Instruments 27: Run Comparisons & Top Functions

import SwiftUI
import OSLog

// MARK: - Signposter setup
// Using the Points of Interest category causes Instruments to automatically
// display this data in the Points of Interest track in Instruments 27.
private let signposter = OSSignposter(
    subsystem: "com.example.NoteApp",
    category: .pointsOfInterest
)

// MARK: - Canvas model using concrete types instead of existentials
// Before: var strokes: [any DrawingElement] — causes swift_project_boxed_opaque_existential overhead
// After: concrete generic approach avoids existential boxing entirely
struct Stroke: Identifiable {
    let id = UUID()
    var points: [CGPoint]
    var color: Color
}

final class CanvasModel: ObservableObject {
    @Published var strokes: [Stroke] = []
    @Published var lassoSelection: [Stroke] = []

    /// Performs lasso hit-testing, wrapped in an OSSignpost interval so
    /// Instruments 27 can isolate and compare this work across runs.
    func performLassoSelection(in region: CGRect) {
        let state = signposter.beginInterval(
            "Lasso Selection",
            id: signposter.makeSignpostID()
        )
        defer { signposter.endInterval("Lasso Selection", state) }

        // Concrete type iteration — no existential unwrap overhead
        lassoSelection = strokes.filter { stroke in
            stroke.points.contains { region.contains($0) }
        }
    }
}

// MARK: - SwiftUI View
struct CanvasView: View {
    @StateObject private var model = CanvasModel()
    @State private var showingSelection = false

    var body: some View {
        ZStack {
            Canvas { context, size in
                for stroke in model.strokes {
                    var path = Path()
                    guard let first = stroke.points.first else { continue }
                    path.move(to: first)
                    stroke.points.dropFirst().forEach { path.addLine(to: $0) }
                    context.stroke(path, with: .color(stroke.color), lineWidth: 3)
                }
            }
            .onTapGesture { location in
                let sampleStroke = Stroke(
                    points: [location, CGPoint(x: location.x + 40, y: location.y + 40)],
                    color: .blue
                )
                model.strokes.append(sampleStroke)
            }

            VStack {
                Spacer()
                Button("Simulate Lasso (profile me)") {
                    // This call is wrapped in an OSSignpost interval;
                    // visible as "Lasso Selection" in the Points of Interest
                    // track in Instruments 27, enabling Run Comparisons.
                    model.performLassoSelection(in: CGRect(x: 0, y: 0, width: 300, height: 300))
                    showingSelection = true
                }
                .padding()
                .background(.ultraThinMaterial, in: Capsule())
                .padding(.bottom, 40)
            }
        }
        .alert("Selected \(model.lassoSelection.count) strokes", isPresented: $showingSelection) {
            Button("OK", role: .cancel) {}
        }
    }
}

#Preview {
    CanvasView()
}