feat(gamut): second-profile compare and click-inspect (#147)

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Packages/ICCeryCore/Sources/ICCeryCore/Gamut/ApproximateLab.swift

@@ -0,0 +1,64 @@
+import Foundation
+
+/// Approximate sRGB → CIELab D50 conversion for the gamut inspect panel
+/// (issue #147).
+///
+/// This is a fixed-matrix helper, **not** a colour-management module: it
+/// never touches ICC profiles, ColorSync, or lcms. The UI labels its
+/// output "approx. Lab, not ColorSync".
+public enum ApproximateLab {
+
+    /// linear-sRGB → XYZ (D65) matrix, IEC 61966-2-1.
+    private static let srgbToXYZ: [[Double]] = [
+        [0.4124, 0.3576, 0.1805],
+        [0.2126, 0.7152, 0.0722],
+        [0.0193, 0.1192, 0.9505],
+    ]
+
+    /// 8-bit sRGB triple → Lab D50 (approximate).
+    public static func srgb8ToLab(r: Int, g: Int, b: Int) -> LabColor {
+        srgbToLab(DisplayRGB(
+            r: Double(r) / 255.0,
+            g: Double(g) / 255.0,
+            b: Double(b) / 255.0))
+    }
+
+    /// 0–1 sRGB triple → Lab D50 (approximate).
+    public static func srgbToLab(_ rgb: DisplayRGB) -> LabColor {
+        func linear(_ c: Double) -> Double {
+            c <= 0.04045 ? c / 12.92 : pow((c + 0.055) / 1.055, 2.4)
+        }
+        let v = [linear(rgb.r), linear(rgb.g), linear(rgb.b)]
+        // 0–1 XYZ D65 → the 0–100 scale `LabColorMath` works in.
+        let xyz65 = XYZColor(
+            x: (srgbToXYZ[0][0] * v[0] + srgbToXYZ[0][1] * v[1] + srgbToXYZ[0][2] * v[2]) * 100,
+            y: (srgbToXYZ[1][0] * v[0] + srgbToXYZ[1][1] * v[1] + srgbToXYZ[1][2] * v[2]) * 100,
+            z: (srgbToXYZ[2][0] * v[0] + srgbToXYZ[2][1] * v[1] + srgbToXYZ[2][2] * v[2]) * 100)
+        return LabColorMath.xyzToLab(adaptD65ToD50(xyz65))
+    }
+
+    /// Bradford D65 → D50 chromatic adaptation — the mirror of
+    /// `LabColorMath.adaptD50ToD65`.
+    private static func adaptD65ToD50(_ xyz: XYZColor) -> XYZColor {
+        let m = LabColorMath.bradford
+        let inv = LabColorMath.bradfordInv
+        let d65 = LabColorMath.d65White
+        let d50 = LabColorMath.d50White
+        let source = multiply(m, [xyz.x, xyz.y, xyz.z])
+        let srcWhite = multiply(m, [d65.X, d65.Y, d65.Z])
+        let dstWhite = multiply(m, [d50.X, d50.Y, d50.Z])
+        let scaled = [
+            source[0] * (dstWhite[0] / srcWhite[0]),
+            source[1] * (dstWhite[1] / srcWhite[1]),
+            source[2] * (dstWhite[2] / srcWhite[2]),
+        ]
+        return XYZColor(
+            x: inv[0][0] * scaled[0] + inv[0][1] * scaled[1] + inv[0][2] * scaled[2],
+            y: inv[1][0] * scaled[0] + inv[1][1] * scaled[1] + inv[1][2] * scaled[2],
+            z: inv[2][0] * scaled[0] + inv[2][1] * scaled[1] + inv[2][2] * scaled[2])
+    }
+
+    private static func multiply(_ m: [[Double]], _ v: [Double]) -> [Double] {
+        m.map { row in zip(row, v).reduce(0) { $0 + $1.0 * $1.1 } }
+    }
+}

Packages/ICCeryCore/Sources/ICCeryCore/Gamut/GamutContainment.swift

@@ -0,0 +1,115 @@
+import Foundation
+import simd
+
+/// Result of a point-in-gamut test (issue #147).
+public enum GamutContainment: String, Sendable, Equatable {
+    /// The point lies inside the mesh volume.
+    case inside
+    /// The point lies outside the mesh volume.
+    case outside
+    /// The mesh has no faces to test against.
+    case unknown
+}
+
+/// Point-in-mesh containment and volume estimation for ``GamutMesh``.
+///
+/// Both tests run on the scene-space positions stored on
+/// ``GamutVertex/position`` (`x = a*`, `y = L*`, `z = b*`), the same
+/// mapping the SceneKit viewer uses. No colour management is involved.
+public enum GamutGeometry {
+
+    /// Whether `lab` is inside `mesh`.
+    ///
+    /// Ray-casts through the face list: an odd crossing count means the
+    /// point is inside a closed surface. A ray that grazes a vertex or
+    /// edge gives an ambiguous count, so the test retries with off-axis
+    /// directions before answering. Meshes without faces report
+    /// ``GamutContainment/unknown``.
+    public static func containment(of lab: LabColor, in mesh: GamutMesh) -> GamutContainment {
+        guard !mesh.faces.isEmpty else { return .unknown }
+        let origin = SIMD3<Double>(lab.a, lab.l, lab.b)
+        for direction in rayDirections {
+            if let inside = castRay(from: origin, direction: direction, mesh: mesh) {
+                return inside ? .inside : .outside
+            }
+        }
+        return .unknown
+    }
+
+    /// Approximate mesh volume in Lab-cubic units.
+    ///
+    /// Sums signed tetrahedra from the vertex centroid to each face; for
+    /// a closed surface the magnitude equals the enclosed volume
+    /// regardless of face winding. Returns 0 for empty or face-less
+    /// meshes.
+    public static func volume(of mesh: GamutMesh) -> Double {
+        guard !mesh.faces.isEmpty, !mesh.vertices.isEmpty else { return 0 }
+        var centroid = SIMD3<Double>.zero
+        for vertex in mesh.vertices {
+            centroid += SIMD3<Double>(vertex.position)
+        }
+        centroid /= Double(mesh.vertices.count)
+
+        var sum = 0.0
+        let count = mesh.vertices.count
+        for face in mesh.faces {
+            guard Int(face.a) < count, Int(face.b) < count, Int(face.c) < count else {
+                continue
+            }
+            let a = SIMD3<Double>(mesh.vertices[Int(face.a)].position) - centroid
+            let b = SIMD3<Double>(mesh.vertices[Int(face.b)].position) - centroid
+            let c = SIMD3<Double>(mesh.vertices[Int(face.c)].position) - centroid
+            sum += simd_dot(a, simd_cross(b, c)) / 6.0
+        }
+        return abs(sum)
+    }
+
+    // MARK: - Ray casting
+
+    /// Primary +X ray, then off-axis retries for degenerate edge hits.
+    private static let rayDirections: [SIMD3<Double>] = [
+        SIMD3(1, 0, 0),
+        simd_normalize(SIMD3<Double>(0.71, 1.0, 0.53)),
+        simd_normalize(SIMD3<Double>(0.53, 0.71, 1.0)),
+    ]
+
+    /// Möller–Trumbore crossing count. Returns `nil` when a crossing
+    /// lands on a triangle edge or vertex (ambiguous parity) so the
+    /// caller can retry with a different direction.
+    private static func castRay(
+        from origin: SIMD3<Double>,
+        direction dir: SIMD3<Double>,
+        mesh: GamutMesh
+    ) -> Bool? {
+        let epsilon = 1e-9
+        var crossings = 0
+        let count = mesh.vertices.count
+        for face in mesh.faces {
+            guard Int(face.a) < count, Int(face.b) < count, Int(face.c) < count else {
+                continue
+            }
+            let va = SIMD3<Double>(mesh.vertices[Int(face.a)].position)
+            let vb = SIMD3<Double>(mesh.vertices[Int(face.b)].position)
+            let vc = SIMD3<Double>(mesh.vertices[Int(face.c)].position)
+
+            let e1 = vb - va
+            let e2 = vc - va
+            let p = simd_cross(dir, e2)
+            let det = simd_dot(e1, p)
+            if abs(det) < 1e-12 { continue }  // ray parallel to face
+            let inv = 1.0 / det
+            let tvec = origin - va
+            let u = simd_dot(tvec, p) * inv
+            let q = simd_cross(tvec, e1)
+            let v = simd_dot(dir, q) * inv
+            let t = simd_dot(e2, q) * inv
+
+            guard t > epsilon else { continue }
+            if u < -epsilon || v < -epsilon || u + v > 1 + epsilon { continue }
+            // Crossing on an edge or vertex — parity is ambiguous.
+            if u < epsilon || v < epsilon || u + v > 1 - epsilon { return nil }
+            crossings += 1
+        }
+        return crossings % 2 == 1
+    }
+}

Packages/ICCeryCore/Sources/ICCeryCore/Gamut/NamedGamut.swift

@@ -0,0 +1,39 @@
+import Foundation
+
+/// A parsed gamut mesh plus the display metadata the compare viewer
+/// needs (issue #147).
+///
+/// `displayName` is user-derived (a file name); views must render it
+/// through `Text` only (#114).
+public struct NamedGamut: Sendable, Equatable, Identifiable {
+
+    /// What the layer is used for in the compare UI.
+    public enum Role: String, Sendable, Equatable {
+        /// Bundled reference space (sRGB). Cannot be removed, only hidden.
+        case reference
+        /// The workflow's own profile gamut.
+        case profileA
+        /// The user-added compare gamut. Replaced, never stacked.
+        case profileB
+    }
+
+    public var id: String
+    public var displayName: String
+    public var role: Role
+    public var mesh: GamutMesh
+    public var sourceURL: URL
+
+    public init(
+        id: String,
+        displayName: String,
+        role: Role,
+        mesh: GamutMesh,
+        sourceURL: URL
+    ) {
+        self.id = id
+        self.displayName = displayName
+        self.role = role
+        self.mesh = mesh
+        self.sourceURL = sourceURL
+    }
+}

Sources/ICCery/AppEnvironment.swift

@@ -83,6 +83,12 @@ enum UITestHooks {
     static var presetExportURL: URL? { url("ICCERY_TEST_PRESET_EXPORT") }
     /// Spot-read CSV export destination (`selectCsvSavePath`, #148).
     static var csvExportURL: URL? { url("ICCERY_TEST_CSV_EXPORT") }
+    /// `.gam` compare picker result (gamut sheet, #147). Unset → cancel.
+    static var gamutFileURL: URL? { url("ICCERY_TEST_GAMUT_FILE") }
+    /// `.icc/.icm` compare picker result (gamut sheet, #147). Unset → cancel.
+    static var gamutProfileURL: URL? { url("ICCERY_TEST_GAMUT_PROFILE") }
+    /// TIFF sample picker result (gamut sheet, #147). Unset → cancel.
+    static var gamutTiffURL: URL? { url("ICCERY_TEST_GAMUT_TIFF") }
 
     // MARK: - Print panel / CUPS stubs (issue 13/17)
 

Sources/ICCery/FileDialogService.swift

@@ -70,6 +70,19 @@ final class FileDialogService {
              message: "Choose a calibration file (.cal)")
     }
 
+    /// `selectGamutFile` — `.gam` surface mesh for the compare slot (#147).
+    func selectGamutFile(startingAt start: URL? = nil) -> URL? {
+        open(extensions: ["gam"], startingAt: start,
+             message: "Choose a .gam surface mesh",
+             allowsOtherFileTypes: false)
+    }
+
+    /// `selectTiffFile` — `.tif`/`.tiff` target page for gamut sampling (#147).
+    func selectTiffFile(startingAt start: URL? = nil) -> URL? {
+        open(extensions: ["tif", "tiff"], startingAt: start,
+             message: "Choose a target TIFF page")
+    }
+
     /// `btnImportPreset` — open a `.json` preset file.
     func selectPresetFile(startingAt start: URL? = nil) -> URL? {
         open(extensions: ["json"], startingAt: start,
@@ -102,14 +115,15 @@ final class FileDialogService {
     private func open(
         extensions: [String],
         startingAt start: URL?,
-        message: String?
+        message: String?,
+        allowsOtherFileTypes: Bool = true
     ) -> URL? {
         let panel = NSOpenPanel()
         panel.canChooseDirectories = false
         panel.canChooseFiles = true
         panel.allowsMultipleSelection = false
         panel.allowedContentTypes = utTypes(extensions)
-        panel.allowsOtherFileTypes = true
+        panel.allowsOtherFileTypes = allowsOtherFileTypes
         panel.directoryURL = start
         if let message { panel.message = message }
         return run(panel)

Sources/ICCery/GamutView.swift

@@ -1,5 +1,6 @@
 import SwiftUI
 import SceneKit
+import Metal
 import ICCeryCore
 import simd
 
@@ -62,72 +63,300 @@ internal struct GamutSceneGeometryBuilder {
     }
 }
 
-/// Native SceneKit 3D gamut viewer.
+/// Native SceneKit 3D gamut viewer (issues #28, #147).
 ///
-/// Displays a profile gamut mesh and the bundled `sRGB.gam` reference.  Uses
+/// Displays the bundled `sRGB.gam` reference plus up to two profile
-/// the CIELAB coordinate convention `x = a*`, `y = L*`, `z = b*` so that the
+/// meshes with independent visibility toggles, a status line, and an
-/// a* (green-red) axis is horizontal, L* (lightness) is vertical, and b*
+/// inspect panel (click a mesh, type a Lab value, or sample a TIFF
-/// (blue-yellow) is depth.
+/// pixel). Uses the CIELAB coordinate convention `x = a*`, `y = L*`,
+/// `z = b*`.
 struct GamutView: View {
     @StateObject private var viewModel: GamutViewModel
     @State private var pause: () -> Void = {}
     @FocusState private var isFocused: Bool
+    @Binding var showingAllHelp: Bool
 
-    init(profileGamURL: URL? = nil) {
+    init(
-        _viewModel = StateObject(wrappedValue: GamutViewModel(profileGamURL: profileGamURL))
+        environment: AppEnvironment,
+        profileGamURL: URL? = nil,
+        showingAllHelp: Binding<Bool>
+    ) {
+        _viewModel = StateObject(wrappedValue: GamutViewModel(
+            environment: environment, profileGamURL: profileGamURL))
+        _showingAllHelp = showingAllHelp
     }
 
     var body: some View {
-        ZStack {
+        VStack(spacing: 0) {
-            GamutSceneView(
+            toolbar
-                profileMesh: viewModel.profileMesh,
+            Divider().overlay(Theme.border)
-                referenceMesh: viewModel.sRGBMesh,
+            sceneArea
-                onReset: $viewModel.resetCamera,
+            Divider().overlay(Theme.border)
-                onPause: $pause
+            statusLine
-            )
+            inspectPanel
-            .focusable()
-            .focused($isFocused)
-            .onAppear { isFocused = true }
-
-            VStack {
-                HStack {
-                    Spacer()
-                    Button(action: { viewModel.resetCamera() }) {
-                        Text("Reset view")
-                    }
-                    .accessibilityIdentifier("btnResetGamutCamera")
-                    .padding(8)
-                }
-                Spacer()
-                HStack {
-                    Text(viewModel.status)
-                        .font(.caption)
-                        .padding(8)
-                        .background(.thinMaterial)
-                        .cornerRadius(6)
-                        .accessibilityIdentifier("gamutStatusText")
-                    Spacer()
-                }
-                .padding(8)
-            }
         }
-        .frame(minWidth: 500, minHeight: 400)
+        .frame(minWidth: 720, minHeight: 520)
+        .background(Theme.background)
         .onDisappear { pause() }
         .accessibilityElement(children: .contain)
         .accessibilityIdentifier("gamutView")
+        .sheet(isPresented: $viewModel.showingTiffPreview) {
+            tiffPreviewSheet
+        }
+    }
+
+    // MARK: - Toolbar
+
+    private var toolbar: some View {
+        HStack(spacing: 12) {
+            layerToggle(id: GamutViewModel.srgbLayerID, fallback: "sRGB")
+            layerToggle(id: GamutViewModel.profileLayerID, fallback: "Profile")
+            layerToggle(id: GamutViewModel.compareLayerID, fallback: "Compare")
+            Spacer()
+            addCompareMenu
+            Button("Remove compare") { viewModel.removeCompare() }
+                .disabled(viewModel.layer(id: GamutViewModel.compareLayerID) == nil)
+                .accessibilityIdentifier("btnGamutRemoveCompare")
+            Button("Sample TIFF…") { viewModel.openTiffSample() }
+                .accessibilityIdentifier("btnGamutSampleTiff")
+                .helpOverlay(
+                    "Sample a colour from a target TIFF page.",
+                    showing: $showingAllHelp)
+        }
+        .padding(.horizontal, 12)
+        .padding(.vertical, 8)
+    }
+
+    private func layerToggle(id: String, fallback: String) -> some View {
+        let layer = viewModel.layer(id: id)
+        return Toggle(isOn: Binding(
+            get: { layer != nil && viewModel.visibleIDs.contains(id) },
+            set: { on in
+                if on {
+                    viewModel.visibleIDs.insert(id)
+                } else {
+                    viewModel.visibleIDs.remove(id)
+                }
+            }
+        )) {
+            Text(layer?.displayName ?? fallback)
+        }
+        .toggleStyle(.checkbox)
+        .disabled(layer == nil || viewModel.viewerUnavailable)
+        .help(layer.map { $0.sourceURL.lastPathComponent } ?? "No profile .gam loaded")
+        .accessibilityIdentifier("gamutLayer-\(id)")
+    }
+
+    private var addCompareMenu: some View {
+        Menu("Add compare…") {
+            Button("Open .gam…") { viewModel.openCompareGam() }
+                .accessibilityIdentifier("btnGamutOpenGam")
+            Button("Open profile…") { viewModel.openCompareProfile() }
+                .accessibilityIdentifier("btnGamutOpenProfile")
+        }
+        .accessibilityIdentifier("btnGamutAddCompare")
+        .helpOverlay(
+            "Add a second profile or .gam mesh to compare against.",
+            showing: $showingAllHelp)
+    }
+
+    // MARK: - Scene
+
+    private var sceneArea: some View {
+        ZStack(alignment: .topTrailing) {
+            if viewModel.viewerUnavailable {
+                Text("3D gamut viewer is unavailable on this Mac; the rest of ICCery still works.")
+                    .font(.callout)
+                    .foregroundStyle(.secondary)
+                    .frame(maxWidth: .infinity, maxHeight: .infinity)
+                    .accessibilityIdentifier("gamutViewerUnavailable")
+            } else {
+                GamutSceneView(
+                    layers: viewModel.layers,
+                    visibleIDs: viewModel.visibleIDs,
+                    onReset: $viewModel.resetCamera,
+                    onPause: $pause,
+                    onUnavailable: { viewModel.viewerUnavailable = true },
+                    onInspect: { point, layerID in
+                        if let layerID {
+                            viewModel.inspectSceneHit(world: point, layerID: layerID)
+                        } else {
+                            viewModel.clearInspect()
+                        }
+                    }
+                )
+                .focusable()
+                .focused($isFocused)
+                .onAppear { isFocused = true }
+            }
+            Button(action: { viewModel.resetCamera() }) {
+                Text("Reset view")
+            }
+            .accessibilityIdentifier("btnResetGamutCamera")
+            .padding(8)
+        }
+        .frame(maxWidth: .infinity, maxHeight: .infinity)
+    }
+
+    // MARK: - Status
+
+    private var statusLine: some View {
+        HStack(spacing: 10) {
+            Text(viewModel.status)
+                .font(.caption)
+                .foregroundStyle(Theme.text)
+                .accessibilityIdentifier("gamutStatusText")
+            if let notice = viewModel.noticeText {
+                Text(notice)
+                    .font(.caption)
+                    .foregroundStyle(.secondary)
+                    .accessibilityIdentifier("gamutNoticeText")
+            }
+            Spacer()
+        }
+        .padding(.horizontal, 12)
+        .padding(.vertical, 6)
+    }
+
+    // MARK: - Inspect panel
+
+    private var inspectPanel: some View {
+        HStack(spacing: 12) {
+            if let lab = viewModel.inspectLab {
+                inspectSwatch
+                labReadout(lab)
+                containmentColumn
+                if viewModel.inspectIsApproximate {
+                    Text("approx. Lab, not ColorSync")
+                        .font(.caption2)
+                        .foregroundStyle(.secondary)
+                        .accessibilityIdentifier("gamutInspectApprox")
+                }
+            } else {
+                Text("Click the mesh, or enter Lab, to inspect.")
+                    .font(.caption)
+                    .foregroundStyle(.secondary)
+                    .accessibilityIdentifier("gamutInspectIdle")
+            }
+            Spacer()
+            labEntryFields
+        }
+        .padding(.horizontal, 12)
+        .padding(.vertical, 8)
+        .frame(minHeight: 56)
+        .background(Theme.panel)
+        .accessibilityElement(children: .contain)
+        .accessibilityIdentifier("gamutInspectPanel")
+        .helpOverlay(
+            "Inspect a Lab point against each loaded gamut.",
+            showing: $showingAllHelp)
+    }
+
+    @ViewBuilder
+    private var inspectSwatch: some View {
+        if let swatch = viewModel.inspectSwatch {
+            Color(red: swatch.r, green: swatch.g, blue: swatch.b)
+                .frame(width: 16, height: 16)
+                .clipShape(RoundedRectangle(cornerRadius: 2))
+                .overlay(RoundedRectangle(cornerRadius: 2).stroke(Theme.border))
+                .accessibilityIdentifier("gamutInspectSwatch")
+        }
+    }
+
+    private func labReadout(_ lab: LabColor) -> some View {
+        HStack(spacing: 10) {
+            Text(String(format: "L %.1f", lab.l))
+                .accessibilityIdentifier("gamutInspectL")
+            Text(String(format: "a %.1f", lab.a))
+                .accessibilityIdentifier("gamutInspectA")
+            Text(String(format: "b %.1f", lab.b))
+                .accessibilityIdentifier("gamutInspectB")
+        }
+        .font(.caption.monospacedDigit())
+        .foregroundStyle(Theme.text)
+    }
+
+    private var containmentColumn: some View {
+        HStack(spacing: 10) {
+            ForEach(viewModel.inspectResults, id: \.id) { result in
+                Text("\(result.name) \(containmentWord(result.containment))")
+                    .font(.caption)
+                    .foregroundStyle(Theme.text)
+                    .accessibilityIdentifier("gamutInspect-\(result.id)")
+            }
+        }
+    }
+
+    private func containmentWord(_ containment: GamutContainment) -> String {
+        switch containment {
+        case .inside: return "in"
+        case .outside: return "out"
+        case .unknown: return "?"
+        }
+    }
+
+    private var labEntryFields: some View {
+        HStack(spacing: 6) {
+            Text("Lab 0–100 · ±128")
+                .font(.caption2)
+                .foregroundStyle(.secondary)
+            TextField("L", text: $viewModel.labEntryL)
+                .textFieldStyle(.roundedBorder)
+                .frame(width: 56)
+                .accessibilityIdentifier("gamutLabEntryL")
+            TextField("a", text: $viewModel.labEntryA)
+                .textFieldStyle(.roundedBorder)
+                .frame(width: 56)
+                .accessibilityIdentifier("gamutLabEntryA")
+            TextField("b", text: $viewModel.labEntryB)
+                .textFieldStyle(.roundedBorder)
+                .frame(width: 56)
+                .accessibilityIdentifier("gamutLabEntryB")
+            Button("Inspect") { viewModel.inspectEnteredLab() }
+                .disabled(!viewModel.canInspectLab)
+                .accessibilityIdentifier("btnGamutInspectLab")
+        }
+    }
+
+    // MARK: - TIFF sample sheet
+
+    private var tiffPreviewSheet: some View {
+        VStack(spacing: 12) {
+            Text("Click a pixel to sample its colour.")
+                .font(.headline)
+                .foregroundStyle(Theme.text)
+            if let png = viewModel.tiffPreviewPNG {
+                TiffSampleImageView(pngData: png) { r, g, b in
+                    viewModel.sampleTiffPixel(r: r, g: g, b: b)
+                }
+                .frame(minWidth: 320, minHeight: 240)
+            }
+            HStack {
+                Spacer()
+                Button("Cancel") { viewModel.showingTiffPreview = false }
+                    .accessibilityIdentifier("btnCloseGamutTiffPreview")
+            }
+        }
+        .padding(16)
+        .background(Theme.background)
+        .accessibilityElement(children: .contain)
+        .accessibilityIdentifier("gamutTiffPreview")
     }
 }
 
-/// `NSViewRepresentable` wrapper around an `SCNView` that builds the scene from
+/// `NSViewRepresentable` wrapper around an `SCNView` rendering one node
-/// one or two ``GamutMesh`` values.
+/// per ``NamedGamut`` layer.
 ///
-/// Scene construction and camera reset are coordinated through a typed callback
+/// Layer toggles hide/show `SCNNode`s — the scene is built once and the
-/// binding owned by the view model.
+/// camera is only reset through the explicit reset path, never on a
+/// mesh or visibility update.
 private struct GamutSceneView: NSViewRepresentable {
-    var profileMesh: GamutMesh?
+    var layers: [NamedGamut]
-    var referenceMesh: GamutMesh?
+    var visibleIDs: Set<String>
     var onReset: Binding<() -> Void>
     var onPause: Binding<() -> Void>
+    var onUnavailable: () -> Void
+    var onInspect: (SIMD3<Float>, String?) -> Void
 
     func makeNSView(context: Context) -> SCNView {
         let scnView = SCNView()
@@ -142,14 +371,23 @@ private struct GamutSceneView: NSViewRepresentable {
 
         context.coordinator.scnView = scnView
         context.coordinator.scene = scene
-        context.coordinator.buildScene(profile: profileMesh, reference: referenceMesh)
+        context.coordinator.onInspect = onInspect
+        context.coordinator.buildSceneOnce()
+        context.coordinator.syncLayers(layers, visibleIDs: visibleIDs)
         context.coordinator.installKeyMonitor()
+        context.coordinator.installClickGesture()
+
+        // No GPU → the docs/18 fallback; never respawn the view in a loop.
+        if MTLCreateSystemDefaultDevice() == nil {
+            DispatchQueue.main.async { onUnavailable() }
+        }
 
         return scnView
     }
 
     func updateNSView(_ nsView: SCNView, context: Context) {
-        context.coordinator.buildScene(profile: profileMesh, reference: referenceMesh)
+        context.coordinator.onInspect = onInspect
+        context.coordinator.syncLayers(layers, visibleIDs: visibleIDs)
     }
 
     func makeCoordinator() -> Coordinator {
@@ -165,6 +403,9 @@ private struct GamutSceneView: NSViewRepresentable {
 
     static func dismantleNSView(_ nsView: SCNView, coordinator: Coordinator) {
         coordinator.removeKeyMonitor()
+        if let click = coordinator.clickGesture {
+            nsView.removeGestureRecognizer(click)
+        }
         nsView.isPlaying = false
     }
 
@@ -172,11 +413,14 @@ private struct GamutSceneView: NSViewRepresentable {
     final class Coordinator: NSObject {
         weak var scnView: SCNView?
         weak var scene: SCNScene?
+        var onInspect: (SIMD3<Float>, String?) -> Void = { _, _ in }
+        private(set) var clickGesture: NSClickGestureRecognizer?
         private var keyMonitor: Any?
 
-        private let profileNode = SCNNode()
+        /// One `SCNNode` per loaded layer, keyed by `NamedGamut.id`.
-        private let referenceGroup = SCNNode()
+        private var layerNodes: [String: SCNNode] = [:]
         private let axisNode = SCNNode()
+        private let layerGroup = SCNNode()
         private let cameraNode: SCNNode = {
             let node = SCNNode()
             node.camera = SCNCamera()
@@ -184,33 +428,97 @@ private struct GamutSceneView: NSViewRepresentable {
             return node
         }()
 
-        func buildScene(profile: GamutMesh?, reference: GamutMesh?) {
+        /// Builds the static scene furniture exactly once — axis
-            guard let scene else { return }
+        /// scaffold, lights, camera home. Layer content lives under
+        /// `layerGroup` and is managed by `syncLayers`.
+        func buildSceneOnce() {
+            guard let scene, scene.rootNode.childNodes.isEmpty else { return }
 
-            // Rebuild from scratch on every mesh change to avoid stale geometry.
-            scene.rootNode.childNodes.forEach { $0.removeFromParentNode() }
             scene.rootNode.addChildNode(axisNode)
-            scene.rootNode.addChildNode(profileNode)
+            scene.rootNode.addChildNode(layerGroup)
-            scene.rootNode.addChildNode(referenceGroup)
             scene.rootNode.addChildNode(cameraNode)
 
             buildAxisScaffold()
-
-            if let profile {
-                profileNode.addChildNode(profileMeshNode(profile, name: "profile"))
-            } else {
-                profileNode.childNodes.forEach { $0.removeFromParentNode() }
-            }
-
-            if let reference {
-                referenceGroup.childNodes.forEach { $0.removeFromParentNode() }
-                referenceGroup.addChildNode(referenceMeshNode(reference))
-            }
-
             addLights(to: scene)
             resetCamera()
         }
 
+        /// Reconciles the node set with `layers` and `visibleIDs`.
+        ///
+        /// New layers get a node; removed layers lose theirs; hidden
+        /// layers keep their mesh (`isHidden` only). Never rebuilds the
+        /// scene, so the camera is untouched by a checkbox toggle.
+        func syncLayers(_ layers: [NamedGamut], visibleIDs: Set<String>) {
+            guard scene != nil else { return }
+            let wanted = Set(layers.map { $0.id })
+            for (id, node) in layerNodes where !wanted.contains(id) {
+                node.removeFromParentNode()
+                layerNodes.removeValue(forKey: id)
+            }
+            for layer in layers {
+                if layerNodes[layer.id] == nil {
+                    let node = makeLayerNode(for: layer)
+                    layerNodes[layer.id] = node
+                    layerGroup.addChildNode(node)
+                }
+                layerNodes[layer.id]?.isHidden = !visibleIDs.contains(layer.id)
+            }
+        }
+
+        private func makeLayerNode(for layer: NamedGamut) -> SCNNode {
+            let node: SCNNode
+            switch layer.role {
+            case .reference:
+                node = referenceMeshNode(layer.mesh)
+            case .profileA:
+                node = profileMeshNode(layer.mesh)
+            case .profileB:
+                node = compareMeshNode(layer.mesh)
+            }
+            node.name = layer.id
+            return node
+        }
+
+        // MARK: - Click inspect (#147)
+
+        /// Click (not drag) hit-tests the scene. `NSClickGestureRecognizer`
+        /// only fires on a press+release in place, so orbit drags are
+        /// untouched.
+        func installClickGesture() {
+            guard let scnView, clickGesture == nil else { return }
+            let gesture = NSClickGestureRecognizer(target: self, action: #selector(handleClick(_:)))
+            scnView.addGestureRecognizer(gesture)
+            clickGesture = gesture
+        }
+
+        @objc private func handleClick(_ gesture: NSClickGestureRecognizer) {
+            guard let scnView else { return }
+            let point = gesture.location(in: scnView)
+            for hit in scnView.hitTest(point, options: nil) {
+                if let layerID = layerID(for: hit.node) {
+                    let world = hit.worldCoordinates
+                    onInspect(
+                        SIMD3<Float>(Float(world.x), Float(world.y), Float(world.z)),
+                        layerID)
+                    return
+                }
+            }
+            // Axis scaffold / empty background → back to idle.
+            onInspect(.zero, nil)
+        }
+
+        /// Walks the hit node's ancestor chain looking for a layer node.
+        private func layerID(for node: SCNNode) -> String? {
+            var current: SCNNode? = node
+            while let node = current {
+                if let name = node.name, layerNodes[name] != nil { return name }
+                current = node.parent
+            }
+            return nil
+        }
+
+        // MARK: - Scene furniture (unchanged from #28)
+
         private func addLights(to scene: SCNScene) {
             let ambient = SCNNode()
             ambient.light = SCNLight()
@@ -351,7 +659,8 @@ private struct GamutSceneView: NSViewRepresentable {
             return SCNNode(geometry: geometry)
         }
 
-        private func profileMeshNode(_ mesh: GamutMesh, name: String) -> SCNNode {
+        /// Profile A: solid vertex-coloured surface.
+        private func profileMeshNode(_ mesh: GamutMesh) -> SCNNode {
             let (geometry, _) = scnGeometry(for: mesh)
 
             let material = SCNMaterial()
@@ -361,11 +670,26 @@ private struct GamutSceneView: NSViewRepresentable {
             material.isDoubleSided = true
             geometry.materials = [material]
 
-            let node = SCNNode(geometry: geometry)
+            return SCNNode(geometry: geometry)
-            node.name = name
-            return node
         }
 
+        /// Compare profile B: same vertex colours at ~30 % opacity so
+        /// overlaps with A and the sRGB reference stay readable.
+        private func compareMeshNode(_ mesh: GamutMesh) -> SCNNode {
+            let (geometry, _) = scnGeometry(for: mesh)
+
+            let material = SCNMaterial()
+            material.lightingModel = .lambert
+            material.diffuse.contents = NSColor.white
+            material.transparency = 0.30
+            material.isDoubleSided = true
+            material.writesToDepthBuffer = false
+            geometry.materials = [material]
+
+            return SCNNode(geometry: geometry)
+        }
+
+        /// Bundled sRGB reference: faint fill + structural edge lines.
         private func referenceMeshNode(_ mesh: GamutMesh) -> SCNNode {
             let (geometry, _) = scnGeometry(for: mesh)
 
@@ -488,3 +812,81 @@ private struct GamutSceneView: NSViewRepresentable {
         }
     }
 }
+
+/// Click-to-sample image view for the TIFF preview sheet (#147).
+///
+/// The TIFF is already decoded to PNG on the host side (#58); the view
+/// reports 8-bit sRGB pixel values at the clicked point — the Lab
+/// conversion is the documented approximate matrix helper, not a CMM.
+private struct TiffSampleImageView: NSViewRepresentable {
+    let pngData: Data
+    var onSample: (Int, Int, Int) -> Void
+
+    func makeNSView(context: Context) -> TiffSampleNSView {
+        let view = TiffSampleNSView()
+        view.image = NSImage(data: pngData)
+        view.onSample = onSample
+        return view
+    }
+
+    func updateNSView(_ nsView: TiffSampleNSView, context: Context) {
+        nsView.onSample = onSample
+    }
+}
+
+private final class TiffSampleNSView: NSView {
+    var image: NSImage? {
+        didSet {
+            bitmapRep = image?.cgImage(forProposedRect: nil, context: nil, hints: nil)
+                .flatMap { NSBitmapImageRep(cgImage: $0) }
+            invalidateIntrinsicContentSize()
+            needsDisplay = true
+        }
+    }
+    var onSample: ((Int, Int, Int) -> Void)?
+    private var bitmapRep: NSBitmapImageRep?
+
+    override var intrinsicContentSize: NSSize {
+        image?.size ?? NSSize(width: 320, height: 240)
+    }
+
+    override var acceptsFirstResponder: Bool { true }
+
+    override func draw(_ dirtyRect: NSRect) {
+        NSColor(red: 0.055, green: 0.055, blue: 0.078, alpha: 1).setFill()
+        dirtyRect.fill()
+        guard let image else { return }
+        image.draw(in: imageRect())
+    }
+
+    override func mouseUp(with event: NSEvent) {
+        guard let rep = bitmapRep else { return }
+        let rect = imageRect()
+        let location = convert(event.locationInWindow, from: nil)
+        guard rect.contains(location), rect.width > 0, rect.height > 0 else { return }
+
+        let x = Int((location.x - rect.minX) / rect.width * CGFloat(rep.pixelsWide))
+        // This view is not flipped: y grows up, bitmap rows grow down.
+        let y = rep.pixelsHigh - 1
+            - Int((location.y - rect.minY) / rect.height * CGFloat(rep.pixelsHigh))
+        guard x >= 0, x < rep.pixelsWide, y >= 0, y < rep.pixelsHigh else { return }
+
+        guard let color = rep.colorAt(x: x, y: y)?.usingColorSpace(.sRGB) else { return }
+        onSample?(
+            Int((color.redComponent * 255).rounded()),
+            Int((color.greenComponent * 255).rounded()),
+            Int((color.blueComponent * 255).rounded()))
+    }
+
+    /// Aspect-fit rect of the image inside `bounds`.
+    private func imageRect() -> NSRect {
+        guard let image, image.size.width > 0, image.size.height > 0 else { return .zero }
+        let scale = min(bounds.width / image.size.width, bounds.height / image.size.height)
+        let size = NSSize(width: image.size.width * scale, height: image.size.height * scale)
+        return NSRect(
+            x: (bounds.width - size.width) / 2,
+            y: (bounds.height - size.height) / 2,
+            width: size.width,
+            height: size.height)
+    }
+}

Sources/ICCery/GamutViewModel.swift

@@ -1,53 +1,303 @@
 import Combine
 import Foundation
 import ICCeryCore
+import simd
 
-/// View model for the native SceneKit gamut viewer.
+/// View model for the native SceneKit gamut viewer (issues #28, #147).
 ///
-/// Loads the bundled `sRGB.gam` reference immediately and, optionally, a
+/// Loads the bundled `sRGB.gam` reference immediately, the workflow's own
-/// printer/profile `.gam` from the current working directory.
+/// profile `.gam` when one exists, and an optional compare mesh the user
+/// adds from the sheet toolbar. `iccgamut` failure is an in-sheet info
+/// notice, never fatal (#24).
 @MainActor
 final class GamutViewModel: ObservableObject {
 
-    /// Parsed reference sRGB gamut mesh.
+    /// Stable layer ids — also the `gamutLayer-<id>` a11y suffixes.
-    @Published var sRGBMesh: GamutMesh?
+    static let srgbLayerID = "sRGB"
+    static let profileLayerID = "profile"
+    static let compareLayerID = "compare"
 
-    /// Parsed printer/profile gamut mesh.
+    /// Loaded meshes: bundled sRGB plus up to two profiles.
-    @Published var profileMesh: GamutMesh?
+    @Published var layers: [NamedGamut] = []
 
-    /// User-facing status line.
+    /// Layer ids currently shown in the scene. Toggling never unloads
+    /// the mesh — the `SCNNode` is hidden only.
+    @Published var visibleIDs: Set<String> = [srgbLayerID]
+
+    /// User-facing status line (`gamutStatusText`). Always non-empty
+    /// once set — `Milestone6GamutUITests` asserts it.
     @Published var status = "Loading gamut…"
 
+    /// In-sheet info line (`gamutNoticeText`). The main `NoticeBanner`
+    /// sits behind the sheet, so notices surface here instead.
+    @Published var noticeText: String?
+
+    /// Set when `SCNView` cannot create a render context; the scene is
+    /// replaced by the docs/18 fallback text (`gamutViewerUnavailable`).
+    @Published var viewerUnavailable = false
+
     /// Closure injected into the SceneKit view to request a camera reset.
     @Published var resetCamera: () -> Void = {}
 
-    private let profileGamURL: URL?
+    // MARK: - Inspect panel
 
-    init(profileGamURL: URL? = nil) {
+    /// Lab point currently inspected, or `nil` for the idle state.
+    @Published var inspectLab: LabColor?
+
+    /// Swatch colour: the hit vertex's `rgb`, or the approximate sRGB of
+    /// the inspected Lab.
+    @Published var inspectSwatch: DisplayRGB?
+
+    /// `true` when the swatch/Lab came from the approximate helper or a
+    /// typed value — drives the "approx. Lab, not ColorSync" caption.
+    @Published var inspectIsApproximate = false
+
+    /// Per-layer containment for `inspectLab`, in layer order.
+    @Published var inspectResults: [(id: String, name: String, containment: GamutContainment)] = []
+
+    /// Manual Lab entry fields (`gamutLabEntry*`).
+    @Published var labEntryL = ""
+    @Published var labEntryA = ""
+    @Published var labEntryB = ""
+
+    // MARK: - TIFF sampling
+
+    /// PNG bytes for the preview sheet (`gamutTiffPreview`).
+    @Published var tiffPreviewPNG: Data?
+    @Published var showingTiffPreview = false
+
+    private let environment: AppEnvironment
+    private let profileGamURL: URL?
+    private let fileDialogs = FileDialogService.shared
+
+    init(environment: AppEnvironment, profileGamURL: URL? = nil) {
+        self.environment = environment
         self.profileGamURL = profileGamURL
-        Task { await load() }
+        loadTask = Task { await load() }
     }
 
+    private var loadTask: Task<Void, Never>?
+
+    /// Awaits the initial sRGB/profile load — used by tests.
+    func awaitInitialLoad() async {
+        await loadTask?.value
+    }
+
+    func layer(id: String) -> NamedGamut? {
+        layers.first { $0.id == id }
+    }
+
+    // MARK: - Initial load
+
     private func load() async {
         do {
-            let referenceURL = BinaryResolver().referenceGamut("sRGB")
+            let referenceURL = environment.runner.binaryResolver.referenceGamut("sRGB")
             let reference = try await parse(url: referenceURL)
-            sRGBMesh = reference
+            layers.append(NamedGamut(
-
+                id: Self.srgbLayerID,
-            if let profileGamURL {
+                displayName: "sRGB",
-                let profile = try await parse(url: profileGamURL)
+                role: .reference,
-                profileMesh = profile
+                mesh: reference,
-                status = "Profile gamut (\(profile.faces.count) faces) vs sRGB reference"
+                sourceURL: referenceURL))
-            } else {
+            visibleIDs.insert(Self.srgbLayerID)
-                status = "sRGB reference gamut (\(reference.faces.count) faces)"
-            }
         } catch {
             status = "Could not load gamut: \(error.localizedDescription)"
+            return
+        }
+
+        if let profileGamURL {
+            do {
+                let profile = try await parse(url: profileGamURL)
+                layers.append(NamedGamut(
+                    id: Self.profileLayerID,
+                    displayName: profileGamURL.deletingPathExtension().lastPathComponent,
+                    role: .profileA,
+                    mesh: profile,
+                    sourceURL: profileGamURL))
+                visibleIDs.insert(Self.profileLayerID)
+            } catch {
+                // #24 — a missing/unparseable profile mesh is info, not fatal.
+                noticeText = "Profile gamut could not be loaded: \(error.localizedDescription)"
+            }
+        }
+        refreshStatus()
+    }
+
+    // MARK: - Compare slot (profile B)
+
+    /// `btnGamutOpenGam` — pick an existing `.gam` for the compare slot.
+    func openCompareGam() {
+        let url = UITestHooks.isEnabled
+            ? UITestHooks.gamutFileURL
+            : fileDialogs.selectGamutFile()
+        guard let url else { return }
+        Task { await loadCompareGam(url: url) }
+    }
+
+    /// `btnGamutOpenProfile` — pick `.icc/.icm`; uses a sibling `.gam`
+    /// when present, otherwise runs bundled `iccgamut -v -d 10` (#24).
+    func openCompareProfile() {
+        let url = UITestHooks.isEnabled
+            ? UITestHooks.gamutProfileURL
+            : fileDialogs.selectProfileFile()
+        guard let url else { return }
+        Task { await loadCompareProfile(url: url) }
+    }
+
+    /// `btnGamutRemoveCompare` — drops layer B, leaves sRGB + A.
+    func removeCompare() {
+        layers.removeAll { $0.id == Self.compareLayerID }
+        visibleIDs.remove(Self.compareLayerID)
+        refreshStatus()
+    }
+
+    /// Parses `url` into the compare slot. Internal for tests — the UI
+    /// reaches it through `openCompareGam` / `openCompareProfile`.
+    func loadCompareGam(url: URL) async {
+        do {
+            let mesh = try await parse(url: url)
+            installCompare(NamedGamut(
+                id: Self.compareLayerID,
+                displayName: url.deletingPathExtension().lastPathComponent,
+                role: .profileB,
+                mesh: mesh,
+                sourceURL: url))
+        } catch {
+            noticeText = "Could not load compare gamut: \(error.localizedDescription)"
         }
     }
 
-    /// Parses a `.gam` file off the main actor so large meshes do not stall
+    /// `.icc/.icm` → sibling `.gam` or `iccgamut` → compare slot.
-    /// the UI.
+    /// Internal for tests.
+    func loadCompareProfile(url: URL) async {
+        let gamURL = url.deletingPathExtension().appendingPathExtension("gam")
+        do {
+            if !FileManager.default.fileExists(atPath: gamURL.path) {
+                _ = try await environment.runner.runIccgamut(
+                    config: IccgamutConfig(profileURL: url))
+            }
+            await loadCompareGam(url: gamURL)
+        } catch {
+            noticeText = "Gamut extraction failed: \(error.localizedDescription)"
+        }
+    }
+
+    /// A third profile replaces B — the compare slot never stacks and
+    /// sRGB is never touched.
+    private func installCompare(_ gamut: NamedGamut) {
+        if layers.contains(where: { $0.id == gamut.id }) {
+            noticeText = "Compare slot holds one profile. The previous compare mesh was replaced."
+        }
+        layers.removeAll { $0.id == gamut.id }
+        layers.append(gamut)
+        visibleIDs.insert(gamut.id)
+        refreshStatus()
+    }
+
+    // MARK: - Status line
+
+    /// `sRGB 448v / 892 faces · Profile 1024v / 2048 faces · vol 62% of sRGB`.
+    /// Unloaded layers are omitted; the volume clause appears only when
+    /// both volumes are finite and positive.
+    private func refreshStatus() {
+        var clauses = layers.map {
+            "\($0.displayName) \($0.mesh.vertices.count)v / \($0.mesh.faces.count) faces"
+        }
+        if let srgb = layer(id: Self.srgbLayerID),
+           let profile = layer(id: Self.profileLayerID) {
+            let srgbVolume = GamutGeometry.volume(of: srgb.mesh)
+            let profileVolume = GamutGeometry.volume(of: profile.mesh)
+            if srgbVolume.isFinite, srgbVolume > 0,
+               profileVolume.isFinite, profileVolume > 0 {
+                clauses.append("vol \(Int((profileVolume / srgbVolume * 100).rounded()))% of sRGB")
+            }
+        }
+        status = clauses.isEmpty ? "No gamut loaded" : clauses.joined(separator: " · ")
+    }
+
+    // MARK: - Inspect
+
+    /// Whether every manual Lab field parses as a number; the Inspect
+    /// button is disabled while this is false.
+    var canInspectLab: Bool {
+        [labEntryL, labEntryA, labEntryB].allSatisfy { Double($0) != nil }
+    }
+
+    /// Runs containment for a Lab point and publishes the inspect row.
+    func inspect(lab: LabColor, swatch: DisplayRGB?, isApproximate: Bool) {
+        inspectLab = lab
+        inspectSwatch = swatch ?? LabColorMath.labToSRGB(lab)
+        inspectIsApproximate = isApproximate
+        inspectResults = layers.map {
+            ($0.id, $0.displayName, GamutGeometry.containment(of: lab, in: $0.mesh))
+        }
+    }
+
+    /// Click on the axis scaffold or empty background returns the panel
+    /// to idle.
+    func clearInspect() {
+        inspectLab = nil
+        inspectSwatch = nil
+        inspectIsApproximate = false
+        inspectResults = []
+    }
+
+    /// SceneKit hit callback: world `(x, y, z)` → Lab `(x→a*, y→L*, z→b*)`.
+    /// The swatch is the nearest vertex colour of the hit layer's mesh.
+    func inspectSceneHit(world: SIMD3<Float>, layerID: String) {
+        let lab = LabColor(l: Double(world.y), a: Double(world.x), b: Double(world.z))
+        var swatch: DisplayRGB?
+        var approximate = true
+        if let mesh = layer(id: layerID)?.mesh,
+           let nearest = mesh.vertices.min(by: {
+               simd_distance($0.position, world) < simd_distance($1.position, world)
+           }) {
+            swatch = nearest.rgb
+            approximate = false
+        }
+        inspect(lab: lab, swatch: swatch, isApproximate: approximate)
+    }
+
+    /// `btnGamutInspectLab` — typed L*a*b* path. No clamping; out-of-axis
+    /// values still run containment and report `?` outside every hull.
+    func inspectEnteredLab() {
+        guard let l = Double(labEntryL),
+              let a = Double(labEntryA),
+              let b = Double(labEntryB) else { return }
+        inspect(lab: LabColor(l: l, a: a, b: b), swatch: nil, isApproximate: true)
+    }
+
+    // MARK: - TIFF sampling
+
+    /// `btnGamutSampleTiff` — pick a target TIFF, decode a host-side PNG
+    /// preview (#58), and open the click-to-sample sheet.
+    func openTiffSample() {
+        let url = UITestHooks.isEnabled
+            ? UITestHooks.gamutTiffURL
+            : fileDialogs.selectTiffFile()
+        guard let url else { return }
+        guard let png = TiffPreview.previewPNG(tiff: url) else {
+            noticeText = "Could not decode TIFF preview."
+            return
+        }
+        tiffPreviewPNG = png
+        showingTiffPreview = true
+    }
+
+    /// Pixel tap inside the preview sheet: sRGB8 → approximate Lab D50.
+    func sampleTiffPixel(r: Int, g: Int, b: Int) {
+        inspect(
+            lab: ApproximateLab.srgb8ToLab(r: r, g: g, b: b),
+            swatch: DisplayRGB(
+                r: Double(r) / 255.0,
+                g: Double(g) / 255.0,
+                b: Double(b) / 255.0),
+            isApproximate: true)
+        showingTiffPreview = false
+    }
+
+    /// Parses a `.gam` file off the main actor so large meshes do not
+    /// stall the UI.
     private func parse(url: URL) async throws -> GamutMesh {
         try await Task.detached {
             try GamutMeshParser.parse(url: url)

Sources/ICCery/RootView.swift

@@ -82,7 +82,10 @@ struct RootView: View {
             get: { workflow.wizard.showingGamutViewer },
             set: { workflow.wizard.showingGamutViewer = $0 }
         )) {
-            GamutView(profileGamURL: workflow.wizard.gamutProfileURL)
+            GamutView(
+                environment: workflow.environment,
+                profileGamURL: workflow.wizard.gamutProfileURL,
+                showingAllHelp: $showingAllHelp)
         }
     }
 

Sources/ICCery/SidebarView.swift

@@ -160,6 +160,9 @@ struct SidebarView: View {
                     .frame(maxWidth: .infinity)
             }
             .controlSize(.large)
+            .helpOverlay(
+                "View the profile gamut in 3D against sRGB.",
+                showing: $showingAllHelp)
             .accessibilityIdentifier("btnViewGamut")
             .padding(.horizontal, 12)
 

Tests/ICCeryCoreTests/ApproximateLabTests.swift

@@ -0,0 +1,39 @@
+import Foundation
+import XCTest
+@testable import ICCeryCore
+
+/// ``ApproximateLab`` sanity tests (issue #147).
+///
+/// These are loose sanity checks on a fixed-matrix approximation — not
+/// ColorSync goldens.
+final class ApproximateLabTests: XCTestCase {
+
+    func testWhiteMapsToHighLStar() {
+        let lab = ApproximateLab.srgb8ToLab(r: 255, g: 255, b: 255)
+        XCTAssertGreaterThan(lab.l, 95)
+        XCTAssertEqual(lab.a, 0, accuracy: 2)
+        XCTAssertEqual(lab.b, 0, accuracy: 2)
+    }
+
+    func testBlackMapsToZeroLStar() {
+        let lab = ApproximateLab.srgb8ToLab(r: 0, g: 0, b: 0)
+        XCTAssertEqual(lab.l, 0, accuracy: 1)
+    }
+
+    func testPureRedIsChromatic() {
+        let lab = ApproximateLab.srgb8ToLab(r: 255, g: 0, b: 0)
+        // sRGB red ≈ Lab D50 (54, 81, 70) — loose bounds only.
+        XCTAssertGreaterThan(lab.l, 40)
+        XCTAssertLessThan(lab.l, 65)
+        XCTAssertGreaterThan(lab.a, 60)
+        XCTAssertGreaterThan(lab.b, 40)
+    }
+
+    func testMidGreyIsNeutral() {
+        let lab = ApproximateLab.srgb8ToLab(r: 128, g: 128, b: 128)
+        XCTAssertGreaterThan(lab.l, 45)
+        XCTAssertLessThan(lab.l, 65)
+        XCTAssertEqual(lab.a, 0, accuracy: 1)
+        XCTAssertEqual(lab.b, 0, accuracy: 1)
+    }
+}

Tests/ICCeryCoreTests/GamutContainmentTests.swift

@@ -0,0 +1,85 @@
+import Foundation
+import XCTest
+@testable import ICCeryCore
+
+/// ``GamutGeometry`` containment and volume goldens on the bundled
+/// `sRGB.gam` reference mesh (issue #147). No GPU involved.
+final class GamutContainmentTests: XCTestCase {
+
+    /// Returns the bundled real `sRGB.gam` in `Resources/Argyll/reference_gamuts`.
+    private var bundledSRGBGamURL: URL {
+        let bundle = Bundle.main
+        let resource = bundle.resourceURL ?? bundle.bundleURL
+        return resource.appendingPathComponent("Argyll/reference_gamuts/sRGB.gam")
+    }
+
+    private func loadSRGB() throws -> GamutMesh {
+        try GamutMeshParser.parse(url: bundledSRGBGamURL)
+    }
+
+    func testNeutralMidGreyIsInsideSRGB() throws {
+        let mesh = try loadSRGB()
+        XCTAssertEqual(
+            GamutGeometry.containment(of: LabColor(l: 50, a: 0, b: 0), in: mesh),
+            .inside)
+    }
+
+    func testSaturatedColourIsOutsideSRGB() throws {
+        let mesh = try loadSRGB()
+        XCTAssertEqual(
+            GamutGeometry.containment(of: LabColor(l: 50, a: 80, b: 80), in: mesh),
+            .outside)
+    }
+
+    func testVolumeIsFiniteAndPositiveOnBundledSRGB() throws {
+        let mesh = try loadSRGB()
+        let volume = GamutGeometry.volume(of: mesh)
+        XCTAssertTrue(volume.isFinite)
+        XCTAssertGreaterThan(volume, 0)
+    }
+
+    func testVertexOnlyMeshReportsUnknown() {
+        let mesh = GamutMesh(
+            vertices: [
+                GamutVertex(lab: LabColor(l: 50, a: 0, b: 0), rgb: DisplayRGB(r: 0.5, g: 0.5, b: 0.5)),
+            ],
+            faces: [])
+        XCTAssertEqual(
+            GamutGeometry.containment(of: LabColor(l: 50, a: 0, b: 0), in: mesh),
+            .unknown)
+        XCTAssertEqual(GamutGeometry.volume(of: mesh), 0)
+    }
+
+    func testKnownCubeFixture() throws {
+        // Unit cube centred at Lab (50, 0, 0): a*,b* ∈ ±10, L* ∈ 40...60.
+        // Two triangles per face, outward winding.
+        let lab = { (l: Double, a: Double, b: Double) in
+            GamutVertex(lab: LabColor(l: l, a: a, b: b), rgb: DisplayRGB(r: 0, g: 0, b: 0))
+        }
+        // Corners in (a, L, b) space.
+        let c = [
+            lab(40, -10, -10), lab(40, 10, -10), lab(40, 10, 10), lab(40, -10, 10),  // bottom
+            lab(60, -10, -10), lab(60, 10, -10), lab(60, 10, 10), lab(60, -10, 10),  // top
+        ]
+        let quad = { (a: UInt32, b: UInt32, c: UInt32, d: UInt32) in
+            [GamutTriangle(a: a, b: b, c: c), GamutTriangle(a: a, b: c, c: d)]
+        }
+        var faces: [GamutTriangle] = []
+        faces += quad(0, 3, 2, 1)  // bottom (y=40)
+        faces += quad(4, 5, 6, 7)  // top (y=60)
+        faces += quad(0, 1, 5, 4)  // z=-10
+        faces += quad(3, 7, 6, 2)  // z=+10
+        faces += quad(1, 2, 6, 5)  // x=+10
+        faces += quad(0, 4, 7, 3)  // x=-10
+        let mesh = GamutMesh(vertices: c, faces: faces)
+
+        XCTAssertEqual(
+            GamutGeometry.containment(of: LabColor(l: 50, a: 0, b: 0), in: mesh),
+            .inside)
+        XCTAssertEqual(
+            GamutGeometry.containment(of: LabColor(l: 50, a: 20, b: 0), in: mesh),
+            .outside)
+        // 20 × 20 × 20 Lab-cube.
+        XCTAssertEqual(GamutGeometry.volume(of: mesh), 8000, accuracy: 1)
+    }
+}

Tests/ICCeryCoreTests/GamutViewModelTests.swift

@@ -0,0 +1,127 @@
+import Foundation
+import XCTest
+@testable import ICCeryCore
+@testable import ICCery
+
+/// Issue #147 — `GamutViewModel` compare-slot behaviour: failed or
+/// missing compare meshes are info, never fatal (#24); sRGB always stays.
+@MainActor
+final class GamutViewModelTests: XCTestCase {
+
+    /// Bundled root that has `reference_gamuts/sRGB.gam` but **no** tool
+    /// binaries, so `iccgamut` spawns deterministically fail.
+    private func bundledRootWithoutTools() throws -> URL {
+        let root = FileManager.default.temporaryDirectory
+            .appendingPathComponent("iccery-gamut-vm-\(UUID().uuidString)")
+        let gamutDir = root.appendingPathComponent("reference_gamuts")
+        try FileManager.default.createDirectory(
+            at: gamutDir, withIntermediateDirectories: true)
+        let bundle = Bundle.main.resourceURL ?? Bundle.main.bundleURL
+        try FileManager.default.copyItem(
+            at: bundle.appendingPathComponent("Argyll/reference_gamuts/sRGB.gam"),
+            to: gamutDir.appendingPathComponent("sRGB.gam"))
+        return root
+    }
+
+    private func makeViewModel(root: URL? = nil) throws -> GamutViewModel {
+        let env = try TestAppEnvironment.make(bundledArgyllRoot: root)
+        return GamutViewModel(environment: env.environment)
+    }
+
+    func testInitialLoadHasSRGBAndFacesStatus() async throws {
+        let vm = try makeViewModel()
+        await vm.awaitInitialLoad()
+
+        XCTAssertNotNil(vm.layer(id: GamutViewModel.srgbLayerID))
+        XCTAssertTrue(vm.status.contains("faces"), "status: \(vm.status)")
+    }
+
+    func testMissingCompareGamLeavesSRGBAndSetsNotice() async throws {
+        let vm = try makeViewModel()
+        await vm.awaitInitialLoad()
+
+        await vm.loadCompareGam(
+            url: URL(fileURLWithPath: "/nonexistent/compare.gam"))
+
+        XCTAssertNotNil(vm.layer(id: GamutViewModel.srgbLayerID))
+        XCTAssertNil(vm.layer(id: GamutViewModel.compareLayerID))
+        XCTAssertNotNil(vm.noticeText)
+    }
+
+    func testFailedIccgamutLeavesSRGBAndSetsNotice() async throws {
+        // bundledRootWithoutTools has no macos-universal/iccgamut.
+        let vm = try makeViewModel(root: bundledRootWithoutTools())
+        await vm.awaitInitialLoad()
+        XCTAssertNotNil(vm.layer(id: GamutViewModel.srgbLayerID))
+
+        let profile = FileManager.default.temporaryDirectory
+            .appendingPathComponent("iccery-gamut-icc-\(UUID().uuidString).icc")
+        try Data("MOCK_ICC".utf8).write(to: profile)
+        defer { try? FileManager.default.removeItem(at: profile) }
+
+        await vm.loadCompareProfile(url: profile)
+
+        XCTAssertNotNil(vm.layer(id: GamutViewModel.srgbLayerID))
+        XCTAssertNil(vm.layer(id: GamutViewModel.compareLayerID))
+        XCTAssertNotNil(vm.noticeText)
+    }
+
+    func testThirdProfileReplacesCompareSlot() async throws {
+        let vm = try makeViewModel()
+        await vm.awaitInitialLoad()
+
+        let bundle = Bundle.main.resourceURL ?? Bundle.main.bundleURL
+        let srgb = bundle.appendingPathComponent("Argyll/reference_gamuts/sRGB.gam")
+        let dir = FileManager.default.temporaryDirectory
+            .appendingPathComponent("iccery-gamut-cmp-\(UUID().uuidString)")
+        try FileManager.default.createDirectory(
+            at: dir, withIntermediateDirectories: true)
+        let first = dir.appendingPathComponent("first.gam")
+        let second = dir.appendingPathComponent("second.gam")
+        try FileManager.default.copyItem(at: srgb, to: first)
+        try FileManager.default.copyItem(at: srgb, to: second)
+        defer { try? FileManager.default.removeItem(at: dir) }
+
+        await vm.loadCompareGam(url: first)
+        XCTAssertNil(vm.noticeText)
+        XCTAssertEqual(vm.layer(id: GamutViewModel.compareLayerID)?.displayName, "first")
+
+        await vm.loadCompareGam(url: second)
+        XCTAssertEqual(vm.layer(id: GamutViewModel.compareLayerID)?.displayName, "second")
+        XCTAssertEqual(
+            vm.layers.filter { $0.role == .profileB }.count, 1,
+            "compare slot holds one profile")
+        XCTAssertNotNil(vm.noticeText)
+        XCTAssertNotNil(vm.layer(id: GamutViewModel.srgbLayerID))
+    }
+
+    func testRemoveCompareLeavesSRGB() async throws {
+        let vm = try makeViewModel()
+        await vm.awaitInitialLoad()
+
+        let bundle = Bundle.main.resourceURL ?? Bundle.main.bundleURL
+        await vm.loadCompareGam(
+            url: bundle.appendingPathComponent("Argyll/reference_gamuts/sRGB.gam"))
+        XCTAssertNotNil(vm.layer(id: GamutViewModel.compareLayerID))
+
+        vm.removeCompare()
+        XCTAssertNil(vm.layer(id: GamutViewModel.compareLayerID))
+        XCTAssertNotNil(vm.layer(id: GamutViewModel.srgbLayerID))
+    }
+
+    func testInspectLabRunsContainmentPerLayer() async throws {
+        let vm = try makeViewModel()
+        await vm.awaitInitialLoad()
+
+        vm.labEntryL = "50"
+        vm.labEntryA = "0"
+        vm.labEntryB = "0"
+        XCTAssertTrue(vm.canInspectLab)
+        vm.inspectEnteredLab()
+
+        let srgb = vm.inspectResults.first { $0.id == GamutViewModel.srgbLayerID }
+        XCTAssertEqual(srgb?.containment, .inside)
+        XCTAssertTrue(vm.inspectIsApproximate)
+        XCTAssertNotNil(vm.inspectSwatch)
+    }
+}

Tests/ICCeryUITests/Milestone10GamutCompareUITests.swift

@@ -0,0 +1,186 @@
+import Foundation
+import XCTest
+
+/// Milestone 10 — Issue #147 gamut compare chrome tests.
+///
+/// Sheet-opened only: no GPU hit-test assertions (no reliable SceneKit
+/// click on the runner). Containment itself is covered by
+/// `GamutContainmentTests`.
+@MainActor
+final class Milestone10GamutCompareUITests: XCTestCase {
+
+    private var app: XCUIApplication!
+    private var testRoot: URL!
+    private var binDir: URL!
+    private var workDir: URL!
+    private var appDataDir: URL!
+    private var referenceGamutURL: URL!
+
+    override func setUp() async throws {
+        continueAfterFailure = false
+        testRoot = FileManager.default.temporaryDirectory
+            .appendingPathComponent("iccery-ui-m10-gamut-\(UUID().uuidString)")
+        binDir = URL(fileURLWithPath: #filePath)
+            .deletingLastPathComponent()
+            .appendingPathComponent("Fixtures/bin")
+        workDir = testRoot.appendingPathComponent("work")
+        appDataDir = testRoot.appendingPathComponent("AppData")
+        referenceGamutURL = URL(fileURLWithPath: #filePath)
+            .deletingLastPathComponent()
+            .deletingLastPathComponent()
+            .deletingLastPathComponent()
+            .appendingPathComponent("Resources/Argyll/reference_gamuts/sRGB.gam")
+
+        try FileManager.default.createDirectory(
+            at: workDir, withIntermediateDirectories: true)
+        try FileManager.default.createDirectory(
+            at: appDataDir, withIntermediateDirectories: true)
+
+        app = XCUIApplication()
+        app.launchEnvironment = [
+            "ICCERY_UI_TESTING": "1",
+            "ICCERY_TEST_ROOT": testRoot.path,
+            "ICCERY_ARGYLL_BINARY_DIR": binDir.path,
+            "ICCERY_TEST_WORKDIR": workDir.path,
+        ]
+    }
+
+    override func tearDown() async throws {
+        app?.terminate()
+        app = nil
+        if let testRoot {
+            try? FileManager.default.removeItem(at: testRoot)
+        }
+        testRoot = nil
+    }
+
+    private func element(_ id: String) -> XCUIElement {
+        let inApp = app.descendants(matching: .any)[id].firstMatch
+        if inApp.exists { return inApp }
+        let inSheet = app.sheets.firstMatch.descendants(matching: .any)[id].firstMatch
+        if inSheet.exists { return inSheet }
+        // Menu popup items live outside the window hierarchy.
+        return app.menuItems[id].firstMatch
+    }
+
+    private func waitFor(_ id: String, timeout: TimeInterval = 15) -> XCUIElement {
+        let deadline = Date().addingTimeInterval(timeout)
+        while Date() < deadline {
+            let el = element(id)
+            if el.exists { return el }
+            RunLoop.current.run(until: Date().addingTimeInterval(0.1))
+        }
+        let el = element(id)
+        XCTAssertTrue(el.exists, "Expected element \(id)")
+        return el
+    }
+
+    private func launchApp() {
+        app.launch()
+        if !app.wait(for: .runningForeground, timeout: 10) {
+            app.activate()
+        }
+    }
+
+    private func openGamutSheet() {
+        launchApp()
+        waitFor("btnViewGamut").click()
+        _ = waitFor("gamutView")
+    }
+
+    func testLayerTogglesExistWithSRGB() throws {
+        openGamutSheet()
+
+        let srgb = waitFor("gamutLayer-sRGB")
+        XCTAssertTrue(srgb.exists)
+        XCTAssertTrue(srgb.isEnabled)
+        // NSButton checkbox value is 1 when checked.
+        XCTAssertEqual(srgb.value as? Int, 1, "sRGB layer should be on")
+
+        let compare = waitFor("gamutLayer-compare")
+        XCTAssertTrue(compare.exists)
+        XCTAssertFalse(compare.isEnabled, "Compare toggle must be disabled before a load")
+    }
+
+    func testAddCompareButtonExists() throws {
+        openGamutSheet()
+
+        waitFor("btnGamutAddCompare").click()
+        // No ICCERY_TEST_GAMUT_FILE set → the stubbed picker cancels;
+        // the sRGB status must stay non-empty.
+        waitFor("btnGamutOpenGam").click()
+
+        let status = waitFor("gamutStatusText")
+        let value = status.value as? String ?? ""
+        XCTAssertTrue(value.contains("sRGB"), "Status should keep the sRGB clause, got: \(value)")
+    }
+
+    func testCompareGamLoadEnablesToggle() throws {
+        let compareURL = workDir.appendingPathComponent("compare.gam")
+        try FileManager.default.copyItem(at: referenceGamutURL, to: compareURL)
+        app.launchEnvironment["ICCERY_TEST_GAMUT_FILE"] = compareURL.path
+
+        openGamutSheet()
+        waitFor("btnGamutAddCompare").click()
+        waitFor("btnGamutOpenGam").click()
+
+        let compare = waitFor("gamutLayer-compare")
+        XCTAssertTrue(compare.isEnabled, "Compare toggle should enable after load")
+
+        let status = waitFor("gamutStatusText")
+        let value = status.value as? String ?? ""
+        XCTAssertTrue(value.contains("compare"), "Status should list the compare layer, got: \(value)")
+
+        let remove = waitFor("btnGamutRemoveCompare")
+        XCTAssertTrue(remove.isEnabled)
+    }
+
+    func testOpenProfileRunsIccgamutForCompare() throws {
+        // A profile with no sibling .gam → the mock iccgamut writes one.
+        let profileURL = workDir.appendingPathComponent("myprinter.icc")
+        try Data("MOCK_ICC".utf8).write(to: profileURL)
+        app.launchEnvironment["ICCERY_TEST_GAMUT_PROFILE"] = profileURL.path
+        app.launchEnvironment["ICCERY_MOCK_GAMUT_SOURCE"] = referenceGamutURL.path
+
+        openGamutSheet()
+        waitFor("btnGamutAddCompare").click()
+        waitFor("btnGamutOpenProfile").click()
+
+        let compare = waitFor("gamutLayer-compare")
+        XCTAssertTrue(compare.isEnabled, "Compare toggle should enable after iccgamut")
+    }
+
+    func testInspectPanelIdleStableHeight() throws {
+        openGamutSheet()
+
+        let panel = waitFor("gamutInspectPanel")
+        XCTAssertTrue(panel.exists)
+        XCTAssertTrue(element("gamutInspectIdle").exists)
+        XCTAssertTrue(element("gamutStatusText").exists)
+    }
+
+    func testManualLabInspectShowsContainment() throws {
+        openGamutSheet()
+
+        waitFor("gamutLabEntryL").click()
+        element("gamutLabEntryL").typeText("50")
+        element("gamutLabEntryA").click()
+        element("gamutLabEntryA").typeText("0")
+        element("gamutLabEntryB").click()
+        element("gamutLabEntryB").typeText("0")
+
+        waitFor("btnGamutInspectLab").click()
+
+        let inside = waitFor("gamutInspect-sRGB")
+        let value = inside.value as? String ?? inside.label
+        XCTAssertTrue(value.contains("in"), "Lab(50,0,0) should be inside sRGB, got: \(value)")
+        XCTAssertTrue(element("gamutInspectL").exists)
+        XCTAssertTrue(element("gamutInspectSwatch").exists)
+    }
+
+    func testResetIdentifierUnchanged() throws {
+        openGamutSheet()
+        let reset = waitFor("btnResetGamutCamera")
+        XCTAssertTrue(reset.isEnabled)
+    }
+}

docs/18-gamut-viewer.md

@@ -827,3 +827,35 @@ HTML ids that `_wireToggles` hard-codes: `chkProfileGamut`, `chkSrgbReference`,
 | #185 axes / EdgesGeometry / vertex colour / legend | All present (GridHelper kept; CSS2D parent-visibility bug). |
 | #212 Node test crash | Polyfill + dynamic import + `typeof window` guard. |
 | #225 Monterey WebGL | Lazy ensure, feature-detect, pause rAF, context-lost, low-power flags. |
+| #147 compare + inspect | macOS native: layer toggles (`gamutLayer-*`), compare slot (one extra profile or `.gam`), click/typed-Lab containment, TIFF pixel sample. |
+
+---
+
+## 13. macOS rewrite notes (#28, #147)
+
+The native viewer (`Sources/ICCery/GamutView.swift` + `GamutViewModel`) keeps
+the v1 contract points that matter — `(a*, L*, b*)` axes, camera home
+(180,120,180) lookAt (0,50,0), R resets via a local `NSEvent` monitor, native
+faces only — and adds the compare/inspect layer model:
+
+- **Layers.** `NamedGamut` (reference / profileA / profileB). sRGB cannot be
+  removed, only hidden. The compare slot holds exactly one profile; picking a
+  third replaces it and posts `gamutNoticeText`.
+- **Toggles hide, not unload.** `visibleIDs` maps to `SCNNode.isHidden`; the
+  scene is built once and a checkbox never resets the camera.
+- **Containment.** `GamutGeometry.containment` ray-casts the face table
+  (`GamutVertex.position` space) with off-axis retries on edge hits; no faces
+  → `.unknown`. `GamutGeometry.volume` sums signed tetrahedra from the vertex
+  centroid (Lab-cubic); the `vol % of sRGB` clause only prints when both
+  volumes are finite and > 0.
+- **Inspect.** Click a mesh (hit-test in the `SCNView` coordinator on
+  mouse-up, never a ZStack tap gesture), type Lab, or sample a TIFF pixel.
+  Per-layer in/out/? + swatch; `gamutInspectApprox` marks samples that went
+  through `ApproximateLab` (fixed-matrix sRGB→Lab D50, **not** ColorSync, no
+  CMM).
+- **Fallback.** No GPU → `gamutViewerUnavailable` text replaces the scene;
+  layer toggles stay visible but disabled; the representable is never
+  respawned in a loop.
+- **iccgamut** still runs only as the bundled sidecar, `-v -d {density}`
+  (density 10 = surface density, not a directory). Failure is an in-sheet
+  info notice — sRGB + profile A stay loaded (#24).