Allow backends to modify the root-level environment (e.g. to handle system dark mode etc)

Author: stackotter

Sources/AppKitBackend/AppKitBackend.swift

@@ -119,6 +119,10 @@ public struct AppKitBackend: AppBackend {
         }
     }
 
+    public func computeRootEnvironment(defaultEnvironment: Environment) -> Environment {
+        defaultEnvironment.with(\.foregroundColor, Color(NSColor.textColor))
+    }
+
     public func show(widget: Widget) {}
 
     class NSContainerView: NSView {
@@ -273,13 +277,7 @@ public struct AppKitBackend: AppBackend {
     public func updateTextView(_ textView: Widget, content: String, environment: Environment) {
         let field = textView.view as! NSTextField
         field.stringValue = content
-        let textColor = environment.foregroundColor
-        field.textColor = NSColor(
-            calibratedRed: CGFloat(textColor.red),
-            green: CGFloat(textColor.green),
-            blue: CGFloat(textColor.blue),
-            alpha: 1
-        )
+        field.textColor = environment.foregroundColor.nsColor
     }
 
     public func createButton() -> Widget {
@@ -526,6 +524,31 @@ public struct AppKitBackend: AppBackend {
     }
 }
 
+extension Color {
+    init(_ nsColor: NSColor) {
+        guard let resolvedNSColor = nsColor.usingColorSpace(.deviceRGB) else {
+            print("error: Failed to convert NSColor to RGB")
+            self = .black
+            return
+        }
+        self.init(
+            Float(resolvedNSColor.redComponent),
+            Float(resolvedNSColor.greenComponent),
+            Float(resolvedNSColor.blueComponent),
+            Float(resolvedNSColor.alphaComponent)
+        )
+    }
+
+    var nsColor: NSColor {
+        NSColor(
+            calibratedRed: CGFloat(red),
+            green: CGFloat(green),
+            blue: CGFloat(blue),
+            alpha: 1
+        )
+    }
+}
+
 // Source: https://gist.github.com/sindresorhus/3580ce9426fff8fafb1677341fca4815
 enum AssociationPolicy {
     case assign

Sources/SwiftCrossUI/Backend/AppBackend.swift

@@ -52,7 +52,7 @@ public protocol AppBackend {
     /// after starting the app, and hence this generic root window creation
     /// API must reflect that. This is always the first method to be called
     /// and is where boilerplate app setup should happen.
-
+    ///
     /// Runs the backend's main run loop. The app will exit when this method
     /// returns. This wall always be the first method called by SwiftCrossUI.
     ///
@@ -116,6 +116,10 @@ public protocol AppBackend {
     /// compatible with dispatching UI updates.
     func runInMainThread(action: @escaping () -> Void)
 
+    /// Computes the root environment for an app (e.g. by checking the system's current
+    /// theme). May fall back on the provided defaults where reasonable.
+    func computeRootEnvironment(defaultEnvironment: Environment) -> Environment
+
     /// Shows a widget after it has been created or updated (may be unnecessary
     /// for some backends). Predominantly used by ``ViewGraphNode`` after
     /// propagating updates.

Sources/SwiftCrossUI/Modifiers/ForegroundColor.swift

@@ -2,7 +2,6 @@ extension View {
     /// Sets the color of the foreground elements displayed by this view.
     public func foregroundColor(_ color: Color) -> some View {
         return EnvironmentModifier(self) { environment in
-            print("Updating fg color")
             return environment.with(\.foregroundColor, color)
         }
     }

Sources/SwiftCrossUI/ViewGraph/Environment.swift

@@ -13,7 +13,7 @@ public struct Environment {
         foregroundColor = .black
     }
 
-    func with<T>(_ keyPath: WritableKeyPath<Self, T>, _ newValue: T) -> Self {
+    public func with<T>(_ keyPath: WritableKeyPath<Self, T>, _ newValue: T) -> Self {
         var environment = self
         environment[keyPath: keyPath] = newValue
         return environment

Sources/SwiftCrossUI/_App.swift

@@ -13,20 +13,20 @@ class _App<AppRoot: App> {
     /// A cancellable handle to observation of the app's state .
     var cancellable: Cancellable?
     /// The root level environment.
-    var environment: Environment
+    var defaultEnvironment: Environment
 
     /// Wraps a user's app implementation.
     init(_ app: AppRoot) {
         backend = app.backend
         self.app = app
-        self.environment = Environment()
+        self.defaultEnvironment = Environment()
     }
 
     func forceRefresh() {
         self.sceneGraphRoot?.update(
             self.app.body,
             backend: self.backend,
-            environment: environment
+            environment: defaultEnvironment
         )
     }
 
@@ -37,17 +37,25 @@ class _App<AppRoot: App> {
             let rootNode = AppRoot.Body.Node(
                 from: self.app.body,
                 backend: self.backend,
-                environment: self.environment
+                environment: self.defaultEnvironment
             )
 
-            rootNode.update(nil, backend: self.backend, environment: self.environment)
+            rootNode.update(
+                nil,
+                backend: self.backend,
+                environment: self.backend.computeRootEnvironment(
+                    defaultEnvironment: self.defaultEnvironment
+                )
+            )
             self.sceneGraphRoot = rootNode
 
             self.cancellable = self.app.state.didChange.observe {
                 self.sceneGraphRoot?.update(
                     self.app.body,
                     backend: self.backend,
-                    environment: self.environment
+                    environment: self.backend.computeRootEnvironment(
+                        defaultEnvironment: self.defaultEnvironment
+                    )
                 )
             }
         }