AppKitBackend: Fix Path construction (flipped coord system)

Also fixed path re-rendering. Before these changes we only set needsDisplay
for the region within the bounds of the path, but we have to set it for the
whole view cause otherwise any out-of-bounds parts of that path don't get
re-rendered at all.

Author: stackotter

Sources/AppKitBackend/AppKitBackend.swift

@@ -1303,18 +1303,29 @@ public final class AppKitBackend: AppBackend {
     public func updatePath(
         _ path: Path,
         _ source: SwiftCrossUI.Path,
+        bounds: SwiftCrossUI.Path.Rect,
         pointsChanged: Bool,
         environment: EnvironmentValues
     ) {
         applyStrokeStyle(source.strokeStyle, to: path)
 
         if pointsChanged {
             path.removeAllPoints()
-            applyActions(source.actions, to: path)
+            applyActions(
+                source.actions,
+                to: path,
+                bounds: bounds,
+                applyCoordinateSystemCorrection: true
+            )
         }
     }
 
-    func applyActions(_ actions: [SwiftCrossUI.Path.Action], to path: NSBezierPath) {
+    func applyActions(
+        _ actions: [SwiftCrossUI.Path.Action],
+        to path: NSBezierPath,
+        bounds: SwiftCrossUI.Path.Rect,
+        applyCoordinateSystemCorrection: Bool
+    ) {
         for action in actions {
             switch action {
                 case .moveTo(let point):
@@ -1392,25 +1403,43 @@ public final class AppKitBackend: AppBackend {
                         radius: CGFloat(radius),
                         startAngle: CGFloat(startAngle * 180.0 / .pi),
                         endAngle: CGFloat(endAngle * 180.0 / .pi),
-                        clockwise: clockwise
+                        // Due to being in a flipped coordinate system (before the
+                        // correction gets applied), we have to reverse all arcs.
+                        clockwise: !clockwise
                     )
                 case .transform(let transform):
-                    path.transform(
-                        using: Foundation.AffineTransform(
-                            m11: CGFloat(transform.linearTransform.x),
-                            m12: CGFloat(transform.linearTransform.z),
-                            m21: CGFloat(transform.linearTransform.y),
-                            m22: CGFloat(transform.linearTransform.w),
-                            tX: CGFloat(transform.translation.x),
-                            tY: CGFloat(transform.translation.y)
-                        )
+                    let affineTransform = Foundation.AffineTransform(
+                        m11: CGFloat(transform.linearTransform.x),
+                        m12: CGFloat(transform.linearTransform.z),
+                        m21: CGFloat(transform.linearTransform.y),
+                        m22: CGFloat(transform.linearTransform.w),
+                        tX: CGFloat(transform.translation.x),
+                        tY: CGFloat(transform.translation.y)
                     )
+                    path.transform(using: affineTransform)
                 case .subpath(let subpathActions):
                     let subpath = NSBezierPath()
-                    applyActions(subpathActions, to: subpath)
+                    // We don't apply the coordinate system correction to the subpath,
+                    // we only want to apply it to the whole path once we're done.
+                    applyActions(
+                        subpathActions,
+                        to: subpath,
+                        bounds: bounds,
+                        applyCoordinateSystemCorrection: false
+                    )
                     path.append(subpath)
             }
         }
+
+        if applyCoordinateSystemCorrection {
+            // AppKit's coordinate system has a flipped Y axis so we have to correct for that
+            // once we've constructed the whole path.
+            var coordinateSystemCorrection = Foundation.AffineTransform(scaleByX: 1, byY: -1)
+            coordinateSystemCorrection.append(
+                Foundation.AffineTransform(translationByX: 0, byY: bounds.maxY + bounds.y)
+            )
+            path.transform(using: coordinateSystemCorrection)
+        }
     }
 
     public func renderPath(
@@ -1429,7 +1458,7 @@ public final class AppKitBackend: AppBackend {
         widget.strokeColor = strokeColor.nsColor
         widget.fillColor = fillColor.nsColor
 
-        widget.setNeedsDisplay(widget.bounds)
+        widget.needsDisplay = true
     }
 }
 

Sources/SwiftCrossUI/Backend/AppBackend.swift

@@ -587,11 +587,16 @@ public protocol AppBackend {
     /// - Parameters:
     ///   - path: The path to be updated.
     ///   - source: The source to copy the path from.
+    ///   - bounds: The bounds that the path is getting rendered in. This gets
+    ///     passed to backends because AppKit uses a different coordinate system
+    ///     (with a flipped y axis) and therefore needs to perform coordinate
+    ///     conversions.
     ///   - pointsChanged: If `false`, the ``Path/actions`` of the source have not changed.
     ///   - environment: The environment of the path.
     func updatePath(
         _ path: Path,
         _ source: SwiftCrossUI.Path,
+        bounds: SwiftCrossUI.Path.Rect,
         pointsChanged: Bool,
         environment: EnvironmentValues
     )

Sources/SwiftCrossUI/Views/Shapes/Shape.swift

@@ -90,9 +90,13 @@ extension Shape {
         let storage = children as! ShapeStorage
         let size = size(fitting: proposedSize)
 
-        let path = path(
-            in: Path.Rect(x: 0.0, y: 0.0, width: Double(size.size.x), height: Double(size.size.y))
+        let bounds = Path.Rect(
+            x: 0.0,
+            y: 0.0,
+            width: Double(size.size.x),
+            height: Double(size.size.y)
         )
+        let path = path(in: bounds)
 
         let pointsChanged = storage.oldPath?.actions != path.actions
         storage.oldPath = path
@@ -101,6 +105,7 @@ extension Shape {
         backend.updatePath(
             backendPath,
             path,
+            bounds: bounds,
             pointsChanged: pointsChanged,
             environment: environment
         )

Sources/SwiftCrossUI/Views/Shapes/StyledShape.swift

@@ -61,9 +61,13 @@ extension StyledShape {
         let storage = children as! ShapeStorage
         let size = size(fitting: proposedSize)
 
-        let path = path(
-            in: Path.Rect(x: 0.0, y: 0.0, width: Double(size.size.x), height: Double(size.size.y))
+        let bounds = Path.Rect(
+            x: 0.0,
+            y: 0.0,
+            width: Double(size.size.x),
+            height: Double(size.size.y)
         )
+        let path = path(in: bounds)
 
         let pointsChanged = storage.oldPath?.actions != path.actions
         storage.oldPath = path
@@ -72,6 +76,7 @@ extension StyledShape {
         backend.updatePath(
             backendPath,
             path,
+            bounds: bounds,
             pointsChanged: pointsChanged,
             environment: environment
         )

Sources/UIKitBackend/UIKitBackend+Path.swift

@@ -49,6 +49,7 @@ extension UIKitBackend {
     public func updatePath(
         _ path: UIBezierPath,
         _ source: SwiftCrossUI.Path,
+        bounds: SwiftCrossUI.Path.Rect,
         pointsChanged: Bool,
         environment: EnvironmentValues
     ) {

Sources/WinUIBackend/WinUIBackend.swift

@@ -1307,6 +1307,7 @@ public final class WinUIBackend: AppBackend {
     public func updatePath(
         _ path: Path,
         _ source: SwiftCrossUI.Path,
+        bounds: SwiftCrossUI.Path.Rect,
         pointsChanged: Bool,
         environment: EnvironmentValues
     ) {