Drawing Canvas

// SwiftUI에서 CoreGraphics를 가장 가볍게 쓰는 방법
Canvas { context, size in
    var path = Path()
    path.move(to: .zero)
    path.addCurve(to: CGPoint(x: size.width, y: size.height),
                  control1: CGPoint(x: size.width, y: 0),
                  control2: CGPoint(x: 0, y: size.height))
    context.stroke(path, with: .color(.purple), lineWidth: 3)
}

struct PencilCanvas: UIViewRepresentable {
    @Binding var canvas: PKCanvasView
    let toolPicker = PKToolPicker()

    func makeUIView(context: Context) -> PKCanvasView {
        canvas.drawingPolicy = .anyInput   // 시뮬레이터에서도 마우스 입력 허용
        canvas.tool = PKInkingTool(.pen, color: .black, width: 5)
        toolPicker.setVisible(true, forFirstResponder: canvas)
        toolPicker.addObserver(canvas)
        canvas.becomeFirstResponder()
        return canvas
    }

    func updateUIView(_ uiView: PKCanvasView, context: Context) {}
}

let image = canvas.drawing.image(from: canvas.bounds, scale: UIScreen.main.scale)

struct Stroke {
    var color: Color
    var lineWidth: CGFloat
    var points: [CGPoint]
}

@State var strokes: [Stroke] = []
@State var current: Stroke?

Canvas { context, size in
    for stroke in strokes + (current.map { [$0] } ?? []) {
        var path = Path()
        path.addLines(stroke.points)
        context.stroke(path, with: .color(stroke.color), lineWidth: stroke.lineWidth)
    }
}
.gesture(
    DragGesture(minimumDistance: 0)
        .onChanged { value in
            if current == nil {
                current = Stroke(color: selectedColor, lineWidth: width, points: [])
            }
            current?.points.append(value.location)
        }
        .onEnded { _ in
            if let s = current { strokes.append(s) }
            current = nil
        }
)

enum ShapeKind { case line, rectangle, ellipse, triangle }

struct DrawnShape {
    var kind: ShapeKind
    var rect: CGRect          // 시작점-끝점이 만드는 경계 사각형
    var stroke: Color
    var fill: Color
}

@State var shapes: [DrawnShape] = []
@State var preview: DrawnShape?

Canvas { context, size in
    for shape in shapes + (preview.map { [$0] } ?? []) {
        let path = path(for: shape)
        context.fill(path, with: .color(shape.fill))
        context.stroke(path, with: .color(shape.stroke), lineWidth: 2)
    }
}
.gesture(
    DragGesture(minimumDistance: 0)
        .onChanged { value in
            let r = CGRect(start: value.startLocation, end: value.location)
            preview = DrawnShape(kind: kind, rect: r, stroke: strokeColor, fill: fillColor)
        }
        .onEnded { _ in
            if let p = preview { shapes.append(p) }
            preview = nil
        }
)