Mobile App Dev 2021W: Assignment 2

This assignment is still being developed.

Questions

1. [3] At the bottom of the screen it shows the current rotation of the image in degrees. This rotation information stored in a different format than it was in Tutorial 4's 1601picviewer-1.
1. [1] What is the difference?
2. [2] Change the program to store the rotation information the same way 1601picviewer-1 did. Be sure to add no new state variables. (Hint: Look at the documentation for TextField.)
2. [3] currentAngle() (lines 71-77):
   1. [1] What does currentAngle() do? (Explain what the function does in English.)
   2. [1] When is it called?
   3. [1] Replace the call to currentAngle() with an expression using the ?? operator (the "Nil-Coalescing Operator").
3. [2] Change rotations so they are quantized to 45 degree increments during and at the end of each rotation gesture. It should still be possible to rotate to arbitrary angles by typing in an angle value.
4. [8] Add TextFields to the bottom of the screen displaying the current X and Y position and the magnification factor (displayed as M) in a similar fashion to the existing one for degrees. The X and Y should be displayed as whole numbers, while the magnification factor should be shown to two decimal places. Each of these values should be editable, and when changes are made the image's state should be updated. Be sure to show an explain each of the changes you made to the code. (4 points for X and Y, 4 for magnification)

Code

picviewer-2.zip

//
//  ContentView.swift
//  picviewer-2
//  COMP 1601 Winter 2021, Carleton University
//

import SwiftUI

struct ContentView: View {
    @State private var theImage = "kittens"
    @State private var moved = false
    @State private var magnification: CGFloat = 1
    @State private var angleS = "0"
    
    func resetState() {
        moved = false
        magnification = 1
        angleS = "0"
    }
    
    var body: some View {
        VStack {
            Menu("Animals!") {
                Button("Kittens", action: {
                    theImage = "kittens"
                    resetState()
                })
                Button("Sad Dog", action: {
                    theImage = "sadDog"
                    resetState()
                })
            }
            ActiveImage(theImage: $theImage, moved: $moved, finalAmount: $magnification,
                        angleS: $angleS)
            HStack{
                Text("D:")
                TextField("", text: $angleS, onCommit: {
                    if Double(angleS) == nil {
                        angleS = "0"
                    }
                })
            }.padding()
        }
    }
}

struct ActiveImage: View {
    @State private var position = CGPoint(x: 0, y: 0)
    @State private var currentAmount: CGFloat = 0
    
    @Binding var theImage: String
    @Binding var moved: Bool
    @Binding var finalAmount: CGFloat
    @Binding var angleS: String
    
    var body: some View {
        GeometryReader {g in
            Image(theImage)
                .resizable()
                .scaledToFit()
                .position(moved ? position :
                            CGPoint(x: g.size.width / 2, y: g.size.height / 2))
                .scaleEffect(finalAmount + currentAmount)
                .rotationEffect(currentAngle())
                .gesture(dragging)
                .gesture(SimultaneousGesture(rotating, magnifying))
                .onTapGesture(count: 1, perform: tapReset)
        }
    }
    
    func currentAngle() -> Angle {
        if let a = Double(self.angleS) {
            return Angle(degrees: a)
        } else {
            return Angle(degrees: 0)
        }
    }
    
    func tapReset() {
        self.finalAmount = 1
        self.moved = false
        self.angleS = "0"
    }
    
    var rotating: some Gesture {
        RotationGesture()
            .onChanged { angle in
                self.angleS = String(format: "%.0f", angle.degrees)
            }
    }
    
    var magnifying: some Gesture {
        MagnificationGesture().onChanged { amount in
            self.currentAmount = amount - 1
        }
        .onEnded { amount in
            self.finalAmount += self.currentAmount
            self.currentAmount = 0
        }
    }
    
    var dragging: some Gesture {
        DragGesture()
            .onChanged {s in
                self.moved = true
                self.position = s.location
            }
            .onEnded {s in
                self.moved = true
                self.position = s.location
            }
    }
}

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