Make image diffing strategies custom scale aware (pointfreeco#336)

* Add scale parameter to image diffing strategies

* Use updated diffing in CALayer, UIView, UIViewController and SwiftUIView strategies

* Pass scale through to CGPath and UIBezierPath strategies

* Re-generate project file

Author: moritzsternemann

Sources/SnapshotTesting/Snapshotting/CALayer.swift

@@ -37,7 +37,7 @@ extension Snapshotting where Value == CALayer, Format == UIImage {
   /// - Parameter precision: The percentage of pixels that must match.
   public static func image(precision: Float = 1, traits: UITraitCollection = .init())
     -> Snapshotting {
-      return SimplySnapshotting.image(precision: precision).pullback { layer in
+      return SimplySnapshotting.image(precision: precision, scale: traits.displayScale).pullback { layer in
         renderer(bounds: layer.bounds, for: traits).image { ctx in
           layer.setNeedsLayout()
           layer.layoutIfNeeded()

Sources/SnapshotTesting/Snapshotting/CGPath.swift

@@ -40,7 +40,7 @@ extension Snapshotting where Value == CGPath, Format == UIImage {
   ///
   /// - Parameter precision: The percentage of pixels that must match.
   public static func image(precision: Float = 1, scale: CGFloat = 1, drawingMode: CGPathDrawingMode = .eoFill) -> Snapshotting {
-    return SimplySnapshotting.image(precision: precision).pullback { path in
+    return SimplySnapshotting.image(precision: precision, scale: scale).pullback { path in
       let bounds = path.boundingBoxOfPath
       let format: UIGraphicsImageRendererFormat
       if #available(iOS 11.0, tvOS 11.0, *) {

Sources/SnapshotTesting/Snapshotting/SwiftUIView.swift

@@ -51,7 +51,7 @@ extension Snapshotting where Value: SwiftUI.View, Format == UIImage {
         config = .init(safeArea: .zero, size: size, traits: traits)
       }
 
-      return SimplySnapshotting.image(precision: precision).asyncPullback { view in
+      return SimplySnapshotting.image(precision: precision, scale: traits.displayScale).asyncPullback { view in
         var config = config
 
         let controller: UIViewController

Sources/SnapshotTesting/Snapshotting/UIBezierPath.swift

@@ -11,7 +11,7 @@ extension Snapshotting where Value == UIBezierPath, Format == UIImage {
   ///
   /// - Parameter precision: The percentage of pixels that must match.
   public static func image(precision: Float = 1, scale: CGFloat = 1) -> Snapshotting {
-    return SimplySnapshotting.image(precision: precision).pullback { path in
+    return SimplySnapshotting.image(precision: precision, scale: scale).pullback { path in
       let bounds = path.bounds
       let format: UIGraphicsImageRendererFormat
       if #available(iOS 11.0, tvOS 11.0, *) {

Sources/SnapshotTesting/Snapshotting/UIImage.swift

@@ -4,16 +4,24 @@ import XCTest
 
 extension Diffing where Value == UIImage {
   /// A pixel-diffing strategy for UIImage's which requires a 100% match.
-  public static let image = Diffing.image(precision: 1)
+  public static let image = Diffing.image(precision: 1, scale: nil)
 
   /// A pixel-diffing strategy for UIImage that allows customizing how precise the matching must be.
   ///
   /// - Parameter precision: A value between 0 and 1, where 1 means the images must match 100% of their pixels.
+  /// - Parameter scale: Scale to use when loading the reference image from disk. If `nil` or the `UITraitCollection`s default value of `0.0`, the screens scale is used.
   /// - Returns: A new diffing strategy.
-  public static func image(precision: Float) -> Diffing {
+  public static func image(precision: Float, scale: CGFloat?) -> Diffing {
+    let imageScale: CGFloat
+    if let scale = scale, scale != 0.0 {
+      imageScale = scale
+    } else {
+        imageScale = UIScreen.main.scale
+    }
+
     return Diffing(
       toData: { $0.pngData() ?? emptyImage().pngData()! },
-      fromData: { UIImage(data: $0, scale: UIScreen.main.scale)! }
+      fromData: { UIImage(data: $0, scale: imageScale)! }
     ) { old, new in
       guard !compare(old, new, precision: precision) else { return nil }
       let difference = SnapshotTesting.diff(old, new)
@@ -48,16 +56,17 @@ extension Diffing where Value == UIImage {
 extension Snapshotting where Value == UIImage, Format == UIImage {
   /// A snapshot strategy for comparing images based on pixel equality.
   public static var image: Snapshotting {
-    return .image(precision: 1)
+    return .image(precision: 1, scale: nil)
   }
 
   /// A snapshot strategy for comparing images based on pixel equality.
   ///
   /// - Parameter precision: The percentage of pixels that must match.
-  public static func image(precision: Float) -> Snapshotting {
+  /// - Parameter scale: The scale of the reference image stored on disk.
+  public static func image(precision: Float, scale: CGFloat?) -> Snapshotting {
     return .init(
       pathExtension: "png",
-      diffing: .image(precision: precision)
+      diffing: .image(precision: precision, scale: scale)
     )
   }
 }

Sources/SnapshotTesting/Snapshotting/UIView.swift

@@ -22,7 +22,7 @@ extension Snapshotting where Value == UIView, Format == UIImage {
     )
     -> Snapshotting {
 
-      return SimplySnapshotting.image(precision: precision).asyncPullback { view in
+      return SimplySnapshotting.image(precision: precision, scale: traits.displayScale).asyncPullback { view in
         snapshotView(
           config: .init(safeArea: .zero, size: size ?? view.frame.size, traits: .init()),
           drawHierarchyInKeyWindow: drawHierarchyInKeyWindow,

Sources/SnapshotTesting/Snapshotting/UIViewController.swift

@@ -22,7 +22,7 @@ extension Snapshotting where Value == UIViewController, Format == UIImage {
     )
     -> Snapshotting {
 
-      return SimplySnapshotting.image(precision: precision).asyncPullback { viewController in
+      return SimplySnapshotting.image(precision: precision, scale: traits.displayScale).asyncPullback { viewController in
         snapshotView(
           config: size.map { .init(safeArea: config.safeArea, size: $0, traits: config.traits) } ?? config,
           drawHierarchyInKeyWindow: false,
@@ -48,7 +48,7 @@ extension Snapshotting where Value == UIViewController, Format == UIImage {
     )
     -> Snapshotting {
 
-      return SimplySnapshotting.image(precision: precision).asyncPullback { viewController in
+      return SimplySnapshotting.image(precision: precision, scale: traits.displayScale).asyncPullback { viewController in
         snapshotView(
           config: .init(safeArea: .zero, size: size, traits: traits),
           drawHierarchyInKeyWindow: drawHierarchyInKeyWindow,