feat: Add image comparison modes for diff view

macgit/Models/ImageComparisonMode.swift

@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+import Foundation
+
+nonisolated enum ImageComparisonMode: String, CaseIterable, Identifiable {
+    case sideBySide
+    case overlay
+    var id: String { rawValue }
+    var title: String { self == .overlay ? "Overlay Slider" : "Side by Side" }
+    var icon: String { self == .overlay ? "slider.horizontal.below.rectangle" : "rectangle.split.2x1" }
+}

macgit/Models/ImageComparisonRequest.swift

@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+import Foundation
+
+nonisolated struct ImageComparisonRequest: Hashable, Sendable {
+    enum Source: Hashable, Sendable {
+        case revision(String, String)
+        case index(String)
+        case indexWithFallback(String, String)
+        case disk(String)
+    }
+    let before: Source?
+    let after: Source?
+
+    static func working(_ file: StatusFile, staged: Bool) -> Self {
+        Self(before: file.status == .untracked || file.status == .added ? nil :
+                (staged ? .revision("HEAD", file.originalPath ?? file.path) :
+                    (file.status == .renamed ? .indexWithFallback(file.path, file.originalPath ?? file.path) : .index(file.path))),
+             after: file.status == .deleted ? nil : (staged ? .index(file.path) : .disk(file.path)))
+    }
+
+    static func commit(path: String, oldPath: String?, status: CommitFileStatus?, ref: String) -> Self {
+        Self(before: status == .added ? nil : .revision("\(ref)^1", oldPath ?? path),
+             after: status == .deleted ? nil : .revision(ref, path))
+    }
+}

macgit/Resources/AppIcon.icon/icon.json

@@ -0,0 +1,67 @@
+{
+  "fill" : {
+    "automatic-gradient" : "extended-srgb:0.00000,0.53333,1.00000,1.00000"
+  },
+  "groups" : [
+    {
+      "layers" : [
+        {
+          "fill" : {
+            "linear-gradient" : [
+              "extended-srgb:1.00000,0.21961,0.23529,1.00000",
+              "extended-srgb:1.00000,0.55294,0.15686,1.00000"
+            ],
+            "orientation" : {
+              "start" : {
+                "x" : 0.5,
+                "y" : 0
+              },
+              "stop" : {
+                "x" : 0.5,
+                "y" : 0.7
+              }
+            }
+          },
+          "glass" : true,
+          "image-name" : "Branch (1).png",
+          "name" : "Branch (1)",
+          "position" : {
+            "scale" : 1.62,
+            "translation-in-points" : [
+              95.921875,
+              -75.0703125
+            ]
+          }
+        },
+        {
+          "blend-mode" : "lighten",
+          "fill" : "automatic",
+          "glass" : true,
+          "image-name" : "Commit (1).png",
+          "name" : "Commit (1)",
+          "position" : {
+            "scale" : 1.35,
+            "translation-in-points" : [
+              -108.4921875,
+              0
+            ]
+          }
+        }
+      ],
+      "shadow" : {
+        "kind" : "neutral",
+        "opacity" : 0.5
+      },
+      "translucency" : {
+        "enabled" : true,
+        "value" : 0.5
+      }
+    }
+  ],
+  "supported-platforms" : {
+    "circles" : [
+      "watchOS"
+    ],
+    "squares" : "shared"
+  }
+}

macgit/Resources/Assets.xcassets/commitplus-logo.imageset/Contents.json

@@ -3,6 +3,16 @@
     {
       "filename": "logo.png",
       "idiom": "universal"
+    },
+    {
+      "filename": "logo-dark.png",
+      "idiom": "universal",
+      "appearances": [
+        {
+          "appearance": "luminosity",
+          "value": "dark"
+        }
+      ]
     }
   ],
   "info": {

macgit/Services/GitStatusService+ImageComparison.swift

@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+import Foundation
+
+extension GitStatusService {
+    func imageData(from source: ImageComparisonRequest.Source, in repositoryURL: URL) async throws -> Data {
+        switch source {
+        case let .revision(ref, path):
+            return try await showFile(at: path, ref: ref, in: repositoryURL)
+        case let .index(path):
+            return try await indexFile(at: path, in: repositoryURL)
+        case let .indexWithFallback(path, originalPath):
+            // Paired worktree renames may have either path in the index.
+            do {
+                return try await indexFile(at: path, in: repositoryURL)
+            } catch {
+                try Task.checkCancellation()
+                guard path != originalPath else { throw error }
+                return try await indexFile(at: originalPath, in: repositoryURL)
+            }
+        case let .disk(path):
+            return try await Task.detached(priority: .userInitiated) {
+                let root = repositoryURL.standardizedFileURL.resolvingSymlinksInPath()
+                let file = repositoryURL.appendingPathComponent(path).standardizedFileURL.resolvingSymlinksInPath()
+                let rootComponents = root.pathComponents
+                guard file.pathComponents.count > rootComponents.count,
+                      Array(file.pathComponents.prefix(rootComponents.count)) == rootComponents else {
+                    throw GitError.commandFailed("Image preview paths must remain inside the repository.")
+                }
+                return try Data(contentsOf: file)
+            }.value
+        }
+    }
+}

macgit/Views/Common/DiffView.swift

@@ -37,6 +37,9 @@ struct DiffView: View {
     let onError: (String) -> Void
     let filePath: String?
     let gitRef: String?
+    let imageComparisonMode: ImageComparisonMode
+    let imageOldPath: String?
+    let imageFileStatus: CommitFileStatus?
     let commitPatchDisabledReason: String?
     let prefersTextDiff: Bool
     let onCommitPatch: (([DiffLine], CommitPatchRequest.Direction, String) -> Void)?
@@ -50,6 +53,9 @@ struct DiffView: View {
         onError: @escaping (String) -> Void = { _ in },
         filePath: String? = nil,
         gitRef: String? = nil,
+        imageComparisonMode: ImageComparisonMode = .overlay,
+        imageOldPath: String? = nil,
+        imageFileStatus: CommitFileStatus? = nil,
         prefersTextDiff: Bool = false,
         commitPatchDisabledReason: String? = nil,
         onCommitPatch: (([DiffLine], CommitPatchRequest.Direction, String) -> Void)? = nil
@@ -62,14 +68,16 @@ struct DiffView: View {
         self.onError = onError
         self.filePath = filePath
         self.gitRef = gitRef
+        self.imageComparisonMode = imageComparisonMode
+        self.imageOldPath = imageOldPath
+        self.imageFileStatus = imageFileStatus
         self.prefersTextDiff = prefersTextDiff
         self.commitPatchDisabledReason = commitPatchDisabledReason
         self.onCommitPatch = onCommitPatch
     }
 
     @State private var selectedLineIDs: Set<UUID> = []
     @State private var lastSelectedLineID: UUID?
-    @State private var loadedImage: NSImage?
 
     private static let imageExtensions: Set<String> = [
         "png", "jpg", "jpeg", "gif", "svg", "webp", "bmp",
@@ -171,51 +179,17 @@ struct DiffView: View {
 
     @ViewBuilder
     private var imagePreview: some View {
-        if let file = file, let url = repositoryURL {
-            let fileURL = url.appendingPathComponent(file.path)
-            diskImagePreview(fileURL: fileURL, filePath: file.path)
-        } else if let ref = gitRef, let url = repositoryURL, let path = filePath {
-            gitImagePreview(ref: ref, url: url, path: path)
+        if let file, let repositoryURL {
+            ImageComparisonView(request: .working(file, staged: file.status == .staged || file.status == .added || file.status == .renamed),
+                                repositoryURL: repositoryURL, mode: imageComparisonMode)
+        } else if let ref = gitRef, let repositoryURL, let path = filePath {
+            ImageComparisonView(request: .commit(path: path, oldPath: imageOldPath, status: imageFileStatus, ref: ref),
+                                repositoryURL: repositoryURL, mode: imageComparisonMode)
         } else {
             EmptyStateView(icon: "photo", message: "Unable to preview image")
         }
     }
 
-    private func diskImagePreview(fileURL: URL, filePath: String) -> some View {
-        Group {
-            if let nsImage = NSImage(contentsOf: fileURL) {
-                FileImagePreview(image: nsImage)
-            } else {
-                EmptyStateView(icon: "photo", message: "Unable to preview image", detail: filePath)
-            }
-        }
-    }
-
-    private func gitImagePreview(ref: String, url: URL, path: String) -> some View {
-        Group {
-            if let image = loadedImage {
-                FileImagePreview(image: image)
-            } else {
-                ProgressView("Loading image…")
-                    .frame(maxWidth: .infinity, maxHeight: .infinity)
-            }
-        }
-        .task {
-            await loadImageFromGit(ref: ref, url: url, path: path)
-        }
-    }
-
-    private func loadImageFromGit(ref: String, url: URL, path: String) async {
-        do {
-            let data = try await GitStatusService.shared.showFile(at: path, ref: ref, in: url)
-            if let image = NSImage(data: data) {
-                loadedImage = image
-            }
-        } catch {
-            onError("Failed to load image: \(error.localizedDescription)")
-        }
-    }
-
 
 }
 

macgit/Views/Common/ImageComparisonModeButton.swift

@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+import SwiftUI
+
+struct ImageComparisonModeButton: View {
+    @Binding var mode: ImageComparisonMode
+
+    private var nextMode: ImageComparisonMode {
+        mode == .overlay ? .sideBySide : .overlay
+    }
+
+    var body: some View {
+        Button {
+            mode = nextMode
+        } label: {
+            Image(systemName: mode.icon)
+                .frame(width: 24, height: 24)
+                .contentShape(Rectangle())
+        }
+        .buttonStyle(.plain)
+        .fixedSize()
+        .help("Switch to \(nextMode.title)")
+        .accessibilityLabel("Switch image comparison to \(nextMode.title)")
+        .accessibilityValue(mode.title)
+    }
+}

macgit/Views/Common/ImageComparisonOverlay.swift

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+import SwiftUI
+
+struct ImageComparisonOverlay: View {
+    let before: NSImage
+    let after: NSImage
+    @Binding var fraction: Double
+
+    var body: some View {
+        GeometryReader { geometry in
+            let size = geometry.size
+            let width = max(before.size.width, after.size.width, 1)
+            let height = max(before.size.height, after.size.height, 1)
+            let scale = max(0, min(size.width / width, size.height / height))
+            let imageWidth = width * scale
+            let imageOffset = (size.width - imageWidth) / 2
+            let dividerX = imageOffset + imageWidth * fraction
+            ZStack {
+                Color(nsColor: .textBackgroundColor)
+                image(after, scale: scale)
+                    .frame(width: width * scale, height: height * scale, alignment: .topLeading)
+                ZStack {
+                    Color(nsColor: .textBackgroundColor)
+                    image(before, scale: scale)
+                        .frame(width: width * scale, height: height * scale, alignment: .topLeading)
+                }
+                    .frame(width: size.width, height: size.height)
+                    .mask(alignment: .leading) {
+                        Rectangle().frame(width: dividerX)
+                    }
+                Rectangle().fill(.primary).frame(width: 2)
+                    .position(x: dividerX, y: size.height / 2)
+                Image(systemName: "arrow.left.and.right")
+                    .font(.caption.bold()).padding(8)
+                    .background(.regularMaterial, in: Circle())
+                    .position(x: dividerX, y: size.height / 2)
+            }
+            .clipped()
+            .contentShape(Rectangle())
+            .gesture(DragGesture(minimumDistance: 0).onChanged { value in
+                fraction = min(1, max(0, (value.location.x - imageOffset) / max(imageWidth, 1)))
+            })
+            .accessibilityElement(children: .ignore)
+            .accessibilityLabel("Before and after image comparison")
+        }.frame(maxWidth: .infinity, maxHeight: .infinity)
+    }
+
+    private func image(_ image: NSImage, scale: CGFloat) -> some View {
+        Image(nsImage: image).resizable()
+            .frame(width: image.size.width * scale, height: image.size.height * scale)
+    }
+}

macgit/Views/Common/ImageComparisonSide.swift

@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+import SwiftUI
+
+struct ImageComparisonSide: View {
+    let title: String?
+    let image: NSImage?
+    let error: String?
+    let isMissing: Bool
+    var body: some View {
+        VStack(spacing: 0) {
+            if let title {
+                Text(title).font(.caption.weight(.semibold)).padding(10)
+                Divider()
+            }
+            if let image {
+                ImagePreviewViewport {
+                    Image(nsImage: image)
+                        .resizable()
+                        .aspectRatio(contentMode: .fit)
+                        .frame(maxWidth: .infinity, maxHeight: .infinity)
+                        .padding(12)
+                }
+            } else {
+                EmptyStateView(icon: "photo", message: isMissing ? "No image" : "Unable to preview image", detail: error)
+            }
+        }.frame(maxWidth: .infinity, maxHeight: .infinity)
+    }
+}