Split View.update into View.computeLayout and View.commit

Author: stackotter

Benchmarks/LayoutPerformanceBenchmark/LayoutPerformanceBenchmark.swift

@@ -35,8 +35,8 @@ struct Benchmarks {
 
         @MainActor
         func updateNode<V: View>(_ node: ViewGraphNode<V, DummyBackend>, _ size: SIMD2<Int>) {
-            _ = node.update(proposedSize: size, environment: environment, dryRun: true)
-            _ = node.update(proposedSize: size, environment: environment, dryRun: false)
+            _ = node.computeLayout(proposedSize: size, environment: environment)
+            _ = node.commit()
         }
 
         #if BENCHMARK_VIZ

Examples/Sources/WindowingExample/WindowingApp.swift

@@ -177,6 +177,8 @@ struct WindowingApp: App {
                     }
 
                     Image(Bundle.module.bundleURL.appendingPathComponent("Banner.png"))
+                        .resizable()
+                        .aspectRatio(contentMode: .fit)
 
                     Divider()
 

Sources/AppKitBackend/AppKitBackend.swift

@@ -31,12 +31,14 @@ public final class AppKitBackend: AppBackend {
         // We assume that all scrollers have their controlSize set to `.regular` by default.
         // The internet seems to indicate that this is true regardless of any system wide
         // preferences etc.
-        Int(
+        let result = Int(
             NSScroller.scrollerWidth(
                 for: .regular,
                 scrollerStyle: NSScroller.preferredScrollerStyle
             ).rounded(.awayFromZero)
         )
+        print(result)
+        return result
     }
 
     private let appDelegate = NSCustomApplicationDelegate()

Sources/AppKitBackend/NSViewRepresentable.swift

@@ -139,15 +139,14 @@ extension View where Self: NSViewRepresentable {
         }
     }
 
-    public func update<Backend: AppBackend>(
+    public func computeLayout<Backend: AppBackend>(
         _ widget: Backend.Widget,
         children: any ViewGraphNodeChildren,
         proposedSize: SIMD2<Int>,
         environment: EnvironmentValues,
-        backend: Backend,
-        dryRun: Bool
-    ) -> ViewUpdateResult {
-        guard let backend = backend as? AppKitBackend else {
+        backend: Backend
+    ) -> ViewLayoutResult {
+        guard backend is AppKitBackend else {
             fatalError("NSViewRepresentable updated by \(Backend.self)")
         }
 
@@ -160,11 +159,17 @@ extension View where Self: NSViewRepresentable {
             context: representingWidget.context!
         )
 
-        if !dryRun {
-            backend.setSize(of: representingWidget, to: size.size)
-        }
+        return ViewLayoutResult.leafView(size: size)
+    }
 
-        return ViewUpdateResult.leafView(size: size)
+    public func commit<Backend: AppBackend>(
+        _ widget: Backend.Widget,
+        children: any ViewGraphNodeChildren,
+        layout: ViewLayoutResult,
+        environment: EnvironmentValues,
+        backend: Backend
+    ) {
+        backend.setSize(of: widget, to: layout.size.size)
     }
 }