0
}
while normalizedDegree < 0.0 {
    normalizedDegree += 360.0
}

can be simplified to this:

var normalizedDegree = angle.degrees % 360;
normalizedDegree = normalizedDegree < 0 ? normalizedDegree + 360 : normalizedDegree;

That first while loop is the definition of the % operator. Using % with a negative value on the left results in a negative number greater than -360 so adding 360 brings in into the range 0-359.