fix: use pixel dimensions for wallpaper images

SpreadPaper/Services/NSImage+PixelSize.swift

@@ -0,0 +1,17 @@
+import AppKit
+
+extension NSImage {
+    nonisolated var pixelSize: CGSize {
+        if let bitmapRep = representations
+            .compactMap({ $0 as? NSBitmapImageRep })
+            .max(by: { ($0.pixelsWide * $0.pixelsHigh) < ($1.pixelsWide * $1.pixelsHigh) }) {
+            return CGSize(width: bitmapRep.pixelsWide, height: bitmapRep.pixelsHigh)
+        }
+
+        if let cgImage = cgImage(forProposedRect: nil, context: nil, hints: nil) {
+            return CGSize(width: cgImage.width, height: cgImage.height)
+        }
+
+        return size
+    }
+}

SpreadPaper/Services/WallpaperManager.swift

@@ -384,7 +384,8 @@ class WallpaperManager {
         deviceScale: CGFloat,
         screenColorSpace: CGColorSpace?
     ) throws -> CGImage {
-        var rect = CGRect(origin: .zero, size: original.size)
+        let imageSize = original.pixelSize
+        var rect = CGRect(origin: .zero, size: imageSize)
         guard let cgImage = original.cgImage(forProposedRect: &rect, context: nil, hints: nil) else {
             throw WallpaperError.imageConversionFailed
         }
@@ -409,8 +410,8 @@ class WallpaperManager {
 
         let realOffsetX_Px = (offset.width / previewScale) * deviceScale
         let realOffsetY_Px = (offset.height / previewScale) * deviceScale
-        let drawnImgWidthPx = original.size.width * imageScale * deviceScale
-        let drawnImgHeightPx = original.size.height * imageScale * deviceScale
+        let drawnImgWidthPx = imageSize.width * imageScale * deviceScale
+        let drawnImgHeightPx = imageSize.height * imageScale * deviceScale
         let totalCanvasWidthPx = totalCanvas.width * deviceScale
         let totalCanvasHeightPx = totalCanvas.height * deviceScale
         let centeringX_Px = (totalCanvasWidthPx - drawnImgWidthPx) / 2.0

SpreadPaper/Views/EditorCanvasView.swift

@@ -27,13 +27,14 @@ struct EditorCanvasView: View {
             ZStack {
                 // Image layer
                 if let img = selectedImage {
+                    let pixelSize = img.pixelSize
                     Image(nsImage: img)
                         .resizable()
                         .aspectRatio(contentMode: .fill)
                         .scaleEffect(x: isFlipped ? -1 : 1, y: 1)
                         .frame(
-                            width: img.size.width * previewScale * imageScale,
-                            height: img.size.height * previewScale * imageScale
+                            width: pixelSize.width * previewScale * imageScale,
+                            height: pixelSize.height * previewScale * imageScale
                         )
                         .offset(imageOffset)
                         .opacity(isDragging ? 0.7 : 1.0)
@@ -47,7 +48,7 @@ struct EditorCanvasView: View {
                                     )
                                     imageOffset = calculateSnapping(
                                         raw: raw,
-                                        imgSize: img.size,
+                                        imgSize: pixelSize,
                                         canvasSize: manager.totalCanvas.size,
                                         previewScale: previewScale,
                                         zoomScale: imageScale

SpreadPaper/Views/EditorView.swift

@@ -431,7 +431,7 @@ struct EditorView: View {
 
     private var staticSubtitle: String {
         guard let img = loadedImages.first else { return "Choose image…" }
-        return "\(Int(img.size.width))×\(Int(img.size.height))"
+        return dimensions(for: img)
     }
 
     private func appearanceImageRow(index: Int, label: String) -> some View {
@@ -499,7 +499,8 @@ struct EditorView: View {
     }
 
     private func dimensions(for image: NSImage) -> String {
-        "\(Int(image.size.width))×\(Int(image.size.height))"
+        let pixelSize = image.pixelSize
+        return "\(Int(pixelSize.width))×\(Int(pixelSize.height))"
     }
 
     // MARK: - Zoom
@@ -646,8 +647,9 @@ struct EditorView: View {
         guard let image = currentImage else { return }
         let canvas = manager.totalCanvas
         guard canvas.width > 0, canvas.height > 0 else { return }
-        let widthRatio = canvas.width / image.size.width
-        let heightRatio = canvas.height / image.size.height
+        let pixelSize = image.pixelSize
+        let widthRatio = canvas.width / pixelSize.width
+        let heightRatio = canvas.height / pixelSize.height
         withAnimation(.spring()) {
             guard selectedVariantIndex < variants.count else { return }
             variants[selectedVariantIndex].scale = max(widthRatio, heightRatio)

SpreadPaper/Views/GalleryView.swift

@@ -699,17 +699,17 @@ private struct ThumbnailResult: @unchecked Sendable {
     let image: NSImage
 }
 
-@Sendable
-private func renderThumbnails(jobs: [ThumbnailJob]) -> [ThumbnailResult] {
+nonisolated private func renderThumbnails(jobs: [ThumbnailJob]) -> [ThumbnailResult] {
     var out: [ThumbnailResult] = []
     out.reserveCapacity(jobs.count)
     for job in jobs {
         guard let image = NSImage(contentsOf: job.imageURL) else { continue }
         let maxDim: CGFloat = 480
-        let ratio = min(maxDim / image.size.width, maxDim / image.size.height, 1.0)
+        let pixelSize = image.pixelSize
+        let ratio = min(maxDim / pixelSize.width, maxDim / pixelSize.height, 1.0)
         let newSize = NSSize(
-            width: image.size.width * ratio,
-            height: image.size.height * ratio
+            width: pixelSize.width * ratio,
+            height: pixelSize.height * ratio
         )
         let thumb = NSImage(size: newSize)
         thumb.lockFocus()